https://issues.dlang.org/show_bug.cgi?id=17654

Vladimir Panteleev <dlang-bugzilla@thecybershadow.net> changed:

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           Hardware|x86_64                      |All
                 OS|Linux                       |All

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https://issues.dlang.org/show_bug.cgi?id=17654

Steven Schveighoffer <schveiguy@yahoo.com> changed:

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                 CC|                            |schveiguy@yahoo.com

--- Comment #1 from Steven Schveighoffer <schveiguy@yahoo.com> ---
I actually think it's a design problem. assumeUTF is marked pure. The input is ubyte and the output is char. This means the compiler can reasonably assume the output is unrelated to the input and therefore unique.

This is quite a pickle. We can't very well unmark it pure, and I think the compiler logic is sound.

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https://issues.dlang.org/show_bug.cgi?id=17654

--- Comment #2 from ag0aep6g@gmail.com ---
(In reply to Steven Schveighoffer from comment #1)
> I actually think it's a design problem. assumeUTF is marked pure. The input is ubyte and the output is char. This means the compiler can reasonably assume the output is unrelated to the input and therefore unique.
> 
> This is quite a pickle. We can't very well unmark it pure, and I think the compiler logic is sound.

I don't agree that the compiler logic is sound. The casts are valid. The compiler cannot assume that they don't occur.

It even happens with classes (no cast needed):

----
class B { int x; }
class C : B {}

B toB(C c) pure { return c; }

void main()
{
    C c = new C;
    c.x = 1;
    immutable B b = toB(c); /* should be rejected */
    assert(b.x == 1); /* passes */
    c.x = 2;
    assert(b.x == 1); /* fails */
}
----

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https://issues.dlang.org/show_bug.cgi?id=17654

--- Comment #3 from Steven Schveighoffer <schveiguy@yahoo.com> ---
I'm not sure the UB rules for D and aliasing. In C you definitely can run into things like the array cast being considered unrelated.

The class case is definitely a bug.

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https://issues.dlang.org/show_bug.cgi?id=17654

--- Comment #4 from ag0aep6g@gmail.com ---
(In reply to Steven Schveighoffer from comment #3)
> I'm not sure the UB rules for D and aliasing. In C you definitely can run into things like the array cast being considered unrelated.

As far as I know, C's strict aliasing rule isn't exactly uncontroversial. Personally, I think it's an abomination.

> The class case is definitely a bug.

Even with the strict aliasing rule, there is a type that is allowed to alias others. In C it's char. That would be ubyte in D, I guess. The non-class examples all involve ubyte. So even with C-like strict aliasing, they should be rejected.

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https://issues.dlang.org/show_bug.cgi?id=17654

--- Comment #5 from Steven Schveighoffer <schveiguy@yahoo.com> ---
Then the example could be changed to wchar and ushort

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https://issues.dlang.org/show_bug.cgi?id=17654

Iain Buclaw <ibuclaw@gdcproject.org> changed:

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           Priority|P1                          |P3

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https://issues.dlang.org/show_bug.cgi?id=17654

--- Comment #6 from dlangBugzillaToGithub <robert.schadek@posteo.de> ---
THIS ISSUE HAS BEEN MOVED TO GITHUB

https://github.com/dlang/dmd/issues/19282

DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB

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