[clang] [C++20][Modules] Fix merging of anonymous members of class templates. (PR #155948)
Michael Park via cfe-commits
cfe-commits at lists.llvm.org
Thu Sep 18 12:07:16 PDT 2025
https://github.com/mpark updated https://github.com/llvm/llvm-project/pull/155948
>From 0e8b6420ec9b1060dbc9fa78d299f5bc6d2d002a Mon Sep 17 00:00:00 2001
From: Michael Park <mcypark at gmail.com>
Date: Thu, 28 Aug 2025 14:38:21 -0700
Subject: [PATCH 1/2] [C++20][Modules] Add tests related to anonymous members
in class templates.
---
.../test/Modules/merge-anon-in-template-2.cpp | 47 +++++++++++++++++++
.../test/Modules/merge-anon-in-template-3.cpp | 45 ++++++++++++++++++
2 files changed, 92 insertions(+)
create mode 100644 clang/test/Modules/merge-anon-in-template-2.cpp
create mode 100644 clang/test/Modules/merge-anon-in-template-3.cpp
diff --git a/clang/test/Modules/merge-anon-in-template-2.cpp b/clang/test/Modules/merge-anon-in-template-2.cpp
new file mode 100644
index 0000000000000..15852f0120798
--- /dev/null
+++ b/clang/test/Modules/merge-anon-in-template-2.cpp
@@ -0,0 +1,47 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -fmodule-name=hu-01 -emit-header-unit -xc++-user-header %t/hu-01.h \
+// RUN: -o %t/hu-01.pcm
+
+// RUN: %clang_cc1 -std=c++20 -fmodule-name=hu-02 -emit-header-unit -xc++-user-header %t/hu-02.h \
+// RUN: -Wno-experimental-header-units \
+// RUN: -fmodule-map-file=%t/hu-01.map -fmodule-file=hu-01=%t/hu-01.pcm \
+// RUN: -o %t/hu-02.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-obj %t/main.cpp \
+// RUN: -Wno-experimental-header-units \
+// RUN: -fmodule-map-file=%t/hu-01.map -fmodule-file=hu-01=%t/hu-01.pcm \
+// RUN: -fmodule-map-file=%t/hu-02.map -fmodule-file=hu-02=%t/hu-02.pcm
+
+//--- hu-01.map
+module "hu-01" {
+ header "hu-01.h"
+ export *
+}
+
+//--- hu-02.map
+module "hu-02" {
+ header "hu-02.h"
+ export *
+}
+
+//--- hu-01.h
+template <typename T>
+struct S { union { T x; }; };
+
+using SI = S<int>;
+
+//--- hu-02.h
+template <typename T>
+struct S { union { T x; }; };
+
+inline void f(S<int> s = {}) { s.x; }
+
+//--- main.cpp
+import "hu-01.h";
+void g(S<int>) {}
+
+import "hu-02.h";
+void h() { f(); }
diff --git a/clang/test/Modules/merge-anon-in-template-3.cpp b/clang/test/Modules/merge-anon-in-template-3.cpp
new file mode 100644
index 0000000000000..1ee447e3e524d
--- /dev/null
+++ b/clang/test/Modules/merge-anon-in-template-3.cpp
@@ -0,0 +1,45 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -fmodule-name=hu-01 -emit-header-unit -xc++-user-header %t/hu-01.h \
+// RUN: -o %t/hu-01.pcm
+
+// RUN: %clang_cc1 -std=c++20 -fmodule-name=hu-02 -emit-header-unit -xc++-user-header %t/hu-02.h \
+// RUN: -Wno-experimental-header-units \
+// RUN: -fmodule-map-file=%t/hu-01.map -fmodule-file=hu-01=%t/hu-01.pcm \
+// RUN: -o %t/hu-02.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-obj %t/main.cpp \
+// RUN: -Wno-experimental-header-units \
+// RUN: -fmodule-map-file=%t/hu-01.map -fmodule-file=hu-01=%t/hu-01.pcm \
+// RUN: -fmodule-map-file=%t/hu-02.map -fmodule-file=hu-02=%t/hu-02.pcm
+
+//--- hu-01.map
+module "hu-01" {
+ header "hu-01.h"
+ export *
+}
+
+//--- hu-02.map
+module "hu-02" {
+ header "hu-02.h"
+ export *
+}
+
+//--- hu-01.h
+template <typename T>
+struct S { union { T x; }; };
+
+using SI = S<int>;
+
+//--- hu-02.h
+import "hu-01.h";
+inline void f(S<int> s = {}) { s.x; }
+
+//--- main.cpp
+import "hu-01.h";
+void g(S<int>) {}
+
+import "hu-02.h";
+void h() { f(); }
>From 40746d0adaccfbc7809ecfacd7d1fe46e540f4c8 Mon Sep 17 00:00:00 2001
From: Michael Park <mcypark at gmail.com>
Date: Wed, 17 Sep 2025 21:26:32 -0700
Subject: [PATCH 2/2] [C++20][Modules] Refine the condition of in-place
numbering of anonymous members.
---
clang/include/clang/AST/Decl.h | 22 ++++++++++++++++++++++
clang/lib/Serialization/ASTReaderDecl.cpp | 14 +++++++++++++-
2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index c24d4124d9fc5..ff035e4605497 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -4521,6 +4521,28 @@ class RecordDecl : public TagDecl {
return field_begin() == field_end();
}
+ /// noload_field_* - Iterate over the fields stored in this record
+ /// that are currently loaded; don't attempt to retrieve anything
+ /// an external source.
+ field_range noload_fields() const {
+ return field_range(noload_field_begin(), noload_field_end());
+ }
+
+ field_iterator noload_field_begin() const {
+ // This is necessary for correctness for C++ with modules.
+ // FIXME: Come up with a test case that breaks without definition.
+ if (RecordDecl *D = getDefinition(); D && D != this)
+ return D->noload_field_begin();
+ return field_iterator(decl_iterator(FirstDecl));
+ }
+
+ field_iterator noload_field_end() const { return field_iterator(decl_iterator()); }
+
+ // Whether there are any fields (non-static data members) in this record.
+ bool noload_field_empty() const {
+ return noload_field_begin() == noload_field_end();
+ }
+
/// Note that the definition of this type is now complete.
virtual void completeDefinition();
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 4356f2b734fb0..cf32d4f56b7c2 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3432,7 +3432,19 @@ NamedDecl *ASTDeclReader::getAnonymousDeclForMerging(ASTReader &Reader,
// If this is the first time, but we have parsed a declaration of the context,
// build the anonymous declaration list from the parsed declaration.
auto *PrimaryDC = getPrimaryDCForAnonymousDecl(DC);
- if (PrimaryDC && !cast<Decl>(PrimaryDC)->isFromASTFile()) {
+ auto needToNumberAnonymousDeclsWithin = [](Decl *D) {
+ if (!D->isFromASTFile())
+ return true;
+ // If this is a class template specialization from an AST file, has at least
+ // one field, but none of the fields have been loaded from external storage,
+ // this is a situation where the class template specialization decl
+ // was imported but the definition was instantiated within the source.
+ // In such a case, we still need to number the anonymous decls.
+ auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(D);
+ return CTSD && !CTSD->noload_field_empty() &&
+ !CTSD->hasLoadedFieldsFromExternalStorage();
+ };
+ if (PrimaryDC && needToNumberAnonymousDeclsWithin(cast<Decl>(PrimaryDC))) {
numberAnonymousDeclsWithin(PrimaryDC, [&](NamedDecl *ND, unsigned Number) {
if (Previous.size() == Number)
Previous.push_back(cast<NamedDecl>(ND->getCanonicalDecl()));
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