checker: fix generic fn with assign reference generic struct (fix #10681) (#10695)

vlib/v/checker/checker.v

@@ -3390,6 +3390,7 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 		c.expected_type = ast.void_type
 	}
 	right_first := node.right[0]
+	node.left_types = []
 	mut right_len := node.right.len
 	mut right_type0 := ast.void_type
 	for i, right in node.right {
@@ -3477,6 +3478,16 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 		}
 		right := if i < node.right.len { node.right[i] } else { node.right[0] }
 		mut right_type := node.right_types[i]
+		if right is ast.Ident {
+			right_sym := c.table.get_type_symbol(right_type)
+			if right_sym.info is ast.Struct {
+				if right_sym.info.generic_types.len > 0 {
+					if obj := right.scope.find(right.name) {
+						right_type = obj.typ
+					}
+				}
+			}
+		}
 		if is_decl {
 			// check generic struct init and return unwrap generic struct type
 			if right is ast.StructInit {
@@ -3484,6 +3495,10 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 					c.expr(right)
 					right_type = right.typ
 				}
+			} else if right is ast.PrefixExpr {
+				if right.op == .amp && right.right is ast.StructInit {
+					right_type = c.expr(right)
+				}
 			}
 			if right.is_auto_deref_var() {
 				left_type = c.table.mktyp(right_type.deref())

vlib/v/gen/c/cgen.v

@@ -2620,8 +2620,27 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 					if is_inside_ternary {
 						g.out.write_string(util.tabs(g.indent - g.inside_ternary))
 					}
+					mut is_used_var_styp := false
 					if ident.name !in g.defer_vars {
+						val_sym := g.table.get_type_symbol(val_type)
+						if val_sym.info is ast.Struct {
+							if val_sym.info.generic_types.len > 0 {
+								if val is ast.StructInit {
+									var_styp := g.typ(val.typ)
+									g.write('$var_styp ')
+									is_used_var_styp = true
+								} else if val is ast.PrefixExpr {
+									if val.op == .amp && val.right is ast.StructInit {
+										var_styp := g.typ(val.right.typ.to_ptr())
+										g.write('$var_styp ')
+										is_used_var_styp = true
+									}
+								}
+							}
+						}
+						if !is_used_var_styp {
 							g.write('$styp ')
+						}
 						if is_auto_heap {
 							g.write('*')
 						}

vlib/v/tests/generics_assign_reference_generic_struct_test.v

@@ -0,0 +1,46 @@
+pub struct List<T> {
+pub mut:
+	head &ListNode<T> = 0
+}
+
+pub struct ListNode<T> {
+pub mut:
+	value T
+	next  &ListNode<T> = 0
+}
+
+pub fn list_new<T>() List<T> {
+	return List<T>{}
+}
+
+pub fn (mut l List<T>) add(value T) {
+	mut node := &ListNode<T>{value, 0}
+	if l.head == 0 {
+		l.head = node
+	} else {
+		node.next = l.head
+		l.head = node
+	}
+}
+
+fn test_generic_assign_reference_generic_struct() {
+	mut list1 := list_new<string>()
+	list1.add('hello')
+	println(list1.head.value)
+	assert list1.head.value == 'hello'
+
+	mut list2 := list_new<int>()
+	list2.add(100)
+	println(list2.head.value)
+	assert list2.head.value == 100
+
+	mut list3 := list_new<f64>()
+	list3.add(22.2)
+	println(list3.head.value)
+	assert list3.head.value == 22.2
+
+	mut list4 := list_new<bool>()
+	list4.add(true)
+	println(list4.head.value)
+	assert list4.head.value == true
+}