Subject: [PATCH] git am: Transform and skip patches via new hook

From 0428b0a1248fb84c584a5a6c1f110770c6615d5e Mon Sep 17 00:00:00 2001

From: Robert Collins <redacted>
Date: Tue, 7 Jul 2015 15:43:24 +1200
Subject: [PATCH] git am: Transform and skip patches via new hook

A thing I need to do quite a lot of is extracting stuff from
Python to backported libraries. This involves changing nearly
every patch but its automatable.

Using a new hook (applypatch-transform) was sufficient to meet all my
needs and should be acceptable upstream as far as I can tell.

Signed-Off-By: Robert Collins <redacted>
---
 Documentation/git-am.txt                     |  6 ++---
 Documentation/githooks.txt                   | 15 ++++++++++++
 git-am.sh                                    | 15 ++++++++++++
 templates/hooks--applypatch-transform.sample | 36 ++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+), 3 deletions(-)
 create mode 100755 templates/hooks--applypatch-transform.sample

diff --git a/Documentation/git-am.txt b/Documentation/git-am.txt
index dbea6e7..9ddcd87 100644
--- a/Documentation/git-am.txt
+++ b/Documentation/git-am.txt

@@ -215,9 +215,9 @@ errors in the "From:" lines).

 HOOKS
 -----
-This command can run `applypatch-msg`, `pre-applypatch`,
-and `post-applypatch` hooks.  See linkgit:githooks[5] for more
-information.
+This command can run `applypatch-msg`, `applypatch-transform`,
+`pre-applypatch`, and `post-applypatch` hooks.  See
+linkgit:githooks[5] for more information.

 SEE ALSO
 --------

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 7ba0ac9..251b604 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt

@@ -45,6 +45,21 @@ the commit after inspecting the message file.
 The default 'applypatch-msg' hook, when enabled, runs the
 'commit-msg' hook, if the latter is enabled.

+applypatch-transform
+~~~~~~~~~~~~~~~~~~~~
+
+This hook is invoked by 'git am' before attempting to apply
+patches.  It takes two parameters - the path to the patch on
+disk, and the path to the proposed commit message (which may
+be absent).  Like applypatch-msg, both files may be edited.
+
+Exiting with 1 will cause 'git am' to skip the patch. Exiting
+with any other non-zero value will cause 'git am' to abort.
+
+The sample 'applypatch-transform' hook demonstrates mangling
+a patch from one tree shape to another while discarding irrelevant
+patches.
+
 pre-applypatch
 ~~~~~~~~~~~~~~

diff --git a/git-am.sh b/git-am.sh
index 8733071..796efea 100755
--- a/git-am.sh
+++ b/git-am.sh

@@ -869,6 +869,21 @@ To restore the original branch and stop patching

run \"\$cmdline --abort\"."

  case "$resolved" in
  '')
+ # Attempt to rewrite the patch.
+ hook="$(git rev-parse --git-path hooks/applypatch-transform)"
+ if test -x "$hook"
+ then
+ "$hook" "$dotest/patch" "$dotest/final-commit"
+ status="$?"
+ if test $status -eq 1
+ then
+ go_next
+ elif test $status -ne 0
+ then
+ stop_here $this
+ fi
+ fi
+
  # When we are allowed to fall back to 3-way later, don't give
  # false errors during the initial attempt.
  squelch=

diff --git a/templates/hooks--applypatch-transform.sample

b/templates/hooks--applypatch-transform.sample
new file mode 100755
index 0000000..97cd789

--- /dev/null
+++ b/templates/hooks--applypatch-transform.sample

@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# An example hook script to transform a patch taken from an email
+# by git am.
+#
+# The hook should exit with non-zero status after issuing an
+# appropriate message if it wants to stop the commit.  The hook is
+# allowed to edit the patch file.
+#
+# To enable this hook, rename this file to "applypatch-transform".
+#
+# This example changes the path of Lib/unittest/mock.py to mock.py
+# Lib/unittest/tests/testmock to tests and Misc/NEWS to NEWS, and
+# finally skips any patches that did not alter mock.py or its tests.
+
+set -eux
+
+patch_path=$1
+
+# Pull out mock.py
+filterdiff --clean --strip 3 --addprefix=a/ -i

'a/Lib/unittest/mock.py' $patch_path > $patch_path.mock
+# And the tests
+filterdiff --clean --strip 5 --addprefix=a/tests/ -i
'a/Lib/unittest/test/testmock/' $patch_path > $patch_path.tests
+# Lastly we want to pick up any NEWS entries.
+filterdiff --strip 2 --addprefix=a/ -i a/Misc/NEWS $patch_path >
$patch_path.NEWS
+cat $patch_path.mock $patch_path.tests > $patch_path
+filtered=$(cat $patch_path)
+if [ -n "${filtered}" ]; then
+  cat $patch_path.NEWS >> $patch_path
+  exitcode=0
+else
+  exitcode=1
+fi
+
+rm $patch_path.mock $patch_path.tests $patch_path.NEWS
+exit $exitcode
-- 
2.1.0


-- 
Robert Collins [off-list ref]
Distinguished Technologist
HP Converged Cloud

On Tue, Jul 7, 2015 at 3:52 AM, Robert Collins
[off-list ref] wrote:

From 0428b0a1248fb84c584a5a6c1f110770c6615d5e Mon Sep 17 00:00:00 2001
From: Robert Collins <redacted>
Date: Tue, 7 Jul 2015 15:43:24 +1200
Subject: [PATCH] git am: Transform and skip patches via new hook

Drop the "From sha1", "Date:", and "Subject:" headers. "From sha1" is
meaningful only in your repository, thus not useful here, and git-am
will pluck the other information directly from your email, so they are
redundant. The "From:" header, however, should be kept since it
differs from your sending email address.

A thing I need to do quite a lot of is extracting stuff from
Python to backported libraries. This involves changing nearly
every patch but its automatable.

Using a new hook (applypatch-transform) was sufficient to meet all my
needs and should be acceptable upstream as far as I can tell.

For a commit message, you want to explain the problem you're solving,
in what way the the current implementation is lacking, and justify why
your solution is desirable (possibly citing alternate approaches you
discarded). Unfortunately, the above paragraphs don't really tell us
much about why applypatch-tranforms is needed or how it solves a
problem which can't be solved with some other existing mechanism. You
do mention that it satisfies your "needs", but we don't know
specifically what those are.

The above paragraphs might be perfectly suitable as additional
commentary to supplement the commit messages, however, such commentary
should be placed below the "---" line under your sign-off and above
the diffstat.

Signed-Off-By: Robert Collins <redacted>

This is typically written "Signed-off-by:".

More below.

This indentation looks botched, as if the patch was pasted into your
email client and the client mangled the whitespace. git-send-email may
be of use here.

It's not clear even from this example what applypatch-transform buys
you over simply running your patches through some transformation and
filtering script *before* feeding them to git-am. The answer to that
question is the sort of thing which should be in the commit message to
justify the patch.

+set -eux
+
+patch_path=$1
+
+# Pull out mock.py
+filterdiff --clean --strip 3 --addprefix=a/ -i
'a/Lib/unittest/mock.py' $patch_path > $patch_path.mock
+# And the tests
+filterdiff --clean --strip 5 --addprefix=a/tests/ -i
'a/Lib/unittest/test/testmock/' $patch_path > $patch_path.tests
+# Lastly we want to pick up any NEWS entries.
+filterdiff --strip 2 --addprefix=a/ -i a/Misc/NEWS $patch_path >
$patch_path.NEWS
+cat $patch_path.mock $patch_path.tests > $patch_path
+filtered=$(cat $patch_path)
+if [ -n "${filtered}" ]; then
+  cat $patch_path.NEWS >> $patch_path
+  exitcode=0
+else
+  exitcode=1
+fi
+
+rm $patch_path.mock $patch_path.tests $patch_path.NEWS
+exit $exitcode
--
2.1.0