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 tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
61 !tcx.is_compiler_builtins(cnum)
62 && !tcx.is_panic_runtime(cnum)
63 && !tcx.has_global_allocator(cnum)
64 && !tcx.has_panic_handler(cnum)
70 // Collect all the extern crates (in a reliable order).
71 let mut crates_to_lint = vec![];
73 for id in tcx.hir().items() {
74 if matches!(tcx.def_kind(id.owner_id), DefKind::ExternCrate) {
75 let item = tcx.hir().item(id);
76 if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
77 crates_to_lint.push(ExternCrateToLint {
78 def_id: item.owner_id.to_def_id(),
81 warn_if_unused: !item.ident.as_str().starts_with('_'),
87 let extern_prelude = &tcx.resolutions(()).extern_prelude;
89 for extern_crate in &crates_to_lint {
90 let def_id = extern_crate.def_id.expect_local();
91 let item = tcx.hir().expect_item(def_id);
93 // If the crate is fully unused, we suggest removing it altogether.
94 // We do this in any edition.
95 if extern_crate.warn_if_unused {
96 if let Some(&span) = unused_extern_crates.get(&def_id) {
97 // Removal suggestion span needs to include attributes (Issue #54400)
98 let id = tcx.hir().local_def_id_to_hir_id(def_id);
99 let span_with_attrs = tcx
103 .map(|attr| attr.span)
104 .fold(span, |acc, attr_span| acc.to(attr_span));
106 tcx.emit_spanned_lint(lint, id, span, UnusedExternCrate { span: span_with_attrs });
111 // If we are not in Rust 2018 edition, then we don't make any further
113 if !tcx.sess.rust_2018() {
117 // If the extern crate isn't in the extern prelude,
118 // there is no way it can be written as a `use`.
119 let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
120 if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
124 // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
125 // would not insert the new name into the prelude, where other imports in the crate may be
127 if extern_crate.orig_name.is_some() {
131 let id = tcx.hir().local_def_id_to_hir_id(def_id);
132 // If the extern crate has any attributes, they may have funky
133 // semantics we can't faithfully represent using `use` (most
134 // notably `#[macro_use]`). Ignore it.
135 if !tcx.hir().attrs(id).is_empty() {
139 let base_replacement = match extern_crate.orig_name {
140 Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
141 None => format!("use {};", item.ident.name),
143 let vis = tcx.sess.source_map().span_to_snippet(item.vis_span).unwrap_or_default();
144 let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
145 tcx.emit_spanned_lint(
149 ExternCrateNotIdiomatic {
150 span: extern_crate.span,
151 msg_code: add_vis("use".to_string()),
152 suggestion_code: add_vis(base_replacement),
158 struct ExternCrateToLint {
159 /// `DefId` of the extern crate
162 /// span from the item
165 /// if `Some`, then this is renamed (`extern crate orig_name as
166 /// crate_name`), and -- perhaps surprisingly -- this stores the
167 /// *original* name (`item.name` will contain the new name)
168 orig_name: Option<Symbol>,
170 /// if `false`, the original name started with `_`, so we shouldn't lint
171 /// about it going unused (but we should still emit idiom lints).
172 warn_if_unused: bool,