[experiment] How expensive are doc comments?

[petrochenkov]

What happens if they are interpreted as usual comments and not converted to attributes, and not stored in AST/HIR?

(This cannot be checked at lexer level, unfortunately, since some popular crates (rayon) rely on /** text */ being matched by #[$meta] in macros.)

r? @ghost

[petrochenkov]

@bors try

[bors]

⌛ Trying commit 0283814 with merge 87205d7...

[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:05e97ec4:start=1558140177232233691,finish=1558140178032247174,duration=800013483
$ 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
---
travis_time:start:test_codegen
Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:26:10] 
[01:26:10] running 143 tests
[01:26:13] i..iii.....iii..iiii.....i......................i...i................i.....i...........iii..i..i.ii. 100/143
[01:26:15] test result: ok. 113 passed; 0 failed; 30 ignored; 0 measured; 0 filtered out
[01:26:15] 
[01:26:15]  finished in 4.519
[01:26:15] travis_fold:end:test_codegen
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:26:17] 
[01:26:17] running 9 tests
[01:26:17] iiiiiiiii
[01:26:17] 
[01:26:17]  finished in 0.161
[01:26:17] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:26:33] 
[01:26:33] running 122 tests
[01:26:59] .iiiii...i.....i..i...i..i.i.i..i.ii..i.i.....i..i....i..........iiii..........i...ii...i.......ii.i 100/122
[01:27:04] .i.i......iii.i.....ii
[01:27:04] 
[01:27:04]  finished in 31.050
[01:27:04] travis_fold:end:test_debuginfo

---

[01:31:17] travis_fold:start:test_rustdoc
travis_time:start:test_rustdoc
Check compiletest suite=rustdoc mode=rustdoc (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:31:17] thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/libcore/result.rs:997:5
[01:31:17] 
[01:31:17] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:31:17] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:31:17] 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" "--rustdoc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustdoc" "--src-base" "/checkout/src/test/rustdoc" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "rustdoc" "--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"
[01:31:17] 
[01:31:17] 
[01:31:17] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:31:17] Build completed unsuccessfully in 0:17:24
[01:31:17] Build completed unsuccessfully in 0:17:24
[01:31:17] Makefile:48: recipe for target 'check' failed
[01:31:17] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:29236e6b
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sat May 18 02:14:25 UTC 2019

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)

[bors]

☀️ Try build successful - checks-travis
Build commit: 87205d7

[Centril]

@rust-timer build 87205d7

[rust-timer]

Success: Queued 87205d7 with parent 73a3a90, comparison URL.

[rust-timer]

Finished benchmarking try commit 87205d7: comparison url

[Centril]

Turns out they are pretty expensive...

[petrochenkov]

I had some optimization ideas for doc comments (#60935, #60936) and wanted to check how much effect they can have.

[nnethercote]

Note that my experiments indicate that the main part of the cost is decoding the attributes from metadata.