Re: git pre-commit hook for merges (WAS: master has switched from Automake to GNU Make)

[Noam Postavsky <npostavs@users.sourceforge.net>]

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On Wed, Apr 12, 2017 at 2:26 PM, Paul Eggert <eggert@cs.ucla.edu> wrote:
>>
>> Perhaps we should change the hook so that it doesn't complain about
>> problems from merges?
>
> Something like that might make sense, yes, for people in Alan's situation.
> When I do a merge, though, I'd rather see problems from the other side (so
> that I can fix them). How about an environment variable that captures the
> user's preference?

Since git only runs the hooks on the merged changes when you pass
--no-commit to 'git merge', defaulting to non-blind merge doesn't
really work anyway. There I propose the opposite default, as in the
attached (also you had a copy-pasto "; done" in your patch).

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From 824e1bac7de365708e92e22b5aa2624e6bf7bd9e Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@Penguin.CS.UCLA.EDU>
Date: Wed, 12 Apr 2017 11:24:41 -0700
Subject: [PATCH v2] Allow bypassing of some checks when merging

* build-aux/git-hooks/pre-commit: Don't check merged in changes unless
GIT_MERGE_CAREFULLY is true.
* admin/notes/repo: Explain how to use GIT_MERGE_CAREFULLY.
---
 admin/notes/repo               |  7 +++++++
 build-aux/git-hooks/pre-commit | 22 +++++++++++++++++++---
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/admin/notes/repo b/admin/notes/repo
index 3ab3da7807..2416563f83 100644
--- a/admin/notes/repo
+++ b/admin/notes/repo
@@ -76,6 +76,13 @@ conflict by choosing either the master or branch version, then run
 'make -C lisp autoloads' to update the md5sums to the correct master
 value before committing.
 
+* Running git commit hooks on merged changes
+
+Normally git does not run the pre-commit hook on merged changes.  In
+order to run the hooks on the branch being merged in, set the
+environment variable GIT_MERGE_CAREFULLY to 'true', and the
+'--no-commit' option to the 'git merge' call.
+
 * Re-adding a file that has been removed from the repository
 
 Let's suppose you've done:
diff --git a/build-aux/git-hooks/pre-commit b/build-aux/git-hooks/pre-commit
index 6483bfc6b3..59bff79df1 100755
--- a/build-aux/git-hooks/pre-commit
+++ b/build-aux/git-hooks/pre-commit
@@ -25,16 +25,32 @@ LC_ALL=
 
 . git-sh-setup
 
+# Unless GIT_MERGE_CAREFULLY is 'true', then when doing a two-way merge,
+# ignore problems that came from the other side of the merge.
+head=HEAD
+if test -e "$GIT_DIR"/MERGE_HEAD && test "$GIT_MERGE_CAREFULLY" != true; then
+  merge_heads=`cat "$GIT_DIR"/MERGE_HEAD` || exit
+  for merge_head in $merge_heads; do
+    case $head in
+      HEAD) head=$merge_head;;
+      # For multi-head merges, there's no easy way to ignore merged in
+      # changes.  But if you're doing multi-head merges, presumably
+      # you know how to handle any ensuing problems.
+      *) head=HEAD; break;;
+    esac
+  done
+fi
+
 git_diff='git diff --cached --name-only --diff-filter=A'
 ok_chars='\0+[=-=]./0-9A-Z_a-z'
-nbadchars=`$git_diff -z HEAD | tr -d "$ok_chars" | wc -c`
+nbadchars=`$git_diff -z $head | tr -d "$ok_chars" | wc -c`
 
 if test "$nbadchars" -ne 0; then
   echo "File name does not consist of -+./_ or ASCII letters or digits."
   exit 1
 fi
 
-for new_name in `$git_diff HEAD`; do
+for new_name in `$git_diff $head`; do
   case $new_name in
     -* | */-*)
       echo "$new_name: File name component begins with '-'."
@@ -53,4 +69,4 @@ nbadchars=
 # tests so that trailing spaces are generated on the fly rather than
 # being committed as source.
 
-exec git diff-index --check --cached HEAD --
+exec git diff-index --check --cached $head --
-- 
2.11.1