checker: fix generics fn inferred structure type (fix #10093) (#10096)

vlib/v/checker/check_types.v

@@ -557,6 +557,13 @@ pub fn (mut c Checker) infer_fn_generic_types(f ast.Fn, mut call_expr ast.CallEx
 					}
 				} else if param.typ.has_flag(.variadic) {
 					to_set = c.table.mktyp(arg.typ)
+				} else if arg_sym.kind == .struct_ && param.typ.has_flag(.generic) {
+					info := arg_sym.info as ast.Struct
+					generic_names := info.generic_types.map(c.table.get_type_symbol(it).name)
+					if gt_name in generic_names {
+						idx := generic_names.index(gt_name)
+						typ = info.concrete_types[idx]
+					}
 				}
 			}
 

vlib/v/tests/generic_fn_infer_struct_test.v

@@ -0,0 +1,19 @@
+struct Node<T> {
+	data T
+}
+
+fn foo<T>(n Node<T>) string {
+	return '$n'
+}
+
+fn test_generics_fn_infer_struct() {
+	ret1 := foo(Node<int>{})
+	println(ret1)
+	assert ret1.contains('Node<int>{')
+	assert ret1.contains('data: 0')
+
+	ret2 := foo(Node<byte>{})
+	println(ret2)
+	assert ret2.contains('Node<byte>{')
+	assert ret2.contains('data: 0')
+}