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

Fix the propagation added in commit 0d490ae 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

Author: hahnjo

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;
   }
 

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(); }