1 use crate::errors::{ExternCrateNotIdiomatic, UnusedExternCrate};
2 use rustc_data_structures::fx::FxHashMap;
3 use rustc_data_structures::unord::UnordSet;
5 use rustc_hir::def::DefKind;
6 use rustc_hir::def_id::{DefId, LocalDefId};
7 use rustc_middle::ty::TyCtxt;
8 use rustc_session::lint;
9 use rustc_span::{Span, Symbol};
11 pub fn check_crate(tcx: TyCtxt<'_>) {
12 let mut used_trait_imports: UnordSet<LocalDefId> = Default::default();
14 for item_def_id in tcx.hir().body_owners() {
15 let imports = tcx.used_trait_imports(item_def_id);
16 debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports);
17 used_trait_imports.extend(imports.items().copied());
20 for &id in tcx.maybe_unused_trait_imports(()) {
21 debug_assert_eq!(tcx.def_kind(id), DefKind::Use);
22 if tcx.visibility(id).is_public() {
25 if used_trait_imports.contains(&id) {
28 let item = tcx.hir().expect_item(id);
29 if item.span.is_dummy() {
32 let hir::ItemKind::Use(path, _) = item.kind else { unreachable!() };
33 let msg = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(path.span) {
34 format!("unused import: `{}`", snippet)
36 "unused import".to_owned()
38 tcx.struct_span_lint_hir(
39 lint::builtin::UNUSED_IMPORTS,
47 unused_crates_lint(tcx);
50 fn unused_crates_lint(tcx: TyCtxt<'_>) {
51 let lint = lint::builtin::UNUSED_EXTERN_CRATES;
53 // Collect first the crates that are completely unused. These we
54 // can always suggest removing (no matter which edition we are
56 let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx
57 .maybe_unused_extern_crates(())
59 .filter(|&&(def_id, _)| {
60 // The `def_id` here actually was calculated during resolution (at least
61 // at the time of this writing) and is being shipped to us via a side
62 // channel of the tcx. There may have been extra expansion phases,
63 // however, which ended up removing the `def_id` *after* expansion.
65 // As a result we need to verify that `def_id` is indeed still valid for
66 // our AST and actually present in the HIR map. If it's not there then
67 // there's safely nothing to warn about, and otherwise we carry on with
70 // Note that if we carry through to the `extern_mod_stmt_cnum` query
71 // below it'll cause a panic because `def_id` is actually bogus at this
72 // point in time otherwise.
73 if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() {
78 .filter(|&&(def_id, _)| {
79 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
80 !tcx.is_compiler_builtins(cnum)
81 && !tcx.is_panic_runtime(cnum)
82 && !tcx.has_global_allocator(cnum)
83 && !tcx.has_panic_handler(cnum)
89 // Collect all the extern crates (in a reliable order).
90 let mut crates_to_lint = vec![];
92 for id in tcx.hir().items() {
93 if matches!(tcx.def_kind(id.def_id), DefKind::ExternCrate) {
94 let item = tcx.hir().item(id);
95 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
96 crates_to_lint.push(ExternCrateToLint {
97 def_id: item.def_id.to_def_id(),
100 warn_if_unused: !item.ident.as_str().starts_with('_'),
106 let extern_prelude = &tcx.resolutions(()).extern_prelude;
108 for extern_crate in &crates_to_lint {
109 let def_id = extern_crate.def_id.expect_local();
110 let item = tcx.hir().expect_item(def_id);
112 // If the crate is fully unused, we suggest removing it altogether.
113 // We do this in any edition.
114 if extern_crate.warn_if_unused {
115 if let Some(&span) = unused_extern_crates.get(&def_id) {
116 // Removal suggestion span needs to include attributes (Issue #54400)
117 let id = tcx.hir().local_def_id_to_hir_id(def_id);
118 let span_with_attrs = tcx
122 .map(|attr| attr.span)
123 .fold(span, |acc, attr_span| acc.to(attr_span));
125 tcx.emit_spanned_lint(lint, id, span, UnusedExternCrate { span: span_with_attrs });
130 // If we are not in Rust 2018 edition, then we don't make any further
132 if !tcx.sess.rust_2018() {
136 // If the extern crate isn't in the extern prelude,
137 // there is no way it can be written as a `use`.
138 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
139 if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
143 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
144 // would not insert the new name into the prelude, where other imports in the crate may be
146 if extern_crate.orig_name.is_some() {
150 let id = tcx.hir().local_def_id_to_hir_id(def_id);
151 // If the extern crate has any attributes, they may have funky
152 // semantics we can't faithfully represent using `use` (most
153 // notably `#[macro_use]`). Ignore it.
154 if !tcx.hir().attrs(id).is_empty() {
158 let base_replacement = match extern_crate.orig_name {
159 Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
160 None => format!("use {};", item.ident.name),
162 let vis = tcx.sess.source_map().span_to_snippet(item.vis_span).unwrap_or_default();
163 let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
164 tcx.emit_spanned_lint(
168 ExternCrateNotIdiomatic {
169 span: extern_crate.span,
170 msg_code: add_vis("use".to_string()),
171 suggestion_code: add_vis(base_replacement),
177 struct ExternCrateToLint {
178 /// `DefId` of the extern crate
181 /// span from the item
184 /// if `Some`, then this is renamed (`extern crate orig_name as
185 /// crate_name`), and -- perhaps surprisingly -- this stores the
186 /// *original* name (`item.name` will contain the new name)
187 orig_name: Option<Symbol>,
189 /// if `false`, the original name started with `_`, so we shouldn't lint
190 /// about it going unused (but we should still emit idiom lints).
191 warn_if_unused: bool,