<format>: fix std::format("{:#.precision}", floating)

stl/inc/format

@@ -2864,7 +2864,7 @@ _NODISCARD _OutputIt _Fmt_write(
 
     auto _To_upper  = false;
     auto _Format    = chars_format::general;
-    auto _Exponent  = '\0';
+    auto _Exponent  = 'e';
     auto _Precision = _Specs._Precision;
 
     switch (_Specs._Type) {
@@ -2882,8 +2882,7 @@ _NODISCARD _OutputIt _Fmt_write(
         if (_Precision == -1) {
             _Precision = 6;
         }
-        _Format   = chars_format::scientific;
-        _Exponent = 'e';
+        _Format = chars_format::scientific;
         break;
     case 'F':
         _To_upper = true;
@@ -2901,8 +2900,7 @@ _NODISCARD _OutputIt _Fmt_write(
         if (_Precision == -1) {
             _Precision = 6;
         }
-        _Format   = chars_format::general;
-        _Exponent = 'e';
+        _Format = chars_format::general;
         break;
     }
 
@@ -3015,7 +3013,7 @@ _NODISCARD _OutputIt _Fmt_write(
             _Zeroes_to_append = _Extra_precision;
             break;
         case chars_format::general:
-            if (_Specs._Alt) {
+            if (_Specs._Alt && (_Specs._Type == 'g' || _Specs._Type == 'G')) {
                 auto _Digits = static_cast<int>(_Exponent_start - _Buffer_start);
 
                 if (!_Append_decimal) {

tests/libcxx/expected_results.txt

@@ -1062,11 +1062,7 @@ std/ranges/range.adaptors/range.take/adaptor.pass.cpp FAIL
 std/ranges/range.factories/range.single.view/cpo.pass.cpp FAIL
 std/thread/futures/futures.task/futures.task.members/ctor2.compile.pass.cpp FAIL
 std/utilities/format/format.functions/escaped_output.ascii.pass.cpp FAIL
-std/utilities/format/format.functions/format.locale.pass.cpp FAIL
-std/utilities/format/format.functions/format.pass.cpp FAIL
 std/utilities/format/format.functions/locale-specific_form.pass.cpp FAIL
-std/utilities/format/format.functions/vformat.locale.pass.cpp FAIL
-std/utilities/format/format.functions/vformat.pass.cpp FAIL
 std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/ctad.static.compile.pass.cpp FAIL
 std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.inv/invoke.pass.cpp:0 FAIL
 std/utilities/function.objects/refwrap/refwrap.const/type_conv_ctor.pass.cpp:0 FAIL

tests/std/test.lst

@@ -218,6 +218,7 @@ tests\GH_002769_handle_deque_block_pointers
 tests\GH_002789_Hash_vec_Tidy
 tests\GH_002989_nothrow_unwrappable
 tests\GH_002992_unwrappable_iter_sent_pairs
+tests\GH_003003_format_decimal_point
 tests\GH_003022_substr_allocator
 tests\GH_003105_piecewise_densities
 tests\GH_003119_error_category_ctor

tests/std/tests/GH_003003_format_decimal_point/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\concepts_20_matrix.lst

tests/std/tests/GH_003003_format_decimal_point/test.cpp

@@ -0,0 +1,33 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <format>
+
+int main() {
+    assert(std::format("{:#.0}", 0.0) == "0.");
+    assert(std::format("{:#.1}", 0.0) == "0.");
+    assert(std::format("{:#.2}", 0.0) == "0.");
+
+    assert(std::format("{:#.0}", 1200.0) == "1.e+03");
+    assert(std::format("{:#.1}", 1200.0) == "1.e+03");
+    assert(std::format("{:#.2}", 1200.0) == "1.2e+03");
+    assert(std::format("{:#.3}", 1200.0) == "1.2e+03");
+    assert(std::format("{:#.4}", 1200.0) == "1200.");
+    assert(std::format("{:#.5}", 1200.0) == "1200.");
+    assert(std::format("{:#.6}", 1200.0) == "1200.");
+
+    assert(std::format("{:#.0}", 0.123) == "0.1");
+    assert(std::format("{:#.1}", 0.123) == "0.1");
+    assert(std::format("{:#.2}", 0.123) == "0.12");
+    assert(std::format("{:#.3}", 0.123) == "0.123");
+    assert(std::format("{:#.4}", 0.123) == "0.123");
+    assert(std::format("{:#.5}", 0.123) == "0.123");
+
+    assert(std::format("{:#.0}", 10.1) == "1.e+01");
+    assert(std::format("{:#.1}", 10.1) == "1.e+01");
+    assert(std::format("{:#.2}", 10.1) == "10.");
+    assert(std::format("{:#.3}", 10.1) == "10.1");
+    assert(std::format("{:#.4}", 10.1) == "10.1");
+    assert(std::format("{:#.5}", 10.1) == "10.1");
+}