minor compiler doc tweaks

[euclio]

No description provided.

[rust-highfive]

r? @cramertj

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[cramertj]

@bors r+ rollup

[bors]

📌 Commit b1c5f8c50043ec8f3193b000468d7c2d43116e15 has been approved by cramertj

[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:05a5cd00:start=1556820342676309860,finish=1556820343451738729,duration=775428869
$ 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
---

[00:03:59] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:59] tidy error: /checkout/src/librustc/lint/context.rs:761: unexplained "```ignore" doctest; try one:
[00:03:59] 
[00:03:59] * make the test actually pass, by adding necessary imports and declarations, or
[00:03:59] * use "```text", if the code is not Rust code, or
[00:03:59] * use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
[00:03:59] * use "```should_panic", if the code is expected to fail at run time, or
[00:03:59] * use "```no_run", if the code should type-check but not necessary linkable/runnable, or
[00:03:59] * explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.
[00:03:59] 
[00:03:59] 
[00:03:59] tidy error: /checkout/src/librustc/lint/context.rs:776: unexplained "```ignore" doctest; try one:
[00:03:59] 
[00:03:59] * make the test actually pass, by adding necessary imports and declarations, or
[00:03:59] * use "```text", if the code is not Rust code, or
[00:03:59] * use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
[00:03:59] * use "```should_panic", if the code is expected to fail at run time, or
[00:03:59] * use "```no_run", if the code should type-check but not necessary linkable/runnable, or
[00:03:59] * explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.
[00:03:59] 
[00:04:01] some tidy checks failed
[00:04:01] 
[00:04:01] 
[00:04:01] 
[00:04:01] 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"
[00:04:01] 
[00:04:01] 
[00:04:01] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:04:01] Build completed unsuccessfully in 0:00:45
[00:04:01] Build completed unsuccessfully in 0:00:45
[00:04:01] make: *** [tidy] Error 1
[00:04:01] Makefile:67: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:19596810
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Thu May  2 18:09:56 UTC 2019
---
travis_time:end:053a75ae:start=1556820596959989074,finish=1556820596964408369,duration=4419295
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:042a493a
$ 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:084e3760
travis_time:start:084e3760
$ 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:111210dc
$ dmesg | grep -i kill

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[euclio]

@cramertj Fixed tidy.

[cramertj]

@bors r+ rollup

[bors]

📌 Commit bbe7b85 has been approved by cramertj