On 3/26/20 5:28 PM, Patrick Palka wrote:
This adds support to detect and recover from the case where an opening brace immediately follows the start of a requires-clause. So rather than emitting the errorerror: expected primary-expression before '{' token followed by a slew of irrevelant errors, we now assume the user had intended to write "requires requires {" and diagnose and recover accordingly. Tested on x86_64-pc-linux-gnu, does this look OK? gcc/cp/ChangeLog: PR c++/94306 * parser.c (cp_parser_requires_clause_opt): Diagnose and recover from "requires {" when "requires requires {" was probably intended. gcc/testsuite/ChangeLog: PR c++/94306 * g++.dg/concepts/diagnostic8.C: New test. --- gcc/cp/parser.c | 17 ++++++++++++++++- gcc/testsuite/g++.dg/concepts/diagnostic8.C | 6 ++++++ 2 files changed, 22 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/concepts/diagnostic8.C diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index 05363653691..73c2c2cb010 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -27639,7 +27639,22 @@ cp_parser_requires_clause_opt (cp_parser *parser, bool lambda_p) } return NULL_TREE; } - cp_lexer_consume_token (parser->lexer); + + cp_token *tok2 = cp_lexer_peek_nth_token (parser->lexer, 2); + if (tok2->type == CPP_OPEN_BRACE)
Do we want to handle an open paren the same way?
+ { + /* An opening brace following the start of a requires-clause is + ill-formed; the user likely forgot the second `requires' that + would start a requires-expression. */ + gcc_rich_location richloc (tok2->location); + richloc.add_fixit_insert_before (" requires"); + error_at (&richloc, "missing additional %<requires%> to start " + "a requires-expression"); + /* Don't consume the `requires', so that it's reused as the start of a + requires-expression. */ + } + else + cp_lexer_consume_token (parser->lexer);if (!flag_concepts_ts)return cp_parser_requires_clause_expression (parser, lambda_p); diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic8.C b/gcc/testsuite/g++.dg/concepts/diagnostic8.C new file mode 100644 index 00000000000..70d7e4a9cc1 --- /dev/null +++ b/gcc/testsuite/g++.dg/concepts/diagnostic8.C @@ -0,0 +1,6 @@ +// PR c++/94306 +// { dg-do compile { target c++2a } } + +template<typename T> struct S { }; +template<typename T> requires { typename T::type; } struct S<T> { }; +// { dg-error "missing additional .requires." "" { target *-*-* } .-1 }
