Make simple requirements starting with requires ill-formed in in requirement body

[cor3ntin]

Summary

This patch implements P2092

Simple requirements in requirement body shall not start with
requires.
A warning was already in place so we just turn this warning into
an error.

In addition, we add tests to make sure typename is optional
in requirement-parameter-list as per the same paper.

[cor3ntin]

Fix cxx_status

[cor3ntin]

Formatting

[cjdb]

LGTM upon inspection. There aren't any cases in libc++ that I'm aware of that will break because of this, but I think it's a good practice to try and bootstrap the library for certainty.

Please also provide a more descriptive Git commit subject (I don't know what P2092 is at a glance).

[• Quuxplusone]

clang/include/clang/Basic/DiagnosticParseKinds.td

810

Typo here.

clang/test/Parser/cxx2a-concepts-requires-expr.cpp

148–158

s/int/T/ otherwise you miss the point of p2092's "Down with typename!" changes.

152–153

s/int/T/ otherwise you miss the point of p2092's "Down with typename!" changes.

clang/www/cxx_status.html

946–948

This should say "partial," unless you have already implemented p2092's "Down with typename!" changes.

[cor3ntin]

• Fix typos
• remove the tests about typenames (don't pass yet)
• Mark as partial until P2092 is implemented

[cor3ntin]

clang/test/Parser/cxx2a-concepts-requires-expr.cpp

152–153

Haha, you are right, thanks.
No wonder it passed...
I've elected to remove these tests for now, until P2092 is implemented (https://reviews.llvm.org/D53847)

[aaron.ballman]

LGTM!

[cor3ntin]

@Quuxplusone Are you happy with the fix? Thanks

[• Quuxplusone]

@cor3ntin: Sure, LGTM.

[aaron.ballman]

I've commit on your behalf in 977bdf6f44edabb857bdff9ca249aa6eccb98e96, thank you!

clang/include/clang/Basic/DiagnosticParseKinds.td

def err_expected_semi_requirement : Error<
   "expected ';' at end of requirement">;
 def err_requires_expr_missing_arrow : Error<
   "expected '->' before expression type requirement">;
 def err_requires_expr_expected_type_constraint : Error<
   "expected concept name with optional arguments">;
 def err_requires_expr_simple_requirement_noexcept : Error<
   "'noexcept' can only be used in a compound requirement (with '{' '}' around "
   "the expression)">;
-def warn_requires_expr_in_simple_requirement : Warning<
-  "this requires expression will only be checked for syntactic validity; did "
+def err_requires_expr_in_simple_requirement : Error<
+  "requires expression in requirement body; did "
   "you intend to place it in a nested requirement? (add another 'requires' "
-  "before the expression)">, InGroup<DiagGroup<"requires-expression">>;
+  "before the expression)">;
 
 def err_missing_dependent_template_keyword : Error<
   "use 'template' keyword to treat '%0' as a dependent template name">;
 def warn_missing_dependent_template_keyword : ExtWarn<
   "use 'template' keyword to treat '%0' as a dependent template name">;
 
 def ext_extern_template : Extension<
   "extern templates are a C++11 extension">, InGroup<CXX11>;

clang/lib/Parse/ParseExprCXX.cpp

while (!Tok.is(tok::r_brace)) {
         SourceLocation StartLoc = Tok.getLocation();
         ExprResult Expression =
             Actions.CorrectDelayedTyposInExpr(ParseExpression());
         if (!Expression.isUsable()) {
           SkipUntil(tok::semi, tok::r_brace, SkipUntilFlags::StopBeforeMatch);
           break;
         }
         if (!Expression.isInvalid() && PossibleRequiresExprInSimpleRequirement)
-          Diag(StartLoc, diag::warn_requires_expr_in_simple_requirement)
+          Diag(StartLoc, diag::err_requires_expr_in_simple_requirement)
               << FixItHint::CreateInsertion(StartLoc, "requires");
         if (auto *Req = Actions.ActOnSimpleRequirement(Expression.get()))
           Requirements.push_back(Req);
         else {
           SkipUntil(tok::semi, tok::r_brace, SkipUntilFlags::StopBeforeMatch);
           break;
         }
         // User may have tried to put some compound requirement stuff here

clang/test/Parser/cxx2a-concepts-requires-expr.cpp

 // expected-error@-1 {{expected ';' at end of requirement}}
 
 bool r36 = requires (bool b) { requires sizeof(b) == 1; };
 
 void r37(bool b) requires requires { 1 } {}
 // expected-error@-1 {{expected ';' at end of requirement}}
 
 bool r38 = requires { requires { 1; }; };
-// expected-warning@-1 {{this requires expression will only be checked for syntactic validity; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
+// expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
 
 bool r39 = requires { requires () { 1; }; };
-// expected-warning@-1 {{this requires expression will only be checked for syntactic validity; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
+// expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
 
 bool r40 = requires { requires (int i) { i; }; };
-// expected-warning@-1 {{this requires expression will only be checked for syntactic validity; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
+// expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
 
 bool r41 = requires { requires (); };
 // expected-error@-1 {{expected expression}}

clang/www/cxx_status.html

</tr>
         <td><a href="https://wg21.link/p1616r1">P1616R1</a></td>
         <td rowspan="2" class="full" align="center">Clang 10</td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p1452r2">P1452R2</a></td>
       </tr>
       <tr> <!-- from Belfast -->
         <td><a href="https://wg21.link/p1972r0">P1972R0</a></td>
-        <td rowspan="5" class="none" align="center">No</td>
+        <td rowspan="3" class="none" align="center">No</td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p1980r0">P1980R0</a></td>
       </tr>
       <tr> <!-- from Prague -->
         <td><a href="https://wg21.link/p2103r0">P2103R0</a></td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p2092r0">P2092R0</a></td>
+        <td rowspan="1" class="partial" align="center">Clang 13</td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p2113r0">P2113R0</a></td>
+        <td rowspan="1" class="none" align="center">No</td>
       </tr>
     <!-- Albuquerque papers -->
     <tr>
       <td>Range-based for statements with initializer</td>
       <td><a href="https://wg21.link/p0614r1">P0614R1</a></td>
       <td class="full" align="center">Clang 8</td>
     </tr>
     <tr>