1 use crate::utils::span_lint;
2 use rustc::hir::{Expr, ExprKind};
3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
5 use rustc::{declare_tool_lint, lint_array};
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.
26 "using `Foo { ..base }` when there are no missing fields"
29 #[derive(Copy, Clone)]
32 impl LintPass for Pass {
33 fn get_lints(&self) -> LintArray {
34 lint_array!(NEEDLESS_UPDATE)
37 fn name(&self) -> &'static str {
42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
43 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
44 if let ExprKind::Struct(_, ref fields, Some(ref base)) = expr.node {
45 let ty = cx.tables.expr_ty(expr);
46 if let ty::Adt(def, _) = ty.sty {
47 if fields.len() == def.non_enum_variant().fields.len() {
52 "struct update has no effect, all the fields in the struct have already been specified",