[clang] [PATCH] [clang][frontend] Fix AllocKind retrieving for `CXXConstructorDecl` refs #132794 (PR #133077)

[Paul Schwabauer via cfe-commits]

https://github.com/koplas updated https://github.com/llvm/llvm-project/pull/133077

>From 686a9a772400316e5597409c7bd14f4d73e353bf Mon Sep 17 00:00:00 2001
From: koplas <paul at schwabauer.co>
Date: Wed, 26 Mar 2025 13:49:44 +0100
Subject: [PATCH] [PATCH] [clang][frontend] Fix AllocKind retrieving for
 `CXXConstructorDecl` refs #132794

When getting the `ExplicitSpecifier` of the `CXXConstructorDecl`, one
of the canonical declaration is returned. When writing the declaration
record with `ExplicitSpecifier`, the `AllocKind` of the canonical
declaration has to be used.
If this is not done it will later crash when on deserialization.
---
 clang/include/clang/AST/DeclCXX.h             |  5 ++-
 .../test/Modules/ComplexExplicitSpecifier.cpp | 45 +++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Modules/ComplexExplicitSpecifier.cpp

diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index dbd02ef7f8011..7728669b3bcec 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -2601,10 +2601,11 @@ class CXXConstructorDecl final
   void anchor() override;
 
   size_t numTrailingObjects(OverloadToken<InheritedConstructor>) const {
-    return CXXConstructorDeclBits.IsInheritingConstructor;
+    return getCanonicalDecl()->CXXConstructorDeclBits.IsInheritingConstructor;
   }
   size_t numTrailingObjects(OverloadToken<ExplicitSpecifier>) const {
-    return CXXConstructorDeclBits.HasTrailingExplicitSpecifier;
+    return getCanonicalDecl()
+        ->CXXConstructorDeclBits.HasTrailingExplicitSpecifier;
   }
 
   ExplicitSpecifier getExplicitSpecifierInternal() const {
diff --git a/clang/test/Modules/ComplexExplicitSpecifier.cpp b/clang/test/Modules/ComplexExplicitSpecifier.cpp
new file mode 100644
index 0000000000000..33501ba264cc6
--- /dev/null
+++ b/clang/test/Modules/ComplexExplicitSpecifier.cpp
@@ -0,0 +1,45 @@
+// Tests complex explicit constructor across modules.
+//
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/Foo.cppm \
+// RUN: -o %t/Foo.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface \
+// RUN: -fmodule-file=Foo=%t/Foo.pcm \
+// RUN: %t/Bar.cppm \
+// RUN: -o %t/Bar.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-obj \
+// RUN: -main-file-name Bar.cppm \
+// RUN: -fmodule-file=Foo=%t/Foo.pcm \
+// RUN: -x pcm %t/Bar.pcm \
+// RUN: -o %t/Bar.o
+
+//--- Foo.cppm
+export module Foo;
+
+export {
+template<class T>
+class Foo {
+  public:
+    template<class... Args>
+    explicit (sizeof...(Args) == 1) Foo(Args&&... args);
+};
+}
+
+template<class T>
+template<class... Args>
+inline Foo<T>::Foo(Args&&... args) {}
+
+//--- Bar.cppm
+export module Bar;
+import Foo;
+
+struct Bar {};
+
+void a() {
+  auto foo = Foo<Bar>{};
+}