Implement the Re-rebalance coherence RFC

[weiznich]

This is the first time I touch anything in the compiler so just tell me if I got something wrong.

Big thanks to @sgrif for the pointers where to look for those things.
cc #55437

[rust-highfive]

r? @varkor

(rust_highfive has picked a reviewer for you, use r? to override)

[varkor]

I haven't checked over the tests yet, but the code looks good. I'll try to look at the tests soon.

[varkor]

Is this "if and only if"?

[weiznich]

That's directly copied from the RFC. I think it should be "if and only if" but's not written there. (cc @sgrif who has written that thing)

[weiznich]

@varkor I've addressed your review comments.

[varkor]

Sorry about the delay @weiznich. I'll get to this soon.

[weiznich]

@varkor I've rebased the PR.

[varkor]

You seem to have accidentally pulled in some extra changes with the rebase.

[varkor]

At the moment, the fact that all the coherence tests have been duplicated under the new feature flag seems a little excessive. I'm not quite sure what the correct approach here is though: we do want to make sure we don't break anything. I wonder if it would be appropriate to run the tests in two modes, a bit like NLL does at the moment. Alternatively, we could have a few tests that cover a representative sample of existing cases, under the assumption that the algorithm is mostly the same anyway and when stabilised, the existing tests are going to come into effect anyway.

Could you point out which tests are new (and demonstrate the new behaviour), so I can check those in particular?

I think @nikomatsakis will have better ideas about the right solution re. tests, so I'm going to reassign. The actual change looks good to me, though (once the rebase issues are fixed).

r? @nikomatsakis

[weiznich]

Could you point out which tests are new (and demonstrate the new behaviour), so I can check those in particular?

This one and this one is new. All other tests are just a copied version of the old coherence tests with the re_rebalance feature enabled.

At the moment, the fact that all the coherence tests have been duplicated under the new feature flag seems a little excessive. I'm not quite sure what the correct approach here is though: we do want to make sure we don't break anything. I wonder if it would be appropriate to run the tests in two modes, a bit like NLL does at the moment. Alternatively, we could have a few tests that cover a representative sample of existing cases, under the assumption that the algorithm is mostly the same anyway and when stabilised, the existing tests are going to come into effect anyway.

I'm not sure what would be a representative sample of the existing test cases here, nor I'm knowing what needs to be changed to run the existing tests using two modes. Would be great to get some more input here.

[weiznich]

I'm not sure why those 2 tests fail. The corresponding .stderr files containing exactly those error messages...

[weiznich]

@varkor@nikomatsakis Any news here?

[nikomatsakis]

Seems great! I would like before r+'ing though to spend a bit more time checking over the tests.

[nikomatsakis]

This comment needs to be //~^ -- no space

[rust-highfive]

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:0e6e87c0:start=1544786423331187056,finish=1544786477558750623,duration=54227563567
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout
Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#Pull-Requests-and-Security-Restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-5.0
---
472 ./src/libstd/sys/unix
468 ./src/test/ui/resolve
460 ./src/test/ui/rust-2018
448 ./src/test/ui/traits
448 ./src/test/ui/re_rebalance_coherence
444 ./src/test/ui/privacy
436 ./src/librustc_resolve
420 ./src/doc/unstable-book
416 ./src/test/ui/associated-types
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86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-re-rebalance-coherence/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-re-rebalance-coherence/auxiliary" "-A" "unused"
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] ------------------------------------------
[00:45:59] stderr:
[00:45:59] stderr:
[00:45:59] ------------------------------------------
[00:45:59] {"message":"type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)","code":{"code":"E0210","explanation":"\nThis error indicates a violation of one of Rust's orphan rules for trait\nimplementations. The rule concerns the use of type parameters in an\nimplementation of a foreign trait (a trait defined in another crate), and\nstates that type parameters must be \"covered\" by a local type. To understand\nwhat this means, it is perhaps easiest to consider a few examples.\n\nIf `ForeignTrait` is a trait defined in some external crate `foo`, then the\nfollowing trait `impl` is an error:\n\n```compile_fail,E0210\n# #[cfg(for_demonstration_only)]\nextern crate foo;\n# #[cfg(for_demonstration_only)]\nuse foo::ForeignTrait;\n# use std::panic::UnwindSafe as ForeignTrait;\n\nimpl<T> ForeignTrait for T { } // error\n# fn main() {}\n```\n\nTo work around this, it can be covered with a local type, `MyType`:\n\n```\n# use std::panic::on the design of the orphan rules, see [RFC 1023].\n\n[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/feature-gates/feature-gate-re-rebalance-coherence.rs","byte_start":226,"byte_end":295,"line_start":10,"line_end":10,"column_start":1,"column_end":70,"is_primary":true,"text":[{"text":"impl<'a, T:'a, Tab> QueryFragment<Oracle> for BatchInsert<'a, T, Tab> {}","highlight_start":1,"highlight_end":70}],"label":"type parameter `T` must be used as the type parameter for some local type","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"only traits defined in the current crate can be implemented for a type parameter","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)\n --> /checkout/src/test/ui/feature-gates/feature-gate-re-rebalance-coherence.rs:10:1\n |\nLL | impl<'a, T:'a, Tab> QueryFragment<Oracle> for BatchInsert<'a, T, Tab> {}\n | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type parameter `T` must be used as the type parameter for some local type\n |\n = note: only traits defined in the current crate can be implemented for a type parameter\n\n"}
[00:45:59] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:45:59] {"message":"For more information about this error, try `rustc --explain E0210`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0210`.\n"}
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] [00:45:59] thread '[ui] ui/feature-gates/feature-gate-re-rebalance-coherence.rs' panicked at 'explicit panic', src/tools/compiletest/src/runtest.rs:3252:9
[00:45:59] [00:45:59] [00:45:59] ---- [ui] ui/re_rebalance_coherence/coherence-all-remote.rs stdout ----
[00:45:59] [00:45:59] [00:45:59] - error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g. `MyStruct<T>`)
[00:45:59] + error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
[00:45:59] 2 --> $DIR/coherence-all-remote.rs:18:1
[00:45:59] 3 |
[00:45:59] 4 LL | impl<T> Remote1<T> for isize { }
[00:45:59] [00:45:59] The actual stderr differed from the expected stderr.
[00:45:59] The actual stderr differed from the expected stderr.
[00:45:59] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-all-remote/coherence-all-remote.stderr
[00:45:59] To update references, rerun the tests and pass the `--bless` flag
[00:45:59] To only update this specific test, also pass `--test-args re_rebalance_coherence/coherence-all-remote.rs`
[00:45:59] error: 1 errors occurred comparing output.
[00:45:59] status: exit code: 1
[00:45:59] status: exit code: 1
[00:45:59] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/re_rebalance_coherence/coherence-all-remote.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-all-remote/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-all-remote/auxiliary" "-A" "unused"
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] ------------------------------------------
[00:45:59] stderr:
[00:45:59] stderr:
[00:45:59] ------------------------------------------
[00:45:59] {"message":"type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)","code":{"code":"E0210","explanation":"\nThis error indicates a violation of one of Rust's orphan rules for trait\nimplementations. The rule concerns the use of type parameters in an\nimplementation of a foreign trait (a trait defined in another crate), and\nstates that type parameters must be \"covered\" by a local type. To understand\nwhat this means, it is perhaps easiest to consider a few examples.\n\nIf `ForeignTrait` is a trait defined in some external crate `foo`, then the\nfollowing trait `impl` is an error:\n\n```compile_fail,E0210\n# #[cfg(for_demonstration_only)]\nextern crate foo;\n# #[cfg(for_demonstration_only)]\nuse foo::ForeignTrait;\n# use std::panic::UnwindSafe as ForeignTrait;\n\nimpl<T> ForeignTrait for T { } // error\n# fn main() {}\n```\n\nTo work around this, it can be covered with a local type, `MyType`:\n\n```\n# use std::panic::UnwindSafe as ForeignTrait;\nstruct MyType<T>(T);\nimpl<T> ForeignTrait for MyType<T> { } // Ok\n```\n\nPlease note that a type alias is not sufficient.\n\nFor another example of an error, suppose there's another trait defined in `foo`\nnamed `ForeignTrait2` that takes two type parameters. Then this `impl` results\nin the same rule violation:\n\n```ignore (cannot-doctest-multicrate-project)\nstruct MyType2;\nimpl<T> ForeignTrait2<T, MyType<T>> for MyType2 { } // error\n```\n\nThe reason for this is that there are two appearances of type parameter `T` in\nthe `impl` header, both as parameters for `ForeignTrait2`. The first appearance\nis uncovered, and so runs afoul of the orphan rule.\n\nConsider one more example:\n\n```ignore (cannot-doctest-multicrate-project)\nimpl<T> ForeignTrait2<MyType<T>, T> for MyType2 { } // Ok\n```\n\nThis only differs from the previous `impl` in that the parameters `T` and\n`MyType<T>` for `ForeignTrait2` have been swapped. This example does *not*\nviolate the orphan rule; it is permitted.\n\nTo see why that last example was allowed, you need to understand the general\nrule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:\n\n```ignore (only-for-syntax-highlight)\nimpl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }\n```\n\nwhere `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`\nare types. One of the types `T0, ..., Tn` must be a local type (this is another\norphan rule, see the explanation for E0117). Let `i` be the smallest integer\nsuch that `Ti` is a local type. Then no type parameter can appear in any of the\n`Tj` for `j < i`.\n\nFor information on the design of the orphan rules, see [RFC 1023].\n\n[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/re_rebalance_coherence/coherence-all-remote.rs","byte_start":589,"byte_end":617,"line_start":18,"line_end":18,"column_start":1,"column_end":29,"is_primary":true,"text":[{"text":"impl<T> Remote1<T> for isize { }","highlight_start":1,"highlight_end":29}],"label":"type parameter `T` must be used as the type parameter for some local type","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"only traits defined in the current crate can be implemented for a type parameter","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)\n --> /checkout/src/test/ui/re_rebalance_coherence/coherence-all-remote.rs:18:1\n |\nLL | impl<T> Remote1<T> for isize { }\n | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type parameter `T` must be used as the type parameter for some local type\n |\n = note: only traits defined in the current crate can be implemented for a type parameter\n\n"}
[00:45:59] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:45:59] {"message":"For more information about this error, try `rustc --explain E0210`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0210`.\n"}t-param/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-bigint-param/auxiliary" "-A" "unused"
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] ------------------------------------------
[00:45:59] stderr:
[00:45:59] stderr:
[00:45:59] ------------------------------------------
[00:45:59] {"message":"type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)","code":{"code":"E0210","explanation":"\nThis error indicates a violation of one of Rust's orphan rules for trait\nimplementations. The rule concerns the use of type parameters in an\nimplementation of a foreign trait (a trait defined in another crate), and\nstates that type parameters must be \"covered\" by a local type. To understand\nwhat this means, it is perhaps easiest to consider a few examples.\n\nIf `ForeignTrait` is a trait defined in some external crate `foo`, then the\nfollowing trait `impl` is an error:\n\n```compile_fail,E0210\n# #[cfg(for_demonstration_only)]\nextern crate foo;\n# #[cfg(for_demonstration_only)]\nuse foo::ForeignTrait;\n# use std::panic::UnwindSafe as ForeignTrait;\n\nimpl<T> ForeignTrait for T { } // error\n# fn main() {}\n```\n\nTo work around this, it can be covered with a local type, `MyType`:\n\n```\n# use std::panic::UnwindSafe as ForeignTrait;\nstruct MyType<T>(T);\nimpl<T> ForeignTrait for MyType<T> { } // Ok\n```\n\nPlease note that a type alias is not sufficient.\n\nFor another example of an error, suppose there's another trait defined in `foo`\nnamed `ForeignTrait2` that takes two type parameters. Then this `impl` results\nin the same rule violation:\n\n```ignore (cannot-doctest-multicrate-project)\nstruct MyType2;\nimpl<T> ForeignTrait2<T, MyType<T>> for MyType2 { } // error\n```\n\nThe reason for this is that there are two appearances of type parameter `T` in\nthe `impl` header, both as parameters for `ForeignTrait2`. The first appearance\nis uncovered, and so runs afoul of the orphan rule.\n\nConsider one more example:\n\n```ignore (cannot-doctest-multicrate-project)\nimpl<T> ForeignTrait2<MyType<T>, T> for MyType2 { } // Ok\n```\n\nThis only differs from the previous `impl` in that the parameters `T` and\n`MyType<T>` for `ForeignTrait2` have been swapped. This example does *not*\nviolate the orphan rule; it is permitted.\n\nTo see why that last example was allowed, you need to understand the general\nrule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:\n\n```ignore (only-for-syntax-highlight)\nimpl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }\n```\n\nwhere `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`\nare types. One of the types `T0, ..., Tn` must be a local type (this is another\norphan rule, see the explanation for E0117). Let `i` be the smallest integer\nsuch that `Ti` is a local type. Then no type parameter can appear in any of the\n`Tj` for `j < i`.\n\nFor information on the design of the orphan rules, see [RFC 1023].\n\n[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/re_rebalance_coherence/coherence-bigint-param.rs","byte_start":609,"byte_end":638,"line_start":20,"line_end":20,"column_start":1,"column_end":30,"is_primary":true,"text":[{"text":"impl<T> Remote1<BigInt> for T { }","highlight_start":1,"highlight_end":30}],"label":"type parameter `T` must be used as the type parameter for some local type","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"only traits defined in the current crate can be implemented for a type parameter","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)\n --> /checkout/src/test/ui/re_rebalance_coherence/coherence-bigint-param.rs:20:1\n |\nLL | impl<T> Remote1<BigInt> for T { }\n | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type parameter `T` must be used as the type parameter for some local type\n |\n = note: only traits defined in the current crate can be implemented for a type parameter\n\n"}
[00:45:59] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:45:59] {"message":"For more information about this error, try `rustc --explain E0210`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0210`.\n"}
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] [00:45:59] thread '[ui] ui/re_rebalance_coherence/coherence-bigint-param.rs' panicked at 'explicite:\n\n```\ntrait MyTrait {\n fn get(&self) -> usize;\n}\n\nimpl<T> MyTrait for T {\n fn get(&self) -> usize { 0 }\n}\n\nstruct Foo;\n\nfn main() {\n let f = Foo;\n\n f.get(); // the trait is implemented so we can use it\n}\n```\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/re_rebalance_coherence/coherence-cross-crate-conflict.rs","byte_start":703,"byte_end":720,"line_start":20,"line_end":20,"column_start":1,"column_end":18,"is_primary":true,"text":[{"text":"impl<A> Foo for A {","highlight_start":1,"highlight_end":18}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"conflicting implementation in crate `trait_impl_conflict`:\n- impl trait_impl_conflict::Foo for isize;","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0119]: conflicting implementations of trait `trait_impl_conflict::Foo` for type `isize`:\n --> /checkout/src/test/ui/re_rebalance_coherence/coherence-cross-crate-conflict.rs:20:1\n |\nLL | impl<A> Foo for A {\n | ^^^^^^^^^^^^^^^^^\n |\n = note: conflicting implementation in crate `trait_impl_conflict`:\n - impl trait_impl_conflict::Foo for isize;\n\n"}
[00:45:59] {"message":"type parameter `A` must be used as the type parameter for some local type (e.g., `MyStruct<A>`)","code":{"code":"E0210","explanation":"\nThis error indicates a violation of one of Rust's orphan rules for trait\nimplementations. The rule concerns the use of type parameters in an\nimplementation of a foreign trait (a trait defined in another crate), and\nstates that type parameters must be need to understand the general\nrule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:\n\n```ignore (only-for-syntax-highlight)\nimpl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }\n```\n\nwhere `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`\nare types. One of the types `T0, ..., Tn` must be a local type (this is another\norphan rule, see the explanation for E0117). Let `i` be the smallest integer\nsuch that `Ti` is a local type. Then no type parameter can appear in any of the\n`Tj` for `j < i`.\n\nFor information on the design of the orphan rules, see [RFC 1023].\n\n[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/re_rebalance_coherence/coherence-cross-crate-conflict.rs","byte_start":703,"byte_end":720,"line_start":20,"line_end":20,"column_start":1,"column_end":18,"is_primary":true,"text":[{"text":"impl<A> Foo for A {","highlight_start":1,"highlight_end":18}],"label":"type parameter `A` must be used as the type parameter for some local type","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"only traits defined in the current crate can be implemented for a type parameter","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0210]: type parameter `A` must be used as the type parameter for some local type (e.g., `MyStruct<A>`)\n --> /checkout/src/test/ui/re_rebalance_coherence/coherence-cross-crate-conflict.rs:20:1\n |\nLL | impl<A> Foo for A {\n | ^^^^^^^^^^^^^^^^^ type parameter `A` must be used as the type parameter for some local type\n |\n = note: only traits defined in the current crate can be implemented for a type parameter\n\n"}
[00:45:59] {"message":"aborting due to 2 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 2 previous errors\n\n"}
[00:45:59] {"message":"Some errors occurred: E0119, E0210.","code":null,"level":"","spans":[],"children":[],"rendered":"Some errors occurred: E0119, E0210.\n"}
[00:45:59] {"message":"For more information about an error, try `rustc --explain E0119`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about an error, try `rustc --explain E0119`.\n"}
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] [00:45:59] thread '[ui] ui/re_rebalance_coherence/coherence-cross-crate-conflict.rs' panicked at 'explicit panic', src/tools/compiletest/src/runtest.rs:3252:9
[00:45:59] [00:45:59] ---- [ui] ui/re_rebalance_coherence/coherence-lone-type-parameter.rs stdout ----
[00:45:59] [00:45:59] [00:45:59] - error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g. `MyStruct<T>`)
[00:45:59] + error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
[00:45:59] 2 --> $DIR/coherence-lone-type-parameter.rs:18:1
[00:45:59] 3 |
[00:45:59] 4 LL | impl<T> Remote for T { }
[00:45:59] [00:45:59] The actual stderr differed from the expected stderr.
[00:45:59] The actual stderr differed from the expected stderr.
[00:45:59] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-lone-type-parameter/coherence-lone-type-parameter.stderr
[00:45:59] To update references, rerun the tests and pass the `--bless` flag
[00:45:59] To only update this specific test, also pass `--test-args re_rebalance_coherence/coherence-lone-type-parameter.rs`
[00:45:59] error: 1 errors occurred comparing output.
[00:45:59] status: exit code: 1
[00:45:59] status: exit code: 1
[00:45:59] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/re_rebalance_coherence/coherence-lone-type-parameter.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-lone-type-parameter/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/re_rebalance_coherence/coherence-lone-type-parameter/auxiliary" "-A" "unused"
[00:45:59] ------------------------------------------
[00:45:59] [00:45:59] ------------------------------------------
[00:45:59] stderr:
[00:45:59] stderr:
[00:45:59] ------------------------------------------
[00:45:59] {"message":"type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)","code":{"code":"E0210","explanation":"\nThis error indicates a violation of one of Rust's orphan rules for trait\nimplementations. The rule concerns the use of type parameters in an\nimplementation of a foreign trait (a trait defined in another crate), and\nstates that type parameters must be \"covered\" by a local type. To understand\nwhat this means, it is perhaps easiest to consider a few examples.\n\nIf `ForeignTrait` is a trait defined in some external crate `foo`, then the\nfollowing trait `impl` is an error:\n\n```compile_fail,E0210\n# #[cfg(for_demonstration_only)]\nextern crate foo;\n# #[cfg(for_demonstration_only)]\nuse foo::ForeignTrait;\n# use std::panic::UnwindSafe as ForeignTrait;\n\nimpl<T> ForeignTrait for T { } // error\n# fn main() {}\n```\n\nTo work around this, it can be covered with a local type, `MyType`:\n\n```\n# use std::panic::UnwindSafe as ForeignTrait;\nstruct MyType<T>(T);\nimpl<T> ForeignTrait for MyType<T> { } // Ok\n```\n\nPlease note that a type alias is not sufficient.\n\nFor another example of an error, suppose there's another trait defined in `foo`\nnamed `ForeignTrait2` that takes two type parameters. Then this `impl` results\nin the same rule violation:\n\n```ignore (cannot-doctest-multicrate-project)\nstruct MyType2;\nimpl<T> ForeignTrait2<T, MyType<T>> for MyType2 { } // error\n```\n\nThe reason for this is that there are two appearances of type parameter `T` in\nthe `impl` header, both as parameters for `ForeignTrait2`. The first appearance\nis uncovered, and so runs afoul of the orphan rule.\n\nConsider one more example:\n\n```ignore (cannot-doctest-multicrate-project)\nimpl<T> ForeignTrait2<MyType<T>, T> for MyType2 { } // Ok\n```\n\nThis only differs from the previous `impl` in that the parameters `T` and\n`MyType<T>` for `ForeignTrait2` have been swapped. This example does *not*\nviolate the orphan rule; it is permitted.\n\nTo see why that last example was allowed, you need to understand the general\nrule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:\n\n```ignore (only-for-syntax-highlight)\nimpl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }\n```\n\nwhere `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`\nare types. One of the types `T0, ..., Tn` must be a local type (this is another\norphan rule, see the explanation for E0117). Let `i` be the smallest integer\nsuch that `Ti` is a local type. Then no type parameter can appear in any of the\n`Tj` for `j < i`.\n\nFor information on the design of the orphan rules, see [RFC 1023].\n\n[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/re_rebalance_coherence/coherence-lone-type-parameter.rs","byte_start":588,"byte_end":608,"line_start":18,"line_end":18,"column_start":1,"column_end":21,"is_primary":true,"text":[{"text":"impl<T> Remote for T { }","highlight_start":1,"highlight_end":21}],"label":"type parameter `T` must be used as the type parameter for some local type","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"only traits defined in the current crate can be implemented for a type parameter","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)\n --> /checkout/src/test/ui/re_rebalance_coherence/coherence-lone-type-parameter.rs:18:1\n |\nLL | impl<T> Remote for T { }\n | ^^^^^-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-5.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "5.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[00:45:59] [00:45:59] [00:45:59] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:45:59] Build completed unsuccessfully in 0:03:47
[00:45:59] Build completed unsuccessfully in 0:03:47
[00:45:59] Makefile:58: recipe for target 'check' failed
[00:45:59] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:00dcfdc5
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Fri Dec 14 12:07:25 UTC 2018

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[weiznich]

@nikomatsakis Tests are fixed.

[nikomatsakis]

I forgot about this question that @varkor raised:

At the moment, the fact that all the coherence tests have been duplicated under the new feature flag seems a little excessive.

One option here is to rewrite the duplicated tests using revisions. The idea is to include a comment like:

// revisions: old new

This will cause the same test to be built twice, once with #[cfg(old)] and once with #[cfg(new)] in scope.

You can then do things like:

#![cfg_attr(new, feature(new_algorithm))]

@weiznich -- do you want to take a shot at collapsing the tests this way?

[weiznich]

@nikomatsakis I will try that. What's the right strategy here? In that case there are already revisions.

[nikomatsakis]

Well, in this case you would have to add another set of three revisions, I suppose. e.g., a, re_a, b, re_b, c, re_c

[bors]

☔ The latest upstream changes (presumably #55517) made this pull request unmergeable. Please resolve the merge conflicts.

[cramertj]

@bors r=nikomatsakis

[bors]

📌 Commit d758e4d has been approved by nikomatsakis

[bors]

⌛ Testing commit d758e4d with merge 244b05d...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 244b05d to master...