v.checker: fix panic for `a, b, c = fn_returning_several_maps()`

vlib/v/checker/checker.v

@@ -4019,13 +4019,20 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 			// `map = {}`
 			if left_type != 0 {
 				sym := c.table.get_type_symbol(left_type)
-				if sym.kind == .map && node.right[i] is ast.StructInit {
+				if sym.kind == .map {
+					if node.right.len <= i {
+						// `map_1, map_2, map_3 = f()`, where f returns (map[int]int, map[int]int, map[int]int)
+						// i.e. 3 left parts of the assignment, but just 1 right part
+					} else {
+						if node.right[i] is ast.StructInit {
 							c.warn('assigning a struct literal to a map is deprecated - use `map{}` instead',
 								node.right[i].position())
 							node.right[i] = ast.MapInit{}
 						}
 					}
 				}
+			}
+		}
 		if node.right_types.len < node.left.len { // first type or multi return types added above
 			old_inside_ref_lit := c.inside_ref_lit
 			if left is ast.Ident {

vlib/v/tests/multiret_with_maps_test.v

@@ -0,0 +1,32 @@
+fn many_maps() (map[int]int, map[int]int, map[int]int) {
+	return {
+		1: 2
+	}, {
+		3: 4
+	}, {
+		5: 1000
+	}
+}
+
+fn test_fn_returning_many_maps_at_the_same_time() {
+	mut a, mut b, mut c := {
+		0: 0
+	}, {
+		0: 0
+	}, {
+		0: 0
+	}
+	a, b, c = many_maps()
+	dump(a)
+	dump(b)
+	dump(c)
+	assert a == {
+		1: 2
+	}
+	assert b == {
+		3: 4
+	}
+	assert c == {
+		5: 1000
+	}
+}