Getting "error: mismatched types: expected std::result::Result<(BUG[0u],uint),~str>..."

[utkarshkukreti]

I'm getting the following error when trying to compile a library I wrote - https://github.com/utkarshkukreti/parley.rs

➜ r1 git:(master) make
test/parser_test.rs:5:41: 16:3 error: mismatched types: expected `std::result::Result<(BUG[0u],uint),~str>` but found `std::result::Result<(~str,<VI2>),~str>` (expected type parameter but found ~str)
test/parser_test.rs:5 let zero: Parser<~str> = do Parser |s| {
test/parser_test.rs:6 match s.len() {
test/parser_test.rs:7 0 => Err(~"Expected `0` but found EOF"),
test/parser_test.rs:8 _ => {
test/parser_test.rs:9 match s[0] as char {
test/parser_test.rs:10 '0' => Ok((~"Yes!", 1)),
...
test/parser_test.rs:5:27: 16:3 error: mismatched types: expected `parley::parser::Parser<~str>` but found `parley::parser::Parser<BUG[0u]>` (expected ~str but found type parameter)
test/parser_test.rs:5 let zero: Parser<~str> = do Parser |s| {
test/parser_test.rs:6 match s.len() {
test/parser_test.rs:7 0 => Err(~"Expected `0` but found EOF"),
test/parser_test.rs:8 _ => {
test/parser_test.rs:9 match s[0] as char {
test/parser_test.rs:10 '0' => Ok((~"Yes!", 1)),
...
error: aborting due to 2 previous errors
task '<unnamed>' failed at 'explicit failure', /Users/utkarsh/dev/git/rust/src/libsyntax/diagnostic.rs:98
task '<unnamed>' failed at 'explicit failure', /Users/utkarsh/dev/git/rust/src/librustc/rustc.rs:395
make: *** [test] Error 101

utkarshkukreti/parley.rs@9b8ac76 is the commit which caused this; just a re-arrangement of the code, making the core part of the library a crate.

I grepped the error message in the Rust's codebase, and found only one result - https://github.com/mozilla/rust/blob/8c97c5ebfd64de87b3868fc8dbfd79a74c4be3cb/src/librustc/util/ppaux.rs#L449 which says

                  // This should not happen...
                  format!("BUG[{:?}]", id)

[utkarshkukreti]

I've made a reduced test case here - https://gist.github.com/37693cca7676c3033d22

➜ cat mod.rs
#[link(name = "min", vers = "0.1")];

pub struct Wrap<A>(A);
➜ cat test.rs
extern mod min;

#[test]
fn min_test() {
  let x: min::Wrap<int> = min::Wrap(10);
}
➜ rustc --lib mod.rs
warning: no debug symbols in executable (-arch x86_64)
➜ rustc --test -L . test.rs
test.rs:5:36: 5:38 error: mismatched types: expected `BUG[0u]` but found `<VI0>` (expected type parameter but found integral variable)
test.rs:5   let x: min::Wrap<int> = min::Wrap(10);
                                              ^~
test.rs:5:26: 5:40 error: mismatched types: expected `min::Wrap<int>` but found `min::Wrap<BUG[0u]>` (expected int but found type parameter)
test.rs:5   let x: min::Wrap<int> = min::Wrap(10);
                                    ^~~~~~~~~~~~~~
error: aborting due to 2 previous errors
task '<unnamed>' failed at 'explicit failure', /Users/utkarsh/dev/git/rust/src/libsyntax/diagnostic.rs:98
task '<unnamed>' failed at 'explicit failure', /Users/utkarsh/dev/git/rust/src/librustc/rustc.rs:395

[eholk]

I just saw a bug that looks similar to this.

[pnkfelix]

i just encountered this at well. Will take a stab at resolving it.

[pnkfelix]

okay I think I found the problem. In rustc::metadata::encoder, the encode_info_for_struct_ctor, which, AFAICT, emits the same metadata that you would for a function that also does the construction, seems to be missing a call to encode_bounds_and_type. (Not quite sure how we have gotten away with that info missing from the crate...)