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digitalmars.D.bugs - [Issue 6385] New: isInputRange!(ubyte[2u]) is a failure when used in global scope

reply d-bugmail puremagic.com writes:
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           Summary: isInputRange!(ubyte[2u]) is a failure when used in
                    global scope
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Keywords: rejects-valid
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: schveiguy yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy yahoo.com> 2011-07-26
11:18:02 PDT ---
The following code incorrectly produces an error:

import std.range;

pragma(msg, isInputRange!(ubyte[2u]).stringof);

Error: template instance std.array.front!(ubyte[2u]) incompatible arguments for
template instantiation

The code of isInputRange looks like this:

template isInputRange(R)
{
    enum bool isInputRange = is(typeof(
    {
        R r;              // can define a range object
        if (r.empty) {}   // can test for empty
        r.popFront();     // can invoke popFront()
        auto h = r.front; // can get the front of the range
    }()));
}

It was my impression that is(typeof(...)) should just return false on
compilation failure.  I don't think isInputRange is incorrectly implemented.

The error is eliminated if you put the isInputRange call inside a function:

import std.range;

void main() { 
pragma(msg, isInputRange!(ubyte[2u]).stringof);
}

outputs:

false

during compilation, and successfully compiles.

See related discussion here:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=28422

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--- Comment #1 from Steven Schveighoffer <schveiguy yahoo.com> 2011-07-26
11:21:28 PDT ---
BTW, this compiles on 2.051, fails on 2.052

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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #2 from Don <clugdbug yahoo.com.au> 2011-08-26 04:37:04 PDT ---
Reduced test case. It seems this bug is quite complicated, it requires two
semantic errors, plus uniform function call syntax, and a template constraint:

template template6385(T)
{
    enum template6385 = false;
}

void bug6385(A)(A a) if (template6385!A)
{
    this_is_an_error();
}

const bool bool6385 =
    is(typeof(
    {
        ubyte[2] r;
        this_is_another_error();
        r.bug6385;
    }()
    ));

The test case was accidentally fixed by commit:
https://github.com/D-Programming-Language/dmd/commit/dc83c
but I don't really understand why. It seems to be just luck.

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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yebblies gmail.com


--- Comment #3 from yebblies <yebblies gmail.com> 2011-08-27 21:06:24 EST ---
(In reply to comment #2)

 The test case was accidentally fixed by commit:
 https://github.com/D-Programming-Language/dmd/commit/dc83c
 but I don't really understand why. It seems to be just luck.


dc83c prevents dmd from re-evaluating the template constraint when the args
match an instance that already exists.  Previously the constraint would be run
unless all template args had a spec.  You can see this by changing 'void
bug6385(A)(A a) if (template6385!A)' to 'void bug6385(A : ubyte[2])(A a) if
(template6385!A)'.

Slightly smaller test case:
void templ6385(A)(A a) if ( { return false; }() )
{
    this_is_an_error();
}

const bool bool6385 =
    is(typeof(
    {
        this_is_another_error();
        templ6385(1);
    }()
    ));

    void main() {}

Using an older commit, it seems that the cause is re-running semantic on
templ6385, as it's been added to the list of module members.  This seems to be
similar to issue 4302 (caused by the fix to bug 4042) but missed by the patch
in 4302.

Changing
- if (!(sc->flags & SCOPEstaticif))
+ if (!(sc->flags & SCOPEstaticif) && !sc->intypeof)
from that patch seems to fix it, but I have no idea if there are any other
missing cases.

My guess at a correct solution is that
http://www.dsource.org/projects/dmd/changeset/477 is incorrect, and should
instead remove the TemplateInstance from the module's list of members.

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klickverbot <code klickverbot.at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |code klickverbot.at
         Resolution|                            |DUPLICATE


--- Comment #4 from klickverbot <code klickverbot.at> 2011-09-05 14:31:14 PDT
---
*** This issue has been marked as a duplicate of issue 6602 ***

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--- Comment #5 from klickverbot <code klickverbot.at> 2011-09-05 14:37:06 PDT
---
I think the problem described above didn't occur if the isInputRange
instantiation is inside a function, because then the instance was added to the
global list later, during semantic3, and TemplateInstance::semantic3
immediately exists if this.error is set, whereas TemplateInstance::semantic
doesn't bail out early.

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