1 use clippy_utils::diagnostics::span_lint;
2 use rustc_hir::{Expr, ExprKind};
3 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// Checks for needlessly including a base struct on update
10 /// when all fields are changed anyway.
12 /// This lint is not applied to structs marked with
13 /// [non_exhaustive](https://doc.rust-lang.org/reference/attributes/type_system.html).
15 /// ### Why is this bad?
16 /// This will cost resources (because the base has to be
17 /// somewhere), and make the code less readable.
26 /// # let zero_point = Point { x: 0, y: 0, z: 0 };
43 #[clippy::version = "pre 1.29.0"]
46 "using `Foo { ..base }` when there are no missing fields"
49 declare_lint_pass!(NeedlessUpdate => [NEEDLESS_UPDATE]);
51 impl<'tcx> LateLintPass<'tcx> for NeedlessUpdate {
52 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
53 if let ExprKind::Struct(_, fields, Some(base)) = expr.kind {
54 let ty = cx.typeck_results().expr_ty(expr);
55 if let ty::Adt(def, _) = ty.kind() {
56 if fields.len() == def.non_enum_variant().fields.len()
57 && !def.variants[0_usize.into()].is_field_list_non_exhaustive()
63 "struct update has no effect, all the fields in the struct have already been specified",