ICE in typeck subst

[pnkfelix]

(This may be an artifact of trying to make progress after encountering a different type error.)

Test case:

extern mod extra;

mod g {
    use extra::treemap::TreeMap;

    struct LF<T> { o: ~[T] }

    fn step<T>(rules: &[T]) -> Option<LF<T>> { None }

    fn f<T:Clone+Eq+Ord+TotalOrd>(t:&T) {
        let rules : TreeMap<T, ~[T]> = TreeMap::new();
        let LF { o: _ } = step(rules.get(t)).unwrap();
    }
}

fn main() { }

The ICE:

% RUST_LOG=rustc=1 rustc /tmp/bad.rs
/tmp/bad.rs:12:31: 12:44 error: type `extra::treemap::TreeMap<T,~[T]>` does not implement any method in scope named `get`
/tmp/bad.rs:12         let LF { o: _ } = step(rules.get(t)).unwrap();
                                              ^~~~~~~~~~~~~
task <unnamed> failed at 'index out of bounds: the len is 0 but the index is 0', /Users/fklock/Dev/Mozilla/rust.git/src/librustc/middle/subst.rs:58
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=1 to get further details and report the results to github.com/mozilla/rust/issues
task <unnamed> failed at 'explicit failure', /Users/fklock/Dev/Mozilla/rust.git/src/librustc/rustc.rs:376

[nikomatsakis]

cc me

[bill-myers]

Another simpler test case that hits that same out-of-bounds issue:

struct A<T> {
    a: T
}

fn f<T>(v: A<T>) {
    let ~A{a: ref a} = v;
}

The code is incorrect, but shouldn't ICE.

[eddyb]

I've replaced the ICE with an error as part of the fix for #11964, is this acceptable?

error: missing type param `T` in the substitution of `T`
<anon>:1:42: 1:54 error: mismatched types: expected `A<T>` but found a ~-box pattern
<anon>:1 struct A<T> {a: T} fn f<T>(v: A<T>) {let ~A{a: ref a} = v;} fn main(){}