1 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
2 use rustc_errors::Applicability;
4 use rustc_hir::def::DefKind;
5 use rustc_hir::def_id::{DefId, LocalDefId};
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<LocalDefId> = FxHashSet::default();
13 for item_def_id in tcx.hir().body_owners() {
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 for id in tcx.hir().items() {
20 if matches!(tcx.hir().def_kind(id.def_id), DefKind::Use) {
21 let item = tcx.hir().item(id);
22 if item.vis.node.is_pub() || item.span.is_dummy() {
25 if let hir::ItemKind::Use(path, _) = item.kind {
26 check_import(tcx, &mut used_trait_imports, item.item_id(), path.span);
31 unused_crates_lint(tcx);
34 fn check_import<'tcx>(
36 used_trait_imports: &mut FxHashSet<LocalDefId>,
40 if !tcx.maybe_unused_trait_import(item_id.def_id) {
44 if used_trait_imports.contains(&item_id.def_id) {
48 tcx.struct_span_lint_hir(lint::builtin::UNUSED_IMPORTS, item_id.hir_id(), span, |lint| {
49 let msg = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(span) {
50 format!("unused import: `{}`", snippet)
52 "unused import".to_owned()
54 lint.build(&msg).emit();
58 fn unused_crates_lint(tcx: TyCtxt<'_>) {
59 let lint = lint::builtin::UNUSED_EXTERN_CRATES;
61 // Collect first the crates that are completely unused. These we
62 // can always suggest removing (no matter which edition we are
64 let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx
65 .maybe_unused_extern_crates(())
67 .filter(|&&(def_id, _)| {
68 // The `def_id` here actually was calculated during resolution (at least
69 // at the time of this writing) and is being shipped to us via a side
70 // channel of the tcx. There may have been extra expansion phases,
71 // however, which ended up removing the `def_id` *after* expansion.
73 // As a result we need to verify that `def_id` is indeed still valid for
74 // our AST and actually present in the HIR map. If it's not there then
75 // there's safely nothing to warn about, and otherwise we carry on with
78 // Note that if we carry through to the `extern_mod_stmt_cnum` query
79 // below it'll cause a panic because `def_id` is actually bogus at this
80 // point in time otherwise.
81 if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() {
86 .filter(|&&(def_id, _)| {
87 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
88 !tcx.is_compiler_builtins(cnum)
89 && !tcx.is_panic_runtime(cnum)
90 && !tcx.has_global_allocator(cnum)
91 && !tcx.has_panic_handler(cnum)
97 // Collect all the extern crates (in a reliable order).
98 let mut crates_to_lint = vec![];
100 for id in tcx.hir().items() {
101 if matches!(tcx.hir().def_kind(id.def_id), DefKind::ExternCrate) {
102 let item = tcx.hir().item(id);
103 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
104 crates_to_lint.push(ExternCrateToLint {
105 def_id: item.def_id.to_def_id(),
108 warn_if_unused: !item.ident.as_str().starts_with('_'),
114 let extern_prelude = &tcx.resolutions(()).extern_prelude;
116 for extern_crate in &crates_to_lint {
117 let def_id = extern_crate.def_id.expect_local();
118 let item = tcx.hir().expect_item(def_id);
120 // If the crate is fully unused, we suggest removing it altogether.
121 // We do this in any edition.
122 if extern_crate.warn_if_unused {
123 if let Some(&span) = unused_extern_crates.get(&def_id) {
124 let id = tcx.hir().local_def_id_to_hir_id(def_id);
125 tcx.struct_span_lint_hir(lint, id, span, |lint| {
126 // Removal suggestion span needs to include attributes (Issue #54400)
127 let span_with_attrs = tcx
128 .get_attrs(extern_crate.def_id)
130 .map(|attr| attr.span)
131 .fold(span, |acc, attr_span| acc.to(attr_span));
133 lint.build("unused extern crate")
134 .span_suggestion_short(
138 Applicability::MachineApplicable,
146 // If we are not in Rust 2018 edition, then we don't make any further
148 if !tcx.sess.rust_2018() {
152 // If the extern crate isn't in the extern prelude,
153 // there is no way it can be written as a `use`.
154 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
155 if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
159 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
160 // would not insert the new name into the prelude, where other imports in the crate may be
162 if extern_crate.orig_name.is_some() {
166 // If the extern crate has any attributes, they may have funky
167 // semantics we can't faithfully represent using `use` (most
168 // notably `#[macro_use]`). Ignore it.
169 if !tcx.get_attrs(extern_crate.def_id).is_empty() {
172 let id = tcx.hir().local_def_id_to_hir_id(def_id);
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),
179 let vis = tcx.sess.source_map().span_to_snippet(item.vis.span).unwrap_or_default();
180 let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
181 lint.build("`extern crate` is not idiomatic in the new edition")
182 .span_suggestion_short(
184 &format!("convert it to a `{}`", add_vis("use".to_string())),
185 add_vis(base_replacement),
186 Applicability::MachineApplicable,
193 struct ExternCrateToLint {
194 /// `DefId` of the extern crate
197 /// span from the item
200 /// if `Some`, then this is renamed (`extern crate orig_name as
201 /// crate_name`), and -- perhaps surprisingly -- this stores the
202 /// *original* name (`item.name` will contain the new name)
203 orig_name: Option<Symbol>,
205 /// if `false`, the original name started with `_`, so we shouldn't lint
206 /// about it going unused (but we should still emit idiom lints).
207 warn_if_unused: bool,