handle underscore bounds in unexpected places

[nikomatsakis]

Per the discussion on #54902, I made it a hard error to use lifetime bounds in various places where they used to be permitted:

• where Foo: Bar<'_> for example

I also moved error reporting to HIR lowering and added Error variants to let us suppress downstream errors that result.

I (imo) improved the error message wording to be clearer, as well.

In the process, I fixed the ICE in #52098.

Fixes #54902
Fixes #52098

[nikomatsakis]

@bors p=1 -- this is an RC2 blocker

[rust-highfive]

r? @pnkfelix

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

[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.

[00:03:46] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:47] tidy error: /checkout/src/librustc/middle/resolve_lifetime.rs:2355: line longer than 100 chars
[00:03:48] some tidy checks failed
[00:03:48] 
[00:03:48] 
[00:03:48] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:48] 
[00:03:48] 
[00:03:48] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:48] Build completed unsuccessfully in 0:00:45
[00:03:48] Build completed unsuccessfully in 0:00:45
[00:03:48] make: *** [tidy] Error 1
[00:03:48] Makefile:79: recipe for target 'tidy' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:23d4130b
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:0ed8d160:start=1539811653702153235,finish=1539811653705932237,duration=3779002
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0d1ce5d2
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:08a840c4
travis_time:start:08a840c4
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:18e28feb
$ dmesg | grep -i kill

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)

[nikomatsakis]

r? @estebank

@pnkfelix has a lot on their plate right now =)

[nikomatsakis]

cc @rust-lang/compiler — anyone care to review this? I think that @estebank may not have time :) and it's a RC2 blocker

[tmandry]

I'm taking a look now, but if anyone else wants to review, feel free

[tmandry]

Looks good, I caught a couple small things in the tests. r=me once those are resolved

[tmandry]

I think you meant to make this an enum. The error is a parse error

[tmandry]

Since the name of this test is where-clauses.rs I think you may have meant to use a where clause here :)

[nikomatsakis]

@bors r=tmandry

[bors]

📌 Commit c294ec6 has been approved by tmandry

[bors]

⌛ Testing commit c294ec6 with merge 42dde96...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: tmandry
Pushing 42dde96 to master...