diff mbox series

c++: Allow template lambdas without lambda-declarator [PR97839]

Message ID 20201117180520.2364601-1-polacek@redhat.com
State New
Headers show
Series c++: Allow template lambdas without lambda-declarator [PR97839] | expand

Commit Message

Marek Polacek Nov. 17, 2020, 6:05 p.m. UTC 
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


base-commit: 8661f4faa875f361cd22a197774c1fa04cd0580b

Comments

Marek Polacek Nov. 18, 2020, 6:16 p.m. UTC | #1 
On Tue, Nov 17, 2020 at 01:05:20PM -0500, Marek Polacek via Gcc-patches wrote:
> 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:

This might be necessary to handle <wg21.link/p1102> anyway.

> 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
> 

Marek
Jason Merrill Nov. 20, 2020, 10:14 p.m. UTC | #2 
On 11/17/20 1:05 PM, Marek Polacek wrote:
> 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?

Yes: this is a bugfix, not new functionality.

> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> 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
>
Jason Merrill Nov. 20, 2020, 10:15 p.m. UTC | #3 
On 11/18/20 1:16 PM, Marek Polacek wrote:
> On Tue, Nov 17, 2020 at 01:05:20PM -0500, Marek Polacek via Gcc-patches wrote:
>> 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:
> 
> This might be necessary to handle <wg21.link/p1102> anyway.

Agreed.

>> 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
>>
> 
> Marek
>
diff mbox series

Patch

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>();
+}