Internal compiler error when matching integers against casted enum constants

[andersk]

I get “error: internal compiler error: unexpected panic” when running cargo test on andersk/image-rs@a9d74e9, which contains the image crate patched as follows. (I was trying to find an alternative to the unstable FromPrimitive.)

--- a/src/png/decoder.rs
+++ b/src/png/decoder.rs
@@ -242,9 +242,12 @@ impl<R: Read> PNGDecoder<R> {
             )))
         }

-        self.interlace_method = match FromPrimitive::from_u8(try!(try!(m.by_ref().bytes().next().ok_or(ImageError::ImageEnd)))) {
-            Some(method) => method,
-            None => return Err(ImageError::UnsupportedError(
+        const NONE_U8: u8 = InterlaceMethod::None as u8;
+        const ADAM7_U8: u8 = InterlaceMethod::Adam7 as u8;
+        self.interlace_method = match try!(try!(m.by_ref().bytes().next().ok_or(ImageError::ImageEnd))) {
+            NONE_U8 => InterlaceMethod::None,
+            ADAM7_U8 => InterlaceMethod::Adam7,
+            _ => return Err(ImageError::UnsupportedError(
                 "Unsupported interlace method.".to_string()
             ))
         };

$ rustc --version --verbose
rustc 1.0.0-nightly (083b8a404 2015-04-05) (built 2015-04-05)
binary: rustc
commit-hash: 083b8a40413eb3dfec7430150b8895f6c8bbafca
commit-date: 2015-04-05
build-date: 2015-04-05
host: x86_64-unknown-linux-gnu
release: 1.0.0-nightly
$ git clone https://github.com/andersk/image.git -b ice-non-constant-path
$ cd image
$ cargo test
    Updating registry `https://github.com/rust-lang/crates.io-index`
   Compiling byteorder v0.3.5
   Compiling glob v0.2.9
   Compiling libc v0.1.5
   Compiling rustc-serialize v0.3.12
   Compiling log v0.3.1
   Compiling rand v0.3.7
   Compiling num v0.1.22
   Compiling image v0.3.6 (file:///tmp/image)
src/png/decoder.rs:245:29: 245:56 error: non-constant path in constant expr
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 'compare_list_exprs: type mismatch', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/librustc_trans/trans/_match.rs:238


Build failed, waiting for other jobs to finish...
src/png/decoder.rs:245:29: 245:56 error: non-constant path in constant expr
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 'compare_list_exprs: type mismatch', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/librustc_trans/trans/_match.rs:238


Could not compile `image`.

To learn more, run the command again with --verbose.
$ RUST_BACKTRACE=1 cargo test
   Compiling image v0.3.6 (file:///tmp/image)
src/png/decoder.rs:245:29: 245:56 error: non-constant path in constant expr
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 'compare_list_exprs: type mismatch', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/librustc_trans/trans/_match.rs:238

stack backtrace:
   1:     0x7f409eb1c7b8 - sys::backtrace::write::h4618bbda30a2c1fakHC
   2:     0x7f409eb47b87 - panicking::on_panic::h94b32ff0a2406463uUI
   3:     0x7f409ea7f893 - rt::unwind::begin_unwind_inner::h310b6bce2d1d1820CzI
   4:     0x7f409e0f232c - rt::unwind::begin_unwind::h13934619924931650302
   5:     0x7f409e23549e - trans::_match::compile_submatch_continue::h1d04a0fa292db3f4rsw
   6:     0x7f409e23181e - trans::_match::compile_submatch::hf239162a447365b4vmw
   7:     0x7f409e23b60f - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
   8:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
   9:     0x7f409e18ba50 - trans::expr::trans_unadjusted::h85803b42d44a1ac7TXh
  10:     0x7f409e1431b4 - trans::expr::trans::h33635d14dc9ce441Blh
  11:     0x7f409e190543 - trans::expr::trans_rvalue_stmt_unadjusted::h0b3806dbe8a23414Bni
  12:     0x7f409e1419b9 - trans::expr::trans_into::h697e5a8350e86c68gfh
  13:     0x7f409e1408c6 - trans::controlflow::trans_stmt_semi::h956c9896cfc4a4efL5d
  14:     0x7f409e142515 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  15:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  16:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
  17:     0x7f409e12ce07 - trans::monomorphize::monomorphic_fn::h21abcb97c3717924Ytd
  18:     0x7f409e16ec3c - trans::callee::trans_fn_ref_with_substs::hd39a6e0257b1ea36Zbg
  19:     0x7f409e16cffb - trans::callee::trans_fn_ref::hae42401196387f572Zf
  20:     0x7f409e1842fd - trans::meth::trans_method_callee::h97933408a6916e9eEvy
  21:     0x7f409e1824a0 - trans::callee::trans_call_inner::h2971582447602048389
  22:     0x7f409e18cbaf - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  23:     0x7f409e18ba50 - trans::expr::trans_unadjusted::h85803b42d44a1ac7TXh
  24:     0x7f409e1431b4 - trans::expr::trans::h33635d14dc9ce441Blh
  25:     0x7f409e23a2f0 - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
  26:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  27:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  28:     0x7f409e1408c6 - trans::controlflow::trans_stmt_semi::h956c9896cfc4a4efL5d
  29:     0x7f409e142515 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  30:     0x7f409e18d358 - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  31:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  32:     0x7f409e23b6b8 - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
  33:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  34:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  35:     0x7f409e1408c6 - trans::controlflow::trans_stmt_semi::h956c9896cfc4a4efL5d
  36:     0x7f409e142515 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  37:     0x7f409e190e82 - trans::expr::trans_rvalue_stmt_unadjusted::h0b3806dbe8a23414Bni
  38:     0x7f409e1419b9 - trans::expr::trans_into::h697e5a8350e86c68gfh
  39:     0x7f409e1408c6 - trans::controlflow::trans_stmt_semi::h956c9896cfc4a4efL5d
  40:     0x7f409e142515 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  41:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  42:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
  43:     0x7f409e12ce07 - trans::monomorphize::monomorphic_fn::h21abcb97c3717924Ytd
  44:     0x7f409e16ec3c - trans::callee::trans_fn_ref_with_substs::hd39a6e0257b1ea36Zbg
  45:     0x7f409e16cffb - trans::callee::trans_fn_ref::hae42401196387f572Zf
  46:     0x7f409e1842fd - trans::meth::trans_method_callee::h97933408a6916e9eEvy
  47:     0x7f409e1824a0 - trans::callee::trans_call_inner::h2971582447602048389
  48:     0x7f409e18cbaf - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  49:     0x7f409e18ba50 - trans::expr::trans_unadjusted::h85803b42d44a1ac7TXh
  50:     0x7f409e1431b4 - trans::expr::trans::h33635d14dc9ce441Blh
  51:     0x7f409e23a2f0 - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
  52:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  53:     0x7f409e18bb64 - trans::expr::trans_unadjusted::h85803b42d44a1ac7TXh
  54:     0x7f409e1431b4 - trans::expr::trans::h33635d14dc9ce441Blh
  55:     0x7f409e140c11 - trans::base::init_local::hd82fb8d63aae5490NMs
  56:     0x7f409e142542 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  57:     0x7f409e18e1f1 - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  58:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  59:     0x7f409e1408c6 - trans::controlflow::trans_stmt_semi::h956c9896cfc4a4efL5d
  60:     0x7f409e142515 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  61:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  62:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
  63:     0x7f409e12ce07 - trans::monomorphize::monomorphic_fn::h21abcb97c3717924Ytd
  64:     0x7f409e16ec3c - trans::callee::trans_fn_ref_with_substs::hd39a6e0257b1ea36Zbg
  65:     0x7f409e1867e1 - trans::meth::trans_method_callee::h97933408a6916e9eEvy
  66:     0x7f409e1824a0 - trans::callee::trans_call_inner::h2971582447602048389
  67:     0x7f409e18cbaf - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  68:     0x7f409e18ba50 - trans::expr::trans_unadjusted::h85803b42d44a1ac7TXh
  69:     0x7f409e1431b4 - trans::expr::trans::h33635d14dc9ce441Blh
  70:     0x7f409e23a2f0 - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
  71:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  72:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  73:     0x7f409e25649f - trans::_match::mk_binding_alloca::h1923058631601932975
  74:     0x7f409e140b3c - trans::base::init_local::hd82fb8d63aae5490NMs
  75:     0x7f409e142542 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  76:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  77:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
  78:     0x7f409e12cd62 - trans::monomorphize::monomorphic_fn::h21abcb97c3717924Ytd
  79:     0x7f409e16ec3c - trans::callee::trans_fn_ref_with_substs::hd39a6e0257b1ea36Zbg
  80:     0x7f409e16cffb - trans::callee::trans_fn_ref::hae42401196387f572Zf
  81:     0x7f409e16aa5d - trans::callee::trans::he76dd5bb3190a87djPf
  82:     0x7f409e180738 - trans::callee::trans_call_inner::h13603331029633186103
  83:     0x7f409e18ddf3 - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  84:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  85:     0x7f409e23b6b8 - trans::_match::trans_match_inner::h9fda511bd32f1e22gUw
  86:     0x7f409e18d2fc - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  87:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  88:     0x7f409e1428b2 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  89:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  90:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
  91:     0x7f409e12cd62 - trans::monomorphize::monomorphic_fn::h21abcb97c3717924Ytd
  92:     0x7f409e16ec3c - trans::callee::trans_fn_ref_with_substs::hd39a6e0257b1ea36Zbg
  93:     0x7f409e16cffb - trans::callee::trans_fn_ref::hae42401196387f572Zf
  94:     0x7f409e16aa5d - trans::callee::trans::he76dd5bb3190a87djPf
  95:     0x7f409e180738 - trans::callee::trans_call_inner::h13603331029633186103
  96:     0x7f409e18ddf3 - trans::expr::trans_rvalue_dps_unadjusted::h5cec7ac55049a34amti
  97:     0x7f409e141848 - trans::expr::trans_into::h697e5a8350e86c68gfh
  98:     0x7f409e1428b2 - trans::controlflow::trans_block::h4d71ce810e64920fH6d
  99:     0x7f409e21958f - trans::base::trans_closure::hf8f2acf635294d9bQtt
  100:     0x7f409e12b4e6 - trans::base::trans_fn::hcf32337a6c531893zEt
 ... <frames omitted>

Build failed, waiting for other jobs to finish...
[another copy of the same backtrace]

Could not compile `image`.

To learn more, run the command again with --verbose.

[andersk]

Here’s a minimized test case.

$ rustc --version --verbose
rustc 1.0.0-nightly (083b8a404 2015-04-05) (built 2015-04-05)
binary: rustc
commit-hash: 083b8a40413eb3dfec7430150b8895f6c8bbafca
commit-date: 2015-04-05
build-date: 2015-04-05
host: x86_64-unknown-linux-gnu
release: 1.0.0-nightly
$ cat foo.rs
#![crate_type = "rlib"]

enum E { E0 = 0, E1 = 1 }
const E0_U8: u8 = E::E0 as u8;
const E1_U8: u8 = E::E1 as u8;

pub fn go<T>() {
    match 0 {
        E0_U8 => (),
        E1_U8 => (),
        _ => (),
    }
}

$ cat bar.rs
extern crate foo;

fn main() {
    foo::go::<()>();
}

$ rustc foo.rs
$ rustc bar.rs -L .
foo.rs:4:19: 4:30 error: non-constant path in constant expr
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 'compare_list_exprs: type mismatch', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/librustc_trans/trans/_match.rs:238

[steveklabnik]

This no longer ICEs

[TheNeikos]

I would like to have a go at this issue since it is marked E-easy.

I do wonder though how I would go about making a test case.
This only panics if you use two seperate files.

[mitaa]

@TheNeikos
You can put foo.rs in test/auxiliary and use use // aux-build:foo.rs in bar.rs, like demonstrated here cebb118

(aux-build should probably be added to COMPILER_TESTS.md)

[TheNeikos]

So what I found out that happens:

src/librustc_trans/trans/_match.rs:243 gets a None value

I added a println! to get an idea of what is going on:

println!("{:?} =?= {:?}", self.0, other.0); 

The output of that println is: expr(28: E::E0 as u8) =?= expr(34: E::E1 as u8)

Where as the error that occurs through which a None is returned is:
"non-constant path in constant expression"

I am not sure what I should check out first, any pointers?

[jonas-schievink]

This still ICEs and isn't E-needstest and probably not E-easy either.