[Bug c++/127008] New: `if (type a(1))` should have a better error message

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127008

            Bug ID: 127008
           Summary: `if (type a(1))` should have a better error message
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
struct type1
{
  type1(int);
};

void f(int a)
{
    if (type1 s(a))
      return;
}
```

Currently this gives:
```
<source>: In function 'void f(int)':
<source>:10:16: error: expected initializer before '(' token
   10 |     if (type1 s(a))
      |                ^
```

Which does not teach me that you can't have a parenthesized initializer in an
if stement.
Clang message is:
```
<source>:10:15: error: variable declaration in condition cannot have a
parenthesized initializer
   10 |     if (type1 s(a))
      |               ^~~~
```

Which is so much better and makes it easier to understand what is going wrong.

And I found this while writing GCC code :).