help.c: help.autocorrect=never means "do not compute suggestions"

While help.autocorrect can be set to 0 to decline auto-execution of
possibly mistyped commands, it still spends cycles to compute the
suggestions, and it wastes screen real estate.

Update help.autocorrect to accept the string "never" to just exit
with error upon mistyped commands to help users who prefer to never
see suggested corrections at all.

While at it, introduce "immediate" as a more readable way to
immediately execute the auto-corrected command, which can be done
with negative value.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/help.txt

@@ -8,13 +8,14 @@ help.format::
 	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.
+	If git detects typos and can identify exactly one valid command similar
+	to the error, git will automatically run the intended command after
+	waiting a duration of time defined by this configuration value in
+	deciseconds (0.1 sec).  If this value is 0, the suggested corrections
+	will be shown, but not executed. If it is a negative integer, or
+	"immediate", the suggested command
+	is run immediately. If "never", suggestions are not shown at all. The
+	default value is zero.
 
 help.htmlPath::
 	Specify the path where the HTML documentation resides. File system paths

help.c

@@ -472,12 +472,26 @@ int is_in_cmdlist(struct cmdnames *c, const char *s)
 static int autocorrect;
 static struct cmdnames aliases;
 
+#define AUTOCORRECT_NEVER (-2)
+#define AUTOCORRECT_IMMEDIATELY (-1)
+
 static int git_unknown_cmd_config(const char *var, const char *value, void *cb)
 {
 	const char *p;
 
-	if (!strcmp(var, "help.autocorrect"))
-		autocorrect = git_config_int(var,value);
+	if (!strcmp(var, "help.autocorrect")) {
+		if (!value)
+			return config_error_nonbool(var);
+		if (!strcmp(value, "never")) {
+			autocorrect = AUTOCORRECT_NEVER;
+		} else if (!strcmp(value, "immediate")) {
+			autocorrect = AUTOCORRECT_IMMEDIATELY;
+		} else {
+			int v = git_config_int(var, value);
+			autocorrect = (v < 0)
+				? AUTOCORRECT_IMMEDIATELY : v;
+		}
+	}
 	/* Also use aliases for command lookup */
 	if (skip_prefix(var, "alias.", &p))
 		add_cmdname(&aliases, p, strlen(p));
@@ -525,6 +539,11 @@ const char *help_unknown_cmd(const char *cmd)
 
 	read_early_config(git_unknown_cmd_config, NULL);
 
+	if (autocorrect == AUTOCORRECT_NEVER) {
+		fprintf_ln(stderr, _("git: '%s' is not a git command. See 'git --help'."), cmd);
+		exit(1);
+	}
+
 	load_command_list("git-", &main_cmds, &other_cmds);
 
 	add_cmd_list(&main_cmds, &aliases);
@@ -594,7 +613,7 @@ const char *help_unknown_cmd(const char *cmd)
 			   _("WARNING: You called a Git command named '%s', "
 			     "which does not exist."),
 			   cmd);
-		if (autocorrect < 0)
+		if (autocorrect == AUTOCORRECT_IMMEDIATELY)
 			fprintf_ln(stderr,
 				   _("Continuing under the assumption that "
 				     "you meant '%s'."),

t/t9003-help-autocorrect.sh

@@ -37,16 +37,30 @@ test_expect_success 'autocorrect showing candidates' '
 	grep "^	distimdistim" actual
 '
 
-test_expect_success 'autocorrect running commands' '
-	git config help.autocorrect -1 &&
+for immediate in -1 immediate
+do
+	test_expect_success 'autocorrect running commands' '
+		git config help.autocorrect $immediate &&
 
-	git lfg >actual &&
-	echo "a single log entry" >expect &&
-	test_cmp expect actual &&
+		git lfg >actual &&
+		echo "a single log entry" >expect &&
+		test_cmp expect actual &&
 
-	git distimdist >actual &&
-	echo "distimdistim was called" >expect &&
-	test_cmp expect actual
+		git distimdist >actual &&
+		echo "distimdistim was called" >expect &&
+		test_cmp expect actual
+	'
+done
+
+test_expect_success 'autocorrect can be declined altogether' '
+	git config help.autocorrect never &&
+
+	test_must_fail git lfg 2>actual &&
+	if test_have_prereq C_LOCALE_OUTPUT
+	then
+		grep "is not a git command" actual &&
+		test_line_count = 1 actual
+	fi
 '
 
 test_done