parse-options: Allow abbreviated options when unambiguous

When there is an option "--amend", the option parser now recognizes
"--am" for that option, provided that there is no other option beginning
with "--am".

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

parse-options.c

@@ -113,6 +113,13 @@ static int parse_short_opt(struct optparse_t *p, const struct option *options)
 static int parse_long_opt(struct optparse_t *p, const char *arg,
                           const struct option *options)
 {
+	const char *arg_end = strchr(arg, '=');
+	const struct option *abbrev_option = NULL;
+	int abbrev_flags = 0;
+
+	if (!arg_end)
+		arg_end = arg + strlen(arg);
+
 	for (; options->type != OPTION_END; options++) {
 		const char *rest;
 		int flags = 0;
@@ -122,10 +129,38 @@ static int parse_long_opt(struct optparse_t *p, const char *arg,
 
 		rest = skip_prefix(arg, options->long_name);
 		if (!rest) {
+			/* abbreviated? */
+			if (!strncmp(options->long_name, arg, arg_end - arg)) {
+is_abbreviated:
+				if (abbrev_option)
+					return error("Ambiguous option: %s "
+						"(could be --%s%s or --%s%s)",
+						arg,
+						(flags & OPT_UNSET) ?
+							"no-" : "",
+						options->long_name,
+						(abbrev_flags & OPT_UNSET) ?
+							"no-" : "",
+						abbrev_option->long_name);
+				if (!(flags & OPT_UNSET) && *arg_end)
+					p->opt = arg_end + 1;
+				abbrev_option = options;
+				abbrev_flags = flags;
+				continue;
+			}
+			/* negated and abbreviated very much? */
+			if (!prefixcmp("no-", arg)) {
+				flags |= OPT_UNSET;
+				goto is_abbreviated;
+			}
+			/* negated? */
 			if (strncmp(arg, "no-", 3))
 				continue;
 			flags |= OPT_UNSET;
 			rest = skip_prefix(arg + 3, options->long_name);
+			/* abbreviated and negated? */
+			if (!rest && !prefixcmp(options->long_name, arg + 3))
+				goto is_abbreviated;
 			if (!rest)
 				continue;
 		}
@@ -136,6 +171,8 @@ static int parse_long_opt(struct optparse_t *p, const char *arg,
 		}
 		return get_value(p, options, flags);
 	}
+	if (abbrev_option)
+		return get_value(p, abbrev_option, abbrev_flags);
 	return error("unknown option `%s'", arg);
 }
 

t/t0040-parse-options.sh

@@ -67,4 +67,27 @@ test_expect_success 'intermingled arguments' '
 	git diff expect output
 '
 
+cat > expect << EOF
+boolean: 0
+integer: 2
+string: (not set)
+EOF
+
+test_expect_success 'unambiguously abbreviated option' '
+	test-parse-options --int 2 --boolean --no-bo > output 2> output.err &&
+	test ! -s output.err &&
+	git diff expect output
+'
+
+test_expect_success 'unambiguously abbreviated option with "="' '
+	test-parse-options --int=2 > output 2> output.err &&
+	test ! -s output.err &&
+	git diff expect output
+'
+
+test_expect_failure 'ambiguously abbreviated option' '
+	test-parse-options --strin 123;
+        test $? != 129
+'
+
 test_done