Add help.autocorrect to enable/disable autocorrecting

It is off(0) by default, to avoid scaring people unless they asked to.
If set to a non-0 value, wait for that amount of deciseconds before
running the corrected command.

Suggested by Junio, so he has a chance to hit Ctrl-C.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -790,6 +790,15 @@ help.format::
 	Values 'man', 'info', 'web' and 'html' are supported. 'man' is
 	the default. 'web' and 'html' are the same.
 
+help.autocorrect::
+	Automatically correct and execute mistyped commands after
+	waiting for the given number of deciseconds (0.1 sec). If more
+	than one command can be deduced from the entered text, nothing
+	will be executed.  If the value of this option is negative,
+	the corrected command will be executed immediately. If the
+	value is 0 - the command will be just shown but not executed.
+	This is the default.
+
 http.proxy::
 	Override the HTTP proxy, normally configured using the 'http_proxy'
 	environment variable (see linkgit:curl[1]).  This can be overridden

help.c

@@ -268,6 +268,16 @@ int is_in_cmdlist(struct cmdnames *c, const char *s)
 	return 0;
 }
 
+static int autocorrect;
+
+static int git_unknown_cmd_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "help.autocorrect"))
+		autocorrect = git_config_int(var,value);
+
+	return git_default_config(var, value, cb);
+}
+
 static int levenshtein_compare(const void *p1, const void *p2)
 {
 	const struct cmdname *const *c1 = p1, *const *c2 = p2;
@@ -285,6 +295,8 @@ const char *help_unknown_cmd(const char *cmd)
 	memset(&main_cmds, 0, sizeof(main_cmds));
 	memset(&other_cmds, 0, sizeof(main_cmds));
 
+	git_config(git_unknown_cmd_config, NULL);
+
 	load_command_list("git-", &main_cmds, &other_cmds);
 
 	ALLOC_GROW(main_cmds.names, main_cmds.cnt + other_cmds.cnt,
@@ -309,14 +321,19 @@ const char *help_unknown_cmd(const char *cmd)
 	n = 1;
 	while (n < main_cmds.cnt && best_similarity == main_cmds.names[n]->len)
 		++n;
-	if (n == 1) {
+	if (autocorrect && n == 1) {
 		const char *assumed = main_cmds.names[0]->name;
 		main_cmds.names[0] = NULL;
 		clean_cmdnames(&main_cmds);
 		fprintf(stderr, "WARNING: You called a Git program named '%s', "
 			"which does not exist.\n"
 			"Continuing under the assumption that you meant '%s'\n",
 			cmd, assumed);
+		if (autocorrect > 0) {
+			fprintf(stderr, "in %0.1f seconds automatically...\n",
+				(float)autocorrect/10.0);
+			poll(NULL, 0, autocorrect * 100);
+		}
 		return assumed;
 	}