[Concepts] Diagnose when return type of a function concept or declaration type of a variable concept is not bool.

[nwilson]

Summary

Adding checks and diagnostics which fall under Concepts TS[dcl.spec.concept]p5:
function concepts are required to have 'bool' return type.
Adding checks and diagnostics which fall under Concepts TS[dcl.spec.concept]p6:
variable concepts are required to have 'bool' declaration type.

Remove a test in Parser which caused a regression due to the new checks.

[nwilson]

Please let me know if the subject or summary of this Patch is ambiguous.

[hubert.reinterpretcast]

Please add tests for const bool for both the function and variable cases (should get the error).

test/CXX/concepts-ts/dcl.dcl/dcl.spec/dcl.spec.concept/p5.cpp

22

The declared return type here is bool (N4567 subclause 7.1.6.4 [dcl.spec.auto] paragraph 2).

test/Parser/cxx-concept-declaration.cpp

17 ↗

(On Diff #44811)

This is valid.

[nwilson]

• Take qualifiers into account.
• Check VarDecl is valid when checking declaration type to account for constexpr being specified. Is there any opinion on a better way to handle this? I *could* check for both diagnostics in the test...
• Remove erroneous check for auto (containsPlaceholderType) and associated function concept test.
• Removed the use of Diagnostic Range because we'd need to enumerate over the various qualifiers.

[nwilson]

test/CXX/concepts-ts/dcl.dcl/dcl.spec/dcl.spec.concept/p5.cpp

22

The erroneous test which Hubert was referring to has been removed.

[hubert.reinterpretcast]

LGTM.

include/clang/Basic/DiagnosticSemaKinds.td

def err_var_concept_not_initialized : Error<
   "variable concept declaration must be initialized">;
 def err_function_concept_exception_spec : Error<
   "function concept cannot have exception specification">;
 def err_concept_decl_invalid_specifiers : Error<
   "%select{variable|function}0 concept cannot be declared "
   "'%select{thread_local|inline|friend|constexpr}1'">;
 def err_function_concept_with_params : Error<
   "function concept cannot have any parameters">;
+def err_function_concept_bool_ret : Error<
+  "declared return type of function concept must be 'bool'">;
+def err_variable_concept_bool_decl : Error<
+  "declared type of variable concept must be 'bool'">;
 
 // C++11 char16_t/char32_t
 def warn_cxx98_compat_unicode_type : Warning<
   "'%0' type specifier is incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
 
 // __make_integer_seq
 def err_integer_sequence_negative_length : Error<

lib/Sema/SemaDecl.cpp

if (D.getDeclSpec().isConceptSpecified()) {
       }
 
       if (D.getDeclSpec().isConstexprSpecified()) {
         Diag(D.getDeclSpec().getConstexprSpecLoc(),
              diag::err_concept_decl_invalid_specifiers)
             << 0 << 3;
         NewVD->setInvalidDecl(true);
       }
+
+      // C++ Concepts TS [dcl.spec.concept]p6: A variable concept has the
+      // following restrictions:
+      // - The declared type shall have the type bool.
+      if (!Context.hasSameType(NewVD->getType(), Context.BoolTy) &&
+          !NewVD->isInvalidDecl()) {
+        Diag(D.getIdentifierLoc(), diag::err_variable_concept_bool_decl);
+        NewVD->setInvalidDecl(true);
+      }
     }
   }
 
   // Set the lexical context. If the declarator has a C++ scope specifier, the
   // lexical context will be different from the semantic context.
   NewVD->setLexicalDeclContext(CurContext);
   if (NewTemplate)
     NewTemplate->setLexicalDeclContext(CurContext);
if (isConcept) {
               << FixItHint::CreateRemoval(Range);
           NewFD->setInvalidDecl();
         } else {
           Context.adjustExceptionSpec(NewFD, EST_BasicNoexcept);
         }
 
         // C++ Concepts TS [dcl.spec.concept]p5: A function concept has the
         // following restrictions:
+        // - The declared return type shall have the type bool.
+        if (!Context.hasSameType(FPT->getReturnType(), Context.BoolTy)) {
+          Diag(D.getIdentifierLoc(), diag::err_function_concept_bool_ret);
+          NewFD->setInvalidDecl();
+        }
+
+        // C++ Concepts TS [dcl.spec.concept]p5: A function concept has the
+        // following restrictions:
         // - The declaration's parameter list shall be equivalent to an empty
         //   parameter list.
         if (FPT->getNumParams() > 0 || FPT->isVariadic())
           Diag(NewFD->getLocation(), diag::err_function_concept_with_params);
       }
 
       // C++ Concepts TS [dcl.spec.concept]p2: Every concept definition is
       // implicity defined to be a constexpr declaration (implicitly inline)

test/CXX/concepts-ts/dcl.dcl/dcl.spec/dcl.spec.concept/p5.cpp

 // RUN:  %clang_cc1 -std=c++14 -fconcepts-ts -x c++ -verify %s
 
 template<typename T>
 concept bool fcpv(void) { return true; }
 
 template<typename T>
 concept bool fcpi(int i = 0) { return true; } // expected-error {{function concept cannot have any parameters}}
 
 template<typename... Ts>
 concept bool fcpp(Ts... ts) { return true; } // expected-error {{function concept cannot have any parameters}}
 
 template<typename T>
 concept bool fcpva(...) { return true; } // expected-error {{function concept cannot have any parameters}}
+
+template<typename T>
+concept const bool fcrtc() { return true; } // expected-error {{declared return type of function concept must be 'bool'}}
+
+template<typename T>
+concept int fcrti() { return 5; } // expected-error {{declared return type of function concept must be 'bool'}}
+
+template<typename T>
+concept float fcrtf() { return 5.5; } // expected-error {{declared return type of function concept must be 'bool'}}
+
+template<typename T>
+concept decltype(auto) fcrtd(void) { return true; } // expected-error {{declared return type of function concept must be 'bool'}}

test/CXX/concepts-ts/dcl.dcl/dcl.spec/dcl.spec.concept/p6.cpp

+// RUN:  %clang_cc1 -std=c++14 -fconcepts-ts -x c++ -verify %s
+
+template<typename T>
+concept bool vc { true };
+
+template<typename T>
+struct B { typedef bool Boolean; };
+
+template<int N>
+B<void>::Boolean concept vctb(!0);
+
+template<typename T>
+concept const bool vctc { true }; // expected-error {{declared type of variable concept must be 'bool'}}
+
+template<typename T>
+concept int vcti { 5 }; // expected-error {{declared type of variable concept must be 'bool'}}
+
+template<typename T>
+concept float vctf { 5.5 }; // expected-error {{declared type of variable concept must be 'bool'}}
+
+template<typename T>
+concept auto vcta { true }; // expected-error {{declared type of variable concept must be 'bool'}}
+
+template<typename T>
+concept decltype(auto) vctd { true }; // expected-error {{declared type of variable concept must be 'bool'}}