checker: fix warning of unnnecessary default none value for option struct fields (#17305)

Author: zakuro9715

vlib/v/checker/struct.v

@@ -161,20 +161,35 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 						}
 					}
 				}
-				if field.default_expr is ast.IntegerLiteral {
-					if field.default_expr.val == '0' {
-						c.warn('unnecessary default value of `0`: struct fields are zeroed by default',
-							field.default_expr.pos)
-					}
-				} else if field.default_expr is ast.StringLiteral {
-					if field.default_expr.val == '' {
-						c.warn("unnecessary default value of '': struct fields are zeroed by default",
+
+				if field.typ.has_flag(.option) {
+					if field.default_expr is ast.None {
+						c.warn('unnecessary default value of `none`: struct fields are zeroed by default',
 							field.default_expr.pos)
 					}
-				} else if field.default_expr is ast.BoolLiteral {
-					if field.default_expr.val == false {
-						c.warn('unnecessary default value `false`: struct fields are zeroed by default',
-							field.default_expr.pos)
+				} else if field.typ.has_flag(.result) {
+					// struct field does not support result. Nothing to do
+				} else {
+					match field.default_expr {
+						ast.IntegerLiteral {
+							if field.default_expr.val == '0' {
+								c.warn('unnecessary default value of `0`: struct fields are zeroed by default',
+									field.default_expr.pos)
+							}
+						}
+						ast.StringLiteral {
+							if field.default_expr.val == '' {
+								c.warn("unnecessary default value of '': struct fields are zeroed by default",
+									field.default_expr.pos)
+							}
+						}
+						ast.BoolLiteral {
+							if field.default_expr.val == false {
+								c.warn('unnecessary default value `false`: struct fields are zeroed by default',
+									field.default_expr.pos)
+							}
+						}
+						else {}
 					}
 				}
 			}

vlib/v/checker/tests/struct_unneeded_default.out

@@ -1,20 +1,27 @@
-vlib/v/checker/tests/struct_unneeded_default.vv:2:10: warning: unnecessary default value of `0`: struct fields are zeroed by default
+vlib/v/checker/tests/struct_unneeded_default.vv:2:18: warning: unnecessary default value of `0`: struct fields are zeroed by default
     1 | struct Test {
-    2 |     n int = 0
-      |             ^
-    3 |     s string = ''
-    4 |     b bool = false
-vlib/v/checker/tests/struct_unneeded_default.vv:3:13: warning: unnecessary default value of '': struct fields are zeroed by default
-    1 | struct Test {
-    2 |     n int = 0
-    3 |     s string = ''
-      |                ~~
-    4 |     b bool = false
-    5 | }
-vlib/v/checker/tests/struct_unneeded_default.vv:4:11: warning: unnecessary default value `false`: struct fields are zeroed by default
-    2 |     n int = 0
-    3 |     s string = ''
-    4 |     b bool = false
-      |              ~~~~~
-    5 | }
-    6 |
+    2 |     n      int    = 0
+      |                     ^
+    3 |     n_ok   int    = 1
+    4 |     s      string = ''
+vlib/v/checker/tests/struct_unneeded_default.vv:4:18: warning: unnecessary default value of '': struct fields are zeroed by default
+    2 |     n      int    = 0
+    3 |     n_ok   int    = 1
+    4 |     s      string = ''
+      |                     ~~
+    5 |     s_ok   string = 's'
+    6 |     b      bool   = false
+vlib/v/checker/tests/struct_unneeded_default.vv:6:18: warning: unnecessary default value `false`: struct fields are zeroed by default
+    4 |     s      string = ''
+    5 |     s_ok   string = 's'
+    6 |     b      bool   = false
+      |                     ~~~~~
+    7 |     b_ok   bool   = true
+    8 |     opt    ?int   = none
+vlib/v/checker/tests/struct_unneeded_default.vv:8:18: warning: unnecessary default value of `none`: struct fields are zeroed by default
+    6 |     b      bool   = false
+    7 |     b_ok   bool   = true
+    8 |     opt    ?int   = none
+      |                     ~~~~
+    9 |     opt_ok ?int   = 1
+   10 | }

vlib/v/checker/tests/struct_unneeded_default.vv

@@ -1,7 +1,12 @@
 struct Test {
-	n int = 0
-	s string = ''
-	b bool = false
+	n      int    = 0
+	n_ok   int    = 1
+	s      string = ''
+	s_ok   string = 's'
+	b      bool   = false
+	b_ok   bool   = true
+	opt    ?int   = none
+	opt_ok ?int   = 1
 }
 
 fn main() {