Unexpected panic while compiling a a piece of code with destructuring

[astonbitecode]

Hello,

I would like to report an issue, after the compiler prompted me to do so.

I am using toml-rs to get some configuration data, so I have a function like the following:

extern crate toml;

use toml::Value;

fn read(toml: &Value, path: &'static str, typ: &'static str) -> DefinitionResult {
    match toml.lookup(path) {
        Some(v) => {
            match typ {
                "String" => DefinitionResult::String(v.as_str().unwrap().to_string()),
                "Integer" => DefinitionResult::Integer(v.as_integer().unwrap()),
                _ => DefinitionResult::Err("Cannot handle type")
            }
        }
        None => {
            DefinitionResult::Err("Path does not exist in TOML")
        }
    }
}

With DefinitionResult being an enum:

pub enum DefinitionResult {
    String(String),
    Integer(i64),
    Long(u64),
    Err(&'static str)
}

I have created a Unit test like the following:

#[test]
fn get_string() {
    let toml_string = r#"
        [table1]
        key1 = "value1"
        key2 = "value2"
        [table2]
        key1 = "value1"
        key2 = "value2"
    "#.to_string();
    let toml = toml_string.parse().unwrap();

    let DefinitionResult::String(v1) = super::read(&toml, "table1.key1", "String");
    assert!(v1 == "value1");
}

and once I want to compile and run the test with cargo test I get the following error from the compiler:

error: internal compiler error: unexpected panic
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 'assertion failed: (left == right) (left: 3, right: 1)', ../src/librustc/middle/check_match.rs:1051
note: Run with RUST_BACKTRACE=1 for a backtrace.

I guess that has to do with the destructuring here:

DefinitionResult::String(v1) = super::read(&toml, "table1.key1", "String")

To be honest I am not sure if destructuring an enum like that using let is supported anyway.

If I re-write the destructure like:

match super::read(&toml, "table1.key1", "String") {
    DefinitionResult::String(v1) => assert!(v1 == "value1"),
    _ => assert!(true),
}

everything works great.

Thank you!

Meta

rustc --version --verbose:

rustc 1.8.0-nightly (c8fc481 2016-02-22)
binary: rustc
commit-hash: c8fc481
commit-date: 2016-02-22
host: x86_64-unknown-linux-gnu
release: 1.8.0-nightly

stack backtrace:

1: 0x7fea61f9f340 - sys::backtrace::tracing:: imp::write::h2bb24970c1600d4fNyu
2: 0x7fea61fa86ab - panicking::default_handler::$u7b$$u7b$closure$u7d$$u7d$::closure.43727
3: 0x7fea61fa8203 - panicking::default_handler::hb760707c7feda3cdbez
4: 0x7fea61f70d7c - sys_common::unwind::begin_unwind_inner::h78583c314295e3926mt
5: 0x7fea61f71818 - sys_common::unwind::begin_unwind_fmt::h903be369b05a3ccccmt
6: 0x7fea5f2811d8 - middle::check_match::check_irrefutable::h8d1ba0bed3fbea2aQ4j
7: 0x7fea5f251f42 - middle::check_match::check_local::h2d216d4e5ead2573K2j
8: 0x7fea5f252197 - middle::check_match::check_fn::h082db3cfa9cb9bc8A3j
9: 0x7fea5f252901 - middle::check_match::check_crate::hc28c1fe732f94679kSi
10: 0x7fea624c142e - driver::phase_3_run_analysis_passes::$u7b$$u7b$closure$u7d$$u7d$::closure.28446
11: 0x7fea624be1e5 - middle::ty::context::ctxt<'tcx>::create_and_enter::h6911830796927350595
12: 0x7fea624bad3f - driver::phase_3_run_analysis_passes::h10607465921210735652
13: 0x7fea6248c5b5 - driver::compile_input::h9417f7071f41b0b1Bca
14: 0x7fea6247c907 - run_compiler::h1d04446f72d95b52HOc
15: 0x7fea6247a0b1 - sys_common::unwind::try::try_fn::h2224149726337910613
16: 0x7fea61f9cd9b - __rust_try
17: 0x7fea61f9534d - sys_common::unwind::inner_try::hdfdf33e7068c9cb28jt
18: 0x7fea6247a900 - boxed::F.FnBox::call_box::h8331008289514682961
19: 0x7fea61fa6c79 - sys::thread::Thread:: new::thread_start::h1272204999bddc95vby
20: 0x7fea5a735423 - start_thread
21: 0x7fea61c25cbc - clone
22: 0x0 -

[mitaa]

This should have been fixed recently (#31561)

[alexcrichton]

Thanks @mitaa!

[astonbitecode]

I would like to confirm that, after upgrading to the latest nightly (rustc 1.9.0-nightly (eabfc16 2016-03-08)), the compiler states:

src/main.rs:52:6: 52:34 error: refutable pattern in local binding: Integer(_) not covered [E0005]
src/main.rs:52 let DefinitionResult::String(v1) = super::read(&toml, "table1.key1", "String");

Thank you both!