2 // Unused import checking
4 // Although this is mostly a lint pass, it lives in here because it depends on
5 // resolve data structures and because it finalises the privacy information for
8 // Unused trait imports can't be checked until the method resolution. We save
9 // candidates here, and do the actual check in librustc_typeck/check_unused.rs.
11 // Checking for unused imports is split into three steps:
13 // - `UnusedImportCheckVisitor` walks the AST to find all the unused imports
14 // inside of `UseTree`s, recording their `NodeId`s and grouping them by
15 // the parent `use` item
17 // - `calc_unused_spans` then walks over all the `use` items marked in the
18 // previous step to collect the spans associated with the `NodeId`s and to
19 // calculate the spans that can be removed by rustfix; This is done in a
20 // separate step to be able to collapse the adjacent spans that rustfix
23 // - `check_crate` finally emits the diagnostics based on the data generated
26 use crate::imports::ImportKind;
30 use rustc_ast::node_id::NodeMap;
31 use rustc_ast::visit::{self, Visitor};
32 use rustc_ast_lowering::ResolverAstLowering;
33 use rustc_data_structures::fx::FxHashSet;
34 use rustc_errors::pluralize;
36 use rustc_session::lint::builtin::{MACRO_USE_EXTERN_CRATE, UNUSED_IMPORTS};
37 use rustc_session::lint::BuiltinLintDiagnostics;
38 use rustc_span::{MultiSpan, Span, DUMMY_SP};
40 struct UnusedImport<'a> {
41 use_tree: &'a ast::UseTree,
42 use_tree_id: ast::NodeId,
44 unused: FxHashSet<ast::NodeId>,
47 impl<'a> UnusedImport<'a> {
48 fn add(&mut self, id: ast::NodeId) {
49 self.unused.insert(id);
53 struct UnusedImportCheckVisitor<'a, 'b> {
54 r: &'a mut Resolver<'b>,
55 /// All the (so far) unused imports, grouped path list
56 unused_imports: NodeMap<UnusedImport<'a>>,
57 base_use_tree: Option<&'a ast::UseTree>,
62 impl<'a, 'b> UnusedImportCheckVisitor<'a, 'b> {
63 // We have information about whether `use` (import) items are actually
64 // used now. If an import is not used at all, we signal a lint error.
65 fn check_import(&mut self, id: ast::NodeId) {
67 self.r.per_ns(|this, ns| used |= this.used_imports.contains(&(id, ns)));
68 let def_id = self.r.local_def_id(id);
70 if self.r.maybe_unused_trait_imports.contains(&def_id) {
74 self.unused_import(self.base_id).add(id);
76 // This trait import is definitely used, in a way other than
78 self.r.maybe_unused_trait_imports.remove(&def_id);
79 if let Some(i) = self.unused_imports.get_mut(&self.base_id) {
85 fn unused_import(&mut self, id: ast::NodeId) -> &mut UnusedImport<'a> {
86 let use_tree_id = self.base_id;
87 let use_tree = self.base_use_tree.unwrap();
88 let item_span = self.item_span;
90 self.unused_imports.entry(id).or_insert_with(|| UnusedImport {
94 unused: FxHashSet::default(),
99 impl<'a, 'b> Visitor<'a> for UnusedImportCheckVisitor<'a, 'b> {
100 fn visit_item(&mut self, item: &'a ast::Item) {
101 self.item_span = item.span;
103 // Ignore is_public import statements because there's no way to be sure
104 // whether they're used or not. Also ignore imports with a dummy span
105 // because this means that they were generated in some fashion by the
106 // compiler and we don't need to consider them.
107 if let ast::ItemKind::Use(..) = item.kind {
108 if item.vis.kind.is_pub() || item.span.is_dummy() {
113 visit::walk_item(self, item);
116 fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: ast::NodeId, nested: bool) {
117 // Use the base UseTree's NodeId as the item id
118 // This allows the grouping of all the lints in the same item
121 self.base_use_tree = Some(use_tree);
124 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
125 if items.is_empty() {
126 self.unused_import(self.base_id).add(id);
129 self.check_import(id);
132 visit::walk_use_tree(self, use_tree, id);
136 enum UnusedSpanResult {
138 FlatUnused(Span, Span),
139 NestedFullUnused(Vec<Span>, Span),
140 NestedPartialUnused(Vec<Span>, Vec<Span>),
143 fn calc_unused_spans(
144 unused_import: &UnusedImport<'_>,
145 use_tree: &ast::UseTree,
146 use_tree_id: ast::NodeId,
147 ) -> UnusedSpanResult {
148 // The full span is the whole item's span if this current tree is not nested inside another
149 // This tells rustfix to remove the whole item if all the imports are unused
150 let full_span = if unused_import.use_tree.span == use_tree.span {
151 unused_import.item_span
155 match use_tree.kind {
156 ast::UseTreeKind::Simple(..) | ast::UseTreeKind::Glob => {
157 if unused_import.unused.contains(&use_tree_id) {
158 UnusedSpanResult::FlatUnused(use_tree.span, full_span)
160 UnusedSpanResult::Used
163 ast::UseTreeKind::Nested(ref nested) => {
164 if nested.is_empty() {
165 return UnusedSpanResult::FlatUnused(use_tree.span, full_span);
168 let mut unused_spans = Vec::new();
169 let mut to_remove = Vec::new();
170 let mut all_nested_unused = true;
171 let mut previous_unused = false;
172 for (pos, (use_tree, use_tree_id)) in nested.iter().enumerate() {
173 let remove = match calc_unused_spans(unused_import, use_tree, *use_tree_id) {
174 UnusedSpanResult::Used => {
175 all_nested_unused = false;
178 UnusedSpanResult::FlatUnused(span, remove) => {
179 unused_spans.push(span);
182 UnusedSpanResult::NestedFullUnused(mut spans, remove) => {
183 unused_spans.append(&mut spans);
186 UnusedSpanResult::NestedPartialUnused(mut spans, mut to_remove_extra) => {
187 all_nested_unused = false;
188 unused_spans.append(&mut spans);
189 to_remove.append(&mut to_remove_extra);
193 if let Some(remove) = remove {
194 let remove_span = if nested.len() == 1 {
196 } else if pos == nested.len() - 1 || !all_nested_unused {
197 // Delete everything from the end of the last import, to delete the
199 nested[pos - 1].0.span.shrink_to_hi().to(use_tree.span)
201 // Delete everything until the next import, to delete the trailing commas
202 use_tree.span.to(nested[pos + 1].0.span.shrink_to_lo())
205 // Try to collapse adjacent spans into a single one. This prevents all cases of
206 // overlapping removals, which are not supported by rustfix
207 if previous_unused && !to_remove.is_empty() {
208 let previous = to_remove.pop().unwrap();
209 to_remove.push(previous.to(remove_span));
211 to_remove.push(remove_span);
214 previous_unused = remove.is_some();
216 if unused_spans.is_empty() {
217 UnusedSpanResult::Used
218 } else if all_nested_unused {
219 UnusedSpanResult::NestedFullUnused(unused_spans, full_span)
221 UnusedSpanResult::NestedPartialUnused(unused_spans, to_remove)
228 crate fn check_unused(&mut self, krate: &ast::Crate) {
229 for import in self.potentially_unused_imports.iter() {
231 _ if import.used.get()
232 || import.vis.get() == ty::Visibility::Public
233 || import.span.is_dummy() =>
235 if let ImportKind::MacroUse = import.kind {
236 if !import.span.is_dummy() {
237 self.lint_buffer.buffer_lint(
238 MACRO_USE_EXTERN_CRATE,
241 "deprecated `#[macro_use]` attribute used to \
242 import macros should be replaced at use sites \
243 with a `use` item to import the macro \
249 ImportKind::ExternCrate { .. } => {
250 let def_id = self.local_def_id(import.id);
251 self.maybe_unused_extern_crates.push((def_id, import.span));
253 ImportKind::MacroUse => {
254 let msg = "unused `#[macro_use]` import";
255 self.lint_buffer.buffer_lint(UNUSED_IMPORTS, import.id, import.span, msg);
261 let mut visitor = UnusedImportCheckVisitor {
263 unused_imports: Default::default(),
265 base_id: ast::DUMMY_NODE_ID,
268 visit::walk_crate(&mut visitor, krate);
270 for unused in visitor.unused_imports.values() {
271 let mut fixes = Vec::new();
272 let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
273 UnusedSpanResult::Used => continue,
274 UnusedSpanResult::FlatUnused(span, remove) => {
275 fixes.push((remove, String::new()));
278 UnusedSpanResult::NestedFullUnused(spans, remove) => {
279 fixes.push((remove, String::new()));
282 UnusedSpanResult::NestedPartialUnused(spans, remove) => {
284 fixes.push((*fix, String::new()));
290 let len = spans.len();
292 let ms = MultiSpan::from_spans(spans.clone());
293 let mut span_snippets = spans
295 .filter_map(|s| match visitor.r.session.source_map().span_to_snippet(*s) {
296 Ok(s) => Some(format!("`{}`", s)),
299 .collect::<Vec<String>>();
300 span_snippets.sort();
304 if !span_snippets.is_empty() {
305 format!(": {}", span_snippets.join(", "))
311 let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
312 "remove the whole `use` item"
313 } else if spans.len() > 1 {
314 "remove the unused imports"
316 "remove the unused import"
319 visitor.r.lint_buffer.buffer_lint_with_diagnostic(
324 BuiltinLintDiagnostics::UnusedImports(fix_msg.into(), fixes),