1 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
2 use rustc_errors::Applicability;
4 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
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 &body_id in tcx.hir().krate().bodies.keys() {
13 let item_def_id = tcx.hir().body_owner_def_id(body_id);
14 let imports = tcx.used_trait_imports(item_def_id);
15 debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports);
16 used_trait_imports.extend(imports.iter());
19 let mut visitor = CheckVisitor { tcx, used_trait_imports };
20 tcx.hir().krate().visit_all_item_likes(&mut visitor);
22 unused_crates_lint(tcx);
25 impl ItemLikeVisitor<'v> for CheckVisitor<'tcx> {
26 fn visit_item(&mut self, item: &hir::Item<'_>) {
27 if item.vis.node.is_pub() || item.span.is_dummy() {
30 if let hir::ItemKind::Use(ref path, _) = item.kind {
31 self.check_import(item.hir_id, path.span);
35 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
37 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
40 struct CheckVisitor<'tcx> {
42 used_trait_imports: FxHashSet<LocalDefId>,
45 impl CheckVisitor<'tcx> {
46 fn check_import(&self, id: hir::HirId, span: Span) {
47 let def_id = self.tcx.hir().local_def_id(id);
48 if !self.tcx.maybe_unused_trait_import(def_id) {
52 if self.used_trait_imports.contains(&def_id) {
56 self.tcx.struct_span_lint_hir(lint::builtin::UNUSED_IMPORTS, id, span, |lint| {
57 let msg = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
58 format!("unused import: `{}`", snippet)
60 "unused import".to_owned()
62 lint.build(&msg).emit();
67 fn unused_crates_lint(tcx: TyCtxt<'_>) {
68 let lint = lint::builtin::UNUSED_EXTERN_CRATES;
70 // Collect first the crates that are completely unused. These we
71 // can always suggest removing (no matter which edition we are
73 let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx
74 .maybe_unused_extern_crates(LOCAL_CRATE)
76 .filter(|&&(def_id, _)| {
77 // The `def_id` here actually was calculated during resolution (at least
78 // at the time of this writing) and is being shipped to us via a side
79 // channel of the tcx. There may have been extra expansion phases,
80 // however, which ended up removing the `def_id` *after* expansion such
81 // as the `ReplaceBodyWithLoop` pass (which is a bit of a hack, but hey)
83 // As a result we need to verify that `def_id` is indeed still valid for
84 // our AST and actually present in the HIR map. If it's not there then
85 // there's safely nothing to warn about, and otherwise we carry on with
88 // Note that if we carry through to the `extern_mod_stmt_cnum` query
89 // below it'll cause a panic because `def_id` is actually bogus at this
90 // point in time otherwise.
91 if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() {
96 .filter(|&&(def_id, _)| {
97 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
98 !tcx.is_compiler_builtins(cnum)
99 && !tcx.is_panic_runtime(cnum)
100 && !tcx.has_global_allocator(cnum)
101 && !tcx.has_panic_handler(cnum)
107 // Collect all the extern crates (in a reliable order).
108 let mut crates_to_lint = vec![];
109 tcx.hir().krate().visit_all_item_likes(&mut CollectExternCrateVisitor {
111 crates_to_lint: &mut crates_to_lint,
114 for extern_crate in &crates_to_lint {
115 let def_id = extern_crate.def_id.expect_local();
116 let id = tcx.hir().local_def_id_to_hir_id(def_id);
117 let item = tcx.hir().expect_item(id);
119 // If the crate is fully unused, we suggest removing it altogether.
120 // We do this in any edition.
121 if extern_crate.warn_if_unused {
122 if let Some(&span) = unused_extern_crates.get(&def_id) {
123 tcx.struct_span_lint_hir(lint, id, span, |lint| {
124 // Removal suggestion span needs to include attributes (Issue #54400)
125 let span_with_attrs = tcx
126 .get_attrs(extern_crate.def_id)
128 .map(|attr| attr.span)
129 .fold(span, |acc, attr_span| acc.to(attr_span));
131 lint.build("unused extern crate")
132 .span_suggestion_short(
136 Applicability::MachineApplicable,
144 // If we are not in Rust 2018 edition, then we don't make any further
146 if !tcx.sess.rust_2018() {
150 // If the extern crate isn't in the extern prelude,
151 // there is no way it can be written as an `use`.
152 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
153 if !tcx.extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
157 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
158 // would not insert the new name into the prelude, where other imports in the crate may be
160 if extern_crate.orig_name.is_some() {
164 // If the extern crate has any attributes, they may have funky
165 // semantics we can't faithfully represent using `use` (most
166 // notably `#[macro_use]`). Ignore it.
167 if !tcx.get_attrs(extern_crate.def_id).is_empty() {
170 tcx.struct_span_lint_hir(lint, id, extern_crate.span, |lint| {
171 // Otherwise, we can convert it into a `use` of some kind.
172 let base_replacement = match extern_crate.orig_name {
173 Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
174 None => format!("use {};", item.ident.name),
176 let vis = tcx.sess.source_map().span_to_snippet(item.vis.span).unwrap_or_default();
177 let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
178 lint.build("`extern crate` is not idiomatic in the new edition")
179 .span_suggestion_short(
181 &format!("convert it to a `{}`", add_vis("use".to_string())),
182 add_vis(base_replacement),
183 Applicability::MachineApplicable,
190 struct CollectExternCrateVisitor<'a, 'tcx> {
192 crates_to_lint: &'a mut Vec<ExternCrateToLint>,
195 struct ExternCrateToLint {
196 /// `DefId` of the extern crate
199 /// span from the item
202 /// if `Some`, then this is renamed (`extern crate orig_name as
203 /// crate_name`), and -- perhaps surprisingly -- this stores the
204 /// *original* name (`item.name` will contain the new name)
205 orig_name: Option<Symbol>,
207 /// if `false`, the original name started with `_`, so we shouldn't lint
208 /// about it going unused (but we should still emit idiom lints).
209 warn_if_unused: bool,
212 impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for CollectExternCrateVisitor<'a, 'tcx> {
213 fn visit_item(&mut self, item: &hir::Item<'_>) {
214 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
215 let extern_crate_def_id = self.tcx.hir().local_def_id(item.hir_id);
216 self.crates_to_lint.push(ExternCrateToLint {
217 def_id: extern_crate_def_id.to_def_id(),
220 warn_if_unused: !item.ident.as_str().starts_with('_'),
225 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
227 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}