read-cache: add post-index-change hook

Add a post-index-change hook that is invoked after the index is written in
do_write_locked_index().

This hook is meant primarily for notification, and cannot affect
the outcome of git commands that trigger the index write.

The hook is passed a flag to indicate whether the working directory was
updated or not and a flag indicating if a skip-worktree bit could have
changed.  These flags enable the hook to optimize its response to the
index change notification.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 182 insertions, 3 deletions

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 959044347e..bfb0be3659 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -492,6 +492,24 @@ This hook is invoked by `git-p4 submit`. It takes no parameters and nothing
 from standard input. Exiting with non-zero status from this script prevent
 `git-p4 submit` from launching. Run `git-p4 submit --help` for details.
 
+post-index-change
+~~~~~~~~~~~~~~~~~
+
+This hook is invoked when the index is written in read-cache.c
+do_write_locked_index.
+
+The first parameter passed to the hook is the indicator for the
+working directory being updated.  "1" meaning working directory
+was updated or "0" when the working directory was not updated.
+
+The second parameter passed to the hook is the indicator for whether
+or not the index was updated and the skip-worktree bit could have
+changed.  "1" meaning skip-worktree bits could have been updated
+and "0" meaning they were not.
+
+Only one parameter should be set to "1" when the hook runs.  The hook
+running passing "1", "1" should not be possible.
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/builtin/reset.c b/builtin/reset.c
index 4d18a461fa..e173afcaac 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -380,6 +380,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			int flags = quiet ? REFRESH_QUIET : REFRESH_IN_PORCELAIN;
 			if (read_from_tree(&pathspec, &oid, intent_to_add))
 				return 1;
+			the_index.updated_skipworktree = 1;
 			if (!quiet && get_git_work_tree()) {
 				uint64_t t_begin, t_delta_in_ms;
 
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 02ace602b9..cf731640fa 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -1071,6 +1071,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	if (entries < 0)
 		die("cache corrupted");
 
+	the_index.updated_skipworktree = 1;
+
 	/*
 	 * Custom copy of parse_options() because we want to handle
 	 * filename arguments as they come.
diff --git a/cache.h b/cache.h
index 27fe635f62..46eb862d3e 100644
--- a/cache.h
+++ b/cache.h
@@ -338,7 +338,9 @@ struct index_state {
 	struct cache_time timestamp;
 	unsigned name_hash_initialized : 1,
 		 initialized : 1,
-		 drop_cache_tree : 1;
+		 drop_cache_tree : 1,
+		 updated_workdir : 1,
+		 updated_skipworktree : 1;
 	struct hashmap name_hash;
 	struct hashmap dir_hash;
 	struct object_id oid;
diff --git a/read-cache.c b/read-cache.c
index 0e0c93edc9..862bdf383d 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -17,6 +17,7 @@
 #include "commit.h"
 #include "blob.h"
 #include "resolve-undo.h"
+#include "run-command.h"
 #include "strbuf.h"
 #include "varint.h"
 #include "split-index.h"
@@ -2999,8 +3000,17 @@ static int do_write_locked_index(struct index_state *istate, struct lock_file *l
 	if (ret)
 		return ret;
 	if (flags & COMMIT_LOCK)
-		return commit_locked_index(lock);
-	return close_lock_file_gently(lock);
+		ret = commit_locked_index(lock);
+	else
+		ret = close_lock_file_gently(lock);
+
+	run_hook_le(NULL, "post-index-change",
+			istate->updated_workdir ? "1" : "0",
+			istate->updated_skipworktree ? "1" : "0", NULL);
+	istate->updated_workdir = 0;
+	istate->updated_skipworktree = 0;
+
+	return ret;
 }
 
 static int write_split_index(struct index_state *istate,
diff --git a/t/t7113-post-index-change-hook.sh b/t/t7113-post-index-change-hook.sh
new file mode 100755
index 0000000000..f011ad7eec
--- /dev/null
+++ b/t/t7113-post-index-change-hook.sh
@@ -0,0 +1,144 @@
+#!/bin/sh
+
+test_description='post index change hook'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir -p dir1 &&
+	touch dir1/file1.txt &&
+	echo testing >dir1/file2.txt &&
+	git add . &&
+	git commit -m "initial"
+'
+
+test_expect_success 'test status, add, commit, others trigger hook without flags set' '
+	mkdir -p .git/hooks &&
+	write_script .git/hooks/post-index-change <<-\EOF &&
+		if test "$1" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir is set." >testfailure
+			exit 1
+		fi
+		if test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_skipworktree is set." >testfailure
+			exit 1
+		fi
+		if test -f ".git/index.lock"; then
+			echo ".git/index.lock exists" >testfailure
+			exit 3
+		fi
+		if ! test -f ".git/index"; then
+			echo ".git/index does not exist" >testfailure
+			exit 3
+		fi
+		echo "success" >testsuccess
+	EOF
+	mkdir -p dir2 &&
+	touch dir2/file1.txt &&
+	touch dir2/file2.txt &&
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git status &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git add . &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git commit -m "second" &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -- dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure &&
+	git reset --soft &&
+	test_path_is_missing testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test checkout and reset trigger the hook' '
+	write_script .git/hooks/post-index-change <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$1" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_workdir set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_workdir set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "update_workdir should be set for checkout" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout master &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git checkout HEAD &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --hard &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git checkout -B test &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_expect_success 'test reset --mixed and update-index triggers the hook' '
+	write_script .git/hooks/post-index-change <<-\EOF &&
+		if test "$1" -eq 1 && test "$2" -eq 1; then
+			echo "Invalid combination of flags passed to hook; updated_workdir and updated_skipworktree are both set." >testfailure
+			exit 1
+		fi
+		if test "$1" -eq 0 && test "$2" -eq 0; then
+			echo "Invalid combination of flags passed to hook; neither updated_workdir or updated_skipworktree are set." >testfailure
+			exit 2
+		fi
+		if test "$2" -eq 1; then
+			if test -f ".git/index.lock"; then
+				echo "updated_skipworktree set but .git/index.lock exists" >testfailure
+				exit 3
+			fi
+			if ! test -f ".git/index"; then
+				echo "updated_skipworktree set but .git/index does not exist" >testfailure
+				exit 3
+			fi
+		else
+			echo "updated_skipworktree should be set for reset --mixed and update-index" >testfailure
+			exit 4
+		fi
+		echo "success" >testsuccess
+	EOF
+	: force index to be dirty &&
+	test-tool chmtime +60 dir1/file1.txt &&
+	git reset --mixed --quiet HEAD~1 &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git hash-object -w --stdin <dir1/file2.txt >expect &&
+	git update-index --cacheinfo 100644 "$(cat expect)" dir1/file1.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure &&
+	git update-index --skip-worktree dir1/file2.txt &&
+	git update-index --remove dir1/file2.txt &&
+	test_path_is_file testsuccess && rm -f testsuccess &&
+	test_path_is_missing testfailure
+'
+
+test_done
diff --git a/unpack-trees.c b/unpack-trees.c
index 3563daae1a..8665a4a7c0 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1637,6 +1637,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
+
+		o->result.updated_workdir = 1;
 		discard_index(o->dst_index);
 		*o->dst_index = o->result;
 	} else {