[C++20] [Modules] Reference all the possible declarations for ADL

In no transitive change mode, the unresolved ADL may not
be referenced, then it is problematic if the change didn't get
propagated correctly. This patch add references to all the possible
module files for the unresolved ADL to solve the problem.

Author: ChuanqiXu9

clang/lib/Serialization/ASTWriterStmt.cpp

@@ -19,6 +19,7 @@
 #include "clang/AST/ExprOpenMP.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Lex/Token.h"
+#include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/ASTRecordWriter.h"
 #include "llvm/Bitstream/BitstreamWriter.h"
 using namespace clang;
@@ -2099,6 +2100,22 @@ void ASTStmtWriter::VisitUnresolvedLookupExpr(UnresolvedLookupExpr *E) {
   CurrentPackingBits.addBit(E->requiresADL());
   Record.AddDeclRef(E->getNamingClass());
   Code = serialization::EXPR_CXX_UNRESOLVED_LOOKUP;
+
+  if (Writer.isWritingStdCXXNamedModules() && Writer.getChain()) {
+    // Referencing all the possible declarations to make sure the change get
+    // propagted.
+    DeclarationName Name = E->getName();
+    for (auto *Found :
+         Writer.getASTContext().getTranslationUnitDecl()->lookup(Name))
+      if (Found->isFromASTFile())
+        Writer.GetDeclRef(Found);
+
+    llvm::SmallVector<NamespaceDecl *> ExternalNSs;
+    Writer.getChain()->ReadKnownNamespaces(ExternalNSs);
+    for (auto *NS : ExternalNSs)
+      for (auto *Found : NS->lookup(Name))
+        Writer.GetDeclRef(Found);
+  }
 }
 
 void ASTStmtWriter::VisitTypeTraitExpr(TypeTraitExpr *E) {

clang/test/Modules/transitive-adl-change.cppm

@@ -0,0 +1,112 @@
+// Test that a change related to an ADL can be propagated correctly.
+//
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/Common.cppm -emit-reduced-module-interface -o %t/Common.pcm
+//
+// RUN: %clang_cc1 -std=c++20 %t/m-partA.cppm -emit-reduced-module-interface -o %t/m-partA.pcm \
+// RUN:     -fmodule-file=Common=%t/Common.pcm
+// RUN: %clang_cc1 -std=c++20 %t/m-partA.v1.cppm -emit-reduced-module-interface -o \
+// RUN:     %t/m-partA.v1.pcm -fmodule-file=Common=%t/Common.pcm
+// RUN: %clang_cc1 -std=c++20 %t/m-partB.cppm -emit-reduced-module-interface -o %t/m-partB.pcm
+// RUN: %clang_cc1 -std=c++20 %t/m.cppm -emit-reduced-module-interface -o %t/m.pcm \
+// RUN:     -fmodule-file=m:partA=%t/m-partA.pcm -fmodule-file=m:partB=%t/m-partB.pcm \
+// RUN:     -fmodule-file=Common=%t/Common.pcm
+// RUN: %clang_cc1 -std=c++20 %t/m.cppm -emit-reduced-module-interface -o %t/m.v1.pcm \
+// RUN:     -fmodule-file=m:partA=%t/m-partA.v1.pcm -fmodule-file=m:partB=%t/m-partB.pcm \
+// RUN:     -fmodule-file=Common=%t/Common.pcm
+//
+// Produce B.pcm and B.v1.pcm
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -emit-reduced-module-interface -o %t/B.pcm \
+// RUN:     -fmodule-file=m=%t/m.pcm -fmodule-file=m:partA=%t/m-partA.pcm \
+// RUN:     -fmodule-file=m:partB=%t/m-partB.pcm -fmodule-file=Common=%t/Common.pcm
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -emit-reduced-module-interface -o %t/B.v1.pcm \
+// RUN:     -fmodule-file=m=%t/m.v1.pcm -fmodule-file=m:partA=%t/m-partA.v1.pcm \
+// RUN:     -fmodule-file=m:partB=%t/m-partB.pcm -fmodule-file=Common=%t/Common.pcm
+//
+// Verify that both B.pcm and B.v1.pcm can work as expected.
+// RUN: %clang_cc1 -std=c++20 %t/use.cpp -fsyntax-only -verify -fmodule-file=m=%t/m.pcm \
+// RUN:     -fmodule-file=m:partA=%t/m-partA.pcm -fmodule-file=m:partB=%t/m-partB.pcm \
+// RUN:     -fmodule-file=B=%t/B.pcm -fmodule-file=Common=%t/Common.pcm \
+// RUN:     -DEXPECTED_VALUE=false
+// RUN: %clang_cc1 -std=c++20 %t/use.cpp -fsyntax-only -verify -fmodule-file=m=%t/m.v1.pcm \
+// RUN:     -fmodule-file=m:partA=%t/m-partA.v1.pcm -fmodule-file=m:partB=%t/m-partB.pcm \
+// RUN:     -fmodule-file=B=%t/B.v1.pcm -fmodule-file=Common=%t/Common.pcm \
+// RUN:     -DEXPECTED_VALUE=true
+//
+// Since we add new ADL function in m-partA.v1.cppm, B.v1.pcm is expected to not be the same with
+// B.pcm.
+// RUN: not diff %t/B.pcm %t/B.v1.pcm &> /dev/null
+ 
+// Test that BMI won't differ if it doesn't refer adl.
+// RUN: %clang_cc1 -std=c++20 %t/C.cppm -emit-reduced-module-interface -o %t/C.pcm \
+// RUN:     -fmodule-file=m=%t/m.pcm -fmodule-file=m:partA=%t/m-partA.pcm \
+// RUN:     -fmodule-file=m:partB=%t/m-partB.pcm -fmodule-file=Common=%t/Common.pcm
+// RUN: %clang_cc1 -std=c++20 %t/C.cppm -emit-reduced-module-interface -o %t/C.v1.pcm \
+// RUN:     -fmodule-file=m=%t/m.v1.pcm -fmodule-file=m:partA=%t/m-partA.v1.pcm \
+// RUN:     -fmodule-file=m:partB=%t/m-partB.pcm -fmodule-file=Common=%t/Common.pcm
+// RUN: diff %t/C.pcm %t/C.v1.pcm &> /dev/null
+ 
+//--- Common.cppm
+export module Common;
+ 
+export namespace N {
+    struct A {
+        constexpr operator int() {
+            return 43;
+        }
+    };
+}
+ 
+//--- m-partA.cppm
+export module m:partA;
+import Common;
+ 
+export namespace N {}
+ 
+//--- m-partA.v1.cppm
+export module m:partA;
+import Common;
+ 
+export namespace N {
+constexpr bool adl(A) { return true; }
+}
+ 
+//--- m-partB.cppm
+export module m:partB;
+ 
+export constexpr bool adl(int) { return false; }
+ 
+//--- m.cppm
+export module m;
+export import :partA;
+export import :partB;
+ 
+//--- B.cppm
+export module B;
+import m;
+ 
+export template <class C>
+constexpr bool test_adl(C c) {
+    return adl(c);
+}
+ 
+//--- use.cpp
+// expected-no-diagnostics
+import B;
+import Common;
+ 
+void test() {
+    N::A a;
+    static_assert(test_adl(a) == EXPECTED_VALUE);
+}
+ 
+//--- C.cppm
+export module B;
+import m;
+ 
+export template <class C>
+constexpr bool not_test_adl(C c) {
+    return false;
+}