ast, checker, cgen: fix array of sumtype initialisation with a default `init:` (#13178)

vlib/v/ast/ast.v

@@ -1166,9 +1166,10 @@ pub:
 	has_default   bool
 	has_it        bool // true if temp variable it is used
 pub mut:
-	expr_types []Type // [Dog, Cat] // also used for interface_types
-	elem_type  Type   // element type
-	typ        Type   // array type
+	expr_types   []Type // [Dog, Cat] // also used for interface_types
+	elem_type    Type   // element type
+	default_type Type   // default value type
+	typ          Type   // array type
 }
 
 pub struct ArrayDecompose {

vlib/v/checker/containers.v

@@ -20,6 +20,7 @@ pub fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 		if node.has_default {
 			default_expr := node.default_expr
 			default_typ := c.check_expr_opt_call(default_expr, c.expr(default_expr))
+			node.default_type = default_typ
 			c.check_expected(default_typ, node.elem_type) or {
 				c.error(err.msg, default_expr.position())
 			}

vlib/v/gen/c/array.v

@@ -213,7 +213,7 @@ fn (mut g Gen) array_init(node ast.ArrayInit) {
 			g.write('}[0])')
 		} else if node.has_default {
 			g.write('&($elem_styp[]){')
-			g.expr(node.default_expr)
+			g.expr_with_cast(node.default_expr, node.default_type, node.elem_type)
 			g.write('})')
 		} else if node.has_len && node.elem_type == ast.string_type {
 			g.write('&($elem_styp[]){')

vlib/v/tests/array_of_sumtype_with_default_test.v

@@ -0,0 +1,11 @@
+type Abc = int | string
+
+fn test_array_of_sumtype_with_default() {
+	a1 := []Abc{len: 1, init: 22}
+	println(a1)
+	assert '$a1' == '[Abc(22)]'
+
+	a2 := []Abc{len: 1, init: 'hello'}
+	println(a2)
+	assert '$a2' == "[Abc('hello')]"
+}