http://d.puremagic.com/issues/show_bug.cgi?id=5274

           Summary: Impure function call inside impure function nested
                    inside pure function
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: diagnostic
          Severity: minor
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-11-24 16:50:31 PST ---
This D2 code is formally correct because bar() is never called:


import core.stdc.stdio: putchar;
pure void foo() {
    static void bar() {
        putchar('a');
    }
}
void main() {}


DMD 2.050 prints:

test.d(4): Error: pure function 'foo' cannot call impure function 'putchar'

Despite foo() doesn't contain calls to putchar().

Even if I modify this program, adding a call to bar() inside foo(), that
strange error message doesn't change.

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |clugdbug@yahoo.com.au
         Resolution|                            |INVALID


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-11-24 19:06:38 PST ---
(In reply to comment #0)
> This D2 code is formally correct because bar() is never called:

No, the code is incorrect.
The error message occurs because bar() cannot be compiled.
Think about it -- its mangled name must have 'pure' in it.

The fact that there's no way that the function can actually be called, is irrelevant: it was marked as pure, but it violates pure.

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--- Comment #2 from bearophile_hugs@eml.cc 2010-11-24 19:34:49 PST ---
I have not expressed myself well enough, I am sorry. This bug report is a "diagnostic" one, it's not a "rejects valid". So I agree that this code needs to be refused at compile time, but is this a good message?

test.d(4): Error: pure function 'foo' cannot call impure function 'putchar'

foo() doesn't contain putchar(), it's bar() that calls it.

I don't know what is a good error message for this situation. This is a reduced test case:


void foo() {}
pure void bar() {
    void spam() {
        foo();
    }
}
void main() {}


Maybe you are right, there is no much better error message to be invented here.

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--- Comment #3 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-11-29 07:43:03 PST ---
(In reply to comment #2)

> Maybe you are right, there is no much better error message to be invented here.

Hm... I'd expect a message like:

Error: pure function 'foo.bar' cannot call impure function 'putchar'

But this doesn't seem to be a very critical problem, the line number is correct, so you can see where the problem is.

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--- Comment #4 from Don <clugdbug@yahoo.com.au> 2010-11-29 14:25:47 PST ---
(In reply to comment #3)
> (In reply to comment #2)
> 
> > Maybe you are right, there is no much better error message to be invented here.
> 
> Hm... I'd expect a message like:
> 
> Error: pure function 'foo.bar' cannot call impure function 'putchar'

At present, you get that error message if you explicitly mark bar as pure. But, the existing error message tells you why bar is pure. It's because foo is pure. This is helpful if there are several levels of nesting: it tells you the level which was pure.

> 
> But this doesn't seem to be a very critical problem, the line number is correct, so you can see where the problem is.

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