funkiness related to static constants in match patterns

[pnkfelix]

Some code:

#![crate_type="lib"]

pub mod variant0 {
    pub enum A { A(()) }
    pub static B: A = A(());

    pub fn main() {
    }
}

#[cfg(variant1)]
pub mod variant1 {
    pub enum A { A(()) }
    pub static B: A = A(()); // <-- error here ...

    // /tmp/s.rs:6:23: 6:28 error: unsupported constant expr
    // /tmp/s.rs:6     pub static B: A = A(());
    //                                  ^~~~~

    pub fn main() {
        match A(()) {
            B => (), // ... introduced by use of `B` here
            _ => (), }
    }
}

#[cfg(variant2)]
pub mod variant2 {
    pub enum C { D=3, E=4 }
    pub static F : C = D;

    pub fn main() {
        match D { F => (), _ => (), }
    }
}

pub mod variant3 {
    pub enum C { D=3, E=4 }
    pub static F : int = 3;

    pub fn main() {
        match D as int { F => (), _ => (), }
    }
}

Some funkiness:

% rustc /tmp/s.rs
% rustc --cfg variant1 /tmp/s.rs
/tmp/s.rs:14:23: 14:28 error: unsupported constant expr
/tmp/s.rs:14     pub static B: A = A(()); // <-- error here ...
                                   ^~~~~
% rustc --cfg variant2 /tmp/s.rs
error: internal compiler error: only scalars and strings supported in compare_values
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at '~Any', /Users/fklock/Dev/Mozilla/rust.git/src/libsyntax/diagnostic.rs:155

%  

The oddity in variant1, as noted in the comments, is that the use of B in a match pattern is causing the compiler to complain about its definition as a static item.

The oddity in variant2 is that we hit an ICE. :)

[jfager]

See also funkiness in #11940

[lifthrasiir]

Duplicate of #13626.