[clang] [clang] Propagate definition data to all redecls (PR #170090)

[Jonas Hahnfeld via cfe-commits]

https://github.com/hahnjo created 
https://github.com/llvm/llvm-project/pull/170090

Fix the propagation added in commit 0d490ae55f to include all redecls, not only 
previous ones. This fixes another instance of the assertion "Cannot get layout 
of forward declarations" in `getASTRecordLayout()`.

Kudos to Alexander Kornienko for providing an initial version of the reproducer 
that I further simplified.

Fixes #170084

>From 4d0c4c133f5a720f052488b982ec3eae7bacde59 Mon Sep 17 00:00:00 2001
From: Jonas Hahnfeld <jonas.hahnf...@cern.ch>
Date: Mon, 1 Dec 2025 09:45:13 +0100
Subject: [PATCH] [clang] Propagate definition data to all redecls

Fix the propagation added in commit 0d490ae55f to include all redecls,
not only previous ones. This fixes another instance of the assertion
"Cannot get layout of forward declarations" in getASTRecordLayout().

Kudos to Alexander Kornienko for providing an initial version of the
reproducer that I further simplified.

Fixes #170084
---
 clang/lib/Serialization/ASTReaderDecl.cpp |  4 +-
 clang/test/Modules/GH170084.cpp           | 75 +++++++++++++++++++++++
 2 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Modules/GH170084.cpp

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp 
b/clang/lib/Serialization/ASTReaderDecl.cpp
index 5456e73956659..882d54f31280a 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2107,8 +2107,8 @@ void ASTDeclMerger::MergeDefinitionData(
     auto *Def = DD.Definition;
     DD = std::move(MergeDD);
     DD.Definition = Def;
-    while ((Def = Def->getPreviousDecl()))
-      cast<CXXRecordDecl>(Def)->DefinitionData = &DD;
+    for (auto *D : Def->redecls())
+      cast<CXXRecordDecl>(D)->DefinitionData = &DD;
     return;
   }
 
diff --git a/clang/test/Modules/GH170084.cpp b/clang/test/Modules/GH170084.cpp
new file mode 100644
index 0000000000000..950499467a6bb
--- /dev/null
+++ b/clang/test/Modules/GH170084.cpp
@@ -0,0 +1,75 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -fmodule-name=stl -fno-cxx-modules -emit-module -fmodules 
-xc++ stl.cppmap -o stl.pcm
+// RUN: %clang_cc1 -fmodule-name=d -fno-cxx-modules -emit-module -fmodules 
-fmodule-file=stl.pcm -xc++ d.cppmap -o d.pcm
+// RUN: %clang_cc1 -fmodule-name=b -fno-cxx-modules -emit-module -fmodules 
-fmodule-file=stl.pcm -xc++ b.cppmap -o b.pcm
+// RUN: %clang_cc1 -fmodule-name=a -fno-cxx-modules -emit-module -fmodules 
-fmodule-file=stl.pcm -fmodule-file=d.pcm -fmodule-file=b.pcm -xc++ a.cppmap -o 
a.pcm
+// RUN: %clang_cc1 -fno-cxx-modules -fmodules -fmodule-file=a.pcm -emit-llvm 
-o /dev/null main.cpp
+
+//--- a.cppmap
+module "a" {
+header "a.h"
+}
+
+//--- a.h
+#include "b.h"
+namespace {
+void a(absl::set<char> c) {
+  absl::set<int> b;
+  c.end();
+  c.contains();
+}
+}  // namespace
+
+//--- b.cppmap
+module "b" {
+header "b.h"
+}
+
+//--- b.h
+#include "c.h"
+void b() { absl::set<char> x; }
+
+//--- c.h
+#include "stl.h"
+namespace absl {
+template <typename>
+class set {
+ public:
+  struct iterator {
+    void u() const;
+  };
+  iterator end() const { return {}; }
+  void contains() const { end().u(); }
+  pair<iterator> e();
+};
+}  // namespace absl
+
+//--- d.cppmap
+module "d" {
+header "d.h"
+}
+
+//--- d.h
+#include "c.h"
+void d() { absl::set<char> x; }
+
+//--- stl.cppmap
+module "stl" {
+header "stl.h"
+}
+
+//--- stl.h
+#ifndef _STL_H_
+#define _STL_H_
+template <class>
+struct pair;
+#endif
+
+//--- main.cpp
+// expected-no-diagnostics
+#include "c.h"
+void f(absl::set<char> o) { o.contains(); }

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