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 /// **Why is this bad?** This will cost resources (because the base has to be
12 /// somewhere), and make the code less readable.
14 /// **Known problems:** None.
23 /// # let zero_point = Point { x: 0, y: 0, z: 0 };
32 "using `Foo { ..base }` when there are no missing fields"
35 declare_lint_pass!(NeedlessUpdate => [NEEDLESS_UPDATE]);
37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessUpdate {
38 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
39 if let ExprKind::Struct(_, ref fields, Some(ref base)) = expr.kind {
40 let ty = cx.tables.expr_ty(expr);
41 if let ty::Adt(def, _) = ty.kind {
42 if fields.len() == def.non_enum_variant().fields.len() {
47 "struct update has no effect, all the fields in the struct have already been specified",