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rustc: fix ICE when trait alias has bare Self #59118

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merged 1 commit into from
Mar 16, 2019

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seanmonstar
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Fixes #59029

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r? @oli-obk

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 11, 2019
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cc @alexreg

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alexreg commented Mar 12, 2019

@seanmonstar Thanks! I'm glad the simple fix seems to have worked. Would you mind creating a new test under src/test/run-pass/issues/issue-59029.rs and writing a bit of code there that actually uses a trait alias with a Self bound in some meaningful way (simple is fine, but at least have an assert)? You can just revert the existing test file then.

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alexreg commented Mar 12, 2019

r? @alexreg

@rust-highfive rust-highfive assigned alexreg and unassigned oli-obk Mar 12, 2019
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alexreg commented Mar 12, 2019

Okay, so this fix isn't actually enough, it seems... Could you try the following locally and let me know if they succeed?

trait SelfWhere<One, Two> = Assoc<Two> where Assoc<Two>::Out: Assoc<One>;

and

trait SelfWhere<One, Two> = Assoc<Two> where <Self as Assoc<Two>>::Out: Assoc<One>;

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The second one does work, it's part of the initial bug report. I haven't tried the first yet.

If Self should be qualified, I can just change this to a compile-fail test checking for the right error.

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The first one (Assoc<Two> where Assoc<Two>::Out: Assoc<One>) complains about "abiguous associated type".

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alexreg commented Mar 12, 2019

As a loose analogy to this example (insofar as it involves trait bounds on an associated type), I'm of the opinion that it's fine for Self alone not to work (so long as it doesn't ICE, of course).

So, now that we've solved the ICE, the question is: do we want better diagnostics when, e.g., trait SelfWhere<One, Two> = Assoc<Two> where <Self as Assoc<Two>>::Out: Assoc<One>; is used. @estebank, what do you think about the error message in the above CI test failure. Should we be doing better?

@seanmonstar Let's have a ui test for the failing case (just Self), and a run-pass test for the case that should pass (<Self as ...>). Two new test files. You can put them both in the ui/issues/ dir though, maybe, and just annotate the passing one with // run-pass as its first line.

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estebank commented Mar 12, 2019

@alexreg it's probably fine. The ideal output would be to provide a suggestion to use <Self as Svc<Target>>::Res, but to do that you'd have to peek into Svc to see if the assoc type not found exists in it. I'm ok with merging this PR as is.

error[E0220]: associated type `Res` not found for `Self`
  --> $DIR/issue-59029-1.rs:5:46
   |
LL | trait MkSvc<Target, Req> = Svc<Target> where Self::Res: Svc<Req>;
   |                                              ^^^^^^^^^
   |                                              |
   |                                              associated type `Res` not found
   |                                              help: you might have meant to use the fully qualified path: `<Self as Svc<Target>>::Res`

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alexreg commented Mar 12, 2019

@estebank Great. I'm okay with merging this as-is too, in that case.

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alexreg commented Mar 12, 2019

@bors r+

Thanks @seanmonstar!

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bors commented Mar 12, 2019

📌 Commit df05fbf has been approved by alexreg

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 12, 2019
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pietroalbini added a commit to pietroalbini/rust that referenced this pull request Mar 13, 2019
…=alexreg

rustc: fix ICE when trait alias has bare Self

Fixes rust-lang#59029
kennytm added a commit to kennytm/rust that referenced this pull request Mar 15, 2019
…=alexreg

rustc: fix ICE when trait alias has bare Self

Fixes rust-lang#59029
kennytm added a commit to kennytm/rust that referenced this pull request Mar 16, 2019
…=alexreg

rustc: fix ICE when trait alias has bare Self

Fixes rust-lang#59029
bors added a commit that referenced this pull request Mar 16, 2019
Rollup of 37 pull requests

Successful merges:

 - #58854 (appveyor: Use VS2017 for all our images)
 - #58855 (std: Spin for a global malloc lock on wasm32)
 - #58873 (Fix "Auto-hide item methods documentation" setting)
 - #58901 (Change `std::fs::copy` to use `copyfile` on MacOS and iOS)
 - #58933 (Move alloc::prelude::* to alloc::prelude::v1, make alloc a subset of std)
 - #58938 (core: ensure VaList passes improper_ctypes lint)
 - #58941 (MIPS: add r6 support)
 - #58949 (SGX target: Expose thread id function in os module)
 - #58959 (Add release notes for PR #56243)
 - #58976 (Default to integrated `rust-lld` linker for UEFI targets)
 - #59009 (Fix SGX implementations of read/write_vectored.)
 - #59025 (Fix generic argument lookup for Self)
 - #59036 (Fix ICE in MIR pretty printing)
 - #59037 (Avoid some common false positives in intra doc link checking)
 - #59072 (we can now skip should_panic tests with the libtest harness)
 - #59079 (add suggestions to invalid macro item error)
 - #59082 (A few improvements to comments in user-facing crates)
 - #59102 (Consistent naming for duration_float methods and additional f32 methods)
 - #59118 (rustc: fix ICE when trait alias has bare Self)
 - #59139 (Unregress using scalar unions in constants.)
 - #59146 (Suggest return lifetime when there's only one named lifetime)
 - #59147 (Make std time tests more robust for platform differences)
 - #59152 (Stabilize Range*::contains.)
 - #59156 ([wg-async-await] Add regression test for #55809.)
 - #59158 (Revert "Don't generate minification variable if minification disabled")
 - #59169 (Add `-Z allow_features=...` flag)
 - #59173 (bootstrap: Default to a sensible llvm-suffix.)
 - #59175 (Don't run test launching `echo` since that doesn't exist on Windows)
 - #59180 (Use try blocks in rustc_codegen_ssa)
 - #59185 (No old chestnuts in iter::repeat docs)
 - #59201 (Remove restriction on isize/usize in repr(simd))
 - #59204 (Output diagnostic information for rustdoc)
 - #59206 (Improved test output)
 - #59208 (Reduce a Code Repetition Related to Bit Operation)
 - #59212 (Add x86_64 musl host to the manifest)
 - #59221 (Option and Result: Add references to documentation of as_ref and as_mut)
 - #59231 (Stabilize Option::copied)
@bors bors merged commit df05fbf into rust-lang:master Mar 16, 2019
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6 participants