Disallow narrowing conversions to bool in noexcept specififers.

[cor3ntin]

Summary

Completes the support for P1401R5

[cor3ntin]

Rebase

[cor3ntin]

Fix cxx_status

[aaron.ballman]

clang/lib/Sema/SemaOverload.cpp

5638–5642

This function is checking converted constant expressions which was not touched by p1401r5, and it looks like this will break anything attempting to to contextual conversion constant expressions of type bool per http://eel.is/c++draft/expr.const#10 because it's removing the attempt to contextually convert to bool here.

5638–5642

Also, I don't think P1401 was applied as a DR (but we should double check!) so I'd expect some checks for the language standard to gate the behavior. If P1401 was applied as a DR, then we should add some tests to clang/test/CXX with the proper DR markings so that our DR status page gets updated.

clang/test/SemaCXX/cxx2a-explicit-bool.cpp

731

Curiously, these tests already have this behavior without this patch applied: https://godbolt.org/z/13PojdWEe

[cor3ntin]

It turns out that explicit was doing the right thing (as outlined in P1401),
but noexcept was not.

I've reworked the handling of noexcept so that noexcept and explicit specifier
use the same code paths, as they have the same expected behavior and wording.
This also make sure their diagnostics are consistent.

[cor3ntin]

clang/lib/Sema/SemaOverload.cpp

5638–5642

It's in the air http://lists.isocpp.org/ext/2021/06/16918.php - Bur Richard took the decision to consider it as a DR
However the changes this patch intends to fix pertaining to preexisting wording, and clang was non-conforming.
P1401 merely put this non-conformity to light.

[cor3ntin]

Fix tests

[cor3ntin]

Remove whitespace only change

[aaron.ballman]

clang/lib/Sema/SemaExceptionSpec.cpp

81 ↗

(On Diff #364719)

You should just get rid of this parameter entirely if it's no longer going to be used.

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

879 ↗

(On Diff #364719)

Was there a reason this test needed to change?

clang/www/cxx_status.html

1299

We're on Clang 14 now.

[cor3ntin]

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

879 ↗

(On Diff #364719)

yup, 2 is not convertible to bool here. I use 0+1 to keep the kind of expression the same

[aaron.ballman]

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

879 ↗

(On Diff #364719)

I kinda figured that was the case, thanks for confirming!

[cor3ntin]

• Update the release version to Clang 14 in cxx_status
• Remove unused parameter
• Remove WS only changes

[aaron.ballman]

LGTM!

[aaron.ballman]

I've committed on your behalf in 3c8e94bc20e5829ab5167d21d242b6b624dd934e, thank you for the fix!

clang/lib/Sema/SemaOverload.cpp

if (checkPlaceholderForOverload(S, From))
     return ExprError();
 
   // C++1z [expr.const]p3:
   //  A converted constant expression of type T is an expression,
   //  implicitly converted to type T, where the converted
   //  expression is a constant expression and the implicit conversion
   //  sequence contains only [... list of conversions ...].
   ImplicitConversionSequence ICS =
-      CCE == Sema::CCEK_ExplicitBool
-          ? TryContextuallyConvertToBool(S, From)
-          : TryCopyInitialization(S, From, T,
-                                  /*SuppressUserConversions=*/false,
-                                  /*InOverloadResolution=*/false,
-                                  /*AllowObjCWritebackConversion=*/false,
-                                  /*AllowExplicit=*/false);
+      TryCopyInitialization(S, From, T,
   StandardConversionSequence *SCS = nullptr;
   switch (ICS.getKind()) {
   case ImplicitConversionSequence::StandardConversion:
     SCS = &ICS.Standard;
     break;
   case ImplicitConversionSequence::UserDefinedConversion:
     if (T->isRecordType())
       SCS = &ICS.UserDefined.Before;

clang/test/SemaCXX/cxx2a-explicit-bool.cpp

 
 template <size_t N>
 Str::Str(char const(&str)[N]) { }
 
 Str a = "short";
 Str b = "not so short";// expected-error {{no viable conversion}}
 
 }
+
+namespace P1401 {
+
+const int *ptr;
+
+struct S {
+  explicit(sizeof(char[2])) S(char); // expected-error {{explicit specifier argument evaluates to 2, which cannot be narrowed to type 'bool'}}
+  explicit(ptr) S(long);             // expected-error {{conversion from 'const int *' to 'bool' is not allowed in a converted constant expression}}
+  explicit(nullptr) S(int);          // expected-error {{value of type 'nullptr_t' is not implicitly convertible to 'bool'}}
+  explicit(42L) S(int, int);         // expected-error {{explicit specifier argument evaluates to 42, which cannot be narrowed to type 'bool'}}
+  explicit(sizeof(char)) S();
+  explicit(0) S(char, char);
+  explicit(1L) S(char, char, char);
+};
+} // namespace P1401

clang/www/cxx_status.html

</tr>
     <tr>
       <td>Allow duplicate attributes</td>
       <td><a href="https://wg21.link/P2156R1">P2156R1</a></td>
       <td class="unreleased" align="center">Clang 13</td>
     </tr>
     <tr>
       <td>Narrowing contextual conversions to bool</td>
       <td><a href="https://wg21.link/P1401R5">P1401R5</a></td>
-      <td class="partial" align="center">Clang 13</td>
+      <td class="full" align="center">Clang 13</td>
     </tr>
     <tr>
       <td>Trimming whitespaces before line splicing</td>
       <td><a href="https://wg21.link/P2223R2">P2223R2</a></td>
       <td class="full" align="center">Yes</td>
     </tr>
     <tr>
       <td>Make declaration order layout mandated</td>