567 lines
22 KiB
Rust
567 lines
22 KiB
Rust
//
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// Unused import checking
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//
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// Although this is mostly a lint pass, it lives in here because it depends on
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// resolve data structures and because it finalises the privacy information for
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// `use` items.
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//
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// Unused trait imports can't be checked until the method resolution. We save
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// candidates here, and do the actual check in rustc_hir_analysis/check_unused.rs.
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//
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// Checking for unused imports is split into three steps:
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//
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// - `UnusedImportCheckVisitor` walks the AST to find all the unused imports
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// inside of `UseTree`s, recording their `NodeId`s and grouping them by
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// the parent `use` item
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//
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// - `calc_unused_spans` then walks over all the `use` items marked in the
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// previous step to collect the spans associated with the `NodeId`s and to
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// calculate the spans that can be removed by rustfix; This is done in a
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// separate step to be able to collapse the adjacent spans that rustfix
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// will remove
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//
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// - `check_unused` finally emits the diagnostics based on the data generated
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// in the last step
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use rustc_ast as ast;
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use rustc_ast::visit::{self, Visitor};
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use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
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use rustc_data_structures::unord::UnordSet;
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use rustc_errors::MultiSpan;
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use rustc_hir::def::{DefKind, Res};
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use rustc_session::lint::BuiltinLintDiag;
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use rustc_session::lint::builtin::{
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MACRO_USE_EXTERN_CRATE, UNUSED_EXTERN_CRATES, UNUSED_IMPORTS, UNUSED_QUALIFICATIONS,
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};
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use rustc_span::{DUMMY_SP, Ident, Span, kw};
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use crate::imports::{Import, ImportKind};
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use crate::{LexicalScopeBinding, NameBindingKind, Resolver, module_to_string};
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struct UnusedImport {
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use_tree: ast::UseTree,
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use_tree_id: ast::NodeId,
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item_span: Span,
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unused: UnordSet<ast::NodeId>,
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}
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impl UnusedImport {
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fn add(&mut self, id: ast::NodeId) {
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self.unused.insert(id);
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}
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}
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struct UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
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r: &'a mut Resolver<'ra, 'tcx>,
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/// All the (so far) unused imports, grouped path list
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unused_imports: FxIndexMap<ast::NodeId, UnusedImport>,
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extern_crate_items: Vec<ExternCrateToLint>,
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base_use_tree: Option<&'a ast::UseTree>,
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base_id: ast::NodeId,
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item_span: Span,
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}
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struct ExternCrateToLint {
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id: ast::NodeId,
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/// Span from the item
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span: Span,
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/// Span to use to suggest complete removal.
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span_with_attributes: Span,
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/// Span of the visibility, if any.
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vis_span: Span,
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/// Whether the item has attrs.
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has_attrs: bool,
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/// Name used to refer to the crate.
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ident: Ident,
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/// Whether the statement renames the crate `extern crate orig_name as new_name;`.
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renames: bool,
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}
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impl<'a, 'ra, 'tcx> UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
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// We have information about whether `use` (import) items are actually
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// used now. If an import is not used at all, we signal a lint error.
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fn check_import(&mut self, id: ast::NodeId) {
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let used = self.r.used_imports.contains(&id);
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let def_id = self.r.local_def_id(id);
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if !used {
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if self.r.maybe_unused_trait_imports.contains(&def_id) {
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// Check later.
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return;
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}
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self.unused_import(self.base_id).add(id);
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} else {
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// This trait import is definitely used, in a way other than
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// method resolution.
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// FIXME(#120456) - is `swap_remove` correct?
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self.r.maybe_unused_trait_imports.swap_remove(&def_id);
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if let Some(i) = self.unused_imports.get_mut(&self.base_id) {
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i.unused.remove(&id);
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}
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}
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}
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fn unused_import(&mut self, id: ast::NodeId) -> &mut UnusedImport {
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let use_tree_id = self.base_id;
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let use_tree = self.base_use_tree.unwrap().clone();
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let item_span = self.item_span;
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self.unused_imports.entry(id).or_insert_with(|| UnusedImport {
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use_tree,
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use_tree_id,
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item_span,
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unused: Default::default(),
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})
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}
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fn check_import_as_underscore(&mut self, item: &ast::UseTree, id: ast::NodeId) {
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match item.kind {
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ast::UseTreeKind::Simple(Some(ident)) => {
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if ident.name == kw::Underscore
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&& !self.r.import_res_map.get(&id).is_some_and(|per_ns| {
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per_ns.iter().filter_map(|res| res.as_ref()).any(|res| {
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matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
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})
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})
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{
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self.unused_import(self.base_id).add(id);
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}
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}
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ast::UseTreeKind::Nested { ref items, .. } => self.check_imports_as_underscore(items),
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_ => {}
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}
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}
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fn check_imports_as_underscore(&mut self, items: &[(ast::UseTree, ast::NodeId)]) {
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for (item, id) in items {
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self.check_import_as_underscore(item, *id);
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}
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}
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fn report_unused_extern_crate_items(
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&mut self,
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maybe_unused_extern_crates: FxHashMap<ast::NodeId, Span>,
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) {
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let tcx = self.r.tcx();
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for extern_crate in &self.extern_crate_items {
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let warn_if_unused = !extern_crate.ident.name.as_str().starts_with('_');
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// If the crate is fully unused, we suggest removing it altogether.
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// We do this in any edition.
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if warn_if_unused {
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if let Some(&span) = maybe_unused_extern_crates.get(&extern_crate.id) {
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self.r.lint_buffer.buffer_lint(
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UNUSED_EXTERN_CRATES,
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extern_crate.id,
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span,
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BuiltinLintDiag::UnusedExternCrate {
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removal_span: extern_crate.span_with_attributes,
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},
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);
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continue;
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}
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}
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// If we are not in Rust 2018 edition, then we don't make any further
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// suggestions.
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if !tcx.sess.at_least_rust_2018() {
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continue;
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}
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// If the extern crate has any attributes, they may have funky
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// semantics we can't faithfully represent using `use` (most
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// notably `#[macro_use]`). Ignore it.
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if extern_crate.has_attrs {
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continue;
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}
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// If the extern crate is renamed, then we cannot suggest replacing it with a use as this
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// would not insert the new name into the prelude, where other imports in the crate may be
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// expecting it.
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if extern_crate.renames {
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continue;
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}
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// If the extern crate isn't in the extern prelude,
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// there is no way it can be written as a `use`.
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if self
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.r
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.extern_prelude
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.get(&extern_crate.ident)
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.is_none_or(|entry| entry.introduced_by_item)
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{
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continue;
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}
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let vis_span = extern_crate
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.vis_span
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.find_ancestor_inside(extern_crate.span)
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.unwrap_or(extern_crate.vis_span);
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let ident_span = extern_crate
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.ident
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.span
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.find_ancestor_inside(extern_crate.span)
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.unwrap_or(extern_crate.ident.span);
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self.r.lint_buffer.buffer_lint(
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UNUSED_EXTERN_CRATES,
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extern_crate.id,
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extern_crate.span,
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BuiltinLintDiag::ExternCrateNotIdiomatic { vis_span, ident_span },
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);
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}
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}
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}
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impl<'a, 'ra, 'tcx> Visitor<'a> for UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
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fn visit_item(&mut self, item: &'a ast::Item) {
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match item.kind {
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// Ignore is_public import statements because there's no way to be sure
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// whether they're used or not. Also ignore imports with a dummy span
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// because this means that they were generated in some fashion by the
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// compiler and we don't need to consider them.
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ast::ItemKind::Use(..) if item.span.is_dummy() => return,
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ast::ItemKind::ExternCrate(orig_name) => {
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self.extern_crate_items.push(ExternCrateToLint {
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id: item.id,
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span: item.span,
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vis_span: item.vis.span,
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span_with_attributes: item.span_with_attributes(),
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has_attrs: !item.attrs.is_empty(),
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ident: item.ident,
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renames: orig_name.is_some(),
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});
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}
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_ => {}
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}
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self.item_span = item.span_with_attributes();
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visit::walk_item(self, item);
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}
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fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: ast::NodeId, nested: bool) {
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// Use the base UseTree's NodeId as the item id
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// This allows the grouping of all the lints in the same item
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if !nested {
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self.base_id = id;
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self.base_use_tree = Some(use_tree);
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}
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if self.r.effective_visibilities.is_exported(self.r.local_def_id(id)) {
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self.check_import_as_underscore(use_tree, id);
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return;
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}
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if let ast::UseTreeKind::Nested { ref items, .. } = use_tree.kind {
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if items.is_empty() {
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self.unused_import(self.base_id).add(id);
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}
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} else {
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self.check_import(id);
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}
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visit::walk_use_tree(self, use_tree, id);
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}
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}
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enum UnusedSpanResult {
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Used,
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Unused { spans: Vec<Span>, remove: Span },
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PartialUnused { spans: Vec<Span>, remove: Vec<Span> },
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}
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fn calc_unused_spans(
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unused_import: &UnusedImport,
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use_tree: &ast::UseTree,
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use_tree_id: ast::NodeId,
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) -> UnusedSpanResult {
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// The full span is the whole item's span if this current tree is not nested inside another
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// This tells rustfix to remove the whole item if all the imports are unused
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let full_span = if unused_import.use_tree.span == use_tree.span {
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unused_import.item_span
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} else {
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use_tree.span
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};
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match use_tree.kind {
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ast::UseTreeKind::Simple(..) | ast::UseTreeKind::Glob => {
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if unused_import.unused.contains(&use_tree_id) {
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UnusedSpanResult::Unused { spans: vec![use_tree.span], remove: full_span }
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} else {
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UnusedSpanResult::Used
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}
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}
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ast::UseTreeKind::Nested { items: ref nested, span: tree_span } => {
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if nested.is_empty() {
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return UnusedSpanResult::Unused { spans: vec![use_tree.span], remove: full_span };
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}
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let mut unused_spans = Vec::new();
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let mut to_remove = Vec::new();
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let mut used_children = 0;
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let mut contains_self = false;
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let mut previous_unused = false;
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for (pos, (use_tree, use_tree_id)) in nested.iter().enumerate() {
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let remove = match calc_unused_spans(unused_import, use_tree, *use_tree_id) {
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UnusedSpanResult::Used => {
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used_children += 1;
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None
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}
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UnusedSpanResult::Unused { mut spans, remove } => {
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unused_spans.append(&mut spans);
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Some(remove)
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}
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UnusedSpanResult::PartialUnused { mut spans, remove: mut to_remove_extra } => {
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used_children += 1;
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unused_spans.append(&mut spans);
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to_remove.append(&mut to_remove_extra);
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None
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}
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};
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if let Some(remove) = remove {
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let remove_span = if nested.len() == 1 {
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remove
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} else if pos == nested.len() - 1 || used_children > 0 {
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// Delete everything from the end of the last import, to delete the
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// previous comma
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nested[pos - 1].0.span.shrink_to_hi().to(use_tree.span)
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} else {
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// Delete everything until the next import, to delete the trailing commas
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use_tree.span.to(nested[pos + 1].0.span.shrink_to_lo())
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};
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// Try to collapse adjacent spans into a single one. This prevents all cases of
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// overlapping removals, which are not supported by rustfix
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if previous_unused && !to_remove.is_empty() {
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let previous = to_remove.pop().unwrap();
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to_remove.push(previous.to(remove_span));
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} else {
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to_remove.push(remove_span);
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}
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}
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contains_self |= use_tree.prefix == kw::SelfLower
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&& matches!(use_tree.kind, ast::UseTreeKind::Simple(None));
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previous_unused = remove.is_some();
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}
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if unused_spans.is_empty() {
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UnusedSpanResult::Used
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} else if used_children == 0 {
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UnusedSpanResult::Unused { spans: unused_spans, remove: full_span }
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} else {
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// If there is only one remaining child that is used, the braces around the use
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// tree are not needed anymore. In that case, we determine the span of the left
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// brace and the right brace, and tell rustfix to remove them as well.
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//
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// This means that `use a::{B, C};` will be turned into `use a::B;` rather than
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// `use a::{B};`, removing a rustfmt roundtrip.
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//
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// Note that we cannot remove the braces if the only item inside the use tree is
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// `self`: `use foo::{self};` is valid Rust syntax, while `use foo::self;` errors
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// out. We also cannot turn `use foo::{self}` into `use foo`, as the former doesn't
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// import types with the same name as the module.
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if used_children == 1 && !contains_self {
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// Left brace, from the start of the nested group to the first item.
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to_remove.push(
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tree_span.shrink_to_lo().to(nested.first().unwrap().0.span.shrink_to_lo()),
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);
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// Right brace, from the end of the last item to the end of the nested group.
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to_remove.push(
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nested.last().unwrap().0.span.shrink_to_hi().to(tree_span.shrink_to_hi()),
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);
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}
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UnusedSpanResult::PartialUnused { spans: unused_spans, remove: to_remove }
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}
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}
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}
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}
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impl Resolver<'_, '_> {
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pub(crate) fn check_unused(&mut self, krate: &ast::Crate) {
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let tcx = self.tcx;
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let mut maybe_unused_extern_crates = FxHashMap::default();
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for import in self.potentially_unused_imports.iter() {
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match import.kind {
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_ if import.vis.is_public()
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|| import.span.is_dummy()
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|| self.import_use_map.contains_key(import) =>
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{
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if let ImportKind::MacroUse { .. } = import.kind {
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if !import.span.is_dummy() {
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self.lint_buffer.buffer_lint(
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MACRO_USE_EXTERN_CRATE,
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import.root_id,
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import.span,
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BuiltinLintDiag::MacroUseDeprecated,
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);
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}
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}
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}
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ImportKind::ExternCrate { id, .. } => {
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let def_id = self.local_def_id(id);
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if self.extern_crate_map.get(&def_id).is_none_or(|&cnum| {
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!tcx.is_compiler_builtins(cnum)
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&& !tcx.is_panic_runtime(cnum)
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&& !tcx.has_global_allocator(cnum)
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&& !tcx.has_panic_handler(cnum)
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}) {
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maybe_unused_extern_crates.insert(id, import.span);
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}
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}
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ImportKind::MacroUse { .. } => {
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self.lint_buffer.buffer_lint(
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UNUSED_IMPORTS,
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import.root_id,
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import.span,
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BuiltinLintDiag::UnusedMacroUse,
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);
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}
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_ => {}
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}
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}
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let mut visitor = UnusedImportCheckVisitor {
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r: self,
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unused_imports: Default::default(),
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extern_crate_items: Default::default(),
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base_use_tree: None,
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base_id: ast::DUMMY_NODE_ID,
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item_span: DUMMY_SP,
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};
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visit::walk_crate(&mut visitor, krate);
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visitor.report_unused_extern_crate_items(maybe_unused_extern_crates);
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for unused in visitor.unused_imports.values() {
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let (spans, remove_spans) =
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match calc_unused_spans(unused, &unused.use_tree, unused.use_tree_id) {
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UnusedSpanResult::Used => continue,
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UnusedSpanResult::Unused { spans, remove } => (spans, vec![remove]),
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UnusedSpanResult::PartialUnused { spans, remove } => (spans, remove),
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};
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let ms = MultiSpan::from_spans(spans);
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let mut span_snippets = ms
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.primary_spans()
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.iter()
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.filter_map(|span| tcx.sess.source_map().span_to_snippet(*span).ok())
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.map(|s| format!("`{s}`"))
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.collect::<Vec<String>>();
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span_snippets.sort();
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let remove_whole_use = remove_spans.len() == 1 && remove_spans[0] == unused.item_span;
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let num_to_remove = ms.primary_spans().len();
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// If we are in the `--test` mode, suppress a help that adds the `#[cfg(test)]`
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// attribute; however, if not, suggest adding the attribute. There is no way to
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// retrieve attributes here because we do not have a `TyCtxt` yet.
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let test_module_span = if tcx.sess.is_test_crate() {
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None
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} else {
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let parent_module = visitor.r.get_nearest_non_block_module(
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visitor.r.local_def_id(unused.use_tree_id).to_def_id(),
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);
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match module_to_string(parent_module) {
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Some(module)
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if module == "test"
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|| module == "tests"
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|| module.starts_with("test_")
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|| module.starts_with("tests_")
|
|
|| module.ends_with("_test")
|
|
|| module.ends_with("_tests") =>
|
|
{
|
|
Some(parent_module.span)
|
|
}
|
|
_ => None,
|
|
}
|
|
};
|
|
|
|
visitor.r.lint_buffer.buffer_lint(
|
|
UNUSED_IMPORTS,
|
|
unused.use_tree_id,
|
|
ms,
|
|
BuiltinLintDiag::UnusedImports {
|
|
remove_whole_use,
|
|
num_to_remove,
|
|
remove_spans,
|
|
test_module_span,
|
|
span_snippets,
|
|
},
|
|
);
|
|
}
|
|
|
|
let unused_imports = visitor.unused_imports;
|
|
let mut check_redundant_imports = FxIndexSet::default();
|
|
for module in self.arenas.local_modules().iter() {
|
|
for (_key, resolution) in self.resolutions(*module).borrow().iter() {
|
|
let resolution = resolution.borrow();
|
|
|
|
if let Some(binding) = resolution.binding
|
|
&& let NameBindingKind::Import { import, .. } = binding.kind
|
|
&& let ImportKind::Single { id, .. } = import.kind
|
|
{
|
|
if let Some(unused_import) = unused_imports.get(&import.root_id)
|
|
&& unused_import.unused.contains(&id)
|
|
{
|
|
continue;
|
|
}
|
|
|
|
check_redundant_imports.insert(import);
|
|
}
|
|
}
|
|
}
|
|
|
|
let mut redundant_imports = UnordSet::default();
|
|
for import in check_redundant_imports {
|
|
if self.check_for_redundant_imports(import)
|
|
&& let Some(id) = import.id()
|
|
{
|
|
redundant_imports.insert(id);
|
|
}
|
|
}
|
|
|
|
// The lint fixes for unused_import and unnecessary_qualification may conflict.
|
|
// Deleting both unused imports and unnecessary segments of an item may result
|
|
// in the item not being found.
|
|
for unn_qua in &self.potentially_unnecessary_qualifications {
|
|
if let LexicalScopeBinding::Item(name_binding) = unn_qua.binding
|
|
&& let NameBindingKind::Import { import, .. } = name_binding.kind
|
|
&& (is_unused_import(import, &unused_imports)
|
|
|| is_redundant_import(import, &redundant_imports))
|
|
{
|
|
continue;
|
|
}
|
|
|
|
self.lint_buffer.buffer_lint(
|
|
UNUSED_QUALIFICATIONS,
|
|
unn_qua.node_id,
|
|
unn_qua.path_span,
|
|
BuiltinLintDiag::UnusedQualifications { removal_span: unn_qua.removal_span },
|
|
);
|
|
}
|
|
|
|
fn is_redundant_import(
|
|
import: Import<'_>,
|
|
redundant_imports: &UnordSet<ast::NodeId>,
|
|
) -> bool {
|
|
if let Some(id) = import.id()
|
|
&& redundant_imports.contains(&id)
|
|
{
|
|
return true;
|
|
}
|
|
false
|
|
}
|
|
|
|
fn is_unused_import(
|
|
import: Import<'_>,
|
|
unused_imports: &FxIndexMap<ast::NodeId, UnusedImport>,
|
|
) -> bool {
|
|
if let Some(unused_import) = unused_imports.get(&import.root_id)
|
|
&& let Some(id) = import.id()
|
|
&& unused_import.unused.contains(&id)
|
|
{
|
|
return true;
|
|
}
|
|
false
|
|
}
|
|
}
|
|
}
|