Our implementation of template lambdas incorrectly requires the optional
lambda-declarator. This was probably required by an early draft of
generic lambdas, but now the production is [expr.prim.lambda.general]:
lambda-expression:
lambda-introducer lambda-declarator [opt] compound-statement
lambda-introducer < template-parameter-list > requires-clause [opt]
lambda-declarator [opt] compound-statement
Therefore, we should accept the following test.
Incidentally, I noticed we give a terrible diagnostic when the user uses
'mutable', but forgets to type '()' before it, which sounds like a common
mistake. So it seems to me we should handle that specifically, rather
than to emit this:
lambda-generic8.C: In lambda function:
lambda-generic8.C:8:18: error: expected '{' before 'mutable'
8 | []<typename T> mutable {}.operator()<int>();
| ^~~~~~~
lambda-generic8.C: In function 'int main()':
lambda-generic8.C:8:17: error: expected ';' before 'mutable'
8 | []<typename T> mutable {}.operator()<int>();
| ^~~~~~~~
| ;
lambda-generic8.C:8:28: error: expected primary-expression before '.' token
8 | []<typename T> mutable {}.operator()<int>();
| ^
lambda-generic8.C:8:40: error: expected primary-expression before 'int'
8 | []<typename T> mutable {}.operator()<int>();
| ^~~
Is it okay to fix this in stage3?
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
gcc/cp/ChangeLog:
PR c++/97839
* parser.c (cp_parser_lambda_declarator_opt): Don't require ().
gcc/testsuite/ChangeLog:
PR c++/97839
* g++.dg/cpp2a/lambda-generic8.C: New test.
---
gcc/cp/parser.c | 14 ++++++--------
gcc/testsuite/g++.dg/cpp2a/lambda-generic8.C | 9 +++++++++
2 files changed, 15 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-generic8.C
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 42f705266bb..9f09c778c29 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -10604,6 +10604,8 @@ cp_parser_trait_expr (cp_parser* parser, enum rid
keyword)
lambda-expression:
lambda-introducer lambda-declarator [opt] compound-statement
+ lambda-introducer < template-parameter-list > requires-clause [opt]
+ lambda-declarator [opt] compound-statement
Returns a representation of the expression. */
@@ -11061,13 +11063,11 @@ cp_parser_lambda_introducer (cp_parser* parser, tree
lambda_expr)
/* Parse the (optional) middle of a lambda expression.
lambda-declarator:
- < template-parameter-list [opt] >
- requires-clause [opt]
- ( parameter-declaration-clause [opt] )
- attribute-specifier [opt]
+ ( parameter-declaration-clause )
decl-specifier-seq [opt]
- exception-specification [opt]
- lambda-return-type-clause [opt]
+ noexcept-specifier [opt]
+ attribute-specifier-seq [opt]
+ trailing-return-type [opt]
requires-clause [opt]
LAMBDA_EXPR is the current representation of the lambda expression. */
@@ -11217,8 +11217,6 @@ cp_parser_lambda_declarator_opt (cp_parser* parser,
tree lambda_expr)
trailing-return-type in case of decltype. */
pop_bindings_and_leave_scope ();
}
- else if (template_param_list != NULL_TREE) // generate diagnostic
- cp_parser_require (parser, CPP_OPEN_PAREN, RT_OPEN_PAREN);
/* Create the function call operator.
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic8.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-generic8.C
new file mode 100644
index 00000000000..f3c3809b36d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic8.C
@@ -0,0 +1,9 @@
+// PR c++/97839
+// { dg-do compile { target c++20 } }
+// Test that a lambda with <template-param-list> doesn't require
+// a lambda-declarator.
+
+int main()
+{
+ []<typename T>{}.operator()<int>();
+}
base-commit: 8661f4faa875f361cd22a197774c1fa04cd0580b
--
2.28.0
