4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_errors::Applicability;
7 use rustc_hir::def_id::{DefId, DefIdSet, LOCAL_CRATE};
8 use rustc_hir::itemlikevisit::ItemLikeVisitor;
9 use rustc_hir::print::visibility_qualified;
12 pub fn check_crate(tcx: TyCtxt<'_>) {
13 let mut used_trait_imports = DefIdSet::default();
14 for &body_id in tcx.hir().krate().bodies.keys() {
15 let item_def_id = tcx.hir().body_owner_def_id(body_id);
16 let imports = tcx.used_trait_imports(item_def_id);
17 debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports);
18 used_trait_imports.extend(imports.iter());
21 let mut visitor = CheckVisitor { tcx, used_trait_imports };
22 tcx.hir().krate().visit_all_item_likes(&mut visitor);
24 unused_crates_lint(tcx);
27 impl ItemLikeVisitor<'v> for CheckVisitor<'tcx> {
28 fn visit_item(&mut self, item: &hir::Item<'_>) {
29 if item.vis.node.is_pub() || item.span.is_dummy() {
32 if let hir::ItemKind::Use(ref path, _) = item.kind {
33 self.check_import(item.hir_id, path.span);
37 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
39 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
42 struct CheckVisitor<'tcx> {
44 used_trait_imports: DefIdSet,
47 impl CheckVisitor<'tcx> {
48 fn check_import(&self, id: hir::HirId, span: Span) {
49 let def_id = self.tcx.hir().local_def_id(id);
50 if !self.tcx.maybe_unused_trait_import(def_id) {
54 if self.used_trait_imports.contains(&def_id) {
58 self.tcx.struct_span_lint_hir(lint::builtin::UNUSED_IMPORTS, id, span, |lint| {
59 let msg = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
60 format!("unused import: `{}`", snippet)
62 "unused import".to_owned()
64 lint.build(&msg).emit();
69 fn unused_crates_lint(tcx: TyCtxt<'_>) {
70 let lint = lint::builtin::UNUSED_EXTERN_CRATES;
72 // Collect first the crates that are completely unused. These we
73 // can always suggest removing (no matter which edition we are
75 let unused_extern_crates: FxHashMap<DefId, Span> = tcx
76 .maybe_unused_extern_crates(LOCAL_CRATE)
78 .filter(|&&(def_id, _)| {
79 // The `def_id` here actually was calculated during resolution (at least
80 // at the time of this writing) and is being shipped to us via a side
81 // channel of the tcx. There may have been extra expansion phases,
82 // however, which ended up removing the `def_id` *after* expansion such
83 // as the `ReplaceBodyWithLoop` pass (which is a bit of a hack, but hey)
85 // As a result we need to verify that `def_id` is indeed still valid for
86 // our AST and actually present in the HIR map. If it's not there then
87 // there's safely nothing to warn about, and otherwise we carry on with
90 // Note that if we carry through to the `extern_mod_stmt_cnum` query
91 // below it'll cause a panic because `def_id` is actually bogus at this
92 // point in time otherwise.
93 if let Some(id) = tcx.hir().as_local_hir_id(def_id) {
94 if tcx.hir().find(id).is_none() {
100 .filter(|&&(def_id, _)| {
101 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
102 !tcx.is_compiler_builtins(cnum)
103 && !tcx.is_panic_runtime(cnum)
104 && !tcx.has_global_allocator(cnum)
105 && !tcx.has_panic_handler(cnum)
111 // Collect all the extern crates (in a reliable order).
112 let mut crates_to_lint = vec![];
113 tcx.hir().krate().visit_all_item_likes(&mut CollectExternCrateVisitor {
115 crates_to_lint: &mut crates_to_lint,
118 for extern_crate in &crates_to_lint {
119 let id = tcx.hir().as_local_hir_id(extern_crate.def_id).unwrap();
120 let item = tcx.hir().expect_item(id);
122 // If the crate is fully unused, we suggest removing it altogether.
123 // We do this in any edition.
124 if extern_crate.warn_if_unused {
125 if let Some(&span) = unused_extern_crates.get(&extern_crate.def_id) {
126 tcx.struct_span_lint_hir(lint, id, span, |lint| {
127 // Removal suggestion span needs to include attributes (Issue #54400)
128 let span_with_attrs = tcx
129 .get_attrs(extern_crate.def_id)
131 .map(|attr| attr.span)
132 .fold(span, |acc, attr_span| acc.to(attr_span));
134 lint.build("unused extern crate")
135 .span_suggestion_short(
139 Applicability::MachineApplicable,
147 // If we are not in Rust 2018 edition, then we don't make any further
149 if !tcx.sess.rust_2018() {
153 // If the extern crate isn't in the extern prelude,
154 // there is no way it can be written as an `use`.
155 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
156 if !tcx.extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
160 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
161 // would not insert the new name into the prelude, where other imports in the crate may be
163 if extern_crate.orig_name.is_some() {
167 // If the extern crate has any attributes, they may have funky
168 // semantics we can't faithfully represent using `use` (most
169 // notably `#[macro_use]`). Ignore it.
170 if !tcx.get_attrs(extern_crate.def_id).is_empty() {
173 tcx.struct_span_lint_hir(lint, id, extern_crate.span, |lint| {
174 // Otherwise, we can convert it into a `use` of some kind.
175 let base_replacement = match extern_crate.orig_name {
176 Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
177 None => format!("use {};", item.ident.name),
180 let replacement = visibility_qualified(&item.vis, base_replacement);
181 let msg = "`extern crate` is not idiomatic in the new edition";
182 let help = format!("convert it to a `{}`", visibility_qualified(&item.vis, "use"));
185 .span_suggestion_short(
189 Applicability::MachineApplicable,
196 struct CollectExternCrateVisitor<'a, 'tcx> {
198 crates_to_lint: &'a mut Vec<ExternCrateToLint>,
201 struct ExternCrateToLint {
202 /// `DefId` of the extern crate
205 /// span from the item
208 /// if `Some`, then this is renamed (`extern crate orig_name as
209 /// crate_name`), and -- perhaps surprisingly -- this stores the
210 /// *original* name (`item.name` will contain the new name)
211 orig_name: Option<ast::Name>,
213 /// if `false`, the original name started with `_`, so we shouldn't lint
214 /// about it going unused (but we should still emit idiom lints).
215 warn_if_unused: bool,
218 impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for CollectExternCrateVisitor<'a, 'tcx> {
219 fn visit_item(&mut self, item: &hir::Item<'_>) {
220 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
221 let extern_crate_def_id = self.tcx.hir().local_def_id(item.hir_id);
222 self.crates_to_lint.push(ExternCrateToLint {
223 def_id: extern_crate_def_id,
226 warn_if_unused: !item.ident.as_str().starts_with('_'),
231 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
233 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}