flag: fix parse_bool_value() (#22160)

vlib/flag/flag.v

@@ -302,10 +302,20 @@ fn (mut fs FlagParser) parse_bool_value(longhand string, shorthand u8) !string {
 			fs.args.delete(i)
 			return val
 		}
-		if arg.len > 1 && arg[0] == `-` && arg[1] != `-` && arg.index_u8(shorthand) != -1 {
-			// -abc is equivalent to -a -b -c
-			fs.args[i] = arg.replace(shorthand.ascii_str(), '') // -abc -> -bc
-			return 'true'
+		if arg.len > 1 && arg[0] == `-` && arg[1] != `-` {
+			mut found := false
+			for j in 1 .. arg.len - 1 {
+				if arg[j].is_space() {
+					break
+				} else if arg[j] == shorthand {
+					found = true
+				}
+			}
+			if found {
+				// -abc is equivalent to -a -b -c
+				fs.args[i] = arg.replace(shorthand.ascii_str(), '') // -abc -> -bc
+				return 'true'
+			}
 		}
 	}
 	return error("parameter '${longhand}' not found")

vlib/flag/flag_parse_test.v

@@ -0,0 +1,39 @@
+import flag
+
+pub struct Options {
+pub:
+	verbosity  int
+	dump_usage bool
+pub mut:
+	additional_args []string
+	archs           []string
+	v_flags         []string
+	api_level       string
+}
+
+fn test_flag_parse() {
+	args := ['/my/app', '-v', '3', '-f', '-d sdl_memory_no_gc', '-f', '-d shy_use_wren', '--api',
+		'21', '--archs', 'arm64-v8a', '/path/to/input.v']
+
+	mut fp := flag.new_flag_parser(args)
+	fp.application('bug')
+	fp.version('0.2.0')
+	fp.description('bugged')
+	fp.arguments_description('not important')
+
+	fp.skip_executable()
+
+	mut opt := Options{
+		v_flags:    fp.string_multi('flag', `f`, 'Additional flags for the V compiler')
+		archs:      fp.string('archs', 0, 'arm64-v8a,armeabi-v7a,x86,x86_64', 'Comma separated string with any of archs').split(',')
+		dump_usage: fp.bool('help', `h`, false, 'Show this help message and exit')
+		verbosity:  fp.int_opt('verbosity', `v`, 'Verbosity level 1-3') or { 0 }
+		api_level:  fp.string('api', 0, '21', 'Android API level to use (--list-apis)')
+	}
+
+	opt.additional_args = fp.finalize() or { panic(err) }
+
+	assert opt.v_flags[0] == '-d sdl_memory_no_gc'
+	assert opt.v_flags[1] == '-d shy_use_wren' // looks like the builtin support for `-h` eats the "h" in this flag
+	assert opt.dump_usage == false
+}