git-p4: add hooks for p4-changelist

Request for help - if there are any experts with python and Windows, I would appreciate a review of the changes that I have presented here.

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Our company's workflow requires that our P4 check-in messages have a specific format. A helpful feature in the GIT-P4 program would be a hook that occurs after the P4 change list is created but before it is displayed in the editor that would allow an external program to possibly edit the changelist text.

v1:My suggestion for the hook name is p4-pre-edit-changelist.

It would take a single parameter, the full path of the temporary file. If the hook returns a non-zero exit code, it would cancel the current P4 submit.

The hook should be optional.

v2:Instead of a single hook, p4-pre-edit-changelist, follow the git convention for hook names and add the trio of hooks that work together, similar to git commit.

The hook names are:

* p4-prepare-changelist
* p4-changelist
* p4-post-changelist

The hooks should follow the same convention as git commit, so a new command line option for the git-p4 submit function --no-verify should also be added.

v3:2-Feb-2020 This version reorganizes the commits to be easier to read. The function for running the git hook has been rewritten to include suggestions. This version no longer restricts the executable supported by windows for the hook. It will first look for a file with the hook name without an extension and if found, it will pass it to sh.exe (Git for Window's MINGW shell) Otherwise it will take the file with the lowest alphabetical extension and ask Windows to execute the program.

v5:10-Feb-2020 Integrated the suggested changes from the mailing list into this release. The changes are:

* Restructure the commits to pull the p4-pre-submit hook changes into the commit for adding git_run_hook.
* Update the git_run_hook to include additional tests for GIT_DIR being set if getting the environment returns no value.
* Updated the windows file resolution to ensure that the script to be run is NOT the .SAMPLE version of the hooks.
* Split the RCS keyword cleanup message into its own commit.

v6:
14-Feb-2020 Update commit for git-p4: restructure code in submit to be python 3 compatible:

Ben Keene (7):
git-p4: rewrite prompt to be Windows compatible
git-p4: create new function run_git_hook
git-p4: add p4-pre-submit exit text
git-p4: add --no-verify option
git-p4: restructure code in submit
git-p4: add p4 submit hooks
git-p4: add RCS keyword status message

 Documentation/git-p4.txt   |  45 ++++++-
 Documentation/githooks.txt |  51 +++++++-
 git-p4.py                  | 236 ++++++++++++++++++++++++++++---------
 3 files changed, 274 insertions(+), 58 deletions(-)

base-commit: d8437c57fa0752716dde2d3747e7c22bf7ce2e41
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-698%2Fseraphire%2Fseraphire%2Fp4-hook-v6
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-698/seraphire/seraphire/p4-hook-v6
Pull-Request: https://github.com/git/git/pull/698

Range-diff vs v5:

 1:  71c51ccfb0c = 1:  013b27760a0 git-p4: rewrite prompt to be Windows compatible
 2:  a2342f71619 = 2:  72c3d642a97 git-p4: create new function run_git_hook
 3:  5f2b47bf6aa = 3:  ae1a4614ee4 git-p4: add p4-pre-submit exit text
 4:  05b8c7ad673 = 4:  cf4de224f8a git-p4: add --no-verify option
 5:  5299f61e4e1 ! 5:  22ac4384bd5 git-p4: restructure code in submit
     @@ -130,7 +130,7 @@
                       if self.isWindows:
                           message = message.replace("\r\n", "\n")
      -                submitTemplate = message[:message.index(separatorLine)]
     -+                if message.find(separatorLine) <> -1:
     ++                if message.find(separatorLine) != -1:
      +                    submitTemplate = message[:message.index(separatorLine)]
      +                else:
      +                    submitTemplate = message
 6:  7a6d9fafcea = 6:  a240b292a17 git-p4: add p4 submit hooks
 7:  c0aca431858 = 7:  bdf07d8f7aa git-p4: add RCS keyword status message

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