[clang] [C++20][Modules] Load function body from the module that gives canonical decl (PR #111992)

[Dmitry Polukhin via cfe-commits]

https://github.com/dmpolukhin created https://github.com/llvm/llvm-project/pull/111992

Summary:
Fix crash from reproducer provided in https://github.com/llvm/llvm-project/pull/109167#issuecomment-2405289565

Test Plan: TBD (need to further reduce the reproducer)

>From 0d02e79ced894769cfbea45a121670e933e2c886 Mon Sep 17 00:00:00 2001
From: Dmitry Polukhin <dmitry.polukhin at gmail.com>
Date: Fri, 11 Oct 2024 05:35:18 -0700
Subject: [PATCH] [C++20][Modules] Load function body from the module that
 gives cannonical decl

Summary:
Fix crash from reproducer provided in https://github.com/llvm/llvm-project/pull/109167#issuecomment-2405289565

Test Plan: TBD
---
 clang/lib/Serialization/ASTReader.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index e638129897692f..f2853dcf77ae94 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -10057,15 +10057,18 @@ void ASTReader::finishPendingActions() {
       // For a function defined inline within a class template, force the
       // canonical definition to be the one inside the canonical definition of
       // the template. This ensures that we instantiate from a correct view
-      // of the template.
+      // of the template. This behaviour seems to be important only for inline
+      // friend functions. For normal member functions, it might results in
+      // selecting canonical decl from module A but body from module B.
       //
       // Sadly we can't do this more generally: we can't be sure that all
       // copies of an arbitrary class definition will have the same members
       // defined (eg, some member functions may not be instantiated, and some
       // special members may or may not have been implicitly defined).
-      if (auto *RD = dyn_cast<CXXRecordDecl>(FD->getLexicalParent()))
-        if (RD->isDependentContext() && !RD->isThisDeclarationADefinition())
-          continue;
+      if (FD->getFriendObjectKind())
+        if (auto *RD = dyn_cast<CXXRecordDecl>(FD->getLexicalParent()))
+          if (RD->isDependentContext() && !RD->isThisDeclarationADefinition())
+            continue;
 
       // FIXME: Check for =delete/=default?
       const FunctionDecl *Defn = nullptr;