generic: fix return multi array generic (fix #7727 #7753) (#7855)

vlib/v/checker/check_types.v

@@ -427,13 +427,24 @@ pub fn (mut c Checker) infer_fn_types(f table.Fn, mut call_expr ast.CallExpr) {
 		arg_sym := c.table.get_type_symbol(arg.typ)
 		param_type_sym := c.table.get_type_symbol(param.typ)
 		if arg_sym.kind == .array && param_type_sym.kind == .array {
-			param_info := param_type_sym.info as table.Array
-			if param_info.elem_type.has_flag(.generic) {
-				arg_info := arg_sym.info as table.Array
-				typ = arg_info.elem_type
+			mut arg_elem_info := arg_sym.info as table.Array
+			mut param_elem_info := param_type_sym.info as table.Array
+			mut arg_elem_sym := c.table.get_type_symbol(arg_elem_info.elem_type)
+			mut param_elem_sym := c.table.get_type_symbol(param_elem_info.elem_type)
+			for {
+				if arg_elem_sym.kind == .array &&
+					param_elem_sym.kind == .array && param_elem_sym.name != 'T' {
+					arg_elem_info = arg_elem_sym.info as table.Array
+					arg_elem_sym = c.table.get_type_symbol(arg_elem_info.elem_type)
+					param_elem_info = param_elem_sym.info as table.Array
+					param_elem_sym = c.table.get_type_symbol(param_elem_info.elem_type)
+				} else {
+					typ = arg_elem_info.elem_type
 					break
 				}
 			}
+			break
+		}
 	}
 	if typ == table.void_type {
 		c.error('could not infer generic type `$gt_name` in call to `$f.name`', call_expr.pos)

vlib/v/checker/checker.v

@@ -1766,14 +1766,24 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 			}
 			call_expr.return_type = typ
 			return typ
-		} else if return_sym.kind == .array {
-			elem_info := return_sym.info as table.Array
-			elem_sym := c.table.get_type_symbol(elem_info.elem_type)
-			if elem_sym.name == 'T' {
-				idx := c.table.find_or_register_array(call_expr.generic_type, 1)
-				return table.new_type(idx)
+		} else if return_sym.kind == .array && return_sym.name.contains('T') {
+			mut info := return_sym.info as table.Array
+			mut sym := c.table.get_type_symbol(info.elem_type)
+			mut dims := 1
+			for {
+				if sym.kind == .array {
+					info = sym.info as table.Array
+					sym = c.table.get_type_symbol(info.elem_type)
+					dims++
+				} else {
+					break
 				}
 			}
+			idx := c.table.find_or_register_array(call_expr.generic_type, dims)
+			typ := table.new_type(idx)
+			call_expr.return_type = typ
+			return typ
+		}
 	}
 	if call_expr.generic_type.is_full() && !f.is_generic {
 		c.error('a non generic function called like a generic one', call_expr.generic_list_pos)

vlib/v/tests/generics_return_multi_array_test.v

@@ -0,0 +1,25 @@
+fn example1<T>(data []T) [][]T {
+	return [data]
+}
+
+fn example2<T>(data [][]T) [][][]T {
+	return [data]
+}
+
+fn example3<T>(data [][][]T) [][][][]T {
+	return [data]
+}
+
+fn test_generic_return_multi_array() {
+	d1 := [1, 2, 3]
+	d2 := example1(d1)
+	assert d2 == [[1, 2, 3]]
+
+	d11 := [[1, 2, 3]]
+	d22 := example2(d11)
+	assert d22 == [[[1, 2, 3]]]
+
+	d111 := [[[1, 2, 3]]]
+	d222 := example3(d111)
+	assert d222 == [[[[1, 2, 3]]]]
+}