Allow lifetime elision in arbitrary_self_types by taiki-e · Pull Request #60944 · rust-lang/rust

taiki-e · 2019-05-18T18:36:54Z

Currently, self except &Self and &mut Self is skipped. By this, other selfs with lifetime is also ignored.
This PR changes it to only skip Self, &Self and &mut Self, and to handle other selfs like normal arguments.

Closes#52675

rust-highfive · 2019-05-18T18:37:05Z

r? @alexcrichton

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

taiki-e · 2019-05-19T12:24:53Z

cc @nikomatsakis @cramertj @matthewjasper

taiki-e · 2019-05-20T09:48:23Z

Seems the current master accepts the following code:

#![allow(dead_code)]#![feature(arbitrary_self_types)]structFoo;implFoo{fnb(self:&Box<Foo>,f:&Foo) -> &Foo{ f }}

I expected:

error[E0106]: missing lifetime specifier
|
LL | fn b(self: &Box<Foo>, f: &Foo) -> &Foo { f }
| ^ expected lifetime parameter
|
= help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `self` or `f`

or

error[E0623]: lifetime mismatch
|
LL | fn b(self: &Box<Foo>, f: &Foo) -> &Foo { f }
| ---- ---- ^ ...but data from `f` is returned here
| |
| this parameter and the return type are declared with different lifetimes...

Playground

This PR rejects (fixes) this. I feel it is right, but I don't know how far it will affect.

taiki-e · 2019-05-20T09:50:24Z

@rustbot modify labels: T-compiler.

taiki-e · 2019-05-20T10:00:50Z

It can reproduce even the stable: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=76eefccd7414faab0a51733c20d6b205

rust-highfive · 2019-05-20T10:57:56Z

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:31e52f32:start=1558345487257250998,finish=1558345572431079970,duration=85173828972
$ 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
---
[01:10:47] .................................................................................................... 4400/5533
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---
[01:11:29] 1 error[E0106]: missing lifetime specifier
[01:11:29] - --> $DIR/arbitrary_self_types_lifetime-2.rs:7:39
[01:11:29] + --> $DIR/arbitrary_self_types_inexact_lifetime.rs:7:39
[01:11:29] 3 |
[01:11:29] - LL | fn b(self: &Box<Foo>, f: &Foo) -> &Foo { f }
[01:11:29] + LL | fn a(self: &Box<Foo>, f: &Foo) -> &Foo { f }
[01:11:29] 6 |
[01:11:29] 6 |
[01:11:29] 7 = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `self` or `f`
[01:11:29] 8 [01:11:29] 9 error[E0106]: missing lifetime specifier
[01:11:29] - --> $DIR/arbitrary_self_types_lifetime-2.rs:9:39
[01:11:29] + --> $DIR/arbitrary_self_types_inexact_lifetime.rs:9:39
[01:11:29] + --> $DIR/arbitrary_self_types_inexact_lifetime.rs:9:39
[01:11:29] 11 |
[01:11:29] - LL | fn c(self: &Box<Foo>, f: &Foo) -> &Box<Foo> { self }
[01:11:29] + LL | fn b(self: &Box<Foo>, f: &Foo) -> &Box<Foo> { self }
[01:11:29] 14 |
[01:11:29] 14 |
[01:11:29] 15 = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `self` or `f`
[01:11:29] 16 [01:11:29] 17 error[E0106]: missing lifetime specifier
[01:11:29] - --> $DIR/arbitrary_self_types_lifetime-2.rs:11:39
[01:11:29] + --> $DIR/arbitrary_self_types_inexact_lifetime.rs:11:39
[01:11:29] + --> $DIR/arbitrary_self_types_inexact_lifetime.rs:11:39
[01:11:29] 19 |
[01:11:29] - LL | fn d(this: &Box<Foo>, f: &Foo) -> &Foo { f }
[01:11:29] + LL | fn c(this: &Box<Foo>, f: &Foo) -> &Foo { f }
[01:11:29] 22 |
[01:11:29] 22 |
[01:11:29] 23 = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `this` or `f`
[01:11:29] [01:11:29] The actual stderr differed from the expected stderr.
[01:11:29] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_inexact_lifetime/arbitrary_self_types_inexact_lifetime.stderr
[01:11:29] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_inexact_lifetime/arbitrary_self_types_inexact_lifetime.stderr
[01:11:29] To update references, rerun the tests and pass the `--bless` flag
[01:11:29] To only update this specific test, also pass `--test-args self/arbitrary_self_types_inexact_lifetime.rs`
[01:11:29] error: 1 errors occurred comparing output.
[01:11:29] status: exit code: 1
[01:11:29] status: exit code: 1
[01:11:29] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/self/arbitrary_self_types_inexact_lifetime.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_inexact_lifetime" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_inexact_lifetime/auxiliary" "-A" "unused"
[01:11:29] ------------------------------------------
[01:11:29] [01:11:29] ------------------------------------------
[01:11:29] stderr:
[01:11:29] stderr:
[01:11:29] ------------------------------------------
[01:11:29] error[E0106]: missing lifetime specifier
[01:11:29] --> /checkout/src/test/ui/self/arbitrary_self_types_inexact_lifetime.rs:7:39
[01:11:29] |
[01:11:29] LL | fn a(self: &Box<Foo>, f: &Foo) -> &Foo { f } //~ ERROR E0106
[01:11:29] |
[01:11:29] |
[01:11:29] = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `self` or `f`
[01:11:29] error[E0106]: missing lifetime specifier
[01:11:29] --> /checkout/src/test/ui/self/arbitrary_self_types_inexact_lifetime.rs:9:39
[01:11:29] |
[01:11:29] |
[01:11:29] LL | fn b(self: &Box<Foo>, f: &Foo) -> &Box<Foo> { self } //~ ERROR E0106
[01:11:29] |
[01:11:29] |
[01:11:29] = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `self` or `f`
[01:11:29] error[E0106]: missing lifetime specifier
[01:11:29] --> /checkout/src/test/ui/self/arbitrary_self_types_inexact_lifetime.rs:11:39
[01:11:29] |
[01:11:29] |
[01:11:29] LL | fn c(this: &Box<Foo>, f: &Foo) -> &Foo { f } //~ ERROR E0106
[01:11:29] |
[01:11:29] |
[01:11:29] = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `this` or `f`
[01:11:29] error: aborting due to 3 previous errors
[01:11:29] [01:11:29] For more information about this error, try `rustc --explain E0106`.
[01:11:29] ---
[01:11:29] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:512:22
[01:11:29] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:11:29] [01:11:29] [01:11:29] 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" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--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" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:11:29] [01:11:29] [01:11:29] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:11:29] Build completed unsuccessfully in 0:04:37
[01:11:29] Build completed unsuccessfully in 0:04:37
[01:11:29] make: *** [check] Error 1
[01:11:29] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:05540370
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Mon May 20 10:57:50 UTC 2019
---
travis_time:end:04f74f1e:start=1558349872089340102,finish=1558349872094391169,duration=5051067
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:06186118
$ 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:246093c4
travis_time:start:246093c4
$ 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:35fb4a88
$ 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)

alexcrichton · 2019-05-20T14:14:13Z

r? @Centril

cramertj · 2019-05-20T16:52:21Z

Seems like we should do a crater run-- this is certainly a breaking change, but it's also definitely something we want to fix. cc @rust-lang/lang

cramertj · 2019-05-20T16:56:21Z

It also seems highly likely that this will affect code using futures, which is stabilized on nightly and soon-to-be-beta (1.36), so this also probably wants a beta backport. I don't know that there are significant other libraries making extensive use of this feature, so it seems like we might be able to fix this without an extra warning period.

cramertj · 2019-05-20T16:57:26Z

@bors try (for crater)

bors · 2019-05-20T16:57:41Z

⌛ Trying commit 8efcf41 with merge 42445de...

… r=<try> Allow lifetime elision in arbitrary_self_types Currently, `self` except `&Self` and `&mut Self` is skipped. By this, other `self`s with lifetime is also ignored. This PR changes it to only skip `Self`, `&Self` and `&mut Self`, and to handle other `self`s like normal arguments. Closes#52675

rust-highfive · 2019-05-20T17:54:22Z

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:043dc8e6:start=1558370374253591278,finish=1558370461491867692,duration=87238276414
$ 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
---
[01:12:23] .................................................................................................... 4400/5533
[01:12:26] .................................................................................................... 4500/5533
[01:12:30] .................................................................................................... 4600/5533
[01:12:34] .................................................................................................... 4700/5533
[01:12:41] ...........................................................................................F........ 4800/5533
[01:12:47] .................................................................................................... 5000/5533
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---
[01:13:06] [01:13:06] ---- [ui] ui/self/arbitrary_self_types_lifetime.rs stdout ----
[01:13:06] diff of stderr:
[01:13:06] [01:13:06] 19 LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug + '_ {
[01:13:06] 21 [01:13:06] - error: aborting due to previous error
[01:13:06] + error[E0034]: multiple applicable items in scope
[01:13:06] + --> $DIR/arbitrary_self_types_lifetime.rs:73:17
[01:13:06] + --> $DIR/arbitrary_self_types_lifetime.rs:73:17
[01:13:06] + |
[01:13:06] + LL | { Bar(&foo).c() };
[01:13:06] + | ^ multiple `c` found
[01:13:06] + |
[01:13:06] + note: candidate #1 is defined in an impl for the type `Foo`
[01:13:06] + --> $DIR/arbitrary_self_types_lifetime.rs:26:5
[01:13:06] + |
[01:13:06] + LL | fn c(self: Bar<'_>) -> Bar<'_> {
[01:13:06] + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[01:13:06] + note: candidate #2 is defined in an impl for the type `Bar<'_>`
[01:13:06] + --> $DIR/arbitrary_self_types_lifetime.rs:51:5
[01:13:06] + |
[01:13:06] + LL | fn c(self: Bar<'a>, f: &Foo) -> (Self, &Foo) { (self, f) }
[01:13:06] 23 [01:13:06] + error: aborting due to 2 previous errors
[01:13:06] + [01:13:06] + For more information about this error, try `rustc --explain E0034`.
[01:13:06] + For more information about this error, try `rustc --explain E0034`.
[01:13:06] 24 [01:13:06] [01:13:06] [01:13:06] The actual stderr differed from the expected stderr.
[01:13:06] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_lifetime/arbitrary_self_types_lifetime.stderr
[01:13:06] To update references, rerun the tests and pass the `--bless` flag
[01:13:06] To only update this specific test, also pass `--test-args self/arbitrary_self_types_lifetime.rs`
[01:13:06] error: 1 errors occurred comparing output.
[01:13:06] status: exit code: 1
[01:13:06] status: exit code: 1
[01:13:06] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_lifetime" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_lifetime/auxiliary" "-A" "unused"
[01:13:06] ------------------------------------------
[01:13:06] [01:13:06] ------------------------------------------
[01:13:06] stderr:
[01:13:06] stderr:
[01:13:06] ------------------------------------------
[01:13:06] error: cannot infer an appropriate lifetime
[01:13:06] --> /checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs:39:9
[01:13:06] |
[01:13:06] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:13:06] | -------------------- this return type evaluates to the `'static` lifetime...
[01:13:06] | ^^^^ ...but this borrow...
[01:13:06] |
[01:13:06] |
[01:13:06] note: ...can't outlive the anonymous lifetime #1 defined on the method body at 38:5
[01:13:06] --> /checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs:38:5
[01:13:06] |
[01:13:06] LL | / fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:13:06] LL | | //~^ ERROR cannot infer an appropriate lifetime
[01:13:06] LL | | }
[01:13:06] | |_____^
[01:13:06] | |_____^
[01:13:06] help: you can add a constraint to the return type to make it last less than `'static` and match the anonymous lifetime #1 defined on the method body at 38:5
[01:13:06] |
[01:13:06] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug + '_ {
[01:13:06] [01:13:06] error[E0034]: multiple applicable items in scope
[01:13:06] --> /checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs:73:17
[01:13:06] |
[01:13:06] |
[01:13:06] LL | { Bar(&foo).c() };
[01:13:06] | ^ multiple `c` found
[01:13:06] |
[01:13:06] note: candidate #1 is defined in an impl for the type `Foo`
[01:13:06] --> /checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs:26:5
[01:13:06] |
[01:13:06] LL | fn c(self: Bar<'_>) -> Bar<'_> {
[01:13:06] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[01:13:06] note: candidate #2 is defined in an impl for the type `Bar<'_>`
[01:13:06] --> /checkout/src/test/ui/self/arbitrary_self_types_lifetime.rs:51:5
[01:13:06] |
[01:13:06] LL | fn c(self: Bar<'a>, f: &Foo) -> (Self, &Foo) { (self, f) }
[01:13:06] [01:13:06] error: aborting due to 2 previous errors
[01:13:06] [01:13:06] For more information about this error, try `rustc --explain E0034`.
---
[01:13:06] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:512:22
[01:13:06] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:13:06] [01:13:06] [01:13:06] 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" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--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" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:13:06] [01:13:06] [01:13:06] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:13:06] Build completed unsuccessfully in 0:04:48
[01:13:06] Build completed unsuccessfully in 0:04:48
[01:13:06] make: *** [check] Error 1
[01:13:06] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:20fb96cf
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Mon May 20 17:54:17 UTC 2019

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 · 2019-05-20T19:20:30Z

☀️ Try build successful - checks-travis
Build commit: 42445de

cramertj · 2019-05-20T19:22:33Z

@craterbot run mode=check-only

craterbot · 2019-05-20T19:22:34Z

👌 Experiment pr-60944 created and queued.
🤖 Automatically detected try build 42445de
🔍 You can check out the queue and this experiment's details.

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

@Centril

Move arbitrary self types's tests into ui/self #60944 (comment) r? @Centril

rust-highfive · 2019-05-21T04:15:21Z

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.

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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
---
[01:13:37] .................................................................................................... 4400/5534
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[01:14:08] .................................................................................................... 5200/5534
[01:14:12] .................................................................................................... 5300/5534
---
[01:14:19] normalized stderr:
[01:14:19] error: cannot infer an appropriate lifetime
[01:14:19] --> $DIR/arbitrary_self_types_impl_trait_lifetime.rs:21:9
[01:14:19] |
[01:14:19] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:14:19] | -------------------- this return type evaluates to the `'static` lifetime...
[01:14:19] | ^^^^ ...but this borrow...
[01:14:19] |
[01:14:19] |
[01:14:19] note: ...can't outlive the anonymous lifetime #1 defined on the method body at 20:5
[01:14:19] --> $DIR/arbitrary_self_types_impl_trait_lifetime.rs:20:5
[01:14:19] |
[01:14:19] LL | / fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:14:19] LL | |
[01:14:19] LL | | }
[01:14:19] | |_____^
[01:14:19] | |_____^
[01:14:19] help: you can add a constraint to the return type to make it last less than `'static` and match the anonymous lifetime #1 defined on the method body at 20:5
[01:14:19] |
[01:14:19] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug + '_ {
[01:14:19] [01:14:19] error: aborting due to previous error
[01:14:19] [01:14:19] [01:14:19] [01:14:19] [01:14:19] [01:14:19] The actual stderr differed from the expected stderr.
[01:14:19] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_impl_trait_lifetime/arbitrary_self_types_impl_trait_lifetime.stderr
[01:14:19] To update references, rerun the tests and pass the `--bless` flag
[01:14:19] To only update this specific test, also pass `--test-args self/arbitrary_self_types_impl_trait_lifetime.rs`
[01:14:19] error: 1 errors occurred comparing output.
[01:14:19] status: exit code: 1
[01:14:19] status: exit code: 1
[01:14:19] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/self/arbitrary_self_types_impl_trait_lifetime.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_impl_trait_lifetime" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/self/arbitrary_self_types_impl_trait_lifetime/auxiliary" "-A" "unused"
[01:14:19] ------------------------------------------
[01:14:19] [01:14:19] ------------------------------------------
[01:14:19] stderr:
[01:14:19] stderr:
[01:14:19] ------------------------------------------
[01:14:19] error: cannot infer an appropriate lifetime
[01:14:19] --> /checkout/src/test/ui/self/arbitrary_self_types_impl_trait_lifetime.rs:21:9
[01:14:19] |
[01:14:19] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:14:19] | -------------------- this return type evaluates to the `'static` lifetime...
[01:14:19] | ^^^^ ...but this borrow...
[01:14:19] |
[01:14:19] |
[01:14:19] note: ...can't outlive the anonymous lifetime #1 defined on the method body at 20:5
[01:14:19] |
[01:14:19] |
[01:14:19] LL | / fn f(self: Bar<'_>) -> impl std::fmt::Debug {
[01:14:19] LL | | //~^ ERROR cannot infer an appropriate lifetime
[01:14:19] LL | | }
[01:14:19] | |_____^
[01:14:19] | |_____^
[01:14:19] help: you can add a constraint to the return type to make it last less than `'static` and match the anonymous lifetime #1 defined on the method body at 20:5
[01:14:19] |
[01:14:19] LL | fn f(self: Bar<'_>) -> impl std::fmt::Debug + '_ {
[01:14:19] [01:14:19] error: aborting due to previous error
[01:14:19] [01:14:19] ---
[01:14:19] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:512:22
[01:14:19] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:14:19] [01:14:19] [01:14:19] 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" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--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" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:14:19] [01:14:19] [01:14:19] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:14:19] Build completed unsuccessfully in 0:04:37
[01:14:19] Build completed unsuccessfully in 0:04:37
[01:14:19] Makefile:48: recipe for target 'check' failed
[01:14:19] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0c9b81a0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue May 21 04:15:11 UTC 2019
---
travis_time:end:0a52291a:start=1558412113350049912,finish=1558412113357189671,duration=7139759
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:09191202
$ 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:13d40990
$ 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)

eddyb · 2019-05-22T09:00:54Z


+ // Only skip `Self`, `&Self` and `&mut Self`,
+ // and to handle other `self`s like normal arguments.
+ let mut should_skip = false;


Maybe rename this to skip_self_arg?

eddyb · 2019-05-22T09:15:38Z

This was intentional, in that we didn't want self: &'b Foo<'a, T> (inside impl<'a, T> Foo<'a, T> {...}) to be ambiguous, but rather use 'b - this is due to how particular the original implementation was, and we didn't want breakage.

If you start relying on the is_self_ty helper closure in order to ignore self arguments, you don't even need arbitrary_self_types to observe breakage.
Behavior will change for things like self: TypeAliasToSelf.

Ideally elision would've been syntactic from the start (since it's meant to be syntactically intuitive), but we dropped the ball on that. If we do a crater run, I suggest also experimenting with this part commented out:

rust/src/librustc/middle/resolve_lifetime.rs

Lines 2136 to 2152 in 1cc822c

// Can't always rely on literal (or implied) `Self` due
// to the way elision rules were originally specified.
let impl_self = impl_self.map(|ty| &ty.node);
ifletSome(&hir::TyKind::Path(hir::QPath::Resolved(None,ref path))) = impl_self {
match path.res{
// Whitelist the types that unambiguously always
// result in the same type constructor being used
// (it can't differ between `Self` and `self`).
Res::Def(DefKind::Struct, _)
 | Res::Def(DefKind::Union, _)
 | Res::Def(DefKind::Enum, _)
 | Res::PrimTy(_) => {
return res == path.res
}
 _ => {}
}
}

@cramertj Could we special-case Pin<&mut Self>? Or more generally, use self: &mut Self elision rules even if nested in a Pin?
The fully general case could be a nightmare to untangle, likely for any particular behavior set we may pick.

craterbot · 2019-05-22T14:38:34Z

🎉 Experiment pr-60944 is completed!
📊 1 regressed and 0 fixed (60951 total)
📰 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

Centril · 2019-05-22T14:54:56Z

Looks like we have an ICE in the only "regression".

cramertj · 2019-05-22T19:57:14Z

@eddyb I'm sorry, I'm not sure I understand-- could you write an example or two of the kind of thing that you wanted to support, but which wouldn't be allowed under this PR?

withoutboats · 2019-05-22T22:04:25Z

@eddyb from your comment it seems the concern has to do with self types containing multiple lifetimes. I notice in particular you highlight cases where users have opted for using the actual self type instead of the Self alias in their receivers, something I didn't even realize was possible.

My naive expectation around this behavior:

Lifetimes from within the type that Self aliases to are ignored
Let's not even bother with rules for multiple lifetimes outside the self alias, which on stable should not be possible with the set of valid receivers we have stabilized.

eddyb · 2019-05-23T19:06:49Z

using the actual self type instead of the Self alias in their receivers, something I didn't even realize was possible.

@withoutboats It probably should've been disallowed, yeah. I'd be curious to see the results of a crater run where that is just banned (I suspect we couldn't "just do that", but it would perhaps be useful to know.)

@cramertj Our testsuite might be lacking these examples, but this works on stable:

structFoo<'a>(&'a());impl<'a>Foo<'a>{fnfoo<'b>(self:&'bFoo<'a>) -> &(){self.0}}typeAlias = Foo<'static>;implAlias{fnbar<'a>(self:&Alias,arg:&'a()) -> &(){ arg }}

And AFAICT, this PR changes the behavior in at least the latter case, as it relies on the (rather brittle) is_self_ty predicate to special-case self: S and self: &(mut) S (i.e. when is_self_ty(S)).

It otherwise uses regular rules, even for the self argument, which is inconsistent with the current elision rules (however depressing they may be), and has the "unknown unknowns" scary implication to me.

So what I think we should do is change the special-case of self: &(mut) S to instead visit the type of self and look for &(mut) S (where is_self_ty(S)) within it, which would make Pin<&mut S> work.
And we would still be ignoring the self argument otherwise.

scottmcm · 2019-05-23T20:28:07Z

I see that the reference says

In method signatures there is another rule
If the receiver has type &Self or &mut Self, then the lifetime of that reference to Self is assigned to all elided output lifetime parameters.

Is that an accurate statement of the current rule? Does the self rule override the other rule always (even if it's self-by-value)?

eddyb · 2019-05-24T13:57:13Z

@scottmcm Note that the rule applies to self: &Self and self: &Foo, when you're inside impl Foo {...} and it's not a type alias (so it's semi-syntactical I guess?).
If self is not a reference to Self, then the self argument is ignored, no matter what type it may have, and the general rule is applied to the rest of the arguments.

taiki-e · 2019-05-26T06:00:42Z

Closing this PR in favor of #61207.

@eddyb

…2, r=<try> Allow lifetime elision in `Pin<&(mut) Self>` This replaces #60944. ~~This PR changes elision rules to apply `self: &(mut) Self` elision rules even if nested in `Pin`.~~ This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it Closes#52675 r? @eddyb cc @cramertj @Centril @withoutboats @scottmcm

@eddyb

…me-elision-2, r=Centril Allow lifetime elision in `Pin<&(mut) Self>` This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it Replaces rust-lang#60944Closesrust-lang#52675 r? @eddyb cc @cramertj @Centril @withoutboats @scottmcm

@eddyb

…me-elision-2, r=Centril Allow lifetime elision in `Pin<&(mut) Self>` This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it Replaces rust-lang#60944Closesrust-lang#52675 r? @eddyb cc @cramertj @Centril @withoutboats @scottmcm

@eddyb

…me-elision-2, r=Centril Allow lifetime elision in `Pin<&(mut) Self>` This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it Replaces rust-lang#60944Closesrust-lang#52675 r? @eddyb cc @cramertj @Centril @withoutboats @scottmcm

@eddyb

…me-elision-2, r=Centril Allow lifetime elision in `Pin<&(mut) Self>` This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it Replaces rust-lang#60944Closesrust-lang#52675 r? @eddyb cc @cramertj @Centril @withoutboats @scottmcm

@cramertj

…amertj Stabilize `async_await` in Rust 1.39.0 Here we stabilize: - free and inherent `async fn`s, - the `<expr>.await` expression form, - and the `async move? { ... }` block form. Closesrust-lang#62149. Closesrust-lang#50547. All the blockers are now closed. <details> - [x] FCP in rust-lang#62149 - [x] rust-lang#61949; PR in rust-lang#62849. - [x] rust-lang#62517; PR in rust-lang#63376. - [x] rust-lang#63225; PR in rust-lang#63501 - [x] rust-lang#63388; PR in rust-lang#63499 - [x] rust-lang#63500; PR in rust-lang#63501 - [x] rust-lang#62121 (comment) - [x] Some tests for control flow (PR rust-lang#63387): - `?` - `return` in `async` blocks - `break` - [x] rust-lang#61775 (comment), i.e. tests for rust-lang#60944 with `async fn`s instead). PR in rust-lang#63383 </details> r? @cramertj

rust-highfive assigned alexcrichton May 18, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 18, 2019

taiki-e mentioned this pull request May 18, 2019
Add TryFutureExt::try_flatten_stream rust-lang/futures-rs#1618
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Comment threadsrc/test/ui/arbitrary_self_types_lifetime.rs Outdated

taiki-e force-pushed the arbitrary_self_types-lifetime-elision branch from f85180e to 6eb1f35Compare May 19, 2019 02:37

taiki-e mentioned this pull request May 19, 2019
Move arbitrary self types's tests into ui/self #60950
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rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label May 20, 2019

taiki-e force-pushed the arbitrary_self_types-lifetime-elision branch from 3ae4dc9 to 19c7915Compare May 20, 2019 11:03

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Comment threadsrc/librustc/middle/resolve_lifetime.rs Outdated

taiki-e force-pushed the arbitrary_self_types-lifetime-elision branch 2 times, most recently from c04f346 to 8efcf41Compare May 20, 2019 16:38

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bors added a commit that referenced this pull request May 21, 2019
Auto merge of#60950- taiki-e:arbitrary_self_types-tests, r=Centril
46ad3e1
Move arbitrary self types's tests into ui/self #60944 (comment) r? @Centril

Allow lifetime elision in arbitrary_self_types
76ab65a

taiki-e force-pushed the arbitrary_self_types-lifetime-elision branch from c0e3422 to 76ab65aCompare May 21, 2019 11:27

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taiki-e mentioned this pull request May 26, 2019
Allow lifetime elision in Pin<&(mut) Self>#61207
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taiki-e closed this May 26, 2019

taiki-e deleted the arbitrary_self_types-lifetime-elision branch May 27, 2019 14:17

Centril mentioned this pull request Jun 28, 2019
generalize impl trait to permit multiple lifetime bounds #61775
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Centril mentioned this pull request Aug 2, 2019
Stabilize async_await in Rust 1.39.0 #63209
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traviscross mentioned this pull request May 3, 2025
Oddity with lifetime elision and type aliases #140611
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