runtime: Added support for displaying exception location

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}

src/CMakeLists.txt

@@ -217,6 +217,7 @@ set(RUNTIME_SOURCE_FILES
  runtime/PyType.cpp
  runtime/PyZip.cpp
  runtime/RuntimeError.cpp
+ runtime/SourceManager.cpp
  runtime/StopIteration.cpp
  runtime/SyntaxError.cpp
  runtime/TypeError.cpp
@@ -242,6 +243,7 @@ set(UNITTEST_SOURCES
  runtime/PyNumber_tests.cpp
  runtime/PyString_tests.cpp
  runtime/PyType_tests.cpp
+ runtime/SourceManager_tests.cpp
  testing/main.cpp)
 
 set(PYTHON_LIB_PATH ${cpython_SOURCE_DIR}/Lib)

src/executable/FunctionBlock.hpp

@@ -2,13 +2,21 @@
 
 #include "Program.hpp"
 #include "forward.hpp"
+#include <cstdint>
 #include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 using InstructionVector = std::vector<std::unique_ptr<Instruction>>;
 
+struct InstructionSourceLocation
+{
+	uint32_t instruction_index;
+	uint32_t line;
+	uint32_t column;
+};
+
 struct FunctionMetaData
 {
 	std::string function_name;
@@ -33,6 +41,7 @@ struct FunctionBlock
 {
 	FunctionMetaData metadata;
 	InstructionVector blocks;
+	std::vector<InstructionSourceLocation> instruction_locations;
 	std::string to_string() const;
 };
 

src/executable/bytecode/Bytecode.cpp

@@ -1,4 +1,6 @@
 #include "Bytecode.hpp"
+#include "ast/AST.hpp"
+#include "executable/FunctionBlock.hpp"
 #include "instructions/Instructions.hpp"
 #include "interpreter/Interpreter.hpp"
 #include "runtime/BaseException.hpp"
@@ -8,23 +10,42 @@
 #include "serialization/deserialize.hpp"
 #include "serialization/serialize.hpp"
 
+#include <algorithm>
+#include <optional>
+
 using namespace py;
 
 Bytecode::Bytecode(size_t register_count,
 	size_t locals_count,
 	size_t stack_size,
 	std::string function_name,
 	InstructionVector instructions,
+	std::vector<InstructionSourceLocation> instruction_locations,
 	std::shared_ptr<Program> program)
 	: Function(register_count,
  locals_count,
  stack_size,
  function_name,
  FunctionExecutionBackend::BYTECODE,
  std::move(program)),
- m_instructions(std::move(instructions))
+ m_instructions(std::move(instructions)),
+ m_instruction_locations(std::move(instruction_locations))
 {}
 
+std::optional<InstructionSourceLocation> Bytecode::location_for(size_t instruction_index) const
+{
+	if (m_instruction_locations.empty()) { return std::nullopt; }
+	// Find the last entry whose instruction_index is <= the query.
+	const auto it = std::upper_bound(m_instruction_locations.begin(),
+ m_instruction_locations.end(),
+ instruction_index,
+ [](size_t idx, const InstructionSourceLocation &entry) {
+ return idx < entry.instruction_index;
+ });
+	if (it == m_instruction_locations.begin()) { return std::nullopt; }
+	return *std::prev(it);
+}
+
 std::string Bytecode::to_string() const
 {
 	std::ostringstream os;
@@ -83,6 +104,7 @@ std::unique_ptr<Bytecode> Bytecode::deserialize(std::span<const uint8_t> &buffer
  stack_size,
  function_name,
  std::move(instructions),
+ std::vector<InstructionSourceLocation>{},
  std::move(program));
 }
 
@@ -144,8 +166,9 @@ py::PyResult<py::Value> Bytecode::eval_loop(VirtualMachine &vm, Interpreter &int
  // vm.dump();
  if (result.is_err()) {
  auto *exception = result.unwrap_err();
- size_t tb_lineno = 0;
- size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lasti = std::distance(initial_ip, current_ip);
+ const size_t tb_lineno =
+ location_for(tb_lasti).value_or(InstructionSourceLocation{ 0, 0, 0 }).line;
  PyTraceback *tb_next = exception->traceback();
  auto traceback =
  PyTraceback::create(interpreter.execution_frame(), tb_lasti, tb_lineno, tb_next);

src/executable/bytecode/Bytecode.hpp

@@ -15,18 +15,22 @@
 class Bytecode : public Function
 {
 	const InstructionVector m_instructions;
+	const std::vector<InstructionSourceLocation> m_instruction_locations;
 
  public:
 	Bytecode(size_t register_count,
  size_t locals_count,
  size_t stack_size,
  std::string function_name,
  InstructionVector instructions,
+ std::vector<InstructionSourceLocation> instruction_locations,
  std::shared_ptr<Program> program);
 
 	auto begin() const { return m_instructions.begin(); }
 	auto end() const { return m_instructions.end(); }
 
+	std::optional<InstructionSourceLocation> location_for(size_t instruction_index) const;
+
 	std::string to_string() const override;
 
 	std::vector<uint8_t> serialize() const override;

src/executable/bytecode/BytecodeProgram.cpp

@@ -37,6 +37,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  main_func.metadata.stack_size,
  main_func.metadata.function_name,
  std::move(main_func.blocks),
+ std::move(main_func.instruction_locations),
  program);
 	auto consts = PyTuple::create(main_func.metadata.consts);
 	if (consts.is_err()) { TODO(); }
@@ -69,6 +70,7 @@ std::shared_ptr<BytecodeProgram> BytecodeProgram::create(FunctionBlocks &&func_b
  func.metadata.stack_size,
  func.metadata.function_name,
  std::move(func.blocks),
+ std::move(func.instruction_locations),
  program);
  consts = PyTuple::create(func.metadata.consts);
  if (consts.is_err()) { TODO(); }

src/executable/bytecode/Bytecode_tests.cpp

@@ -7,6 +7,73 @@
 
 #include "gtest/gtest.h"
 
+namespace {
+Bytecode make_bytecode_with_locations(std::vector<InstructionSourceLocation> locations)
+{
+	return Bytecode{ /*register_count=*/0,
+ /*locals_count=*/0,
+ /*stack_size=*/0,
+ /*function_name=*/"<test>",
+ InstructionVector{},
+ std::move(locations),
+ /*program=*/nullptr };
+}
+}// namespace
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenTableIsEmpty)
+{
+	auto bc = make_bytecode_with_locations({});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsNulloptWhenQueryPrecedesFirstEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ /*instruction_index=*/5, /*line=*/10, /*column=*/2 },
+	});
+	EXPECT_FALSE(bc.location_for(0).has_value());
+}
+
+TEST(BytecodeLocationFor, ReturnsExactMatchEntry)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	const auto loc = bc.location_for(3);
+	ASSERT_TRUE(loc.has_value());
+	EXPECT_EQ(loc->line, 7u);
+	EXPECT_EQ(loc->column, 4u);
+}
+
+TEST(BytecodeLocationFor, ExtendsEntryUntilNextOne)
+{
+	auto bc = make_bytecode_with_locations({
+ InstructionSourceLocation{ 0, 1, 0 },
+ InstructionSourceLocation{ 3, 7, 4 },
+ InstructionSourceLocation{ 10, 12, 0 },
+	});
+	// Query between entries should return the most recent preceding entry.
+	for (uint32_t idx : { 0u, 1u, 2u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 1u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 3u, 4u, 9u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 7u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 4u) << "idx=" << idx;
+	}
+	for (uint32_t idx : { 10u, 100u, 9999u }) {
+ const auto loc = bc.location_for(idx);
+ ASSERT_TRUE(loc.has_value()) << "idx=" << idx;
+ EXPECT_EQ(loc->line, 12u) << "idx=" << idx;
+ EXPECT_EQ(loc->column, 0u) << "idx=" << idx;
+	}
+}
 
 // FIXME: think about what should be tested here
 // namespace {

src/executable/bytecode/codegen/BytecodeGenerator.cpp

@@ -3119,6 +3119,7 @@ std::shared_ptr<Program> BytecodeGenerator::generate_executable(std::string file
 	ASSERT(m_frame_stack_value_count.size() == 2);
 	ASSERT(m_frame_free_var_count.size() == 2);
 	relocate_labels(m_functions);
+	for (auto &func : m_functions.functions) { func.metadata.filename = filename; }
 	return BytecodeProgram::create(std::move(m_functions), filename, argv);
 }
 
@@ -3130,6 +3131,20 @@ InstructionVector *BytecodeGenerator::allocate_block(size_t function_id)
 	return &function->blocks;
 }
 
+void BytecodeGenerator::record_location_for_next_instruction()
+{
+	ASSERT(m_function_id < m_functions.functions.size());
+	auto &func = *std::next(m_functions.functions.begin(), m_function_id);
+	const auto line = static_cast<uint32_t>(m_current_source_location.start.row + 1);
+	const auto column = static_cast<uint32_t>(m_current_source_location.start.column);
+	auto &locations = func.instruction_locations;
+	if (!locations.empty() && locations.back().line == line && locations.back().column == column) {
+ return;
+	}
+	const auto next_instruction_index = static_cast<uint32_t>(func.blocks.size());
+	locations.emplace_back(next_instruction_index, line, column);
+}
+
 std::shared_ptr<Program> BytecodeGenerator::compile(std::shared_ptr<ast::Module> node,
 	std::vector<std::string> argv,
 	compiler::OptimizationLevel lvl)

src/executable/bytecode/codegen/BytecodeGenerator.hpp

@@ -248,6 +248,8 @@ class BytecodeGenerator : public ast::CodeGenerator
 	ASTContext m_ctx;
 	std::stack<Scope> m_stack;
 
+	SourceLocation m_current_source_location{};
+
 	std::set<size_t> m_clear_exception_before_return_functions;
 	std::unordered_map<size_t, std::vector<std::function<void(bool)>>> m_return_transform;
 	std::unordered_map<size_t, size_t> m_current_exception_depth;
@@ -264,9 +266,12 @@ class BytecodeGenerator : public ast::CodeGenerator
 	template<typename OpType, typename... Args> void emit(Args &&...args)
 	{
  ASSERT(m_current_block);
+ record_location_for_next_instruction();
  m_current_block->push_back(std::make_unique<OpType>(std::forward<Args>(args)...));
 	}
 
+	void record_location_for_next_instruction();
+
 	friend std::ostream &operator<<(std::ostream &os, BytecodeGenerator &generator);
 
 	std::string to_string() const;
@@ -374,8 +379,11 @@ class BytecodeGenerator : public ast::CodeGenerator
 	{
  m_ctx.push_node(node);
  const auto old_function_id = m_function_id;
+ const auto old_source_location = m_current_source_location;
  m_function_id = function_id;
+ m_current_source_location = node->source_location();
  auto *value = node->codegen(this);
+ m_current_source_location = old_source_location;
  m_function_id = old_function_id;
  m_ctx.pop_node();
  return static_cast<BytecodeValue *>(value);

src/executable/bytecode/codegen/BytecodeGenerator_tests.cpp

@@ -1,8 +1,10 @@
+#include "../Bytecode.hpp"
 #include "../BytecodeProgram.hpp"
 #include "BytecodeGenerator.hpp"
 #include "executable/common.hpp"
 #include "lexer/Lexer.hpp"
 #include "parser/Parser.hpp"
+#include "runtime/PyCode.hpp"
 
 #include "gtest/gtest.h"
 
@@ -44,3 +46,29 @@ TEST(BytecodeGenerator, EmitsProgramWithFunctionDefinitions)
 	ASSERT_EQ(bytecode_generator->functions().size(), 2);
 	ASSERT_TRUE(bytecode_generator->main_function());
 }
+
+TEST(BytecodeGenerator, AttachesSourceLineToMainInstructions)
+{
+	constexpr std::string_view program =
+ "x = 1\n"
+ "y = 2\n"
+ "z = 3\n";
+
+	auto bytecode_generator = generate_bytecode(program);
+	auto *code = static_cast<py::PyCode *>(bytecode_generator->main_function());
+	ASSERT_TRUE(code);
+	const auto *bytecode = static_cast<const Bytecode *>(code->function().get());
+
+	// We don't pin down which instruction maps to which line — that's an
+	// implementation detail of the codegen. We do require that at least one
+	// instruction reports each of the three source lines (1, 2, 3) and that
+	// no instruction reports a bogus line.
+	std::set<uint32_t> observed_lines;
+	for (size_t i = 0; i < static_cast<size_t>(std::distance(bytecode->begin(), bytecode->end()));
+ ++i) {
+ if (const auto loc = bytecode->location_for(i)) { observed_lines.insert(loc->line); }
+	}
+	EXPECT_TRUE(observed_lines.contains(1u));
+	EXPECT_TRUE(observed_lines.contains(2u));
+	EXPECT_TRUE(observed_lines.contains(3u));
+}