https://d.puremagic.com/issues/show_bug.cgi?id=12542

           Summary: No function attribute inference for recursive
                    functions
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: critical
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: monarchdodra@gmail.com


--- Comment #0 from monarchdodra@gmail.com 2014-04-07 23:06:23 PDT ---
I've seen this being mentioned before in other bugs, but haven't been able to find an issue proper for it.

Basically, if a function is recursive, then none of it's attributes are inferred: It's always impure, throwing and unsafe.

//----
int logOf(int n)
{
    if (n)
        return 1 + logOf(n/2);
    return 0;
}

void main() @safe nothrow pure
{
    int log = logOf(9);
}
//----
Error: pure function 'D main' cannot call impure function 'main.logOf'
Error: safe function 'D main' cannot call system function 'main.logOf'
Error: 'main.logOf' is not nothrow
Error: function 'D main' is nothrow yet may throw
//----

The compiler should be able to tell that logOf is nothrow and pure. I think it's safe too: Potential risk of stack overflow aren't considered memory unsafe, are they?

In any case it's blocking the fixing of certain function attributes, such as those of sort, or sum.

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--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2014-04-08 01:13:13 PDT ---
(In reply to comment #0)
> //----
> int logOf(int n)
> {
>     if (n)
>         return 1 + logOf(n/2);
>     return 0;
> }
> 
> void main() @safe nothrow pure
> {
>     int log = logOf(9);
> }

For attribute inference, logOf should be template function.

https://github.com/D-Programming-Language/dmd/pull/3436

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--- Comment #2 from monarchdodra@gmail.com 2014-04-08 02:29:31 PDT ---
(In reply to comment #1)
> For attribute inference, logOf should be template function.

Oops. Sorry!

> https://github.com/D-Programming-Language/dmd/pull/3436

Oh, wow. I didn't expect a fix so quickly. Cool.

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