checker: implement `[required]` struct field attribute (#6276)

examples/2048/main.v

@@ -180,7 +180,7 @@ fn (t TileLine) to_left() TileLine {
 fn (b Board) to_left() Board {
 	mut res := b
 	for y := 0; y < 4; y++ {
-		mut hline := TileLine{y}
+		mut hline := TileLine{ypos: y}
 		for x := 0; x < 4; x++ {
 			hline.field[x] = b.field[y][x]
 		}

examples/sokol/particles/main.v

@@ -36,7 +36,7 @@ mut:
 fn (mut a App) init() {
 	a.frame = 0
 	a.last = time.ticks()
-	a.ps = particle.System{a.width, a.height}
+	a.ps = particle.System{width: a.width, height: a.height}
 	a.ps.init(particle.SystemConfig{
 		pool: 20000
 	})

vlib/v/checker/checker.v

@@ -480,6 +480,20 @@ pub fn (mut c Checker) struct_init(mut struct_init ast.StructInit) table.Type {
 					c.warn('reference field `${type_sym.source_name}.$field.name` must be initialized',
 						struct_init.pos)
 				}
+				// Check for `[required]` struct attr
+				if field.attrs.contains('required') && !struct_init.is_short {
+					mut found := false
+					for init_field in struct_init.fields {
+						if field.name == init_field.name {
+							found = true
+							break
+						}
+					}
+					if !found {
+						c.error('field `${type_sym.source_name}.$field.name` is required',
+							struct_init.pos)
+					}
+				}
 			}
 		}
 		else {}

vlib/v/checker/tests/struct_required_field.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_required_field.vv:12:6: error: field `Abc.f3` is required
+   10 |         f3: 789
+   11 |     }
+   12 |     _ = Abc{
+      |         ~~~~
+   13 |         f1: 123
+   14 |         f2: 789

vlib/v/checker/tests/struct_required_field.vv

@@ -0,0 +1,16 @@
+struct Abc {
+	f1 int [required]
+	f2 int
+	f3 int [required]
+}
+
+fn main() {
+	_ = Abc{
+		f1: 123
+		f3: 789
+	}
+	_ = Abc{
+		f1: 123
+		f2: 789
+	}
+}