git-p4: add the p4-pre-submit hook

The `p4-pre-submit` hook is executed before git-p4 submits code.
If the hook exits with non-zero value, submit process not start.

Signed-off-by: Chen Bin <chenbin.sh@gmail.com>
Reviewed-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-p4.txt

@@ -374,6 +374,14 @@ These options can be used to modify 'git p4 submit' behavior.
     been submitted. Implies --disable-rebase. Can also be set with
     git-p4.disableP4Sync. Sync with origin/master still goes ahead if possible.
 
+Hook for submit
+~~~~~~~~~~~~~~~
+The `p4-pre-submit` hook is executed if it exists and is executable.
+The hook takes no parameters and nothing from standard input. Exiting with
+non-zero status from this script prevents `git-p4 submit` from launching.
+
+One usage scenario is to run unit tests in the hook.
+
 Rebase options
 ~~~~~~~~~~~~~~
 These options can be used to modify 'git p4 rebase' behavior.

Documentation/githooks.txt

@@ -485,6 +485,13 @@ The exit status determines whether git will use the data from the
 hook to limit its search.  On error, it will fall back to verifying
 all files and folders.
 
+p4-pre-submit
+~~~~~~~~~~~~~
+
+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.
+
 GIT
 ---
 Part of the linkgit:git[1] suite

git-p4.py

@@ -1494,7 +1494,13 @@ class P4Submit(Command, P4UserMap):
                 optparse.make_option("--disable-p4sync", dest="disable_p4sync", action="store_true",
                                      help="Skip Perforce sync of p4/master after submit or shelve"),
         ]
-        self.description = "Submit changes from git to the perforce depot."
+        self.description = """Submit changes from git to the perforce depot.\n
+    The `p4-pre-submit` hook is executed if it exists and is executable.
+    The hook takes no parameters and nothing from standard input. Exiting with
+    non-zero status from this script prevents `git-p4 submit` from launching.
+
+    One usage scenario is to run unit tests in the hook."""
+
         self.usage += " [name of git branch to submit into perforce depot]"
         self.origin = ""
         self.detectRenames = False
@@ -2303,6 +2309,14 @@ class P4Submit(Command, P4UserMap):
             sys.exit("number of commits (%d) must match number of shelved changelist (%d)" %
                      (len(commits), num_shelves))
 
+        hooks_path = gitConfig("core.hooksPath")
+        if len(hooks_path) <= 0:
+            hooks_path = os.path.join(os.environ.get("GIT_DIR", ".git"), "hooks")
+
+        hook_file = os.path.join(hooks_path, "p4-pre-submit")
+        if os.path.isfile(hook_file) and os.access(hook_file, os.X_OK) and subprocess.call([hook_file]) != 0:
+            sys.exit(1)
+
         #
         # Apply the commits, one at a time.  On failure, ask if should
         # continue to try the rest of the patches, or quit.

t/t9800-git-p4-basic.sh

@@ -261,6 +261,35 @@ test_expect_success 'unresolvable host in P4PORT should display error' '
 	)
 '
 
+# Test following scenarios:
+#   - Without ".git/hooks/p4-pre-submit" , submit should continue
+#   - With the hook returning 0, submit should continue
+#   - With the hook returning 1, submit should abort
+test_expect_success 'run hook p4-pre-submit before submit' '
+	test_when_finished cleanup_git &&
+	git p4 clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		echo "hello world" >hello.txt &&
+		git add hello.txt &&
+		git commit -m "add hello.txt" &&
+		git config git-p4.skipSubmitEdit true &&
+		git p4 submit --dry-run >out &&
+		grep "Would apply" out &&
+		mkdir -p .git/hooks &&
+		write_script .git/hooks/p4-pre-submit <<-\EOF &&
+		exit 0
+		EOF
+		git p4 submit --dry-run >out &&
+		grep "Would apply" out &&
+		write_script .git/hooks/p4-pre-submit <<-\EOF &&
+		exit 1
+		EOF
+		test_must_fail git p4 submit --dry-run >errs 2>&1 &&
+		! grep "Would apply" errs
+	)
+'
+
 test_expect_success 'submit from detached head' '
 	test_when_finished cleanup_git &&
 	git p4 clone --dest="$git" //depot &&