[Issue 23086] New: spurious case of `expression has no effect` message

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23086

          Issue ID: 23086
           Summary: spurious case of `expression has no effect` message
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: diagnostic, rejects-valid
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: b2.temp at gmx.com

For the following code

```
static int v;

ref int a()
{
    a++;
    return a;
}

int main()
{
    a == 0;
    return v ? 0 : 1;
}
```

we get, with -de, the output

> /tmp/temp_7F3C12CCD670.d:15:5: Error: `a() == 0` has no effect

but the effect of the call directly influences the return code of the program.

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