checker: add an error for `x.method({})` calls, when method expects a struct

vlib/v/checker/check_types.v

@@ -7,6 +7,9 @@ import v.ast
 import v.token
 
 pub fn (mut c Checker) check_expected_call_arg(got ast.Type, expected_ ast.Type, language ast.Language, arg ast.CallArg) ? {
+	if got == 0 {
+		return error('unexpected 0 type')
+	}
 	mut expected := expected_
 	// variadic
 	if expected.has_flag(.variadic) {

vlib/v/checker/checker.v

@@ -7605,8 +7605,14 @@ pub fn (mut c Checker) map_init(mut node ast.MapInit) ast.Type {
 			node.value_type = info.value_type
 			return node.typ
 		} else {
-			c.error('invalid empty map initilization syntax, use e.g. map[string]int{} instead',
+			if sym.kind == .struct_ {
+				c.error('`{}` can not be used for initialising empty structs any more. Use `${c.table.type_to_str(c.expected_type)}{}` instead.',
 					node.pos)
+			} else {
+				c.error('invalid empty map initialisation syntax, use e.g. map[string]int{} instead',
+					node.pos)
+			}
+			return ast.void_type
 		}
 	}
 	// `x := map[string]string` - set in parser

vlib/v/checker/tests/assign_to_typeless_variable_err.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_to_typeless_variable_err.vv:2:10: error: invalid empty map initilization syntax, use e.g. map[string]int{} instead
+vlib/v/checker/tests/assign_to_typeless_variable_err.vv:2:10: error: invalid empty map initialisation syntax, use e.g. map[string]int{} instead
     1 | fn main() {
     2 |   val := {}
       |          ~~

vlib/v/checker/tests/map_init_invalid_syntax.out

@@ -1,6 +1,12 @@
-vlib/v/checker/tests/map_init_invalid_syntax.vv:2:7: error: invalid empty map initilization syntax, use e.g. map[string]int{} instead
+vlib/v/checker/tests/map_init_invalid_syntax.vv:2:7: error: invalid empty map initialisation syntax, use e.g. map[string]int{} instead
     1 | fn main() {
     2 |     a := {}
       |          ~~
     3 |     println(a)
     4 | }
+vlib/v/checker/tests/map_init_invalid_syntax.vv:3:2: error: `println` can not print void expressions
+    1 | fn main() {
+    2 |     a := {}
+    3 |     println(a)
+      |     ~~~~~~~~~~
+    4 | }

vlib/v/checker/tests/method_call_with_empty_struct_init.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/method_call_with_empty_struct_init.vv:10:11: error: `{}` can not be used for initialising empty structs any more. Use `Abc{}` instead.
+    8 | fn main() {
+    9 |     s := Abc{}
+   10 |     s.abc(0, {})
+      |              ~~
+   11 | }

vlib/v/checker/tests/method_call_with_empty_struct_init.vv

@@ -0,0 +1,11 @@
+struct Abc {
+	x int
+}
+
+fn (s Abc) abc(x int, param Abc) {
+}
+
+fn main() {
+	s := Abc{}
+	s.abc(0, {})
+}