Fix inconsistent availability attribute message string literal check.

[nigelp-xmos]

Summary

Function Parser::ParseAvailabilityAttribute checks that the message string of
an availability attribute is not a wide string literal. Test case
clang/test/Parser/attr-availability.c specifies that a string literal is
expected.

The code checked that the first token in a string concatenation is a string
literal, and then that the concatenated string consists of 1-byte characters.
On a target where wide character is 1 byte, a string concatenation "a" L"b"
passes both those checks, but L"b" alone is rejected. More generally, "a" u8"b"
passes the checks, but u8"b" alone is rejected.

So check isAscii() instead of character size.

[nigelp-xmos]

Alternatively, if all 1-byte-character strings are acceptable, should I remove the check that the first token is a string literal, and omit the failing test case on XCore?

[nigelp-xmos]

Run clang-format

[nigelp-xmos]

Run clang-format

[aaron.ballman]

I think this is a good change but would point out that the diagnostic message is pretty confusing as-is. u8"a" is a string literal, so saying that a string literal is expected doesn't make sense. We may want to consider either supporting string literals more generally or changing the diagnostic. The mixing of adjacent string literals with prefixes is something I don't think we need/want to support (esp as both C and C++ are making efforts to make such code ill-formed anyway), but I don't see why we should reject message=u8"whatever" (or any of the other prefixes).

However, that's an orthogonal issue and this is good incremental progress, so LGTM!

[nigelp-xmos]

Many thanks for review and approval. Please could it be committed as I do not have commit access? (I will request.)

[aaron.ballman]

In D92108#2439223, @nigelp-xmos wrote:

Many thanks for review and approval. Please could it be committed as I do not have commit access? (I will request.)

Happy to do so! I've committed on your behalf in 27ea7d0a6e0dc51e0214707bcc265fa6f9dc9bc6, thank you for the patch.

clang/lib/Parse/ParseDecl.cpp

if (Keyword == Ident_message || Keyword == Ident_replacement) {
       }
       if (Keyword == Ident_message)
         MessageExpr = ParseStringLiteralExpression();
       else
         ReplacementExpr = ParseStringLiteralExpression();
       // Also reject wide string literals.
       if (StringLiteral *MessageStringLiteral =
               cast_or_null<StringLiteral>(MessageExpr.get())) {
-        if (MessageStringLiteral->getCharByteWidth() != 1) {
+        if (!MessageStringLiteral->isAscii()) {
           Diag(MessageStringLiteral->getSourceRange().getBegin(),
                diag::err_expected_string_literal)
             << /*Source='availability attribute'*/ 2;
           SkipUntil(tok::r_paren, StopAtSemi);
           return;
         }
       }
       if (Keyword == Ident_message)

clang/test/Parser/attr-availability-xcore.c

+// Test availability message string type when wide characters are 1 byte.
+// REQUIRES: xcore-registered-target
+// RUN: %clang_cc1 -triple xcore -fsyntax-only -verify %s
+
+#if !__has_feature(attribute_availability)
+#  error 'availability' attribute is not available
+#endif
+
+void f7() __attribute__((availability(macosx,message=L"wide"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
+
+void f8() __attribute__((availability(macosx,message="a" L"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}

clang/test/Parser/attr-availability.c

 void f5() __attribute__((availability(macosx,introduced=10.5), availability(ios,unavailable, unavailable))); // expected-error{{redundant 'unavailable' availability change; only the last specified change will be used}}
 
 void f6() __attribute__((availability(macosx,unavailable,introduced=10.5))); // expected-warning{{'unavailable' availability overrides all other availability information}}
 
 void f7() __attribute__((availability(macosx,message=L"wide"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
 
 void f8() __attribute__((availability(macosx,message="a" L"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
 
+void f9() __attribute__((availability(macosx,message=u8"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
+
+void f10() __attribute__((availability(macosx,message="a" u8"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
+
+void f11() __attribute__((availability(macosx,message=u"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
+
+void f12() __attribute__((availability(macosx,message="a" u"b"))); // expected-error {{expected string literal for optional message in 'availability' attribute}}
+
 // rdar://10095131
 enum E{
     gorf __attribute__((availability(macosx,introduced=8.5, message = 10.0))), // expected-error {{expected string literal for optional message in 'availability' attribute}}
     garf __attribute__((availability(macosx,introduced=8.5, message))), // expected-error {{expected '=' after 'message'}}
 
     foo __attribute__((availability(macosx,introduced=8.5,deprecated=9.0, message="Use CTFontCopyPostScriptName()", deprecated=10.0))) // expected-error {{expected ')'}} \
                                                                                                                                        // expected-note {{to match this '('}}
 };