checker: support non-string map.keys method (#7760)

vlib/builtin/map.v

@@ -646,7 +646,7 @@ pub fn (m &map) keys() []string {
 }
 
 // Returns all keys in the map.
-pub fn (m &map) keys_1() array {
+fn (m &map) keys_1() array {
 	mut keys := __new_array(m.len, 0, m.key_bytes)
 	mut item := unsafe { byteptr(keys.data) }
 	if m.key_values.deletes == 0 {
@@ -674,7 +674,7 @@ pub fn (m &map) keys_1() array {
 
 // warning: only copies keys, does not clone
 [unsafe]
-pub fn (d &DenseArray) clone() DenseArray {
+fn (d &DenseArray) clone() DenseArray {
 	res := DenseArray{
 		key_bytes: d.key_bytes
 		value_bytes: d.value_bytes

vlib/builtin/map_test.v

@@ -492,6 +492,7 @@ fn test_int_keys() {
 	same := mc == m
 	assert same
 	assert mc.len == 3
+	assert mc.keys() == [3,4,5]
 	mut all := []int{}
 	for k, v in mc {
 		assert m[k] == v

vlib/v/checker/checker.v

@@ -1256,9 +1256,21 @@ pub fn (mut c Checker) call_method(mut call_expr ast.CallExpr) table.Type {
 			call_expr.return_type = table.int_type
 		}
 		return call_expr.return_type
-	} else if left_type_sym.kind == .map && method_name == 'clone' {
-		call_expr.return_type = left_type
+	} else if left_type_sym.kind == .map && method_name in ['clone', 'keys'] {
+		mut ret_type := table.void_type
+		match method_name {
+			'clone' {
+				ret_type = left_type
+			}
+			'keys' {
+				info := left_type_sym.info as table.Map
+				typ := c.table.find_or_register_array(info.key_type, 1)
+				ret_type = table.Type(typ)
+			}
+			else {}
+		}
 		call_expr.receiver_type = left_type.to_ptr()
+		call_expr.return_type = ret_type
 		return call_expr.return_type
 	} else if left_type_sym.kind == .array && method_name in ['first', 'last', 'pop'] {
 		info := left_type_sym.info as table.Array

vlib/v/gen/fn.v

@@ -408,6 +408,10 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 		if node.name in ['close', 'try_pop', 'try_push'] {
 			name = 'sync__Channel_$node.name'
 		}
+	} else if left_sym.kind == .map {
+		if node.name == 'keys' {
+			name = 'map_keys_1'
+		}
 	}
 	// Check if expression is: arr[a..b].clone(), arr[a..].clone()
 	// if so, then instead of calling array_clone(&array_slice(...))