checker: check unknown array of fn type in struct field (#15502)

vlib/v/checker/checker.v

@@ -3827,6 +3827,13 @@ fn (mut c Checker) ensure_type_exists(typ ast.Type, pos token.Pos) ? {
 				return
 			}
 		}
+		.function {
+			fn_info := sym.info as ast.FnType
+			c.ensure_type_exists(fn_info.func.return_type, fn_info.func.return_type_pos)?
+			for param in fn_info.func.params {
+				c.ensure_type_exists(param.typ, param.type_pos)?
+			}
+		}
 		.array {
 			c.ensure_type_exists((sym.info as ast.Array).elem_type, pos)?
 		}

vlib/v/checker/struct.v

@@ -68,16 +68,6 @@ pub fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 							field.type_pos)
 					}
 				}
-				field_sym := c.table.sym(field.typ)
-				if field_sym.kind == .function {
-					fn_info := field_sym.info as ast.FnType
-					c.ensure_type_exists(fn_info.func.return_type, fn_info.func.return_type_pos) or {
-						return
-					}
-					for param in fn_info.func.params {
-						c.ensure_type_exists(param.typ, param.type_pos) or { return }
-					}
-				}
 			}
 			if sym.kind == .struct_ {
 				info := sym.info as ast.Struct

vlib/v/checker/tests/unknown_array_fn_type_in_struct_field.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/unknown_array_fn_type_in_struct_field.vv:2:22: error: unknown type `UnknownThing`.
+Did you mean `[2]fn (u32) UnknownThing`?
+    1 | struct Virt {
+    2 |     fns [2]fn (num u32) UnknownThing
+      |                         ~~~~~~~~~~~~
+    3 | }
+    4 |

vlib/v/checker/tests/unknown_array_fn_type_in_struct_field.vv

@@ -0,0 +1,10 @@
+struct Virt {
+	fns [2]fn (num u32) UnknownThing
+}
+
+fn (virt Virt) caller() {
+	func := virt.fns[0]
+	func(5)
+}
+
+fn main() {}