1 use if_chain::if_chain;
2 use rustc_hir::{self as hir, HirId, ItemKind, Node};
3 use rustc_lint::{LateContext, LateLintPass};
4 use rustc_middle::ty::{Adt, Ty};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
6 use rustc_target::abi::LayoutOf as _;
7 use rustc_typeck::hir_ty_to_ty;
9 use crate::utils::{is_type_diagnostic_item, match_type, paths, span_lint_and_help};
11 declare_clippy_lint! {
12 /// **What it does:** Checks for maps with zero-sized value types anywhere in the code.
14 /// **Why is this bad?** Since there is only a single value for a zero-sized type, a map
15 /// containing zero sized values is effectively a set. Using a set in that case improves
16 /// readability and communicates intent more clearly.
18 /// **Known problems:**
19 /// * A zero-sized type cannot be recovered later if it contains private fields.
20 /// * This lints the signature of public items
25 /// # use std::collections::HashMap;
26 /// fn unique_words(text: &str) -> HashMap<&str, ()> {
32 /// # use std::collections::HashSet;
33 /// fn unique_words(text: &str) -> HashSet<&str> {
37 pub ZERO_SIZED_MAP_VALUES,
39 "usage of map with zero-sized value type"
42 declare_lint_pass!(ZeroSizedMapValues => [ZERO_SIZED_MAP_VALUES]);
44 impl LateLintPass<'_> for ZeroSizedMapValues {
45 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>) {
47 if !hir_ty.span.from_expansion();
48 if !in_trait_impl(cx, hir_ty.hir_id);
49 let ty = ty_from_hir_ty(cx, hir_ty);
50 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP);
51 if let Adt(_, ref substs) = ty.kind();
52 let ty = substs.type_at(1);
53 if let Ok(layout) = cx.layout_of(ty);
56 span_lint_and_help(cx, ZERO_SIZED_MAP_VALUES, hir_ty.span, "map with zero-sized value type", None, "consider using a set instead");
62 fn in_trait_impl(cx: &LateContext<'_>, hir_id: HirId) -> bool {
63 let parent_id = cx.tcx.hir().get_parent_item(hir_id);
64 if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(parent_id)) {
65 if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
72 fn ty_from_hir_ty<'tcx>(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
73 cx.maybe_typeck_results()
75 if results.hir_owner == hir_ty.hir_id.owner {
76 results.node_type_opt(hir_ty.hir_id)
81 .unwrap_or_else(|| hir_ty_to_ty(cx.tcx, hir_ty))