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;
10 use crate::utils::{is_normalizable, is_type_diagnostic_item, match_type, paths, span_lint_and_help};
12 declare_clippy_lint! {
13 /// **What it does:** Checks for maps with zero-sized value types anywhere in the code.
15 /// **Why is this bad?** Since there is only a single value for a zero-sized type, a map
16 /// containing zero sized values is effectively a set. Using a set in that case improves
17 /// readability and communicates intent more clearly.
19 /// **Known problems:**
20 /// * A zero-sized type cannot be recovered later if it contains private fields.
21 /// * This lints the signature of public items
26 /// # use std::collections::HashMap;
27 /// fn unique_words(text: &str) -> HashMap<&str, ()> {
33 /// # use std::collections::HashSet;
34 /// fn unique_words(text: &str) -> HashSet<&str> {
38 pub ZERO_SIZED_MAP_VALUES,
40 "usage of map with zero-sized value type"
43 declare_lint_pass!(ZeroSizedMapValues => [ZERO_SIZED_MAP_VALUES]);
45 impl LateLintPass<'_> for ZeroSizedMapValues {
46 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>) {
48 if !hir_ty.span.from_expansion();
49 if !in_trait_impl(cx, hir_ty.hir_id);
50 let ty = ty_from_hir_ty(cx, hir_ty);
51 if is_type_diagnostic_item(cx, ty, sym::hashmap_type) || match_type(cx, ty, &paths::BTREEMAP);
52 if let Adt(_, ref substs) = ty.kind();
53 let ty = substs.type_at(1);
54 // Do this to prevent `layout_of` crashing, being unable to fully normalize `ty`.
55 if is_normalizable(cx, cx.param_env, ty);
56 if let Ok(layout) = cx.layout_of(ty);
59 span_lint_and_help(cx, ZERO_SIZED_MAP_VALUES, hir_ty.span, "map with zero-sized value type", None, "consider using a set instead");
65 fn in_trait_impl(cx: &LateContext<'_>, hir_id: HirId) -> bool {
66 let parent_id = cx.tcx.hir().get_parent_item(hir_id);
67 if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(parent_id)) {
68 if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
75 fn ty_from_hir_ty<'tcx>(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
76 cx.maybe_typeck_results()
78 if results.hir_owner == hir_ty.hir_id.owner {
79 results.node_type_opt(hir_ty.hir_id)
84 .unwrap_or_else(|| hir_ty_to_ty(cx.tcx, hir_ty))