tidy: Add a check for empty UI test files

[yaahc]

Check for empty .stderr and .stdout files in UI test directories.
Empty files could still pass testing for compile-pass tests with no output
so they can get into the repo accidentally, but they are not necessary and can
be removed.

This is very much an in progress pull request. I'm having an issue with rustfmt. It wanted to reformat the entire file for almost every file by default. And when I run tidy it just errors out because it catches the empty files that are already in the repo.

My next step is goin got be to remove those empty file and see if running tidy again will actually reformat things outside of the context of cargo fmt

Fixes #50785

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[yaahc]

#50785

[rust-highfive]

The job x86_64-gnu-llvm-3.9 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.

tidy check
[00:05:20] * 540 error codes
[00:05:20] * highest error code: E0911
[00:05:21] * 200 features
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/reachable/expr_oror.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/reachable/expr_andand.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/feature-gate-const-indexing.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/const-eval/const_transmute.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/const-pattern-not-const-evaluable.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/union/union-const-eval.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/nll/maybe-initialized-drop-uninitialized.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/nll/drop-may-dangle.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/nll/ty-outlives/ty-param-implied-bounds.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/print_type_sizes/anonymous.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/print_type_sizes/anonymous.stdout"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/print_type_sizes/repr-align.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/print_type_sizes/multiple_types.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/print_type_sizes/packed.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/issue-38875/issue_38875.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/rfc1598-generic-associated-types/shadowing.stdout"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/rfc1598-generic-associated-types/generic-associated-types-where.stderr"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/compare-method/region-extra.stdout"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/compare-method/region-unrelated.stdout"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/compare-method/proj-outlives-region.stdout"
[00:05:21] Empty file with UI testing output: "/checkout/src/test/ui/const-expr-addr-operator.stderr"
[00:05:21] some tidy checks failed
[00:05:21] 
[00:05:21] 
[00:05:21] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:05:21] 
[00:05:21] 
[00:05:21] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:05:21] Build completed unsuccessfully in 0:02:08
[00:05:21] Build completed unsuccessfully in 0:02:08
[00:05:21] Makefile:79: recipe for target 'tidy' failed
[00:05:21] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0fe93180
$ 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)

[petrochenkov]

Everything looks good, thanks!
@bors r+

[bors]

📌 Commit e8eda65 has been approved by petrochenkov

[kennytm]

@bors r-

Some new empty UI test files appeared. Please rebase on the latest master and retry. (You need to delete src/test/ui/trivial-bounds-inconsistent-associated-functions.stderr which was introduced by #48557)

[kennytm]

@bors r=petrochenkov

[bors]

📌 Commit 6ed200a has been approved by petrochenkov