1 use crate::utils::span_lint;
2 use rustc_hir::{Expr, ExprKind};
3 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
8 /// **What it does:** Checks for needlessly including a base struct on update
9 /// when all fields are changed anyway.
11 /// This lint is not applied to structs marked with
12 /// [non_exhaustive](https://doc.rust-lang.org/reference/attributes/type_system.html).
14 /// **Why is this bad?** This will cost resources (because the base has to be
15 /// somewhere), and make the code less readable.
17 /// **Known problems:** None.
26 /// # let zero_point = Point { x: 0, y: 0, z: 0 };
45 "using `Foo { ..base }` when there are no missing fields"
48 declare_lint_pass!(NeedlessUpdate => [NEEDLESS_UPDATE]);
50 impl<'tcx> LateLintPass<'tcx> for NeedlessUpdate {
51 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
52 if let ExprKind::Struct(_, ref fields, Some(ref base)) = expr.kind {
53 let ty = cx.typeck_results().expr_ty(expr);
54 if let ty::Adt(def, _) = ty.kind() {
55 if fields.len() == def.non_enum_variant().fields.len()
56 && !def.variants[0_usize.into()].is_field_list_non_exhaustive()
62 "struct update has no effect, all the fields in the struct have already been specified",