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
error
error: 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 }