Add post-merge hook, related documentation, and tests.

The post-merge hook enables one to hook in for `git pull` operations in order
to check and/or change attributes of a work tree from the hook.  As an example,
it can be used in combination with a pre-commit hook to save/restore file
ownership and permissions data (or file ACLs) within the repository and
transparently update the working tree after a `git pull` operation.

Signed-off-by: Josh England <jjengla@sandia.gov>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/hooks.txt

@@ -87,6 +87,18 @@ parameter, and is invoked after a commit is made.
 This hook is meant primarily for notification, and cannot affect
 the outcome of `git-commit`.
 
+post-merge
+-----------
+
+This hook is invoked by `git-merge`, which happens when a `git pull`
+is done on a local repository.  The hook takes a single parameter, a status
+flag specifying whether or not the merge being done was a squash merge.
+This hook cannot affect the outcome of `git-merge`.
+
+This hook can be used in conjunction with a corresponding pre-commit hook to
+save and restore any form of metadata associated with the working tree
+(eg: permissions/ownership, ACLS, etc).
+
 [[pre-receive]]
 pre-receive
 -----------

git-merge.sh

@@ -97,6 +97,19 @@ finish () {
 		fi
 		;;
 	esac
+
+	# Run a post-merge hook
+        if test -x "$GIT_DIR"/hooks/post-merge
+        then
+	    case "$squash" in
+	    t)
+                "$GIT_DIR"/hooks/post-merge 1
+		;;
+	    '')
+                "$GIT_DIR"/hooks/post-merge 0
+		;;
+	    esac
+        fi
 }
 
 merge_name () {

t/t5402-post-merge-hook.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+#
+# Copyright (c) 2006 Josh England
+#
+
+test_description='Test the post-merge hook.'
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo Data for commit0. >a &&
+	git update-index --add a &&
+	tree0=$(git write-tree) &&
+	commit0=$(echo setup | git commit-tree $tree0) &&
+	echo Changed data for commit1. >a &&
+	git update-index a &&
+	tree1=$(git write-tree) &&
+	commit1=$(echo modify | git commit-tree $tree1 -p $commit0) &&
+        git update-ref refs/heads/master $commit0 &&
+	git-clone ./. clone1 &&
+	GIT_DIR=clone1/.git git update-index --add a &&
+	git-clone ./. clone2 &&
+	GIT_DIR=clone2/.git git update-index --add a
+'
+
+for clone in 1 2; do
+    cat >clone${clone}/.git/hooks/post-merge <<'EOF'
+#!/bin/sh
+echo $@ >> $GIT_DIR/post-merge.args
+EOF
+    chmod u+x clone${clone}/.git/hooks/post-merge
+done
+
+test_expect_failure 'post-merge does not run for up-to-date ' '
+        GIT_DIR=clone1/.git git merge $commit0 &&
+	test -e clone1/.git/post-merge.args
+'
+
+test_expect_success 'post-merge runs as expected ' '
+        GIT_DIR=clone1/.git git merge $commit1 &&
+	test -e clone1/.git/post-merge.args
+'
+
+test_expect_success 'post-merge from normal merge receives the right argument ' '
+        grep 0 clone1/.git/post-merge.args
+'
+
+test_expect_success 'post-merge from squash merge runs as expected ' '
+        GIT_DIR=clone2/.git git merge --squash $commit1 &&
+	test -e clone2/.git/post-merge.args
+'
+
+test_expect_success 'post-merge from squash merge receives the right argument ' '
+        grep 1 clone2/.git/post-merge.args
+'
+
+test_done