Improve diagnostic on default-initializing const variables (PR20208).

This tweaks the diagnostic wording slighly, and adds a fixit on a note.
An alternative would be to add the fixit directly on the diagnostic, see
the review thread linked to from the bug for a few notes on that approach.

llvm-svn: 213725

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -5203,7 +5203,9 @@ def err_address_space_qualified_delete : Error<
 
 def err_default_init_const : Error<
   "default initialization of an object of const type %0"
-  "%select{| requires a user-provided default constructor}1">;
+  "%select{| without a user-provided default constructor}1">;
+def note_add_initializer : Note<
+  "add an explicit initializer to initialize %0">;
 def err_delete_operand : Error<"cannot delete expression of type %0">;
 def ext_delete_void_ptr_operand : ExtWarn<
   "cannot delete expression with pointer-to-'void' type %0">;

clang/lib/Sema/SemaInit.cpp

@@ -6455,6 +6455,26 @@ static void diagnoseListInit(Sema &S, const InitializedEntity &Entity,
          "Inconsistent init list check result.");
 }
 
+/// Prints a fixit for adding a null initializer for |Entity|. Call this only
+/// right after emitting a diagnostic.
+static void maybeEmitZeroInitializationFixit(Sema &S,
+                                             InitializationSequence &Sequence,
+                                             const InitializedEntity &Entity) {
+  if (Entity.getKind() != InitializedEntity::EK_Variable)
+    return;
+
+  VarDecl *VD = cast<VarDecl>(Entity.getDecl());
+  if (VD->getInit() || VD->getLocEnd().isMacroID())
+    return;
+
+  QualType VariableTy = VD->getType().getCanonicalType();
+  SourceLocation Loc = S.getLocForEndOfToken(VD->getLocEnd());
+  std::string Init = S.getFixItZeroInitializerForType(VariableTy, Loc);
+
+  S.Diag(Loc, diag::note_add_initializer)
+      << VD << FixItHint::CreateInsertion(Loc, Init);
+}
+
 bool InitializationSequence::Diagnose(Sema &S,
                                       const InitializedEntity &Entity,
                                       const InitializationKind &Kind,
@@ -6786,6 +6806,7 @@ bool InitializationSequence::Diagnose(Sema &S,
     } else {
       S.Diag(Kind.getLocation(), diag::err_default_init_const)
           << DestType << (bool)DestType->getAs<RecordType>();
+      maybeEmitZeroInitializationFixit(S, *this, Entity);
     }
     break;
 

clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp

@@ -17,7 +17,7 @@ extern int (*const d)(int);
 
 // A variable declaration which uses the constexpr specifier shall have an
 // initializer and shall be initialized by a constant expression.
-constexpr int ni1; // expected-error {{default initialization of an object of const type 'const int'}}
+constexpr int ni1; // expected-error {{default initialization of an object of const type 'const int'}} expected-note {{add an explicit initializer to initialize 'ni1'}}
 constexpr struct C { C(); } ni2; // expected-error {{cannot have non-literal type 'const struct C'}} expected-note 3{{has no constexpr constructors}}
 constexpr double &ni3; // expected-error {{declaration of reference variable 'ni3' requires an initializer}}
 
@@ -34,4 +34,4 @@ struct pixel {
   int x, y;
 };
 constexpr pixel ur = { 1294, 1024 }; // ok
-constexpr pixel origin;              // expected-error {{default initialization of an object of const type 'const pixel' requires a user-provided default constructor}}
+constexpr pixel origin;              // expected-error {{default initialization of an object of const type 'const pixel' without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'origin'}}

clang/test/CXX/dcl.decl/dcl.fct.def/dcl.fct.def.default/p2.cpp

@@ -36,7 +36,7 @@ struct S3 {
 constexpr S3 s3a = S3(0);
 constexpr S3 s3b = s3a;
 constexpr S3 s3c = S3();
-constexpr S3 s3d; // expected-error {{default initialization of an object of const type 'const S3' requires a user-provided default constructor}}
+constexpr S3 s3d; // expected-error {{default initialization of an object of const type 'const S3' without a user-provided default constructor}} expected-note{{add an explicit initializer to initialize 's3d'}}
 
 struct S4 {
   S4() = default;
@@ -119,6 +119,6 @@ namespace PR13492 {
   };
 
   void f() {
-    const B b; // expected-error {{default initialization of an object of const type 'const PR13492::B' requires a user-provided default constructor}}
+    const B b; // expected-error {{default initialization of an object of const type 'const PR13492::B' without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'b'}}
   }
 }

clang/test/CXX/dcl.decl/dcl.init/p6.cpp

@@ -10,15 +10,15 @@ struct NoUserDefault : public MakeNonPOD { };
 struct HasUserDefault { HasUserDefault(); };
 
 void test_const_default_init() {
-  const NoUserDefault x1; // expected-error{{default initialization of an object of const type 'const NoUserDefault' requires a user-provided default constructor}}
+  const NoUserDefault x1; // expected-error{{default initialization of an object of const type 'const NoUserDefault' without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'x1'}}
   const HasUserDefault x2;
-  const int x3; // expected-error{{default initialization of an object of const type 'const int'}}
+  const int x3; // expected-error{{default initialization of an object of const type 'const int'}} expected-note{{add an explicit initializer to initialize 'x3'}}
 }
 
 // rdar://8501008
 struct s0 {};
 struct s1 { static const s0 foo; };
-const struct s0 s1::foo; // expected-error{{default initialization of an object of const type 'const struct s0' requires a user-provided default constructor}}
+const struct s0 s1::foo; // expected-error{{default initialization of an object of const type 'const struct s0' without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'foo'}}
 
 template<typename T>
 struct s2 {

clang/test/CXX/drs/dr0xx.cpp

@@ -852,7 +852,7 @@ namespace dr77 { // dr77: yes
 namespace dr78 { // dr78: sup ????
   // Under DR78, this is valid, because 'k' has static storage duration, so is
   // zero-initialized.
-  const int k; // expected-error {{default initialization of an object of const}}
+  const int k; // expected-error {{default initialization of an object of const}} expected-note{{add an explicit initializer to initialize 'k'}}
 }
 
 // dr79: na

clang/test/CXX/drs/dr4xx.cpp

@@ -1201,7 +1201,7 @@ namespace dr497 { // dr497: yes
     struct S {
       mutable int i;
     };
-    const S cs; // expected-error {{default initialization}}
+    const S cs; // expected-error {{default initialization}} expected-note {{add an explicit initializer}}
     int S::*pm = &S::i;
     cs.*pm = 88;
   }

clang/test/SemaCXX/constant-expression-cxx11.cpp

@@ -1177,7 +1177,7 @@ namespace ExternConstexpr {
   void f() {
     extern constexpr int i; // expected-error {{constexpr variable declaration must be a definition}}
     constexpr int j = 0;
-    constexpr int k; // expected-error {{default initialization of an object of const type}}
+    constexpr int k; // expected-error {{default initialization of an object of const type}} expected-note{{add an explicit initializer to initialize 'k'}}
   }
 }
 

clang/test/SemaCXX/constexpr-value-init.cpp

@@ -14,7 +14,7 @@ void f() {
   constexpr A a; // expected-error {{constant expression}} expected-note {{in call to 'A()'}}
 }
 
-constexpr B b1; // expected-error {{requires a user-provided default constructor}}
+constexpr B b1; // expected-error {{without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'b1'}}
 constexpr B b2 = B(); // ok
 static_assert(b2.a.a == 1, "");
 static_assert(b2.a.b == 2, "");
@@ -23,9 +23,9 @@ struct C {
   int c;
 };
 struct D : C { int d; };
-constexpr C c1; // expected-error {{requires a user-provided default constructor}}
+constexpr C c1; // expected-error {{without a user-provided default constructor}} expected-note{{add an explicit initializer to initialize 'c1'}}
 constexpr C c2 = C(); // ok
-constexpr D d1; // expected-error {{requires a user-provided default constructor}}
+constexpr D d1; // expected-error {{without a user-provided default constructor}} expected-note{{add an explicit initializer to initialize 'd1'}}
 constexpr D d2 = D(); // ok with DR1452
 static_assert(D().c == 0, "");
 static_assert(D().d == 0, "");

clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp

@@ -25,7 +25,7 @@ void fn1 () {
   non_const_copy ncc2 = ncc;
   ncc = ncc2;
   const non_const_copy cncc{};
-  const non_const_copy cncc1; // expected-error {{default initialization of an object of const type 'const non_const_copy' requires a user-provided default constructor}}
+  const non_const_copy cncc1; // expected-error {{default initialization of an object of const type 'const non_const_copy' without a user-provided default constructor}} expected-note {{add an explicit initializer to initialize 'cncc1'}}
   non_const_copy ncc3 = cncc; // expected-error {{no matching}}
   ncc = cncc; // expected-error {{no viable overloaded}}
 };

clang/test/SemaCXX/cxx1y-variable-templates_in_class.cpp

@@ -58,13 +58,13 @@ namespace out_of_line {
     template<typename T, typename T0> static CONST T b = T(100);
     template<typename T> static CONST T b<T,int>;
   };
-  template<typename T, typename T0> CONST T B4::a; // expected-error {{default initialization of an object of const type 'const int'}}
+  template<typename T, typename T0> CONST T B4::a; // expected-error {{default initialization of an object of const type 'const int'}} expected-note {{add an explicit initializer to initialize 'a<int, char>'}}
   template<typename T> CONST T B4::a<T,int>;
   template CONST int B4::a<int,char>; // expected-note {{in instantiation of}}
   template CONST int B4::a<int,int>;
 
   template<typename T, typename T0> CONST T B4::b;
-  template<typename T> CONST T B4::b<T,int>; // expected-error {{default initialization of an object of const type 'const int'}}
+  template<typename T> CONST T B4::b<T,int>; // expected-error {{default initialization of an object of const type 'const int'}} expected-note {{add an explicit initializer to initialize 'b<int, int>'}}
   template CONST int B4::b<int,char>;
   template CONST int B4::b<int,int>; // expected-note {{in instantiation of}}
 }