1 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
2 use rustc_errors::Applicability;
4 use rustc_hir::def_id::{DefId, LocalDefId};
5 use rustc_hir::itemlikevisit::ItemLikeVisitor;
6 use rustc_middle::ty::TyCtxt;
7 use rustc_session::lint;
8 use rustc_span::{Span, Symbol};
10 pub fn check_crate(tcx: TyCtxt<'_>) {
11 let mut used_trait_imports = FxHashSet::default();
12 for item_def_id in tcx.hir().body_owners() {
13 let imports = tcx.used_trait_imports(item_def_id);
14 debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports);
15 used_trait_imports.extend(imports.iter());
18 let mut visitor = CheckVisitor { tcx, used_trait_imports };
20 for id in tcx.hir().items() {
21 let item = tcx.hir().item(id);
22 visitor.visit_item(item);
25 unused_crates_lint(tcx);
28 impl<'tcx> ItemLikeVisitor<'_> for CheckVisitor<'tcx> {
29 fn visit_item(&mut self, item: &hir::Item<'_>) {
30 if item.vis.node.is_pub() || item.span.is_dummy() {
33 if let hir::ItemKind::Use(path, _) = item.kind {
34 self.check_import(item.item_id(), path.span);
38 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
40 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
42 fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {}
45 struct CheckVisitor<'tcx> {
47 used_trait_imports: FxHashSet<LocalDefId>,
50 impl<'tcx> CheckVisitor<'tcx> {
51 fn check_import(&self, item_id: hir::ItemId, span: Span) {
52 if !self.tcx.maybe_unused_trait_import(item_id.def_id) {
56 if self.used_trait_imports.contains(&item_id.def_id) {
60 self.tcx.struct_span_lint_hir(
61 lint::builtin::UNUSED_IMPORTS,
65 let msg = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
66 format!("unused import: `{}`", snippet)
68 "unused import".to_owned()
70 lint.build(&msg).emit();
76 fn unused_crates_lint(tcx: TyCtxt<'_>) {
77 let lint = lint::builtin::UNUSED_EXTERN_CRATES;
79 // Collect first the crates that are completely unused. These we
80 // can always suggest removing (no matter which edition we are
82 let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx
83 .maybe_unused_extern_crates(())
85 .filter(|&&(def_id, _)| {
86 // The `def_id` here actually was calculated during resolution (at least
87 // at the time of this writing) and is being shipped to us via a side
88 // channel of the tcx. There may have been extra expansion phases,
89 // however, which ended up removing the `def_id` *after* expansion.
91 // As a result we need to verify that `def_id` is indeed still valid for
92 // our AST and actually present in the HIR map. If it's not there then
93 // there's safely nothing to warn about, and otherwise we carry on with
96 // Note that if we carry through to the `extern_mod_stmt_cnum` query
97 // below it'll cause a panic because `def_id` is actually bogus at this
98 // point in time otherwise.
99 if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() {
104 .filter(|&&(def_id, _)| {
105 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
106 !tcx.is_compiler_builtins(cnum)
107 && !tcx.is_panic_runtime(cnum)
108 && !tcx.has_global_allocator(cnum)
109 && !tcx.has_panic_handler(cnum)
115 // Collect all the extern crates (in a reliable order).
116 let mut crates_to_lint = vec![];
117 let mut visitor = CollectExternCrateVisitor { crates_to_lint: &mut crates_to_lint };
119 for id in tcx.hir().items() {
120 let item = tcx.hir().item(id);
121 visitor.visit_item(item);
124 let extern_prelude = &tcx.resolutions(()).extern_prelude;
126 for extern_crate in &crates_to_lint {
127 let def_id = extern_crate.def_id.expect_local();
128 let item = tcx.hir().expect_item(def_id);
130 // If the crate is fully unused, we suggest removing it altogether.
131 // We do this in any edition.
132 if extern_crate.warn_if_unused {
133 if let Some(&span) = unused_extern_crates.get(&def_id) {
134 let id = tcx.hir().local_def_id_to_hir_id(def_id);
135 tcx.struct_span_lint_hir(lint, id, span, |lint| {
136 // Removal suggestion span needs to include attributes (Issue #54400)
137 let span_with_attrs = tcx
138 .get_attrs(extern_crate.def_id)
140 .map(|attr| attr.span)
141 .fold(span, |acc, attr_span| acc.to(attr_span));
143 lint.build("unused extern crate")
144 .span_suggestion_short(
148 Applicability::MachineApplicable,
156 // If we are not in Rust 2018 edition, then we don't make any further
158 if !tcx.sess.rust_2018() {
162 // If the extern crate isn't in the extern prelude,
163 // there is no way it can be written as a `use`.
164 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
165 if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
169 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
170 // would not insert the new name into the prelude, where other imports in the crate may be
172 if extern_crate.orig_name.is_some() {
176 // If the extern crate has any attributes, they may have funky
177 // semantics we can't faithfully represent using `use` (most
178 // notably `#[macro_use]`). Ignore it.
179 if !tcx.get_attrs(extern_crate.def_id).is_empty() {
182 let id = tcx.hir().local_def_id_to_hir_id(def_id);
183 tcx.struct_span_lint_hir(lint, id, extern_crate.span, |lint| {
184 // Otherwise, we can convert it into a `use` of some kind.
185 let base_replacement = match extern_crate.orig_name {
186 Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
187 None => format!("use {};", item.ident.name),
189 let vis = tcx.sess.source_map().span_to_snippet(item.vis.span).unwrap_or_default();
190 let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
191 lint.build("`extern crate` is not idiomatic in the new edition")
192 .span_suggestion_short(
194 &format!("convert it to a `{}`", add_vis("use".to_string())),
195 add_vis(base_replacement),
196 Applicability::MachineApplicable,
203 struct CollectExternCrateVisitor<'a> {
204 crates_to_lint: &'a mut Vec<ExternCrateToLint>,
207 struct ExternCrateToLint {
208 /// `DefId` of the extern crate
211 /// span from the item
214 /// if `Some`, then this is renamed (`extern crate orig_name as
215 /// crate_name`), and -- perhaps surprisingly -- this stores the
216 /// *original* name (`item.name` will contain the new name)
217 orig_name: Option<Symbol>,
219 /// if `false`, the original name started with `_`, so we shouldn't lint
220 /// about it going unused (but we should still emit idiom lints).
221 warn_if_unused: bool,
224 impl<'a, 'v> ItemLikeVisitor<'v> for CollectExternCrateVisitor<'a> {
225 fn visit_item(&mut self, item: &hir::Item<'_>) {
226 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
227 self.crates_to_lint.push(ExternCrateToLint {
228 def_id: item.def_id.to_def_id(),
231 warn_if_unused: !item.ident.as_str().starts_with('_'),
236 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
238 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
240 fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {}