user annotations in patterns

[nikomatsakis]

Fixes #54573

r? @pnkfelix

[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.

[00:23:42]    Compiling syntax_pos v0.0.0 (/checkout/src/libsyntax_pos)
[00:23:46]    Compiling rustc_errors v0.0.0 (/checkout/src/librustc_errors)
[00:25:16]    Compiling proc_macro v0.0.0 (/checkout/src/libproc_macro)
[00:25:25]    Compiling syntax_ext v0.0.0 (/checkout/src/libsyntax_ext)
[00:27:09] error: internal compiler error: librustc_mir/borrow_check/nll/universal_regions.rs:754: cannot convert `ReScope(Remainder { block: ItemLocalId(1359), first_statement_index: 0})` to a region vid
[00:27:09] thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:599:9
[00:27:09] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[00:27:10] error: aborting due to previous error
[00:27:10] 
[00:27:10] 
[00:27:10] 
[00:27:10] note: the compiler unexpectedly panicked. this is a bug.
[00:27:10] 
[00:27:10] note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
[00:27:10] 
[00:27:10] note: rustc 1.31.0-dev running on x86_64-unknown-linux-gnu
[00:27:10] 
[00:27:10] note: compiler flags: -Z force-unstable-if-unmarked -C prefer-dynamic -C opt-level=2 -C prefer-dynamic -C debug-assertions=y -C link-args=-Wl,-rpath,$ORIGIN/../lib --crate-type dylib
[00:27:10] note: some of the compiler flags provided by cargo are hidden
[00:27:10] 
[00:27:10] error: Could not compile `rustc`.
[00:27:10] 
[00:27:10] 
[00:27:10] To learn more, run the command again with --verbose.
[00:27:10] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" " jemalloc" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "--message-format" "json"
[00:27:10] expected success, got: exit code: 101
[00:27:10] thread 'main' panicked at 'cargo must succeed', bootstrap/compile.rs:1112:9
[00:27:10] travis_fold:end:stage1-rustc

[00:27:10] travis_time:end:stage1-rustc:start=1538501328026176391,finish=1538501597202990906,duration=269176814515

---
travis_time:end:2bef507a:start=1538501597933763060,finish=1538501597938549283,duration=4786223
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:1b4dd171
$ 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

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]

oh dear, I didn't see that ICE locally for some reason. Probably --keep-stage 1 =)

[pnkfelix]

@nikomatsakis do you think you're going to have time to address this soon? Or do you want me to attempt to fix the ICE as part of my review?

[pnkfelix]

(also, I am going to retag this as waiting-on-author so @nikomatsakis knows he needs to respond to my Q and/or fix the ICE...)

[nikomatsakis]

OK, I spent all day debugging this ICE (and more of Friday than I care to admit), but I finally found it. In fact, @pnkfelix, the problem is not specific to this PR, and may well be affecting you in other PRs.

[nikomatsakis]

If I am correct — and I'm 99% sure — I'll push a fix soon. The debugging was seriously hampered by my seeming inability to reproduce the ICE outside of a x.py build run. Now that I know the problem, maybe I can come up with a more local reproduction ...

[nikomatsakis]

For those of you following along, the bug was in this code from the region renumberer:

rust/src/librustc_mir/borrow_check/nll/renumber.rs

Lines 115 to 126 in 423d810

	fn visit_ascribe_user_ty(
	&mut self,
	_place: &mut Place<'tcx>,
	_variance: &mut ty::Variance,
	_c_ty: &mut CanonicalTy<'tcx>,
	_location: Location,
	) {
	// User-assert-ty statements represent types that the user added explicitly.
	// We don't want to erase the regions from these types: rather, we want to
	// add them as constraints at type-check time.
	debug!("visit_user_assert_ty: skipping renumber");
	}

In particular, we still need to be visiting the Place, which may have embedded regions. I'm not sure I've so far failed to reproduce this though.

[nikomatsakis]

Pushed what I hope to be a fix (travis will tell =) — I was not able to make a smaller example that reproduced the problem though.

[pnkfelix]

@bors r+ p=1

bumping priority slightly because I believe this ICE is impeding ongoing work in others' development branches

[bors]

📌 Commit ccba716 has been approved by pnkfelix

[bors]

⌛ Testing commit ccba716 with merge e1643a8...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: pnkfelix
Pushing e1643a8 to master...