rustdoc: don't try to get a DefId for a Def that doesn't have one

[QuietMisdreavus]

Fixes #58054

The compiler allows you to write a use statement for a built-in non-macro attribute, since use proc_macro can apply to both the proc_macro crate and the #[proc_macro] attribute. However, if you write a use statement for something that doesn't have this crossover, rustdoc will try to use it the same way as anything else... which resulted in an ICE because it tried to pull a DefId for something that didn't have one. This PR makes rustdoc skip those lookups when it encounters them, allowing it to properly process and render these imports.

[rust-highfive]

r? @steveklabnik

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[QuietMisdreavus]

r? @rust-lang/rustdoc

[GuillaumeGomez]

Thanks!

@bors: r+

[bors]

📌 Commit c955f17 has been approved by GuillaumeGomez

[bors]

⌛ Testing commit c955f17 with merge 900b2b3c375f465044d6538116cfc356dbda1c82...

[bors]

💔 Test failed - checks-travis

[rust-highfive]

The job arm-android 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.

[01:44:30] test string::test_retain ... ok
[01:44:30] test string::test_str_truncate ... ok
[01:44:30] test string::test_str_truncate_split_codepoint ... ok
[01:44:30] test string::test_str_truncate_invalid_len ... ok
[01:44:30] died due to signal 11
[01:44:30] 
[01:44:30] 
[01:44:30] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "arm-linux-androideabi" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--"
[01:44:30] expected success, got: exit code: 3
---
travis_time:end:0931a000:start=1549080281385953111,finish=1549080281395447920,duration=9494809
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:057f3942
$ 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:11a5934c
travis_time:start:11a5934c
$ 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:1d52d65d
$ 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)

[kennytm]

@bors retry #55861

[bors]

⌛ Testing commit c955f17 with merge 0e5a209...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: GuillaumeGomez
Pushing 0e5a209 to master...