[WIP] rustc_typeck: ensure type alias bounds are implied by the type being well-formed.

[eddyb]

NOTE: this is mainly for crater, we'll only emit hard errors on Rust 2018.
This is the second half to a plan outlined in comment on #49441 (see #54033 for the first half).

Fixes #21903 (by disallowing currently unenforceable bounds instead of enforcing them).

This PR includes two hacks: first to not check (usually implied) T: Sized bounds, as they're a common source of breakage and would probably be too annoying in practice, and a second to remove some overlap with #54033, so adding missing bounds is not required to test this PR.
A decision should be made about the former hack, while the latter is only a temporary convenience.

r? @nikomatsakis

[eddyb]

@bors try (hoping for a crater check run)

[bors]

⌛ Trying commit ab3e0d2 with merge 3a2610c2a16575649896925631bf8cec4f4b1961...

[Mark-Simulacrum]

You should be able to start the crater run yourself via the bot, see directions here: https://github.com/rust-lang-nursery/crater/blob/master/docs/bot-usage.md

[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.

[01:07:13] 
[01:07:13] running 258 tests
[01:07:40] .......................i............................................................................
[01:08:04] .........................i..........................................................................
 type Golf<T> where T: Clone = (T, T);
[01:08:13]    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::clone::Clone` is not implemented for `T`
[01:08:13]    |
[01:08:13]    = help: consider adding a `where T: std::clone::Clone` bound
[01:08:13] error: Compilation failed, aborting rustdoc
[01:08:13] 
[01:08:13] 
[01:08:13] ------------------------------------------
---
[01:08:13] 
[01:08:13] thread 'main' panicked at 'Some tests failed', tools/compiletest/src/main.rs:497:22
[01:08:13] 
[01:08:13] 
[01:08:13] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-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" "--rustdoc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustdoc" "--src-base" "/checkout/src/test/rustdoc" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "rustdoc" "--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 " "--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"
[01:08:13] 
[01:08:13] 
[01:08:13] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:08:13] Build completed unsuccessfully in 0:22:08
[01:08:13] Build completed unsuccessfully in 0:22:08
[01:08:13] Makefile:58: recipe for target 'check' failed
[01:08:13] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:18c9276c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

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)

[bors]

☀️ Test successful - status-travis
State: approved= try=True

[Mark-Simulacrum]

@craterbot run p=1 start=master#f50b7758f4dc85dc1c5e38258adaa94213ac6ed1 end=try#3a2610c2a16575649896925631bf8cec4f4b1961 cap-lints=warn mode=check-only

[craterbot]

👌 Experiment pr-54090 created and queued.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-54090 is now running on agent aws-2.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-54090 is completed!
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[eddyb]

Most of the failures come from diesel, and are probably caused by the fact that this is only one half of the check. There are a few legitimate ones. Overall, this seems like not a dent in the ecosystem.

[RalfJung]

About that Sized hack, can we make it so that type Foo<T: Sized> = Box<T> causes an error? I.e., just implicit Sized is ignored?

[eddyb]

@RalfJung I don't want to keep the Sized hack in, I'd rather have an automatically applicable suggestion to add ?Sized - see also #49441 (comment).

[eddyb]

(you can see above I opened 4 PRs - I want to reuse the type_alias_bounds lint name)

[TimNN]

Ping from triage! IIUC, this is waiting on some other PRs to be submitted, so I'm marking this as blocked.

[nikomatsakis]

I'm going to close this PR for now. I do plan to start opening some PRs and issuing warnings, per the plan discussed in #55222