Merge branch 'kw/commit-keep-index-when-pre-commit-is-not-run'

"git commit" used to discard the index and re-read from the filesystem
just in case the pre-commit hook has updated it in the middle; this
has been optimized out when we know we do not run the pre-commit hook.

* kw/commit-keep-index-when-pre-commit-is-not-run:
  commit: skip discarding the index if there is no pre-commit hook

builtin/commit.c

@@ -940,13 +940,16 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		return 0;
 	}
 
-	/*
-	 * Re-read the index as pre-commit hook could have updated it,
-	 * and write it out as a tree.  We must do this before we invoke
-	 * the editor and after we invoke run_status above.
-	 */
-	discard_cache();
+	if (!no_verify && find_hook("pre-commit")) {
+		/*
+		 * Re-read the index as pre-commit hook could have updated it,
+		 * and write it out as a tree.  We must do this before we invoke
+		 * the editor and after we invoke run_status above.
+		 */
+		discard_cache();
+	}
 	read_cache_from(index_file);
+
 	if (update_main_cache_tree(0)) {
 		error(_("Error building trees"));
 		return 0;