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//
// Unused import checking
//
// Although this is mostly a lint pass, it lives in here because it depends on
// resolve data structures and because it finalises the privacy information for
// `use` items.
//
// Unused trait imports can't be checked until the method resolution. We save
// candidates here, and do the actual check in rustc_hir_analysis/check_unused.rs.
//
// Checking for unused imports is split into three steps:
//
// - `UnusedImportCheckVisitor` walks the AST to find all the unused imports
// inside of `UseTree`s, recording their `NodeId`s and grouping them by
// the parent `use` item
//
// - `calc_unused_spans` then walks over all the `use` items marked in the
// previous step to collect the spans associated with the `NodeId`s and to
// calculate the spans that can be removed by rustfix; This is done in a
// separate step to be able to collapse the adjacent spans that rustfix
// will remove
//
// - `check_crate` finally emits the diagnostics based on the data generated
// in the last step
use crate::imports::ImportKind;
use crate::module_to_string;
use crate::Resolver;
use rustc_ast as ast;
use rustc_ast::visit::{self, Visitor};
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_data_structures::unord::UnordSet;
use rustc_errors::{pluralize, MultiSpan};
use rustc_hir::def::{DefKind, Res};
use rustc_session::lint::builtin::{MACRO_USE_EXTERN_CRATE, UNUSED_EXTERN_CRATES, UNUSED_IMPORTS};
use rustc_session::lint::BuiltinLintDiagnostics;
use rustc_span::symbol::{kw, Ident};
use rustc_span::{Span, DUMMY_SP};
struct UnusedImport<'a> {
use_tree: &'a ast::UseTree,
use_tree_id: ast::NodeId,
item_span: Span,
unused: UnordSet<ast::NodeId>,
}
impl<'a> UnusedImport<'a> {
fn add(&mut self, id: ast::NodeId) {
self.unused.insert(id);
}
}
struct UnusedImportCheckVisitor<'a, 'b, 'tcx> {
r: &'a mut Resolver<'b, 'tcx>,
/// All the (so far) unused imports, grouped path list
unused_imports: FxIndexMap<ast::NodeId, UnusedImport<'a>>,
extern_crate_items: Vec<ExternCrateToLint>,
base_use_tree: Option<&'a ast::UseTree>,
base_id: ast::NodeId,
item_span: Span,
base_use_is_pub: bool,
}
struct ExternCrateToLint {
id: ast::NodeId,
/// Span from the item
span: Span,
/// Span to use to suggest complete removal.
span_with_attributes: Span,
/// Span of the visibility, if any.
vis_span: Span,
/// Whether the item has attrs.
has_attrs: bool,
/// Name used to refer to the crate.
ident: Ident,
/// Whether the statement renames the crate `extern crate orig_name as new_name;`.
renames: bool,
}
impl<'a, 'b, 'tcx> UnusedImportCheckVisitor<'a, 'b, 'tcx> {
// We have information about whether `use` (import) items are actually
// used now. If an import is not used at all, we signal a lint error.
fn check_import(&mut self, id: ast::NodeId) {
let used = self.r.used_imports.contains(&id);
let def_id = self.r.local_def_id(id);
if !used {
if self.r.maybe_unused_trait_imports.contains(&def_id) {
// Check later.
return;
}
self.unused_import(self.base_id).add(id);
} else {
// This trait import is definitely used, in a way other than
// method resolution.
self.r.maybe_unused_trait_imports.remove(&def_id);
if let Some(i) = self.unused_imports.get_mut(&self.base_id) {
i.unused.remove(&id);
}
}
}
fn unused_import(&mut self, id: ast::NodeId) -> &mut UnusedImport<'a> {
let use_tree_id = self.base_id;
let use_tree = self.base_use_tree.unwrap();
let item_span = self.item_span;
self.unused_imports.entry(id).or_insert_with(|| UnusedImport {
use_tree,
use_tree_id,
item_span,
unused: Default::default(),
})
}
fn check_import_as_underscore(&mut self, item: &ast::UseTree, id: ast::NodeId) {
match item.kind {
ast::UseTreeKind::Simple(Some(ident)) => {
if ident.name == kw::Underscore
&& !self.r.import_res_map.get(&id).is_some_and(|per_ns| {
per_ns.iter().filter_map(|res| res.as_ref()).any(|res| {
matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
})
})
{
self.unused_import(self.base_id).add(id);
}
}
ast::UseTreeKind::Nested(ref items) => self.check_imports_as_underscore(items),
_ => {}
}
}
fn check_imports_as_underscore(&mut self, items: &[(ast::UseTree, ast::NodeId)]) {
for (item, id) in items {
self.check_import_as_underscore(item, *id);
}
}
}
impl<'a, 'b, 'tcx> Visitor<'a> for UnusedImportCheckVisitor<'a, 'b, 'tcx> {
fn visit_item(&mut self, item: &'a ast::Item) {
match item.kind {
// Ignore is_public import statements because there's no way to be sure
// whether they're used or not. Also ignore imports with a dummy span
// because this means that they were generated in some fashion by the
// compiler and we don't need to consider them.
ast::ItemKind::Use(..) if item.span.is_dummy() => return,
ast::ItemKind::Use(..) => self.base_use_is_pub = item.vis.kind.is_pub(),
ast::ItemKind::ExternCrate(orig_name) => {
self.extern_crate_items.push(ExternCrateToLint {
id: item.id,
span: item.span,
vis_span: item.vis.span,
span_with_attributes: item.span_with_attributes(),
has_attrs: !item.attrs.is_empty(),
ident: item.ident,
renames: orig_name.is_some(),
});
}
_ => {}
}
self.item_span = item.span_with_attributes();
visit::walk_item(self, item);
}
fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: ast::NodeId, nested: bool) {
// Use the base UseTree's NodeId as the item id
// This allows the grouping of all the lints in the same item
if !nested {
self.base_id = id;
self.base_use_tree = Some(use_tree);
}
if self.base_use_is_pub {
self.check_import_as_underscore(use_tree, id);
return;
}
if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
if items.is_empty() {
self.unused_import(self.base_id).add(id);
}
} else {
self.check_import(id);
}
visit::walk_use_tree(self, use_tree, id);
}
}
enum UnusedSpanResult {
Used,
FlatUnused(Span, Span),
NestedFullUnused(Vec<Span>, Span),
NestedPartialUnused(Vec<Span>, Vec<Span>),
}
fn calc_unused_spans(
unused_import: &UnusedImport<'_>,
use_tree: &ast::UseTree,
use_tree_id: ast::NodeId,
) -> UnusedSpanResult {
// The full span is the whole item's span if this current tree is not nested inside another
// This tells rustfix to remove the whole item if all the imports are unused
let full_span = if unused_import.use_tree.span == use_tree.span {
unused_import.item_span
} else {
use_tree.span
};
match use_tree.kind {
ast::UseTreeKind::Simple(..) | ast::UseTreeKind::Glob => {
if unused_import.unused.contains(&use_tree_id) {
UnusedSpanResult::FlatUnused(use_tree.span, full_span)
} else {
UnusedSpanResult::Used
}
}
ast::UseTreeKind::Nested(ref nested) => {
if nested.is_empty() {
return UnusedSpanResult::FlatUnused(use_tree.span, full_span);
}
let mut unused_spans = Vec::new();
let mut to_remove = Vec::new();
let mut all_nested_unused = true;
let mut previous_unused = false;
for (pos, (use_tree, use_tree_id)) in nested.iter().enumerate() {
let remove = match calc_unused_spans(unused_import, use_tree, *use_tree_id) {
UnusedSpanResult::Used => {
all_nested_unused = false;
None
}
UnusedSpanResult::FlatUnused(span, remove) => {
unused_spans.push(span);
Some(remove)
}
UnusedSpanResult::NestedFullUnused(mut spans, remove) => {
unused_spans.append(&mut spans);
Some(remove)
}
UnusedSpanResult::NestedPartialUnused(mut spans, mut to_remove_extra) => {
all_nested_unused = false;
unused_spans.append(&mut spans);
to_remove.append(&mut to_remove_extra);
None
}
};
if let Some(remove) = remove {
let remove_span = if nested.len() == 1 {
remove
} else if pos == nested.len() - 1 || !all_nested_unused {
// Delete everything from the end of the last import, to delete the
// previous comma
nested[pos - 1].0.span.shrink_to_hi().to(use_tree.span)
} else {
// Delete everything until the next import, to delete the trailing commas
use_tree.span.to(nested[pos + 1].0.span.shrink_to_lo())
};
// Try to collapse adjacent spans into a single one. This prevents all cases of
// overlapping removals, which are not supported by rustfix
if previous_unused && !to_remove.is_empty() {
let previous = to_remove.pop().unwrap();
to_remove.push(previous.to(remove_span));
} else {
to_remove.push(remove_span);
}
}
previous_unused = remove.is_some();
}
if unused_spans.is_empty() {
UnusedSpanResult::Used
} else if all_nested_unused {
UnusedSpanResult::NestedFullUnused(unused_spans, full_span)
} else {
UnusedSpanResult::NestedPartialUnused(unused_spans, to_remove)
}
}
}
}
impl Resolver<'_, '_> {
pub(crate) fn check_unused(&mut self, krate: &ast::Crate) {
let tcx = self.tcx;
let mut maybe_unused_extern_crates = FxHashMap::default();
for import in self.potentially_unused_imports.iter() {
match import.kind {
_ if import.used.get()
|| import.expect_vis().is_public()
|| import.span.is_dummy() =>
{
if let ImportKind::MacroUse = import.kind {
if !import.span.is_dummy() {
self.lint_buffer.buffer_lint(
MACRO_USE_EXTERN_CRATE,
import.root_id,
import.span,
"deprecated `#[macro_use]` attribute used to \
import macros should be replaced at use sites \
with a `use` item to import the macro \
instead",
);
}
}
}
ImportKind::ExternCrate { id, .. } => {
let def_id = self.local_def_id(id);
if self.extern_crate_map.get(&def_id).map_or(true, |&cnum| {
!tcx.is_compiler_builtins(cnum)
&& !tcx.is_panic_runtime(cnum)
&& !tcx.has_global_allocator(cnum)
&& !tcx.has_panic_handler(cnum)
}) {
maybe_unused_extern_crates.insert(id, import.span);
}
}
ImportKind::MacroUse => {
let msg = "unused `#[macro_use]` import";
self.lint_buffer.buffer_lint(UNUSED_IMPORTS, import.root_id, import.span, msg);
}
_ => {}
}
}
let mut visitor = UnusedImportCheckVisitor {
r: self,
unused_imports: Default::default(),
extern_crate_items: Default::default(),
base_use_tree: None,
base_id: ast::DUMMY_NODE_ID,
item_span: DUMMY_SP,
base_use_is_pub: false,
};
visit::walk_crate(&mut visitor, krate);
for unused in visitor.unused_imports.values() {
let mut fixes = Vec::new();
let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
UnusedSpanResult::Used => continue,
UnusedSpanResult::FlatUnused(span, remove) => {
fixes.push((remove, String::new()));
vec![span]
}
UnusedSpanResult::NestedFullUnused(spans, remove) => {
fixes.push((remove, String::new()));
spans
}
UnusedSpanResult::NestedPartialUnused(spans, remove) => {
for fix in &remove {
fixes.push((*fix, String::new()));
}
spans
}
};
let len = spans.len();
spans.sort();
let ms = MultiSpan::from_spans(spans.clone());
let mut span_snippets = spans
.iter()
.filter_map(|s| match tcx.sess.source_map().span_to_snippet(*s) {
Ok(s) => Some(format!("`{s}`")),
_ => None,
})
.collect::<Vec<String>>();
span_snippets.sort();
let msg = format!(
"unused import{}{}",
pluralize!(len),
if !span_snippets.is_empty() {
format!(": {}", span_snippets.join(", "))
} else {
String::new()
}
);
let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
"remove the whole `use` item"
} else if spans.len() > 1 {
"remove the unused imports"
} else {
"remove the unused import"
};
// If we are in the `--test` mode, suppress a help that adds the `#[cfg(test)]`
// attribute; however, if not, suggest adding the attribute. There is no way to
// retrieve attributes here because we do not have a `TyCtxt` yet.
let test_module_span = if tcx.sess.is_test_crate() {
None
} else {
let parent_module = visitor.r.get_nearest_non_block_module(
visitor.r.local_def_id(unused.use_tree_id).to_def_id(),
);
match module_to_string(parent_module) {
Some(module)
if module == "test"
|| module == "tests"
|| module.starts_with("test_")
|| module.starts_with("tests_")
|| module.ends_with("_test")
|| module.ends_with("_tests") =>
{
Some(parent_module.span)
}
_ => None,
}
};
visitor.r.lint_buffer.buffer_lint_with_diagnostic(
UNUSED_IMPORTS,
unused.use_tree_id,
ms,
msg,
BuiltinLintDiagnostics::UnusedImports(fix_msg.into(), fixes, test_module_span),
);
}
for extern_crate in visitor.extern_crate_items {
let warn_if_unused = !extern_crate.ident.name.as_str().starts_with('_');
// If the crate is fully unused, we suggest removing it altogether.
// We do this in any edition.
if warn_if_unused {
if let Some(&span) = maybe_unused_extern_crates.get(&extern_crate.id) {
visitor.r.lint_buffer.buffer_lint_with_diagnostic(
UNUSED_EXTERN_CRATES,
extern_crate.id,
span,
"unused extern crate",
BuiltinLintDiagnostics::UnusedExternCrate {
removal_span: extern_crate.span_with_attributes,
},
);
continue;
}
}
// If we are not in Rust 2018 edition, then we don't make any further
// suggestions.
if !tcx.sess.at_least_rust_2018() {
continue;
}
// If the extern crate has any attributes, they may have funky
// semantics we can't faithfully represent using `use` (most
// notably `#[macro_use]`). Ignore it.
if extern_crate.has_attrs {
continue;
}
// If the extern crate is renamed, then we cannot suggest replacing it with a use as this
// would not insert the new name into the prelude, where other imports in the crate may be
// expecting it.
if extern_crate.renames {
continue;
}
// If the extern crate isn't in the extern prelude,
// there is no way it can be written as a `use`.
if !visitor
.r
.extern_prelude
.get(&extern_crate.ident)
.is_some_and(|entry| !entry.introduced_by_item)
{
continue;
}
let vis_span = extern_crate
.vis_span
.find_ancestor_inside(extern_crate.span)
.unwrap_or(extern_crate.vis_span);
let ident_span = extern_crate
.ident
.span
.find_ancestor_inside(extern_crate.span)
.unwrap_or(extern_crate.ident.span);
visitor.r.lint_buffer.buffer_lint_with_diagnostic(
UNUSED_EXTERN_CRATES,
extern_crate.id,
extern_crate.span,
"`extern crate` is not idiomatic in the new edition",
BuiltinLintDiagnostics::ExternCrateNotIdiomatic { vis_span, ident_span },
);
}
}
}