parser, checker: fix array alias (#22175)

vlib/v/checker/check_types.v

@@ -453,6 +453,21 @@ fn (mut c Checker) check_basic(got ast.Type, expected ast.Type) bool {
 	if got == ast.float_literal_type && expected_nonflagged.is_float() {
 		return true
 	}
+	// decode and check array to aliased array type
+	if got_sym.kind == .array && exp_sym.info is ast.Array {
+		exp_elem_sym := c.table.sym(exp_sym.info.elem_type)
+		if exp_elem_sym.info is ast.Alias {
+			parent_elem_sym := c.table.sym(exp_elem_sym.info.parent_type)
+			if parent_elem_sym.info is ast.Array {
+				array_info := parent_elem_sym.array_info()
+				elem_type := c.table.find_or_register_array_with_dims(array_info.elem_type,
+					array_info.nr_dims + exp_sym.info.nr_dims)
+				if c.table.type_to_str(got) == c.table.type_to_str(elem_type) {
+					return true
+				}
+			}
+		}
+	}
 	return false
 }
 

vlib/v/checker/containers.v

@@ -7,7 +7,7 @@ import v.token
 
 fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 	mut elem_type := ast.void_type
-	unwrap_elem_type := c.unwrap_generic(node.elem_type)
+	mut unwrap_elem_type := c.unwrap_generic(node.elem_type)
 	if c.pref.warn_about_allocs {
 		c.warn_alloc('array initialization', node.pos)
 	}
@@ -60,6 +60,15 @@ fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 					if elem_sym.name == 'byte' {
 						c.warn('byte is deprecated, use u8 instead', node.elem_type_pos)
 					}
+					parent_sym := c.table.sym(elem_sym.info.parent_type)
+					// check array to aliased array type
+					if parent_sym.info is ast.Array {
+						node.alias_type = c.table.find_or_register_array(unwrap_elem_type)
+						node.elem_type = c.table.find_or_register_array_with_dims(parent_sym.info.elem_type,
+							parent_sym.info.nr_dims)
+						unwrap_elem_type = node.elem_type
+						node.typ = c.table.find_or_register_array(node.elem_type)
+					}
 				}
 				else {}
 			}

vlib/v/tests/aliases/array_alias_test.v

@@ -0,0 +1,65 @@
+module main
+
+type OneD = []Thing
+
+struct Thing {
+	item int
+}
+
+fn good() [][]Thing {
+	println('start good()')
+	mut two_d := [][]Thing{}
+	mut one_d := []Thing{}
+	one_d << Thing{1}
+	one_d << Thing{2}
+	two_d << one_d
+	assert two_d.len == 1, 'two_d length not 1'
+	for i, one in two_d {
+		for j, item in one {
+			println('two_d[${i}][${j}]=${item}')
+			assert item == Thing{j + 1}
+		}
+	}
+	println('end good()')
+	return two_d
+}
+
+fn bad() []OneD {
+	println('start bad()')
+	mut two_d := []OneD{}
+	mut one_d := OneD{}
+	one_d << Thing{1}
+	one_d << Thing{2}
+	assert one_d.len == 2, 'one_d length not 2'
+	assert one_d[0] == Thing{1}, 'one_d[0] not 1'
+	assert one_d[1] == Thing{2}, 'one_d[1] not 2'
+	two_d << one_d
+	assert two_d.len == 1, 'two_d length not 1'
+	for i, one in two_d {
+		for j, item in one {
+			println('two_d[${i}][${j}]=${item}')
+			assert item == Thing{j + 1}
+		}
+	}
+	println('end bad()')
+	return two_d
+}
+
+fn test_main() {
+	good_two_d := good()
+	assert good_two_d.len == 1, 'good_two_d length not 1'
+	for i, one_d in good_two_d {
+		for j, item in one_d {
+			println('good_two_d[${i}][${j}]=${item}')
+			assert item == Thing{j + 1}
+		}
+	}
+	bad_two_d := bad()
+	assert bad_two_d.len == 1, 'bad_two_d length not 1'
+	for i, one_d in bad_two_d {
+		for j, item in one_d {
+			println('bad_two_d[${i}][${j}]=${item}')
+			assert item == Thing{j + 1}
+		}
+	}
+}