[Bug d/109681] New: suggested preview switches use DMD

[schveiguy at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109681

            Bug ID: 109681
           Summary: suggested preview switches use DMD
           Product: gcc
           Version: 13.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: schveiguy at gmail dot com
  Target Milestone: ---

When you use features that require preview switches, the messages that inform
you of the need to use the switch are worded using DMD frontend style switches.

For example:

```d
struct S {
   int x : 5;
}
```

Result:
```
<source>:3:14: error: use -preview=bitfields for bitfield support
    3 |     int x : 5;
      |              ^
```

What it should say is:

```
<source>:3:14: error: use -fpreview=bitfields for bitfield support
    3 |     int x : 5;
      |              ^
```

I searched for `-preview=` in the source, and found these instances:

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/d/dmd/parse.d;h=36a76f50da20590abc9560533b1901b1258ad00b;hb=HEAD#l1236

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/d/dmd/parse.d;h=36a76f50da20590abc9560533b1901b1258ad00b;hb=HEAD#l1252

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/d/dmd/parse.d;h=36a76f50da20590abc9560533b1901b1258ad00b;hb=HEAD#l4614

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/d/dmd/parse.d;h=36a76f50da20590abc9560533b1901b1258ad00b;hb=HEAD#l5148

There may be more.