ICE: const_fn feature

[ZhangHanDong]

#![feature(const_fn)]
const fn foo(x: usize) -> usize {
    return x;
}
fn main() {
    [0; foo(2)];
}

or

#![feature(const_fn)]
const unsafe fn foo(x: usize) -> usize {
    return x;
}
fn main() {
    [0; unsafe {foo(2)}];

}

Note: rustc 1.21.0-nightly (cbbe17a 2017-08-07) running on x86_64-apple-darwin

Run： Cargo build

ICEs with:

Compiling hello v0.1.0 (file:///.../hello)
error: internal compiler error: src/librustc_mir/hair/cx/expr.rs:472: constant evaluation of repeat count yielded Tuple([])

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: rustc 1.21.0-nightly (cbbe17aa7 2017-08-07) running on x86_64-apple-darwin

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:486:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[Mark-Simulacrum]

cc @eddyb

[eddyb]

Looks like return was disallowed via the AST check while the MIR-based check doesn't see it as being different. Since return only works in functions, and const fn is unstable, this isn't urgent.
After switching to miri, this testcase will do the right thing.

[ZhangHanDong]

@eddyb yes. it does work when remove return.

#![feature(const_fn)]
const fn foo(x: usize) -> usize {
    x
}
fn main() {
    [0; foo(2)];
}

Compiling playground v0.0.1 (file:///playground)
Finished dev [unoptimized + debuginfo] target(s) in 0.73 secs
Running target/debug/playground