[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
Fri Sep 12 20:50:30 PDT 2025
https://github.com/mpark updated https://github.com/llvm/llvm-project/pull/155948
>From 63519ed11294db85a9896e33a6a34bbc8b067dde 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 302a2ea3cd891fb975cb2e5e20f4595552b7e2e9 Mon Sep 17 00:00:00 2001
From: Michael Park <mcypark at gmail.com>
Date: Fri, 12 Sep 2025 20:37:42 -0700
Subject: [PATCH 2/2] [C++20][Modules] Number the anonymous members if the decl
was instantiated locally.
---
clang/include/clang/AST/DeclTemplate.h | 9 +++++++++
clang/lib/AST/DeclTemplate.cpp | 5 +++--
clang/lib/Sema/SemaTemplateInstantiate.cpp | 1 +
clang/lib/Serialization/ASTReaderDecl.cpp | 11 ++++++++++-
4 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/clang/include/clang/AST/DeclTemplate.h b/clang/include/clang/AST/DeclTemplate.h
index bba72365089f9..0a2cc18b00efa 100644
--- a/clang/include/clang/AST/DeclTemplate.h
+++ b/clang/include/clang/AST/DeclTemplate.h
@@ -1874,6 +1874,11 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
LLVM_PREFERRED_TYPE(bool)
unsigned StrictPackMatch : 1;
+ /// Indicate whether this instantiation was performed locally (as opposed to
+ /// performed externally, during a module precompile).
+ LLVM_PREFERRED_TYPE(bool)
+ unsigned LocalInstantiation : 1;
+
protected:
ClassTemplateSpecializationDecl(ASTContext &Context, Kind DK, TagKind TK,
DeclContext *DC, SourceLocation StartLoc,
@@ -1968,6 +1973,10 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
void setStrictPackMatch(bool Val) { StrictPackMatch = Val; }
+ bool isLocalInstantiation() { return LocalInstantiation; }
+
+ void setLocalInstantiation() { LocalInstantiation = true; }
+
/// Get the point of instantiation (if any), or null if none.
SourceLocation getPointOfInstantiation() const {
return PointOfInstantiation;
diff --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
index 3162857aac5d0..cfb845a1728f8 100644
--- a/clang/lib/AST/DeclTemplate.cpp
+++ b/clang/lib/AST/DeclTemplate.cpp
@@ -974,7 +974,8 @@ ClassTemplateSpecializationDecl::ClassTemplateSpecializationDecl(
SpecializedTemplate->getIdentifier(), PrevDecl),
SpecializedTemplate(SpecializedTemplate),
TemplateArgs(TemplateArgumentList::CreateCopy(Context, Args)),
- SpecializationKind(TSK_Undeclared), StrictPackMatch(StrictPackMatch) {
+ SpecializationKind(TSK_Undeclared), StrictPackMatch(StrictPackMatch),
+ LocalInstantiation(false) {
assert(DK == Kind::ClassTemplateSpecialization || StrictPackMatch == false);
}
@@ -982,7 +983,7 @@ ClassTemplateSpecializationDecl::ClassTemplateSpecializationDecl(ASTContext &C,
Kind DK)
: CXXRecordDecl(DK, TagTypeKind::Struct, C, nullptr, SourceLocation(),
SourceLocation(), nullptr, nullptr),
- SpecializationKind(TSK_Undeclared) {}
+ SpecializationKind(TSK_Undeclared), LocalInstantiation(false) {}
ClassTemplateSpecializationDecl *ClassTemplateSpecializationDecl::Create(
ASTContext &Context, TagKind TK, DeclContext *DC, SourceLocation StartLoc,
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index a72c95d6d77cf..cd3bcc1fc6537 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -3699,6 +3699,7 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,
= dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {
Spec->setTemplateSpecializationKind(TSK);
Spec->setPointOfInstantiation(PointOfInstantiation);
+ Spec->setLocalInstantiation();
}
InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 6b35b205079e5..a40d073f32ea0 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3425,7 +3425,16 @@ 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
+ // but the instantiation occurred locally, we still need to number
+ // the anonymous decls.
+ auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(D);
+ return CTSD && CTSD->isLocalInstantiation();
+ };
+ 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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