Fix an issue where `arc diff` would loop indefinitely for a property change

Summary:
When we hit a diff which is missing file context, we try to pull it synthetically later. This works for moves and copies, but currently fails for property changes. Since it failed, we didn't have context, so we'd try to pull it again...

The general problem this creates is that when you mark a file "+x" without changing it, we can't show you the content in Differential. Not a huge deal. In some future diff, I'll build the content synthetically.

Adds commits to cover this behavior:

  commit 1830a13adf764b55743f7edc6066451898d8ffa4
  Author: epriestley <git@epriestley.com>
  Date:   Tue Nov 6 17:11:18 2012 -0800

      Mark koan2 +x and edit it.

  commit 8ecc728bcc9b482a9a91527ea471b04fc1a025cf
  Author: epriestley <git@epriestley.com>
  Date:   Tue Nov 6 17:08:44 2012 -0800

      Move 'text' to 'executable' and mark it +x.

  commit 39c8e7dd3914edff087a6214f0cd996ad08e5b3d
  Author: epriestley <git@epriestley.com>
  Date:   Tue Nov 6 16:36:59 2012 -0800

      Mark koan as +x.

Test Plan: Ran unit tests. Previously, they looped indefinitely. Now, they pass.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3909
Unignore changes in .arc/

Summary:
It's inside `.git/` for some time.
It also ignored changes in `test.arc/`.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3900
Declare abstract method in repository API

Test Plan: This diff.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3911
Remove getLink() from ArcanistLinterTestCase

Summary:
Installations extend this.

Another solution would be to extend `ArcanistLinterTestCase` from `ArcanistArcanistLinterTestCase` and return null in `getLink()` to avoid code duplication but I prefer clean class hierarchy.

Test Plan:
  $ arc unit

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3878
Performance improvements for linting in an HG repo.

Summary:
Run `hg status` as a Future while getting the diff. Add a cache for
getRawDiffText().

Test Plan:
Run `arc lint --trace` on a HG repo and confirm that `diff` is only called once
and `status` is run in the background.

Reviewers: epriestley

Reviewed By: epriestley

CC: yliang, dpepper, aran, Korvin

Maniphest Tasks: T2016

Differential Revision: https://secure.phabricator.com/D3913
ArcanistBundle: fix attribution of $old_phid when building binary changes

Summary:
The variable $old_phid was not being set in a certain situation in
buildBinaryChange(), and that was causing the following error, during
`arc patch <revision>`:

"the patch applies to <file> (<hash>), which does not match the
current contents."

and hence it was failing to download/apply the patch.

Signed-off-by: Sergio Correia <sergio@correia.cc>

Test Plan:
I spotted the problem in a revision where I was renaming
some images, which are binary.

Reviewers: epriestley, vrana, btrahan

Reviewed By: btrahan

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3925
make arc patch workflow preserve author commit information

Summary: assumes D3917 (or something like it that populates 'author' value from conduit call) exists in production

Test Plan: stubbed out 'author' value and verified checkins as author worked

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T479

Differential Revision: https://secure.phabricator.com/D3918
Provide repository API method for getting all files

Test Plan:
  print_r(iterator_to_array($api->getAllFiles())); // Under Git.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2038

Differential Revision: https://secure.phabricator.com/D3940
Provide repository API method for getting changed files

Test Plan:
  print_r($api->getChangedFiles('HEAD~36')); // Under Git.

Verified that deleted files are false.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2038

Differential Revision: https://secure.phabricator.com/D3941
Introduce `arc lint --severity warning`

Summary: I plan to exclude advices from our saved results.

Test Plan:
  $ arc lint src/lint/engine/PhutilLintEngine.php
  $ arc lint --severity advice src/lint/engine/PhutilLintEngine.php
  $ arc lint --severity error src/lint/engine/PhutilLintEngine.php

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2038

Differential Revision: https://secure.phabricator.com/D3936
accommodate git's diff.suppress-blank-empty=true setting

Summary:
accommodate git's diff.suppress-blank-empty=true setting
Without this change, if you were to set diff.suppress-blank-empty=true
in your .gitconfig (as I do), then "arc diff" would always fail with the
cryptic diagnostic, "Diff Parse Exception: Found the wrong number of
hunk lines."

Test Plan:
Put this in ~/.gitconfig or .git/config
[diff]
         suppress-blank-empty = true
and run "arc lint".  It should pass.  Without this chnage,
it would fail as described above.

Reviewers: vrana, epriestley

Reviewed By: vrana

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3963
Allow ArcanistDiffParser to parse `diff.suppress-blank-empty` Git diffs

Summary: See D3963. Instead, parse these diffs so they'll work with `--raw`, etc.

Test Plan:
Generated a failing diff, added it as a test case. Fixed issue. Ran test suite. Ran `arc` against it:

  $ git -c diff.suppress-blank-empty=true diff HEAD | arc diff --raw --only --conduit-uri=http://local.aphront.com:8080/
  Reading diff from stdin...
  Created a new Differential diff:
          Diff URI: http://local.aphront.com:8080/differential/diff/103/

  Included changes:
    M       things

Reviewers: vrana, jiiix, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3969
Revert "accommodate git's diff.suppress-blank-empty=true setting (D3963)"

Summary: Reverts D3963, which is obsoleted by D3969.

Test Plan: Straight revert.

Reviewers: vrana, jiiix, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3970
Allow running `arc diff` without `git commit`

Summary:
There's quite some logic in here:

- It automatically decides whether to create a new commit or amend.
- It partially respects 'default-relative-commit'.
- However if it points to a closed revision then it creates a new commit.

Resolves T2025.

Test Plan:
`arc diff` on:

- Clean committed repository.
- Dirty repository without commit since 'default-relative-commit'.
- Dirty repository with non-revision commit since 'default-relative-commit'.
- Dirty repository with revision commit since 'default-relative-commit'.
- `arc diff HEAD^` on dirty repository on top of closed revision.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2025

Differential Revision: https://secure.phabricator.com/D3967
Reintroduce `arc diff --advice`

Summary:
Some users want be stopped even if there are lint advices.

NOTE: Deleted by D3364.

Test Plan:
On diff with lint advice:

  $ arc diff --preview # advice just printed
  $ arc diff --preview --advice # excuse required

Reviewers: epriestley

Reviewed By: epriestley

CC: akramer, aran, Korvin

Differential Revision: https://secure.phabricator.com/D3982
make arcanist backwards compatible with various conduit versions

Summary: pragmatism wins the day, though I think eventually we might want something really fancy to deal with arcanist and conduit not being up to date with respect to one another

Test Plan: php -l

Reviewers: epriestley

Reviewed By: epriestley

CC: zeeg, aran, Korvin

Maniphest Tasks: T2088

Differential Revision: https://secure.phabricator.com/D3988
Don't use empty commit message in commit from `arc diff`

Summary:
There was a bug in Git: https://github.com/git/git/commit/d9a935

Also fix a bug with discovering existing commits.

Test Plan:
  $ arc diff # yes
  # abort
  $ arc diff # didn't see fatal

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2025

Differential Revision: https://secure.phabricator.com/D3983
Change lint_engine to lint.engine

Summary: Also unit_engine.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, aurelijus

Differential Revision: https://secure.phabricator.com/D4001
Don't amend commits with different author

Summary: Also delete extra newlines.

Test Plan:
  $ arc diff # on top of my commit

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2025

Differential Revision: https://secure.phabricator.com/D3996
Allow caching lint results

Summary:
There is one big decision: How to get linters version.
I've created `getCacheVersion()` which is supposed to be bumped every time engine or any linter is changed.
This is not very nice but the other alternative (detect this automatically) seems worse:

- The engine may be outside repo and may or may not be under version control so getting its version through something like `git log` may not be even possible.
- If it is in the same repo then every rebase will obsolete the whole cache.

Even though bumping the version manually is PITA I still think it's a better solution.

Test Plan:
  $ time arc lint --cache 1
  # verified file
  $ arc arc lint --cache 1
  # added some debug output to see the cached results
  # also observed better time (.57 s instead of 2.19 s)

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2036

Differential Revision: https://secure.phabricator.com/D4006