[llvm-branch-commits] [clang] release/19.x: [C++20] [Modules] Don't diagnose duplicated implicit decl in multiple named modules (#102423) (PR #102425)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/102425

>From 3f193bcc5a72f05a4b2d5f74a0ee16a76b3b32f2 Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Thu, 8 Aug 2024 13:29:59 +0800
Subject: [PATCH] [C++20] [Modules] Don't diagnose duplicated implicit decl in
 multiple named modules (#102423)

Close https://github.com/llvm/llvm-project/issues/102360
Close https://github.com/llvm/llvm-project/issues/102349

http://eel.is/c++draft/basic.def.odr#15.3 makes it clear that the
duplicated deinition are not allowed to be attached to named modules.

But we need to filter the implicit declarations as user can do nothing
about it and the diagnostic message is annoying.

(cherry picked from commit e72d956b99e920b0fe2a7946eb3a51b9e889c73c)
---
 clang/lib/Serialization/ASTReaderDecl.cpp | 65 +++++++++++++++++------
 clang/test/Modules/pr102349.cppm          | 52 ++++++++++++++++++
 clang/test/Modules/pr102360.cppm          | 53 ++++++++++++++++++
 3 files changed, 154 insertions(+), 16 deletions(-)
 create mode 100644 clang/test/Modules/pr102349.cppm
 create mode 100644 clang/test/Modules/pr102360.cppm

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 31ab6c651d59f4..ccc97f65526d6c 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3684,6 +3684,54 @@ static void inheritDefaultTemplateArguments(ASTContext &Context,
   }
 }
 
+// [basic.link]/p10:
+//    If two declarations of an entity are attached to different modules,
+//    the program is ill-formed;
+static void checkMultipleDefinitionInNamedModules(ASTReader &Reader, Decl *D,
+                                                  Decl *Previous) {
+  Module *M = Previous->getOwningModule();
+
+  // We only care about the case in named modules.
+  if (!M || !M->isNamedModule())
+    return;
+
+  // If it is previous implcitly introduced, it is not meaningful to
+  // diagnose it.
+  if (Previous->isImplicit())
+    return;
+
+  // FIXME: Get rid of the enumeration of decl types once we have an appropriate
+  // abstract for decls of an entity. e.g., the namespace decl and using decl
+  // doesn't introduce an entity.
+  if (!isa<VarDecl, FunctionDecl, TagDecl, RedeclarableTemplateDecl>(Previous))
+    return;
+
+  // Skip implicit instantiations since it may give false positive diagnostic
+  // messages.
+  // FIXME: Maybe this shows the implicit instantiations may have incorrect
+  // module owner ships. But given we've finished the compilation of a module,
+  // how can we add new entities to that module?
+  if (auto *VTSD = dyn_cast<VarTemplateSpecializationDecl>(Previous);
+      VTSD && !VTSD->isExplicitSpecialization())
+    return;
+  if (auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(Previous);
+      CTSD && !CTSD->isExplicitSpecialization())
+    return;
+  if (auto *Func = dyn_cast<FunctionDecl>(Previous))
+    if (auto *FTSI = Func->getTemplateSpecializationInfo();
+        FTSI && !FTSI->isExplicitSpecialization())
+      return;
+
+  // It is fine if they are in the same module.
+  if (Reader.getContext().isInSameModule(M, D->getOwningModule()))
+    return;
+
+  Reader.Diag(Previous->getLocation(),
+              diag::err_multiple_decl_in_different_modules)
+      << cast<NamedDecl>(Previous) << M->Name;
+  Reader.Diag(D->getLocation(), diag::note_also_found);
+}
+
 void ASTDeclReader::attachPreviousDecl(ASTReader &Reader, Decl *D,
                                        Decl *Previous, Decl *Canon) {
   assert(D && Previous);
@@ -3697,22 +3745,7 @@ void ASTDeclReader::attachPreviousDecl(ASTReader &Reader, Decl *D,
 #include "clang/AST/DeclNodes.inc"
   }
 
-  // [basic.link]/p10:
-  //    If two declarations of an entity are attached to different modules,
-  //    the program is ill-formed;
-  //
-  // FIXME: Get rid of the enumeration of decl types once we have an appropriate
-  // abstract for decls of an entity. e.g., the namespace decl and using decl
-  // doesn't introduce an entity.
-  if (Module *M = Previous->getOwningModule();
-      M && M->isNamedModule() &&
-      isa<VarDecl, FunctionDecl, TagDecl, RedeclarableTemplateDecl>(Previous) &&
-      !Reader.getContext().isInSameModule(M, D->getOwningModule())) {
-    Reader.Diag(Previous->getLocation(),
-                diag::err_multiple_decl_in_different_modules)
-        << cast<NamedDecl>(Previous) << M->Name;
-    Reader.Diag(D->getLocation(), diag::note_also_found);
-  }
+  checkMultipleDefinitionInNamedModules(Reader, D, Previous);
 
   // If the declaration was visible in one module, a redeclaration of it in
   // another module remains visible even if it wouldn't be visible by itself.
diff --git a/clang/test/Modules/pr102349.cppm b/clang/test/Modules/pr102349.cppm
new file mode 100644
index 00000000000000..2d166c9e93fcfc
--- /dev/null
+++ b/clang/test/Modules/pr102349.cppm
@@ -0,0 +1,52 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -emit-module-interface -o %t/b.pcm \
+// RUN:   -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/c.cppm -emit-module-interface -o %t/c.pcm \
+// RUN:   -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/d.cpp -fsyntax-only -verify \
+// RUN:   -fprebuilt-module-path=%t
+
+//--- a.cppm
+export module a;
+
+export template<typename>
+struct a;
+
+template<typename>
+struct a {
+};
+
+export template<typename T>
+constexpr auto aa = a<T>();
+
+//--- b.cppm
+export module b;
+
+import a;
+
+static void b() {
+	static_cast<void>(a<void>());
+}
+
+//--- c.cppm
+export module c;
+
+import a;
+
+static void c() {
+	static_cast<void>(aa<void>);
+}
+
+//--- d.cpp
+// expected-no-diagnostics
+import a;
+import b;
+import c;
+
+static void d() {
+	static_cast<void>(a<void>());
+}
diff --git a/clang/test/Modules/pr102360.cppm b/clang/test/Modules/pr102360.cppm
new file mode 100644
index 00000000000000..e0dab1a0318015
--- /dev/null
+++ b/clang/test/Modules/pr102360.cppm
@@ -0,0 +1,53 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -emit-module-interface -o %t/b.pcm \
+// RUN:   -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/c.cppm -emit-module-interface -o %t/c.pcm \
+// RUN:   -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/d.cpp -fsyntax-only -verify \
+// RUN:   -fprebuilt-module-path=%t
+
+//--- a.cppm
+export module a;
+
+template<typename>
+constexpr auto impl = true;
+
+export template<typename T>
+void a() {
+}
+
+export template<typename T> requires impl<T>
+void a() {
+}
+
+//--- b.cppm
+export module b;
+
+import a;
+
+static void b() {
+	a<void>();
+}
+
+//--- c.cppm
+export module c;
+
+import a;
+
+static void c() {
+	a<void>();
+}
+
+//--- d.cpp
+// expected-no-diagnostics
+import a;
+import b;
+import c;
+
+static void d() {
+	a<void>();
+}