1 use crate::utils::span_lint;
2 use rustc::declare_lint_pass;
3 use rustc::hir::{Expr, ExprKind};
4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
6 use rustc_session::declare_tool_lint;
9 /// **What it does:** Checks for needlessly including a base struct on update
10 /// when all fields are changed anyway.
12 /// **Why is this bad?** This will cost resources (because the base has to be
13 /// somewhere), and make the code less readable.
15 /// **Known problems:** None.
24 /// # let zero_point = Point { x: 0, y: 0, z: 0 };
33 "using `Foo { ..base }` when there are no missing fields"
36 declare_lint_pass!(NeedlessUpdate => [NEEDLESS_UPDATE]);
38 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessUpdate {
39 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
40 if let ExprKind::Struct(_, ref fields, Some(ref base)) = expr.kind {
41 let ty = cx.tables.expr_ty(expr);
42 if let ty::Adt(def, _) = ty.kind {
43 if fields.len() == def.non_enum_variant().fields.len() {
48 "struct update has no effect, all the fields in the struct have already been specified",