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'Unsupported constant expr' when matching on tuple-struct constants #6533

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brendanzab opened this issue May 16, 2013 · 4 comments
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A-frontend Area: frontend (errors, parsing and HIR)

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@brendanzab
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edited because it no longer ICEs.

pub mod glfw {
    pub struct InputState(uint);

    pub static RELEASE  : InputState = InputState(0);
    pub static PRESS    : InputState = InputState(1);
    pub static REPEAT   : InputState = InputState(2);
}

fn action_to_str(state: glfw::InputState) -> ~str {
    use glfw::{RELEASE, PRESS, REPEAT};
    match state {
        RELEASE => { ~"Released" }
        PRESS   => { ~"Pressed"  }
        REPEAT  => { ~"Repeated" }
        _       => { ~"Unknown"  }
    }
}

fn main() {}

Error:

ice.rs:4:40: 4:53 error: unsupported constant expr
ice.rs:4     pub static RELEASE  : InputState = InputState(0);
                                                ^~~~~~~~~~~~~
@msullivan
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This is now a non-ICE failure. Is this something that we intend to support?

../rust-things/bug-6533.rs:5:39: 5:53 error: Unsupported constant expr
../rust-things/bug-6533.rs:5     pub static PRESS    : InputState = InputState(1);

@alexcrichton
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If the definition were instead InputState { value: uint } then you can create a static, so it seems to be like this should be allowed.

@catamorphism
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Reproduced what @msullivan reported with 2ab4a6f . I agree with @alexcrichton ; doesn't seem like a milestone blocker, though.

@erickt erickt added I-wrong and removed I-ICE labels May 11, 2014
@erickt erickt changed the title ICE: 'Unsupported constant expr' when matching on tuple-struct constants 'Unsupported constant expr' when matching on tuple-struct constants May 11, 2014
@erickt
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erickt commented May 11, 2014

visiting for triage. This code no longer ICEs, but it still can't pattern match on the tuple structs. I updated the body to reflect this.

bors added a commit that referenced this issue Jul 19, 2014
This is accomplished by rewriting static expressions into equivalent patterns.
This way, patterns referencing static variables can both participate
in exhaustiveness analysis as well as be compiled down into the appropriate
branch of the decision trees that match expressions are codegened to.

Fixes #6533.
Fixes #13626.
Fixes #13731.
Fixes #14576.
Fixes #15393.
@bors bors closed this as completed in fba1194 Jul 19, 2014
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5 participants