Make place projections concrete.

[vext01]

I'm not sure if we want this. I'm raising the PR for discussion

Whilst doing some work on our Rust fork, I noticed the following:

Once upon a time (commit 9bd35c0) there were two kinds of
projection: one for places, and one for constants. It therefore made
sense to share the Projection struct for both. Although the different
use-cases used different concrete types, sharing was made possible by
type-parameterisation of Projection.

Since then, however, the usage of projections in constants has
disappeared, meaning that (forgetting lifetimes for a moment) the
parameterised type is only every instantiated under one guise. So it may
as well be a concrete type. Right?

What do people think? This is entirely untested, although it does check.

If we don't want this, then we should at least update the incorrect comment against Projection.

Thanks

[rust-highfive]

r? @eddyb

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

[eddyb]

I thought this was because the MIR borrowck needs to replace the indexing values with an "abstract value" (i.e. treating a[i] and a[j] as potentially-the-same).

cc @pnkfelix@matthewjasper@nikomatsakis

[nikomatsakis]

I think that capability wound up not being used

[matthewjasper]

There's

rust/src/librustc_mir/dataflow/move_paths/abs_domain.rs

Line 21 in 6cc24f2

pubtypeAbstractElem = ProjectionElem<AbstractOperand,AbstractType>;

and

rust/src/librustc/mir/mod.rs

Line 2007 in 6cc24f2

pubtypeProjectionKind = ProjectionElem<(),()>;

But both of those only use ProjectionElem.

This seems fine, but Projection will eventually be refactored away in the Place 2.0 work.

[eddyb]

Oh, wow, this comment has been wrong for most of MIR's existence, I think?
For reasons, Projection<...> isn't used by MIR borrowck, but ProjectionElem is (as AbstractElem).

I think that's why Projection remained parameterized as well, but I'm not sure.

[vext01]

OK, so is there a concensus on this? If you'd like this to go in, then I'll run some tests and check for fallout.

Projection will eventually be refactored away in the Place 2.0 work.

Is there some reading material on this please. This is likely to influence what I'm doing in my fork ;)

[vext01]

./x.py test --stage 1 src/test/{ui,compile-fail,run-pass} passes on my machine.

[bors]

☔ The latest upstream changes (presumably #59897) made this pull request unmergeable. Please resolve the merge conflicts.

[vext01]

Folks, before I go down the path of resolving those conflicts, do you want this change?

[eddyb]

Yes, sorry for not being clearer. This is an accidental leftover that everyone forgot about because of the ProjectionElem parametrization.

[vext01]

synced. OK for me to squash?

[vext01]

I think we should prefer the name Projection.

Oops, I missed this. Leave it with me.

[vext01]

That last commit does the renaming. Quite a lot of churn.

OK to squash?

[oli-obk]

lgtm now, squashing would be good, yes

[bors]

☔ The latest upstream changes (presumably #60984) made this pull request unmergeable. Please resolve the merge conflicts.

[vext01]

If everyone is OK with a4ba4fa, I'll squash.

[rust-highfive]

The job x86_64-gnu-llvm-6.0 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:0ac0be40:start=1558690454608116148,finish=1558690540971523343,duration=86363407195
$ 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
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
[00:01:09] ######################################################################## 100.0%
[00:01:09] extracting /checkout/obj/build/cache/2019-04-11/cargo-beta-x86_64-unknown-linux-gnu.tar.gz
[00:01:09] Updating crates.io index
[00:01:27] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:27] Build completed unsuccessfully in 0:00:31
[00:01:27] make: *** [prepare] Error 1
[00:01:27] Makefile:69: recipe for target 'prepare' failed
[00:01:28] Command failed. Attempt 2/5:
[00:01:28] Command failed. Attempt 2/5:
[00:01:29] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:29] Build completed unsuccessfully in 0:00:00
[00:01:29] make: *** [prepare] Error 1
[00:01:29] Makefile:69: recipe for target 'prepare' failed
[00:01:31] Command failed. Attempt 3/5:
[00:01:31] Command failed. Attempt 3/5:
[00:01:31] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:31] Build completed unsuccessfully in 0:00:00
[00:01:31] Makefile:69: recipe for target 'prepare' failed
[00:01:31] make: *** [prepare] Error 1
[00:01:34] Command failed. Attempt 4/5:
[00:01:34] Command failed. Attempt 4/5:
[00:01:35] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:35] Build completed unsuccessfully in 0:00:00
[00:01:35] make: *** [prepare] Error 1
[00:01:35] Makefile:69: recipe for target 'prepare' failed
[00:01:39] Command failed. Attempt 5/5:
[00:01:39] Command failed. Attempt 5/5:
[00:01:39] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:39] Build completed unsuccessfully in 0:00:00
[00:01:39] Makefile:69: recipe for target 'prepare' failed
[00:01:39] make: *** [prepare] Error 1
[00:01:39] The command has failed after 5 attempts.
---
travis_time:end:019a811a:start=1558690650708242223,finish=1558690650714068415,duration=5826192
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:04cf2ea0
$ 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:08ab9816
travis_time:start:08ab9816
$ 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:1e673699
$ 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)

[vext01]

Sorry, I screwed up the last commit.

[oli-obk]

@vext01 yes, this is looking good now. So a rebase + squash is all that is necessary to get it merged

r? @oli-obk

[vext01]

Squashed.

[oli-obk]

@bors r+

[bors]

📌 Commit 123a456 has been approved by oli-obk

[bors]

⌛ Testing commit 123a456 with merge 5245803...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: oli-obk
Pushing 5245803 to master...