[clang] [C++20] [Modules] Don't set modules owner ship information for builtin declarations (PR #102115)

[Matheus Izvekov via cfe-commits]

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@@ -2376,6 +2376,12 @@ NamedDecl *Sema::LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID,
   FunctionDecl *New = CreateBuiltin(II, R, ID, Loc);
   RegisterLocallyScopedExternCDecl(New, S);
 
+  // Builtin functions shouldn't be owned by any module.
+  if (New->hasOwningModule()) {
+    New->setLocalOwningModule(nullptr);
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mizvekov wrote:

Since as you pointed out we already have this oddness for eagerly created implicit declarations, it seems like it would be an incremental improvement to have the same non-ideal outcome for both.

But I think the means to achieve it as implemented in the current patch looks fragile.

As Corentin suggested, I'd rather change the context around when we lazily create the builtin, than not having to forget to change it later.

https://github.com/llvm/llvm-project/pull/102115