ARROW-2563: [Rust] Poor caching in Travis-CI

[sunchao]

No description provided.

[pitrou]

Can you rebase this PR so we can check it works with the codecov upload command?

[sunchao]

Sure. Done.

[pitrou]

Thanks. It's down to 10 minutes, which is better, though it seems a lot of third-party stuff still gets recompiled during the build?

[sunchao]

Yes. I'm not sure whether there's a way to avoid the recompilation. Will be back.

[pitrou]

Yes, so the problem is that the coverage step panics with that change. I don't know why:
https://travis-ci.org/apache/arrow/jobs/377596737#L731

[sunchao]

Back. @pitrou : I think the issue is that cargo coverage --verbose tries to download kcov into the target directory, which doesn't exist (because we mapped CARGO_TARGET_DIR to $TRAVIS_BUILD_DIR/target). Therefore, the command failed.

In the latest commit I changed the download location to $CARGO_TARGET_DIR, which fixes this issue. The last run is here and it took 5min 24sec. Can you take another look?

[codecov-io]

Codecov Report

Merging #2021 into master will increase coverage by 1.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2021      +/-   ##
==========================================
+ Coverage   86.28%   87.42%   +1.14%     
==========================================
  Files          11      189     +178     
  Lines         773    29298   +28525     
==========================================
+ Hits          667    25615   +24948     
- Misses        106     3683    +3577

Impacted Files	Coverage Δ
cpp/src/plasma/events.h	100% <0%> (ø)
cpp/src/arrow/util/thread-pool.h	92.3% <0%> (ø)
cpp/src/plasma/thirdparty/xxhash.cc	34.98% <0%> (ø)
cpp/src/arrow/python/io.h	100% <0%> (ø)
cpp/src/plasma/events.cc	88.09% <0%> (ø)
cpp/src/arrow/util/memory.h	100% <0%> (ø)
cpp/src/arrow/ipc/reader.cc	87.78% <0%> (ø)
cpp/src/arrow/io/io-memory-test.cc	100% <0%> (ø)
cpp/src/arrow/builder.cc	81.72% <0%> (ø)
cpp/src/arrow/python/decimal.cc	98.93% <0%> (ø)
... and 168 more

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[pitrou]

It seems there is a kcov error:
https://travis-ci.org/apache/arrow/jobs/378030262#L1395-L1399

Did it occur before this PR as well?

[sunchao]

Hmm... seems still because of the target dir not found.

[sunchao]

@pitrou : I changed the code to create a directory target instead, and the latest run succeeded.

[pitrou]

@sunchao, looks great ! Thank you.

[sunchao]

Thanks @pitrou . Could you help to merge this?

[pitrou]

Done! Thanks for the PR!

[sunchao]

Thanks for merging @pitrou !