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Cannot use associated constant in a provided associated method #25046

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ghost opened this issue May 2, 2015 · 1 comment · Fixed by #25091
Closed

Cannot use associated constant in a provided associated method #25046

ghost opened this issue May 2, 2015 · 1 comment · Fixed by #25091
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A-associated-items Area: Associated items such as associated types and consts. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️

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@ghost
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ghost commented May 2, 2015

The compiler fails to compile this:

#![feature(associated_consts)]

pub trait Foo {
    const MIN: i32;

    fn get_min() -> i32 {
        Self::MIN
    }
}

fn main() {}

The error message:

main.rs:4:5: 4:20 error: internal compiler error: Encountered error `Unimplemented` when trying to select an implementation for constant trait item reference.
main.rs:4     const MIN: i32;
              ^~~~~~~~~~~~~~~
thread 'rustc' panicked at 'Box<Any>', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/libsyntax/diagnostic.rs:170

Meta

rustc --version --verbose:
rustc 1.1.0-nightly (c4b23ae 2015-04-29) (built 2015-04-28)
binary: rustc
commit-hash: c4b23ae
commit-date: 2015-04-29
build-date: 2015-04-28
host: x86_64-apple-darwin
release: 1.1.0-nightly

Stack backtrace:

   1:        0x10ae5424f - sys::backtrace::write::h0714aaf7fe41e02dzVr
   2:        0x10ae5c8c0 - panicking::on_panic::hb86b9b356f51f92dEVv
   3:        0x10ae18c35 - rt::unwind::begin_unwind_inner::h58f79e41dbedf2efnDv
   4:        0x10a60998e - rt::unwind::begin_unwind::h17476740655312162035
   5:        0x10a60991a - diagnostic::SpanHandler::span_bug::h6ece18e7aebef0b3cFB
   6:        0x108027cfa - middle::const_eval::resolve_trait_associated_const::hfcf715732ac1e584QMi
   7:        0x107fdba61 - middle::const_eval::lookup_const_by_id::hc5a8309a206ad882OOg
   8:        0x107fd58b2 - middle::check_const::check_expr::h4c113c7ea3d8c1ffB2d
   9:        0x107fcd77c - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_expr::hdb217d3565a2586cGTd
  10:        0x107fd3e7e - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_fn::h37b9b5487c182e36DRd
  11:        0x107fd454e - visit::walk_trait_item::h8343690369834256746
  12:        0x107fd349f - visit::walk_item::h4252660852014709521
  13:        0x107fd2e1c - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_item::h3645f3202d46494bKMd
  14:        0x107fdbeea - middle::check_const::check_crate::ha1c34da7b8765db0Hle
  15:        0x107584171 - driver::phase_3_run_analysis_passes::h2554ff95bce00587tGa
  16:        0x10756618c - driver::compile_input::h7c6cf9b085c57594Qba
  17:        0x107625ac3 - run_compiler::h55b523753cbd518765b
  18:        0x10762322a - boxed::F.FnBox<A>::call_box::h11476165885616507686
  19:        0x107622767 - rt::unwind::try::try_fn::h13518150216340287792
  20:        0x10aedec58 - rust_try_inner
  21:        0x10aedec45 - rust_try
  22:        0x107622a4e - boxed::F.FnBox<A>::call_box::h735039165869315632
  23:        0x10ae5b2bd - sys::thread::Thread::new::thread_start::hf4c42a114072ab47mYu
  24:     0x7fff8cfab267 - _pthread_body
  25:     0x7fff8cfab1e4 - _pthread_start
@huonw huonw added A-associated-items Area: Associated items such as associated types and consts. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ labels May 2, 2015
@quantheory
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This code should be rejected because it involves a constant that depends on a type parameter (Self). I guess I forgot to put in an error message in type checking, which is why you end up with an ICE.

See also rust-lang/rfcs#1062.

This was referenced May 4, 2015
Merged
Merged
bors added a commit that referenced this issue May 12, 2015
@bors
Auto merge of #25171 - quantheory:associated_time_long_paths, r=nikom…
0ad2026 
…atsakis

It is currently broken to use syntax such as `<T as Foo>::U::static_method()` where `<T as Foo>::U` is an associated type. I was able to fix this and simplify the parser a bit at the same time.

This also fixes the corresponding issue with associated types (#22139), but that's somewhat irrelevant because #22519 is still open, so this syntax still causes an error in type checking.

Similarly, although this fix applies to associated consts, #25046 forbids associated constants from using type parameters or `Self`, while #19559 means that associated types have to always have one of those two. Therefore, I think that you can't use an associated const from an associated type anyway.
This was referenced May 19, 2015
Closed
Closed
bors added a commit that referenced this issue May 26, 2015
@bors
Auto merge of #25091 - quantheory:trait_associated_const_fixes, r=nik…
0ea80fa 
…omatsakis

Closes #25046 (by rejecting the code that causes the ICE) and #24946. I haven't been able to deal with the array size or recursion issues yet for associated consts, though my hope was that the change I made for range match patterns might help with array sizes, too.

This PR is pretty much orthogonal to #25065.
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A-associated-items Area: Associated items such as associated types and consts. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️
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Trait-associated const fixes quantheory/rust
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@huonw @quantheory