[clang] [clang][modules] Fix std::initializer_list recognition if it's exported out of a module (PR #118537)

[via cfe-commits]

https://github.com/jijjijj created https://github.com/llvm/llvm-project/pull/118537

If the std::initializer_list is exported out of module, its `DeclContext` is not a namespace as `Sema::isStdInitializerList` expects, but an `Decl::Kind::Export` and only its parent is a namespace. So this commit makes `Sema::isStdInitializerList` account for that.

I'm really new to clang so I'm not 100% sure that was the issue, it seems so and it fixes compilation. Also I probably need to add tests but I'd like someone to approve the idea first.

Fixes https://github.com/llvm/llvm-project/issues/118218

>From d0a3059a10b7ceeb7e9c27068266f8c41e794203 Mon Sep 17 00:00:00 2001
From: jijjijj <realjijjijj at gmail.com>
Date: Tue, 3 Dec 2024 22:57:34 +0300
Subject: [PATCH] Fix std::initializer_list recognition if it's exported out of
 a module

If the std::initializer_list is exported out of module, its DeclContext is not a namespace as `Sema::isStdInitializerList` expects, but an `Decl::Kind::Export` and only its parent is a namespace. So this commit makes `Sema::isStdInitializerList` account for that.
---
 clang/lib/Sema/SemaDeclCXX.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 7e8e321c4b90e6..4572229562ed3b 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11919,8 +11919,12 @@ bool Sema::isStdInitializerList(QualType Ty, QualType *Element) {
     CXXRecordDecl *TemplateClass = Template->getTemplatedDecl();
     if (TemplateClass->getIdentifier() !=
             &PP.getIdentifierTable().get("initializer_list") ||
-        !getStdNamespace()->InEnclosingNamespaceSetOf(
-            TemplateClass->getDeclContext()))
+        !(getStdNamespace()->InEnclosingNamespaceSetOf(
+            TemplateClass->getDeclContext()) ||
+        // if decl context is an export from module we need to check the parent
+        (TemplateClass->getDeclContext()->getDeclKind() == Decl::Kind::Export &&
+            getStdNamespace()->InEnclosingNamespaceSetOf(
+                TemplateClass->getDeclContext()->getParent()))))
       return false;
     // This is a template called std::initializer_list, but is it the right
     // template?