Use crate name for reexported extern crate paths

[estebank]

Fix #43189.

[rust-highfive]

r? @michaelwoerister

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

[estebank]

Tested locally with the ticket's repro, and it seems to be doing the right thing:

error[E0599]: no method named `a` found for type `()` in the current scope
 --> src/main.rs:3:16
  |
3 | fn main() { ().a(); }
  |                ^
  |
  = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope, perhaps add a `use` for it:
  |
3 | use b::a::A;
  |

Need to figure out what the appropriate way to test this is.

[pietroalbini]

Ping from triage @michaelwoerister! This PR needs your review.

[michaelwoerister]

Yes, a test would be great!

[estebank]

Added test.

[michaelwoerister]

Thanks @estebank!

@bors r+

[bors]

📌 Commit 43d863b has been approved by michaelwoerister

[bors]

⌛ Testing commit 43d863b with merge 8a3b0e33872bfb091d6bf352d183104d2dff6b8c...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job x86_64-gnu-aux 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.

[01:47:21] 
[01:47:21] testing https://github.com/BurntSushi/xsv
[01:47:21] Initialized empty Git repository in /checkout/obj/build/ct/xsv/.git/
[01:47:21] fatal: Could not parse object '66956b6bfd62d6ac767a6b6499c982eae20a2c9f'.
[01:47:41] fatal: unable to access 'https://github.com/BurntSushi/xsv/': Could not resolve host: github.com
[01:47:41] thread 'main' panicked at 'assertion failed: status.success()', tools/cargotest/main.rs:128:13
[01:47:41] 
[01:47:41] 
[01:47:41] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/cargotest" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "/checkout/obj/build/ct"
[01:47:41] expected success, got: exit code: 101
[01:47:41] expected success, got: exit code: 101
[01:47:41] 
[01:47:41] 
[01:47:41] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/test/pretty src/test/run-pass/pretty src/test/run-fail/pretty src/test/run-pass-valgrind/pretty src/test/run-pass-fulldeps/pretty src/test/run-fail-fulldeps/pretty src/tools/cargo src/tools/cargotest
[01:47:41] Build completed unsuccessfully in 0:44:32
[01:47:41] Makefile:60: recipe for target 'check-aux' failed
[01:47:41] make: *** [check-aux] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:10fdc69c
$ 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)

[rust-highfive]

The job x86_64-gnu-aux 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.

[01:47:21] 
[01:47:21] testing https://github.com/BurntSushi/xsv
[01:47:21] Initialized empty Git repository in /checkout/obj/build/ct/xsv/.git/
[01:47:21] fatal: Could not parse object '66956b6bfd62d6ac767a6b6499c982eae20a2c9f'.
[01:47:41] fatal: unable to access 'https://github.com/BurntSushi/xsv/': Could not resolve host: github.com
[01:47:41] thread 'main' panicked at 'assertion failed: status.success()', tools/cargotest/main.rs:128:13
[01:47:41] 
[01:47:41] 
[01:47:41] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/cargotest" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "/checkout/obj/build/ct"
[01:47:41] expected success, got: exit code: 101
[01:47:41] expected success, got: exit code: 101
[01:47:41] 
[01:47:41] 
[01:47:41] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/test/pretty src/test/run-pass/pretty src/test/run-fail/pretty src/test/run-pass-valgrind/pretty src/test/run-pass-fulldeps/pretty src/test/run-fail-fulldeps/pretty src/tools/cargo src/tools/cargotest
[01:47:41] Build completed unsuccessfully in 0:44:32
[01:47:41] Makefile:60: recipe for target 'check-aux' failed
[01:47:41] make: *** [check-aux] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:10fdc69c
$ 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)

[michaelwoerister]

@bors retry

[bors]

⌛ Testing commit 43d863b with merge 2408095...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: michaelwoerister
Pushing 2408095 to master...

[alexcrichton]

FWIW it looks like this had a fairly negative impact on perf for a few benchmarks

[estebank]

@alexcrichton wow. Should we immediately revert this change? I'm surprised the performance regression is exclusively in nll-opt.

[michaelwoerister]

I'm surprised this has any perf impact at all. original_crate_name is a trivial query, more or less just a hash table lookup. @rust-lang/wg-compiler-nll any ideas why this could affect NLL performance?

[michaelwoerister]

http://perf.rust-lang.org/ shows a single NLL spike for this PR, then performance is immediately better again. Something might just have gone wrong with that performance measurement. I don't think this is something to worry about.

[alexcrichton]

Oh sorry I just wanted to bring this up as an FYI, no need to immediately revert! I just figured it'd be good to track if there's an easy or "obviously available" solution.

@michaelwoerister it does indeed spike but I was suspicious of this comment because the commit afterwards was an explicit optimization for NLL. In that sense I thought this could be a regression followed immediately by an improvement and may still be worth looking into

[alexcrichton]

One interesting test though would be to submit a try build of reverting this PR and if it shows a performance improvement across the benchmarks that may mean there's something to look into! If it shows no change, however (as expected), then it could safely be filed under "spurious bug"