checker/cgen: fix calling struct field with fn type

vlib/v/checker/checker.v

@@ -346,6 +346,17 @@ pub fn (c mut Checker) call_method(call_expr mut ast.CallExpr) table.Type {
 		call_expr.return_type = table.string_type
 		return table.string_type
 	}
+	// call struct field fn type
+	// TODO: can we use SelectorExpr for all?
+	if field := c.table.struct_find_field(left_type_sym, method_name) {
+		field_type_sym := c.table.get_type_symbol(field.typ)
+		if field_type_sym.kind == .function {
+			call_expr.is_method = false
+			info := field_type_sym.info as table.FnType
+			call_expr.return_type = info.func.return_type
+			return info.func.return_type
+		}
+	}
 	c.error('unknown method: ${left_type_sym.name}.$method_name', call_expr.pos)
 	return table.void_type
 }

vlib/v/gen/fn.v

@@ -242,6 +242,19 @@ fn (g mut Gen) method_call(node ast.CallExpr) {
 }
 
 fn (g mut Gen) fn_call(node ast.CallExpr) {
+	// call struct field with fn type
+	// TODO: test node.left instead
+	// left & left_type will be `x` and `x type` in `x.fieldfn()`
+	// will be `0` for `foo()`
+	if node.left_type != 0 {
+		g.expr(node.left)
+		if table.type_is_ptr(node.left_type) {
+			g.write('->')
+		}
+		else {
+			g.write('.')
+		}
+	}
 	mut name := node.name
 	is_print := name == 'println' || name == 'print'
 	print_method := if name == 'println' { 'println' } else { 'print' }

vlib/v/tests/fn_test.v

@@ -153,7 +153,11 @@ struct MySt {
 fn test_fn_type_call() {
     mut arr := []MyFn
     arr << MyFn(test)
-    assert arr[0](10) == 1010
+	// TODO: `arr[0](10)`
+	// assert arr[0](10) == 1010
+	x1 := arr[0]
+	x2 := x1(10)
+	assert x2 == 1010
 
     st := MySt{f:test}
     assert st.f(10) == 1010