parser,checker: support dates in @[deprecated] as alternative to @[deprecated_after]

Author: dy-tea

test_deprecated_with_date.v

@@ -0,0 +1,30 @@
+@[deprecated: '2025-10-10 use new function instead']
+fn d0() {}
+
+@[deprecated: '1234567890']
+fn d1() {}
+
+@[deprecated: '']
+fn d2() {}
+
+@[deprecated: 'a']
+fn d3() {}
+
+@[deprecated: 'greater than 10 chars']
+fn d4() {}
+
+@[deprecated: '2025-10-10close']
+fn d5() {}
+
+@[deprecated: ' 2025-10-10']
+fn d6() {}
+
+fn main() {
+	d0()
+	d1()
+	d2()
+	d3()
+	d4()
+	d5()
+	d6()
+}

vlib/v/checker/errors.v

@@ -202,6 +202,13 @@ fn (mut c Checker) deprecate(kind string, name string, attrs []ast.Attr, pos tok
 		}
 		if attr.name == 'deprecated' {
 			deprecation_message = attr.arg
+			left_trimmed := attr.arg.trim_left(' ')
+			if left_trimmed.len >= 10 {
+			 	if t := time.parse_iso8601(left_trimmed[..9]) {
+					after_time = t
+					deprecation_message = left_trimmed[10..]
+				}
+			}
 		} else if attr.name == 'deprecated_after' {
 			after_time = time.parse_iso8601(attr.arg) or {
 				c.error('invalid time format', attr.pos)

vlib/v/parser/fn.v

@@ -227,7 +227,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			'manualfree' {
 				is_manualfree = true
 			}
-			'deprecated' {
+			'deprecated', 'deprecated_after' {
 				is_deprecated = true
 			}
 			'direct_array_access' {