Only run CI checks when appropriate files have changed

[brettcannon]

E.g. don't run code coverage or the test suite if only the docs changed (or vice-versa).

[berkerpeksag]

This is now done. @brettcannon could you please close this?

Side note: Should we allow "Core developers" team to close issues on this repo?

[brettcannon]

Closed and now the core team has write permissions (just simply forgot to add the team).

[brettcannon]

And thanks for the change! I'm sure not only PR submitters appreciate the faster turn-around but I bet Travis appreciates us using less free resources. 😄

[ammaraskar]

I don't think the Doc only test works. See this PR here: python/cpython#3072
The travis run: https://travis-ci.org/python/cpython/builds/263366915 (and it's console log)

It triggered a full code rebuild and test even though the only thing that has changed is Doc/library/socket.rst

[brettcannon]

It was working but it seems something has changed such that it didn't succeed in this case.

[ammaraskar]

I've done some investigating and this is due to how Travis gets the merged code from Github.

Following the sequence of commands it used to get the repo here, it went:

1. git clone --depth=50 https://github.com/ammaraskar/cpython.git
2. git fetch origin +refs/pull/5/merge
3. git checkout -qf FETCH_HEAD

I replicated these commands locally and ran git log and the problem became obvious. Github in their special refs/pull/*/merge branch creates a merge commit which means at that point this git log looks something like:

commit 472056eb60b0601dcded798229bebbddfd307945 (HEAD)
Merge: b072c6d0c6 86cece89d5
Date:   Fri Aug 18 05:43:43 2017 +0000

    Merge 86cece89d5c6452a92004af0276147187034d41f into b072c6d0c69849690ff03c0ce4f1911139b02ce6

commit b9ff498793611d1c6a9b99df464812931a1e2d69 (master)
Author: Elmar Ritsch <35851+elritsch@users.noreply.github.com>
Date:   Fri Aug 18 05:23:51 2017 +0200

    Fix broken `Show Source` links on documentation pages (GH-3113)

    The `Show Source` was broken because of a change made in sphinx 1.5.1
    In Sphinx 1.4.9, the sourcename was "index.txt".
    In Sphinx 1.5.1+, it is now "index.rst.txt"

...
EVERY SINGLE COMMIT TO
MASTER ON A TIME AFTER
MY PR COMMIT DATE
...

commit 86cece89d5c6452a92004af0276147187034d41f
Author: Ammar Askar <ammar@ammaraskar.com>
Date:   Sat Aug 12 15:15:07 2017 -0400

    Fix Linux availability version for SO_PEERSEC

And so the git diff picks up on all the commits in the middle because the PR commit ends up in a really old slot in history.

[brettcannon]

OK, so it's basically it's imperfect but isn't hurting anything. Thanks for the detailed report, @ammaraskar ! I'm going to close this again and we can just live with occasionally building more than necessary.

[ammaraskar]

There's a way around it, I opened up a PR to fix it: python/cpython#3129

Whether it's worth the added complexity to the build process, that I don't know.