[PATCH] D85390: [Clang] Add note for bad conversion error when expression is of forward-declared type

[Zequan Wu via Phabricator via cfe-commits]

zequanwu updated this revision to Diff 283744.
zequanwu added a comment.

Add new note and test case.
I think for the class template case, the new note might not be useful, since they might simply caused by mismatch of template arguments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85390/new/

https://reviews.llvm.org/D85390

Files:
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/SemaInit.cpp
  clang/test/Modules/namespaces.cpp
  clang/test/SemaCXX/elaborated-type-specifier.cpp
  clang/test/SemaCXX/pointer-forward-declared-class-conversion.cpp


Index: clang/test/SemaCXX/pointer-forward-declared-class-conversion.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/pointer-forward-declared-class-conversion.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+class A1 {};
+class B1; // expected-note{{forward declaration of class here, conversion will be valid if the class 'B1' is derived from 'A1'}}
+B1 *b1;
+A1 *a1 = b1; // expected-error{{cannot initialize a variable of type 'A1 *' with an lvalue of type 'B1 *'}}
+
+template <class C> class A2 {};
+template <class C> class B2;
+B2<int> *b2;
+A2<int> *a2 = b2; // expected-error{{cannot initialize a variable of type 'A2<int> *' with an lvalue of type 'B2<int> *'}}
Index: clang/test/SemaCXX/elaborated-type-specifier.cpp
===================================================================
--- clang/test/SemaCXX/elaborated-type-specifier.cpp
+++ clang/test/SemaCXX/elaborated-type-specifier.cpp
@@ -26,7 +26,7 @@
 }
 
 void test_X_elab(NS::X x) {
-  struct S4 *s4 = 0;
+  struct S4 *s4 = 0; // expected-note{{forward declaration of class here, conversion will be valid if the struct 'S4' is derived from 'NS::S4'}}
   x.test_elab2(s4); // expected-error{{cannot initialize a parameter of type 'NS::S4 *' with an lvalue of type 'struct S4 *'}}
 }
 
Index: clang/test/Modules/namespaces.cpp
===================================================================
--- clang/test/Modules/namespaces.cpp
+++ clang/test/Modules/namespaces.cpp
@@ -78,7 +78,8 @@
 
 // expected-note at Inputs/namespaces-right.h:60 {{passing argument to parameter here}}
 // expected-note at Inputs/namespaces-right.h:67 {{passing argument to parameter here}}
-
+// expected-note at Inputs/namespaces-left.h:63 {{forward declaration of class here, conversion will be valid if the class 'N11::(anonymous namespace)::Foo' is derived from 'N11::(anonymous namespace)::Foo'}}
+// expected-note at Inputs/namespaces-left.h:70 {{forward declaration of class here, conversion will be valid if the class 'N12::(anonymous namespace)::Foo' is derived from 'N12::(anonymous namespace)::Foo'}}
 // Test that bringing in one name from an overload set does not hide the rest.
 void testPartialImportOfOverloadSet() {
   void (*p)() = N13::p;
Index: clang/lib/Sema/SemaInit.cpp
===================================================================
--- clang/lib/Sema/SemaInit.cpp
+++ clang/lib/Sema/SemaInit.cpp
@@ -8707,6 +8707,16 @@
     if (entity.getKind() == InitializedEntity::EK_Result)
       S.EmitRelatedResultTypeNoteForReturn(destType);
   }
+  QualType fromType = op->getType();
+  auto *fromDecl = fromType.getTypePtr()->getPointeeCXXRecordDecl();
+  auto *destDecl = destType.getTypePtr()->getPointeeCXXRecordDecl();
+  if (fromDecl && destDecl && fromDecl->getDeclKind() == Decl::CXXRecord &&
+      destDecl->getDeclKind() == Decl::CXXRecord &&
+      !fromDecl->isInvalidDecl() && !destDecl->isInvalidDecl() &&
+      !fromDecl->hasDefinition())
+    S.Diag(fromDecl->getLocation(), diag::note_forward_class_conversion)
+        << fromDecl->isStruct() << S.getASTContext().getTagDeclType(fromDecl)
+        << S.getASTContext().getTagDeclType(destDecl);
 }
 
 static void diagnoseListInit(Sema &S, const InitializedEntity &Entity,
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2005,6 +2005,9 @@
   "|: different return type%diff{ ($ vs $)|}5,6"
   "|: different qualifiers (%5 vs %6)"
   "|: different exception specifications}4">;
+def note_forward_class_conversion : Note<"forward declaration of class here, "
+  "conversion will be valid if the %select{class|struct}0 %1 is derived from %2"
+  >;
 
 def err_lvalue_to_rvalue_ref : Error<"rvalue reference %diff{to type $ cannot "
   "bind to lvalue of type $|cannot bind to incompatible lvalue}0,1">;


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