From a9c4dc84f487c4764c5787439ea87962f698d511 Mon Sep 17 00:00:00 2001
From: sin-ack <sin-ack@users.noreply.github.com>
Date: Fri, 12 Aug 2022 21:51:07 +0000
Subject: [PATCH] Sema: Revert sema.err to null if the Decl already has an
 error

Previously we would assign the error message to Sema and then never
clear it even when destroying the error message, which caused memory
corruption.

Closes #12437
---
 src/Sema.zig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index ed8204b346..879ecb4e2f 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -1906,8 +1906,6 @@ fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
     }
 
     const mod = sema.mod;
-    sema.err = err_msg;
-
     {
         errdefer err_msg.destroy(mod.gpa);
         if (err_msg.src_loc.lazy == .unneeded) {
@@ -1925,8 +1923,10 @@ fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
     const gop = mod.failed_decls.getOrPutAssumeCapacity(sema.owner_decl_index);
     if (gop.found_existing) {
         // If there are multiple errors for the same Decl, prefer the first one added.
+        sema.err = null;
         err_msg.destroy(mod.gpa);
     } else {
+        sema.err = err_msg;
         gop.value_ptr.* = err_msg;
     }
     return error.AnalysisFail;