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February 26, 2023
Gravatar of bradley@chatha.devPosted by bradley@chatha.devReply
bradley@chatha.dev
Gravatar of bradley@chatha.dev


Reply
https://issues.dlang.org/show_bug.cgi?id=23744

          Issue ID: 23744
           Summary: Static If Compilation Differences / Attribute
                    inference bug
           Product: D
           Version: D2
          Hardware: Other
                OS: Mac OS X
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: bradley@chatha.dev

I'm uncertain whether this issue is mainly the "Attribute inference on recursion" bug or instead another bug that is only manifesting itself alongside the other bug; but essentially:

```
module test;

bool nextVaryingLengthToken() @safe
{
    bool tryLexLongerOperators(alias TokenType)()
    {
        switch(' ')
        {
                /*
                    Comment out the first two blocks and you
                    will see that the error dissapears.

                    The only difference between the two
                    sets of blocks is that one has braces and
                    the other doesn't.

                    Additionally, commenting out the line `int i`
                    will cause the error to not appear.

                    It appears having _any_ sort of statement there
                    causes the error to show up.
                */

                static if(false)
                    case "=":
                        int i;
                        if(tryLexLongerOperators!"=")
                            return true;
                        return true;

                static if(false)
                    case "*":
                        int i3;
                        if(tryLexLongerOperators!"*")
                            return true;
                        return true;

                static if(false)
                {
                    case "=":
                        int i2;
                        if(tryLexLongerOperators!"=")
                            return true;
                        return true;

                    case "*":
                        int i4;
                        if(tryLexLongerOperators!"*")
                            return true;
                        return true;
                }

            default: return false;
        }
    }

    return tryLexLongerOperators!noreturn;
}
```

It seems that `static if(false) <body>` will still cause the compiler to try
and evaluate the <body>, however `static if(false) { <body> }` causes it to not
bother.

And then since it evaluates the body it triggers the inferrence bug, which is what makes me think this is a separate bug on its own.

However that's more just an observation rather than a truthful assertion; I'm struggling to reproduce this outside of this particular setup.

--