flag: add missing short flag match in flag.to_struct, add test (#22696)

vlib/flag/flag_to.v

@@ -1609,6 +1609,22 @@ fn (mut fm FlagMapper) map_posix_short(flag_ctx FlagContext, field StructField)
 				fm.handled_pos << pos + 1 // next
 			}
 			return true
+		} else if !flag_ctx.next.starts_with(used_delimiter) {
+			if field.short == flag_name {
+				trace_println('${@FN}: found match for (${field.type_name}) ${fm.dbg_match(flag_ctx,
+					field, next, '')}')
+				fm.field_map_flag[field.name] = FlagData{
+					raw:        flag_raw
+					field_name: field.name
+					delimiter:  used_delimiter
+					name:       flag_name
+					arg:        ?string(next)
+					pos:        pos
+				}
+				fm.handled_pos << pos
+				fm.handled_pos << pos + 1 // next
+				return true
+			}
 		}
 	}
 	if (fm.config.style == .short || field.hints.has(.short_only)) && first_letter == field.short {

vlib/flag/flag_to_edge_case_1_test.v

@@ -0,0 +1,25 @@
+import flag
+
+const edge_case = ['appimage', '-v', '3', '-o', '/tmp/lol.appimage', '/home/user/Projects/game/']
+
+pub struct AppImageOptions {
+pub:
+	verbosity    int  @[short: v; xdoc: 'Verbosity level 1-3']
+	dump_usage   bool @[long: help; short: h; xdoc: 'Show this help message and exit']
+	show_version bool @[long: version; xdoc: 'Output version information and exit']
+pub mut:
+	input  string   @[tail]
+	output string   @[short: o; xdoc: 'Path to output (dir/file)']
+	assets []string @[short: a; xdoc: 'Asset dir(s) to include in build']
+}
+
+fn test_edge_case() {
+	aio, no_matches := flag.to_struct[AppImageOptions](edge_case, skip: 1)!
+	assert aio.verbosity == 3
+	assert aio.output == '/tmp/lol.appimage'
+	assert aio.input == '/home/user/Projects/game/'
+	assert aio.dump_usage == false
+	assert aio.show_version == false
+	assert aio.assets == []
+	assert no_matches == []
+}