[Sema] Note member decl when initializer list default constructs member

clang/docs/ReleaseNotes.rst

@@ -113,6 +113,10 @@ Attribute Changes in Clang
 Improvements to Clang's diagnostics
 -----------------------------------
 
+- Improve the diagnostics for deleted default constructor errors for C++ class
+  initializer lists that don't explicitly list a class member and thus attempt
+  to implicitly default construct that member.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6113,6 +6113,8 @@ def note_deleted_special_member_class_subobject : Note<
   "destructor}5"
   "%select{||s||}4"
   "|is an ObjC pointer}6">;
+def note_default_constructed_field
+    : Note<"default constructed field %0 declared here">;
 def note_deleted_default_ctor_uninit_field : Note<
   "%select{default constructor of|constructor inherited by}0 "
   "%1 is implicitly deleted because field %2 of "

clang/lib/Sema/SemaInit.cpp

@@ -9148,6 +9148,17 @@ bool InitializationSequence::Diagnose(Sema &S,
               << (Msg ? Msg->getString() : StringRef()) << ArgsRange;
         }
 
+        // If it's a default constructed member, but it's not in the
+        // constructor's initializer list, explicitly note where the member is
+        // declared so the user can see which member is erroneously initialized
+        // with a deleted default constructor.
+        if (Kind.getKind() == InitializationKind::IK_Default &&
+            (Entity.getKind() == InitializedEntity::EK_Member ||
+             Entity.getKind() == InitializedEntity::EK_ParenAggInitMember)) {
+          S.Diag(Entity.getDecl()->getLocation(),
+                 diag::note_default_constructed_field)
+              << Entity.getDecl();
+        }
         S.NoteDeletedFunction(Best->Function);
         break;
       }

clang/test/CXX/class/class.init/p1.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+namespace test_deleted_ctor_note {
+struct A {
+  int a;
+  A() = delete; // expected-note {{'A' has been explicitly marked deleted here}}
+  A(int a_) : a(a_) { }
+};
+
+struct B {
+  A a1, a2, a3; // expected-note {{default constructed field 'a2' declared here}}
+  B(int a_) : a1(a_), a3(a_) { } // expected-error{{call to deleted constructor of 'A'}}
+};
+}

clang/test/CXX/dcl.decl/dcl.init/p14-0x.cpp

@@ -27,7 +27,7 @@ class Friend {
 
 
 class S {
-  NoDefault nd1;
+  NoDefault nd1; // expected-note {{default constructed field 'nd1' declared here}}
   NoDefault nd2 = 42;
   Explicit e1; // expected-note {{here}}
   Explicit e2 = 42; // expected-error {{no viable conversion}}

clang/test/SemaCUDA/inherited-ctor.cu

@@ -81,7 +81,7 @@ namespace DefaultCtorInvalid {
   };
 
   struct C {
-    struct B b;
+    struct B b; // expected-note{{default constructed field 'b' declared here}}
     C() {} // expected-error{{call to implicitly-deleted default constructor of 'struct B'}}
            // expected-note@-6{{default constructor of 'B' is implicitly deleted because field 's' has a deleted default constructor}}
            // expected-note@-15{{'S' has been explicitly marked deleted here}}