[Bug c++/95724] New: bogue error : "expected '{' before ')' token"

[Bug c++/95724] New: bogue error : "expected '{' before ')' token"

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

            Bug ID: 95724
           Summary: bogue error : "expected '{' before ')' token"
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

This code test.cc, GCC-trunk get a bogus error message and then get confused
with following code parsing.

$cat test.cc
template <(union : decltype(a = 0)>)


$g++-trunk -w -c test.cc
test.cc:1:11: error: expected identifier before ‘(’ token
    1 | template <(union : decltype(a = 0)>)
      |           ^
test.cc:1:29: error: ‘a’ was not declared in this scope
    1 | template <(union : decltype(a = 0)>)
      |                             ^
test.cc:1:29: error: ‘a’ was not declared in this scope
test.cc:1:34: error: expected ‘{’ before ‘)’ token
    1 | template <(union : decltype(a = 0)>)
      |                                  ^
test.cc:1:36: error: expected unqualified-id before ‘)’ token
    1 | template <(union : decltype(a = 0)>)
      |                                    ^

$g++-10 -w -c test.cc
test.cc:1:11: error: expected identifier before ‘(’ token
    1 | template <(union : decltype(a = 0)>)
      |           ^
test.cc:1:29: error: ‘a’ was not declared in this scope
    1 | template <(union : decltype(a = 0)>)
      |                             ^
test.cc:1:29: error: ‘a’ was not declared in this scope
test.cc:1:35: error: expected ‘{’ before ‘>’ token
    1 | template <(union : decltype(a = 0)>)
      |                                   ^
test.cc:1:35: error: expected ‘,’ or ‘...’ before ‘>’ token
test.cc:1:36: error: expected ‘>’ at end of input
    1 | template <(union : decltype(a = 0)>)
      |                                    ^
test.cc:1:36: error: expected unqualified-id at end of input

I guess GCC-trunk emits the bogus error message "expected ‘{’ before ‘)’
token", and the following error messages are inconsistent with GCC-10. So,
GCC-trunk might have something wrong with while parsing this code.

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
For the next time, can you please add 'ice-on-invalid-code' keyword?

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #2 from Haoxin Tu <haoxintu at gmail dot com> ---
(In reply to Martin Liška from comment #1)
> For the next time, can you please add 'ice-on-invalid-code' keyword?

I got it. So sorry for my mistake!

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Haoxin Tu from comment #2)
> (In reply to Martin Liška from comment #1)
> > For the next time, can you please add 'ice-on-invalid-code' keyword?
> 
> I got it. So sorry for my mistake!

It's not a mistake, I just wanted to inform you that it's very unlikely that
we'll fix it. We have a lot of these issues..

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note the testcase does not ICE so ice-on-invalid is wrong.  It's really
a diagnostic only.  If we want sth extra to distinguish error diagnostics
from warning diagnostics then we should add one (can't come up with a good name
right now)

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> Note the testcase does not ICE so ice-on-invalid is wrong.  It's really
> a diagnostic only.  If we want sth extra to distinguish error diagnostics
> from warning diagnostics then we should add one (can't come up with a good
> name right now)

Yes, I was too eager..

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> Note the testcase does not ICE so ice-on-invalid is wrong.  It's really
> a diagnostic only.  If we want sth extra to distinguish error diagnostics
> from warning diagnostics then we should add one (can't come up with a good
> name right now)

It's like a weaker form of error-recovery but for cases that don't ICE.

cascading-errors maybe.

[Bug c++/95724] bogue error : "expected '{' before ')' token"

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #6)
> (In reply to Richard Biener from comment #4)
> > Note the testcase does not ICE so ice-on-invalid is wrong.  It's really
> > a diagnostic only.  If we want sth extra to distinguish error diagnostics
> > from warning diagnostics then we should add one (can't come up with a good
> > name right now)
> 
> It's like a weaker form of error-recovery but for cases that don't ICE.

error-recovery is fine then I guess since it doens't imply ICEing.  We
use the combo of ice-on-invalid-code, error-recovery for that.  But indeed
the description says 'use only for ice-on-invalid-code' ...

> cascading-errors maybe.

[Bug c++/95724] error message could be improved in the cascading error case

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95724

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
            Summary|bogue error : "expected '{' |error message could be
                   |before ')' token"           |improved in the cascading
                   |                            |error case
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-01-07
           Severity|normal                      |enhancement

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't like the error messages from any of the other compilers I tried either:
clang:
<source>:2:29: error: use of undeclared identifier 'a'
template <(union : decltype(a = 0)>)
                            ^
<source>:2:36: error: expected '{' after base class list
template <(union : decltype(a = 0)>)
                                   ^
<source>:2:12: error: '(unnamed union at <source>:2:12)' cannot be defined in a
parameter type
template <(union : decltype(a = 0)>)
           ^
<source>:2:37: error: expected template parameter
template <(union : decltype(a = 0)>)
                                    ^
<source>:2:37: error: expected ',' or '>' in template-parameter-list
<source>:2:37: error: expected unqualified-id

MSVC:

<source>(2): error C2059: syntax error: '('
<source>(2): error C2947: expecting '>' to terminate template-parameter-list,
found '>'
<source>(2): error C2059: syntax error: ')'
<source>(3): fatal error C1004: unexpected end-of-file found

ICC:
<source>(2): error: expected a type specifier
  template <(union : decltype(a = 0)>)
            ^

<source>(2): error: expected a "," or ">"

<source>(2): error: expected a declaration

<source>(2): error: expected a ";"

compilation aborted for <source> (code 2)