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::ImportDirectiveSubclass;
29 use rustc::{lint, ty};
30 use rustc_data_structures::fx::FxHashSet;
31 use rustc_errors::pluralize;
32 use rustc_session::node_id::NodeMap;
33 use rustc_span::{MultiSpan, Span, DUMMY_SP};
35 use syntax::visit::{self, Visitor};
37 struct UnusedImport<'a> {
38 use_tree: &'a ast::UseTree,
39 use_tree_id: ast::NodeId,
41 unused: FxHashSet<ast::NodeId>,
44 impl<'a> UnusedImport<'a> {
45 fn add(&mut self, id: ast::NodeId) {
46 self.unused.insert(id);
50 struct UnusedImportCheckVisitor<'a, 'b> {
51 r: &'a mut Resolver<'b>,
52 /// All the (so far) unused imports, grouped path list
53 unused_imports: NodeMap<UnusedImport<'a>>,
54 base_use_tree: Option<&'a ast::UseTree>,
59 impl<'a, 'b> UnusedImportCheckVisitor<'a, 'b> {
60 // We have information about whether `use` (import) directives are actually
61 // used now. If an import is not used at all, we signal a lint error.
62 fn check_import(&mut self, id: ast::NodeId) {
64 self.r.per_ns(|this, ns| used |= this.used_imports.contains(&(id, ns)));
66 if self.r.maybe_unused_trait_imports.contains(&id) {
70 self.unused_import(self.base_id).add(id);
72 // This trait import is definitely used, in a way other than
74 self.r.maybe_unused_trait_imports.remove(&id);
75 if let Some(i) = self.unused_imports.get_mut(&self.base_id) {
81 fn unused_import(&mut self, id: ast::NodeId) -> &mut UnusedImport<'a> {
82 let use_tree_id = self.base_id;
83 let use_tree = self.base_use_tree.unwrap();
84 let item_span = self.item_span;
86 self.unused_imports.entry(id).or_insert_with(|| UnusedImport {
90 unused: FxHashSet::default(),
95 impl<'a, 'b> Visitor<'a> for UnusedImportCheckVisitor<'a, 'b> {
96 fn visit_item(&mut self, item: &'a ast::Item) {
97 self.item_span = item.span;
99 // Ignore is_public import statements because there's no way to be sure
100 // whether they're used or not. Also ignore imports with a dummy span
101 // because this means that they were generated in some fashion by the
102 // compiler and we don't need to consider them.
103 if let ast::ItemKind::Use(..) = item.kind {
104 if item.vis.node.is_pub() || item.span.is_dummy() {
109 visit::walk_item(self, item);
112 fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: ast::NodeId, nested: bool) {
113 // Use the base UseTree's NodeId as the item id
114 // This allows the grouping of all the lints in the same item
117 self.base_use_tree = Some(use_tree);
120 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
121 if items.is_empty() {
122 self.unused_import(self.base_id).add(id);
125 self.check_import(id);
128 visit::walk_use_tree(self, use_tree, id);
132 enum UnusedSpanResult {
134 FlatUnused(Span, Span),
135 NestedFullUnused(Vec<Span>, Span),
136 NestedPartialUnused(Vec<Span>, Vec<Span>),
139 fn calc_unused_spans(
140 unused_import: &UnusedImport<'_>,
141 use_tree: &ast::UseTree,
142 use_tree_id: ast::NodeId,
143 ) -> UnusedSpanResult {
144 // The full span is the whole item's span if this current tree is not nested inside another
145 // This tells rustfix to remove the whole item if all the imports are unused
146 let full_span = if unused_import.use_tree.span == use_tree.span {
147 unused_import.item_span
151 match use_tree.kind {
152 ast::UseTreeKind::Simple(..) | ast::UseTreeKind::Glob => {
153 if unused_import.unused.contains(&use_tree_id) {
154 UnusedSpanResult::FlatUnused(use_tree.span, full_span)
156 UnusedSpanResult::Used
159 ast::UseTreeKind::Nested(ref nested) => {
160 if nested.len() == 0 {
161 return UnusedSpanResult::FlatUnused(use_tree.span, full_span);
164 let mut unused_spans = Vec::new();
165 let mut to_remove = Vec::new();
166 let mut all_nested_unused = true;
167 let mut previous_unused = false;
168 for (pos, (use_tree, use_tree_id)) in nested.iter().enumerate() {
169 let remove = match calc_unused_spans(unused_import, use_tree, *use_tree_id) {
170 UnusedSpanResult::Used => {
171 all_nested_unused = false;
174 UnusedSpanResult::FlatUnused(span, remove) => {
175 unused_spans.push(span);
178 UnusedSpanResult::NestedFullUnused(mut spans, remove) => {
179 unused_spans.append(&mut spans);
182 UnusedSpanResult::NestedPartialUnused(mut spans, mut to_remove_extra) => {
183 all_nested_unused = false;
184 unused_spans.append(&mut spans);
185 to_remove.append(&mut to_remove_extra);
189 if let Some(remove) = remove {
190 let remove_span = if nested.len() == 1 {
192 } else if pos == nested.len() - 1 || !all_nested_unused {
193 // Delete everything from the end of the last import, to delete the
195 nested[pos - 1].0.span.shrink_to_hi().to(use_tree.span)
197 // Delete everything until the next import, to delete the trailing commas
198 use_tree.span.to(nested[pos + 1].0.span.shrink_to_lo())
201 // Try to collapse adjacent spans into a single one. This prevents all cases of
202 // overlapping removals, which are not supported by rustfix
203 if previous_unused && !to_remove.is_empty() {
204 let previous = to_remove.pop().unwrap();
205 to_remove.push(previous.to(remove_span));
207 to_remove.push(remove_span);
210 previous_unused = remove.is_some();
212 if unused_spans.is_empty() {
213 UnusedSpanResult::Used
214 } else if all_nested_unused {
215 UnusedSpanResult::NestedFullUnused(unused_spans, full_span)
217 UnusedSpanResult::NestedPartialUnused(unused_spans, to_remove)
224 crate fn check_unused(&mut self, krate: &ast::Crate) {
225 for directive in self.potentially_unused_imports.iter() {
226 match directive.subclass {
227 _ if directive.used.get()
228 || directive.vis.get() == ty::Visibility::Public
229 || directive.span.is_dummy() =>
231 if let ImportDirectiveSubclass::MacroUse = directive.subclass {
232 if !directive.span.is_dummy() {
233 self.lint_buffer.buffer_lint(
234 lint::builtin::MACRO_USE_EXTERN_CRATE,
237 "deprecated `#[macro_use]` directive used to \
238 import macros should be replaced at use sites \
239 with a `use` statement to import the macro \
245 ImportDirectiveSubclass::ExternCrate { .. } => {
246 self.maybe_unused_extern_crates.push((directive.id, directive.span));
248 ImportDirectiveSubclass::MacroUse => {
249 let lint = lint::builtin::UNUSED_IMPORTS;
250 let msg = "unused `#[macro_use]` import";
251 self.lint_buffer.buffer_lint(lint, directive.id, directive.span, msg);
257 let mut visitor = UnusedImportCheckVisitor {
259 unused_imports: Default::default(),
261 base_id: ast::DUMMY_NODE_ID,
264 visit::walk_crate(&mut visitor, krate);
266 for unused in visitor.unused_imports.values() {
267 let mut fixes = Vec::new();
268 let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
269 UnusedSpanResult::Used => continue,
270 UnusedSpanResult::FlatUnused(span, remove) => {
271 fixes.push((remove, String::new()));
274 UnusedSpanResult::NestedFullUnused(spans, remove) => {
275 fixes.push((remove, String::new()));
278 UnusedSpanResult::NestedPartialUnused(spans, remove) => {
280 fixes.push((*fix, String::new()));
286 let len = spans.len();
288 let ms = MultiSpan::from_spans(spans.clone());
289 let mut span_snippets = spans
291 .filter_map(|s| match visitor.r.session.source_map().span_to_snippet(*s) {
292 Ok(s) => Some(format!("`{}`", s)),
295 .collect::<Vec<String>>();
296 span_snippets.sort();
300 if !span_snippets.is_empty() {
301 format!(": {}", span_snippets.join(", "))
307 let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
308 "remove the whole `use` item"
309 } else if spans.len() > 1 {
310 "remove the unused imports"
312 "remove the unused import"
315 visitor.r.lint_buffer.buffer_lint_with_diagnostic(
316 lint::builtin::UNUSED_IMPORTS,
320 lint::builtin::BuiltinLintDiagnostics::UnusedImports(fix_msg.into(), fixes),