From d93f1f3c72578bb343dac6431f9901d62ccf7a2e Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Fri, 10 Nov 2023 22:23:56 -0500
Subject: [PATCH] Sema: detect unneeded source locations earlier

This avoids a lot of work that just needs deferred cleanup anyway.
Crucially, also avoids use of undefined in `failWithNeededComptime`.
---
 src/Module.zig | 1 +
 src/Sema.zig   | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/Module.zig b/src/Module.zig
index d475f85c14..8ba856cf68 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -1250,6 +1250,7 @@ pub const ErrorMsg = struct {
         comptime format: []const u8,
         args: anytype,
     ) !*ErrorMsg {
+        assert(src_loc.lazy != .unneeded);
         const err_msg = try gpa.create(ErrorMsg);
         errdefer gpa.destroy(err_msg);
         err_msg.* = try ErrorMsg.init(gpa, src_loc, format, args);
diff --git a/src/Sema.zig b/src/Sema.zig
index b7510cea54..7823b3ae0f 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -2438,8 +2438,9 @@ fn errMsg(
     src: LazySrcLoc,
     comptime format: []const u8,
     args: anytype,
-) error{OutOfMemory}!*Module.ErrorMsg {
+) error{ NeededSourceLocation, OutOfMemory }!*Module.ErrorMsg {
     const mod = sema.mod;
+    if (src == .unneeded) return error.NeededSourceLocation;
     const src_decl = mod.declPtr(block.src_decl);
     return Module.ErrorMsg.create(sema.gpa, src.toSrcLoc(src_decl, mod), format, args);
 }
@@ -2455,14 +2456,13 @@ pub fn fail(
     return sema.failWithOwnedErrorMsg(block, err_msg);
 }
 
-fn failWithOwnedErrorMsg(sema: *Sema, block: ?*Block, err_msg: *Module.ErrorMsg) CompileError {
+fn failWithOwnedErrorMsg(sema: *Sema, block: ?*Block, err_msg: *Module.ErrorMsg) error{ AnalysisFail, OutOfMemory } {
     @setCold(true);
     const gpa = sema.gpa;
     const mod = sema.mod;
 
     ref: {
         errdefer err_msg.destroy(gpa);
-        if (err_msg.src_loc.lazy == .unneeded) return error.NeededSourceLocation;
 
         if (crash_report.is_enabled and mod.comp.debug_compile_errors) {
             var wip_errors: std.zig.ErrorBundle.Wip = undefined;