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ICE: "index is not an integer-constant expression" using enum as array index. #23513

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theemathas opened this issue Mar 19, 2015 · 4 comments
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ICE: "index is not an integer-constant expression" using enum as array index. #23513

theemathas opened this issue Mar 19, 2015 · 4 comments
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I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️

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@theemathas
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Code:

enum E { A, }

const C: [u32; 1] = [1];

fn main() {
    let a = C[E::A as usize];
}

playpen

Error message:

<anon>:6:9: 6:10 warning: unused variable: `a`, #[warn(unused_variables)] on by default
<anon>:6     let a = C[E::A as usize];
                 ^
<anon>:6:15: 6:28 error: internal compiler error: index is not an integer-constant expression
<anon>:6     let a = C[E::A as usize];
                       ^~~~~~~~~~~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:130
@theemathas
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The following modifications eliminate the ICE:

  • change from const to static
  • give explicit discriminant (enum E { A=0, })
  • use a temporary variable to store E::A or E::A as usize

@steveklabnik steveklabnik added the I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ label Mar 19, 2015
@theemathas
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Possibly related to #5873

@quantheory quantheory mentioned this issue Jun 23, 2015
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bors added a commit that referenced this issue Jul 9, 2015
@bors
Auto merge of #26515 - quantheory:check_enum_recursion, r=nrc
afe25a2 
Fixes #23302.

Note that there's an odd situation regarding the following, most likely due to some inadequacy in `const_eval`:

```rust
enum Y {
    A = 1usize,
    B,
}
```

In this case, `Y::B as usize` might be considered a constant expression in some cases, but not others.  (See #23513, for a related problem where there is only one variant, with no discriminant, and it doesn't behave nicely as a constant expression either.)

Most of the complexity in this PR is basically future-proofing, to ensure that when `Y::B as usize` is fully made to be a constant expression, it can't be used to set `Y::A`, and thus indirectly itself.
@frewsxcv
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Visiting for triage: this is still an issue

@steveklabnik steveklabnik mentioned this issue Oct 23, 2015
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bltavares added a commit to bltavares/glacier that referenced this issue Oct 31, 2015
@bltavares
23513
6300969 
Reference rust-lang/rust#23513
@bltavares bltavares mentioned this issue Oct 31, 2015
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@ia0 ia0 mentioned this issue Feb 7, 2016
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@steveklabnik
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This was fixed by #30714 👍

steveklabnik added a commit to rust-lang/glacier that referenced this issue Feb 17, 2016
@steveklabnik
Delete 23513.rs
a40f46c 
This was fixed by rust-lang/rust#23513
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I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️
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@steveklabnik @frewsxcv @theemathas