Add diagnostics which fall under [dcl.spec.concept]p5

[nwilson]

Summary

Diagnose when a function concept declaration has parameter(s)

[hubert.reinterpretcast]

lib/Sema/SemaDecl.cpp

7575

I think the U+2014 should be replaced by the ASCII-friendly U+002D.

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

7

Do we diagnose for the following?
template<typename... T>
concept bool fcpp(T ...t) { return true; }

This is ill-formed as well since either [dcl.spec.concept]p5 is violated or [temp.res]p8 (same paragraph reference in C++14 as in N4527) is.

[hubert.reinterpretcast]

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

7

Also test:
template<typename T>
concept bool fcpva(...) { return true; }

[nwilson]

• Cover variadic arguments in check for no params.
• Add tests to cover variadic arguments.

[nwilson]

• replace hyphen and apostrophe with equivalent ASCII characters

[hubert.reinterpretcast]

LGTM

include/clang/Basic/DiagnosticSemaKinds.td

def err_function_concept_not_defined : Error<
   "function concept declaration must be a definition">;
 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">;
 
 // 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 (isConcept) {
           if (D.isFunctionDeclarator())
             Range = D.getFunctionTypeInfo().getExceptionSpecRange();
           Diag(NewFD->getLocation(), diag::err_function_concept_exception_spec)
               << 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 declaration’s parameter list shall be equivalent to an empty
+        //   parameter list.
+        if (FPT->getNumParams() > 0)
+          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)
       NewFD->setImplicitlyInline();
 
       // C++ Concepts TS [dcl.spec.concept]p2: A concept definition shall not
       // be declared with the thread_local, inline, friend, or constexpr

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}}