Require a trait in the bounds of existential types

[JohnTitor]

Fixes #53090

r? @oli-obk

[oli-obk]

@bors r+

Thanks!

[bors]

📌 Commit db7f265 has been approved by oli-obk

[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:273f9690:start=1556627412079245594,finish=1556627416078293462,duration=3999047868
$ 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
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---
[01:21:14] failures:
[01:21:14] 
[01:21:14] ---- [run-pass] run-pass/existential_type.rs stdout ----
[01:21:14] 
[01:21:14] error: test compilation failed although it shouldn't!
[01:21:14] status: exit code: 1
[01:21:14] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/run-pass/existential_type.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-pass/existential_type/a" "-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/run-pass/existential_type/auxiliary"
[01:21:14] ------------------------------------------
[01:21:14] 
[01:21:14] ------------------------------------------
[01:21:14] stderr:
[01:21:14] stderr:
[01:21:14] ------------------------------------------
[01:21:14] error: at least one trait must be specified
[01:21:14]   --> /checkout/src/test/run-pass/existential_type.rs:71:46
[01:21:14]    |
[01:21:14] LL | existential type GenericBound<'a, T: Trait>: 'a;
[01:21:14] 
[01:21:14] error: at least one trait must be specified
[01:21:14]   --> /checkout/src/test/run-pass/existential_type.rs:78:42
[01:21:14]    |
[01:21:14]    |
[01:21:14] LL |     pub existential type Passthrough<T>: 'static;
[01:21:14] 
[01:21:14] error: aborting due to 2 previous errors
[01:21:14] 
[01:21:14] 
---
[01:21:14] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:517:22
[01:21:14] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:21:14] 
[01:21:14] 
[01:21:14] 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/run-pass" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-pass" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "run-pass" "--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"
[01:21:14] 
[01:21:14] 
[01:21:14] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:21:14] Build completed unsuccessfully in 0:11:27
[01:21:14] Build completed unsuccessfully in 0:11:27
[01:21:14] Makefile:48: recipe for target 'check' failed
[01:21:14] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:15066535
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Apr 30 13:51:39 UTC 2019
---
travis_time:end:0365b980:start=1556632301362664943,finish=1556632301367669463,duration=5004520
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0ac76e6a
$ 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

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[JohnTitor]

Oops, I didn't check the run-pass tests. Will fix them.

[Centril]

@bors r- meanwhile.

[JohnTitor]

@oli-obk Could we remove these lines, or should fix? (These are no longer run-pass.)

rust/src/test/run-pass/existential_type.rs

Lines 70 to 87 in f843ad6

	trait Trait {}
	existential type GenericBound<'a, T: Trait>: 'a;
	fn generic_bound<'a, T: Trait + 'a>(t: T) -> GenericBound<'a, T> {
	t
	}
	mod pass_through {
	pub existential type Passthrough<T>: 'static;
	fn define_passthrough<T: 'static>(t: T) -> Passthrough<T> {
	t
	}
	}
	fn use_passthrough(x: pass_through::Passthrough<u32>) -> pass_through::Passthrough<u32> {
	x
	}

[oli-obk]

@JohnTitor keep them as run-pass, but change the bounds to Sized + 'a or Sized + 'static respectively, which will amount to the same thing that we had before and should the tests compile.

[JohnTitor]

Thank you @oli-obk! I fixed them.

[JohnTitor]

Travis with green

[oli-obk]

@bors r+

Thanks!

[bors]

📌 Commit 748d978 has been approved by oli-obk