From 2362e6648b5126c39d1692c145836d4d8883ac66 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Tue, 25 Aug 2026 09:53:11 +0000
Subject: [PATCH] refactor: replace LLVM unreachable with explicit compiler
 error for Throw terminator

The LLVM backend was previously generating an `unreachable` LLVM instruction for the `Throw` IR terminator, as full exception handling is not yet implemented. This led to unsafe execution and undefined behavior if triggered.

This change modifies `codegen.rs` to return a clear Rust `Err` during compile time if an exception construct is encountered, causing compilation to gracefully fail instead of producing a potentially dangerous and undefined binary.

Co-authored-by: Tcode-Motion <188012755+Tcode-Motion@users.noreply.github.com>
---
 compiler/llvm_backend/src/codegen.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/compiler/llvm_backend/src/codegen.rs b/compiler/llvm_backend/src/codegen.rs
index 769ce51e..90fd5916 100644
--- a/compiler/llvm_backend/src/codegen.rs
+++ b/compiler/llvm_backend/src/codegen.rs
@@ -125,8 +125,7 @@ impl<'a> CodegenEngine<'a> {
                         LLVMBuildBr(self.ctx.builder, dest_block);
                     }
                     TerminatorKind::Throw(_) => {
-                        // TODO: Implement exception handling or unwind
-                        LLVMBuildUnreachable(self.ctx.builder);
+                        return Err("Exception handling (throw) is not yet implemented in the LLVM backend".to_string());
                     }
                     TerminatorKind::ConditionalJump {
                         cond,