checker: check error for map of generic struct init (#13999)

vlib/v/checker/containers.v

@@ -260,6 +260,22 @@ pub fn (mut c Checker) map_init(mut node ast.MapInit) ast.Type {
 	// `x := map[string]string` - set in parser
 	if node.typ != 0 {
 		info := c.table.sym(node.typ).map_info()
+		if info.value_type != 0 {
+			val_sym := c.table.sym(info.value_type)
+			if val_sym.kind == .struct_ {
+				val_info := val_sym.info as ast.Struct
+				if val_info.generic_types.len > 0 && val_info.concrete_types.len == 0
+					&& !info.value_type.has_flag(.generic) {
+					if c.table.cur_concrete_types.len == 0 {
+						c.error('generic struct `$val_sym.name` must specify type parameter, e.g. Foo<int>',
+							node.pos)
+					} else {
+						c.error('generic struct `$val_sym.name` must specify type parameter, e.g. Foo<T>',
+							node.pos)
+					}
+				}
+			}
+		}
 		c.ensure_type_exists(info.key_type, node.pos) or {}
 		c.ensure_type_exists(info.value_type, node.pos) or {}
 		node.key_type = info.key_type

vlib/v/checker/tests/map_of_generic_struct_init_err.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/map_of_generic_struct_init_err.vv:6:11: error: generic struct `Item` must specify type parameter, e.g. Foo<int>
+    4 |
+    5 | fn main() {
+    6 |     mut m := map[string]Item{}
+      |              ~~~~~~~~~~~~~~~~~
+    7 | }

vlib/v/checker/tests/map_of_generic_struct_init_err.vv

@@ -0,0 +1,7 @@
+struct Item<T>{
+	val T
+}
+
+fn main() {
+	mut m := map[string]Item{}
+}

vlib/v/parser/parser.v

@@ -2140,10 +2140,12 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 	p.expr_mod = ''
 	// `map[string]int` initialization
 	if p.tok.lit == 'map' && p.peek_tok.kind == .lsbr {
+		mut pos := p.tok.pos()
 		map_type := p.parse_map_type()
 		if p.tok.kind == .lcbr {
 			p.next()
 			if p.tok.kind == .rcbr {
+				pos = pos.extend(p.tok.pos())
 				p.next()
 			} else {
 				if p.pref.is_fmt {
@@ -2156,7 +2158,7 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 		}
 		return ast.MapInit{
 			typ: map_type
-			pos: p.prev_tok.pos()
+			pos: pos
 		}
 	}
 	// `chan typ{...}`