cgen: fix interface with multiple embedded fields (#19377)

Author: yuyi98

vlib/v/gen/c/cgen.v

@@ -6734,11 +6734,21 @@ fn (mut g Gen) interface_table() string {
 							cast_struct.write_string('/*.... ast.voidptr_type */')
 						} else {
 							if st_sym.kind == .struct_ {
-								for embed_type in st_sym.struct_info().embeds {
-									embed_sym := g.table.sym(embed_type)
-									if _ := embed_sym.find_field(field.name) {
-										cast_struct.write_string(' + __offsetof_ptr(x, ${cctype}, ${embed_sym.embed_name()}) + __offsetof_ptr(x, ${embed_sym.cname}, ${cname})')
-										break
+								if _, embeds := g.table.find_field_from_embeds(st_sym,
+									field.name)
+								{
+									mut typ_name := ''
+									for i, embed in embeds {
+										esym := g.table.sym(embed)
+										if i == 0 {
+											cast_struct.write_string(' + __offsetof_ptr(x, ${cctype}, ${esym.embed_name()})')
+										} else {
+											cast_struct.write_string(' + __offsetof_ptr(x, ${typ_name}, ${esym.embed_name()})')
+										}
+										typ_name = esym.cname
+									}
+									if embeds.len > 0 {
+										cast_struct.write_string(' + __offsetof_ptr(x, ${typ_name}, ${cname})')
 									}
 								}
 							}

vlib/v/tests/interface_with_multi_nested_embed_3_test.v

@@ -0,0 +1,34 @@
+interface NodeInterface {
+mut:
+	node_type NodeType
+	node_name string
+}
+
+enum NodeType {
+	@none
+}
+
+struct Node {
+mut:
+	// removing this field works makes `InterfaceNode(x).node_name.len` below work as expected
+	node_type NodeType
+	node_name string
+}
+
+struct Element {
+	Node
+}
+
+struct HTMLElement {
+	Element
+}
+
+fn test_interface_with_multi_nested_embed() {
+	x := &HTMLElement{}
+	struct_name_len := x.node_name.len
+	interface_name_len := NodeInterface(x).node_name.len
+	println('struct: ${struct_name_len}')
+	assert struct_name_len == 0
+	println('interface: ${interface_name_len}')
+	assert interface_name_len == 0
+}