Remove useless allocations in macro_rules follow logic.

[L117]

Closes #61543

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @pnkfelix (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 Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed.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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[Centril]

@bors try

[bors]

⌛ Trying commit 7a74f33 with merge 3f61c6a...

[bors]

☀️ Try build successful - checks-travis
Build commit: 3f61c6a

[Centril]

@rust-timer build 3f61c6a

[rust-timer]

Success: Queued 3f61c6a with parent d132f54, comparison URL.

[rust-timer]

Finished benchmarking try commit 3f61c6a, comparison URL.

[Centril]

Seems like noise mostly if possibly a perf improvement. 👍

r? @Centril @bors r+ rollup

[bors]

📌 Commit 7a74f33 has been approved by Centril

[bors]

⌛ Testing commit 7a74f33 with merge d8d291c198b40011265e92b583a636bd8658f438...

[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.

[01:48:35] test string::test_str_truncate ... ok
[01:48:35] test string::test_str_truncate_invalid_len ... ok
[01:48:35] test string::test_split_off_ascii ... ok
[01:48:35] test string::test_str_truncate_split_codepoint ... ok
[01:48:35] died due to signal 11
[01:48:35] error: test failed, to rerun pass '-p alloc --test collectionstests'
[01:48:35] 
[01:48:35] 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 compiler-builtins-c" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--"
[01:48:35] expected success, got: exit code: 3
[01:48:35] 
---
travis_time:end:0682308d:start=1560015819387325076,finish=1560015819397171060,duration=9845984
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:1f315e7e
$ 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:2a53cac7
travis_time:start:2a53cac7
$ 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:23fb25dc
$ 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)

[Centril]

@bors retry android-spurious-collectiontests