[dmd-internals] 2.062 regression: Broken AST with mixins and fwd refs

[kenji hara]

How about this?

https://github.com/D-Programming-Language/dmd/pull/1760

Kenji Hara


2013/3/17 David Nadlinger <code at klickverbot.at>

> Hi all,
>
> I'm still working on tracking down the last couple of LDC test suite
> regressions from 2.061 to 2.062. In one of the cases, the problem is
> actually in the frontend, even if it might not cause a visible bug
> for DMD.
>
>
> Consider this test case (reduced from xtest46):
>
> ———
> mixin template DefineCoreType() {
>   struct Faulty {
>     static int x;
>     X164!() xxx;
>   }
> }
>
> mixin DefineCoreType!();
>
> mixin template A164() {}
>
> struct X164() { mixin A164!(); }
>
> ———
>
> The issue is that if sd is the/a 'Faulty' declaration,
> ((TypeStruct*)sd->type)->sym != sd – there seem to be two
> StructDeclaration instances around that both correspond to 'Faulty'!
>
> An easy way to see this is by adding an assertion for this to the end
> of StructDeclaration::semantic:
>
> ———
> --- a/src/struct.c
> +++ b/src/struct.c
> @@ -655,6 +655,8 @@ void StructDeclaration::semantic(Scope *sc)
>          deferred->semantic2(sc);
>          deferred->semantic3(sc);
>      }
> +
> +    assert(static_cast<TypeStruct*>(type)->sym == this);
>  }
>
>  Dsymbol *StructDeclaration::search(Loc loc, Identifier *ident, int flags)
> ———
>
> The commit in which this assertion first triggers on the above test
> case is 14d3c7535, which is a fix for a 2.061 regression, issue 9276.
> I'm not sure, though, if this piece of code is to blame, or if the
> root cause lies in the way the declaration copying for template
> mixins is handled.
>
> I would be glad if somebody could have a look at this (Kenji, maybe
> the issue is obvious to you?), as it wreaks havoc with LDC's codegeń
> (LDC needs type information all over the place, as the LLVM IR is
> typed, and was definitely written with the assumption of having
> a consistent AST to work with.)
>
>
> Similar issues have occured multiple times in the past; one almost
> identical problem is http://d.puremagic.com/issues/show_bug.cgi?id=8626,
> but there have also been problems that later turned out to actually
> trigger DMD bugs as well (such as the inout nested struct mangling
> issue).
>
> As they are additionally quite time-consuming to track down, I have
> been thinking about introducing a śet of »AST validation« checks
> that are run before codegen and are activated by a compile time
> switch (for development and on the CI bots). What do you think? Any
> implementation suggestions?
>
>
> Thanks,
> David
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