diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/check_unused.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/check_unused.rs | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/check_unused.rs b/compiler/rustc_hir_analysis/src/check_unused.rs new file mode 100644 index 00000000000..1d23ed92921 --- /dev/null +++ b/compiler/rustc_hir_analysis/src/check_unused.rs @@ -0,0 +1,187 @@ +use crate::errors::{ExternCrateNotIdiomatic, UnusedExternCrate}; +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_hir as hir; +use rustc_hir::def::DefKind; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_middle::ty::TyCtxt; +use rustc_session::lint; +use rustc_span::{Span, Symbol}; + +pub fn check_crate(tcx: TyCtxt<'_>) { + let mut used_trait_imports: FxHashSet<LocalDefId> = FxHashSet::default(); + + for item_def_id in tcx.hir().body_owners() { + let imports = tcx.used_trait_imports(item_def_id); + debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports); + used_trait_imports.extend(imports.iter()); + } + + for &id in tcx.maybe_unused_trait_imports(()) { + debug_assert_eq!(tcx.def_kind(id), DefKind::Use); + if tcx.visibility(id).is_public() { + continue; + } + if used_trait_imports.contains(&id) { + continue; + } + let item = tcx.hir().expect_item(id); + if item.span.is_dummy() { + continue; + } + let hir::ItemKind::Use(path, _) = item.kind else { unreachable!() }; + tcx.struct_span_lint_hir(lint::builtin::UNUSED_IMPORTS, item.hir_id(), path.span, |lint| { + let msg = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(path.span) { + format!("unused import: `{}`", snippet) + } else { + "unused import".to_owned() + }; + lint.build(&msg).emit(); + }); + } + + unused_crates_lint(tcx); +} + +fn unused_crates_lint(tcx: TyCtxt<'_>) { + let lint = lint::builtin::UNUSED_EXTERN_CRATES; + + // Collect first the crates that are completely unused. These we + // can always suggest removing (no matter which edition we are + // in). + let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx + .maybe_unused_extern_crates(()) + .iter() + .filter(|&&(def_id, _)| { + // The `def_id` here actually was calculated during resolution (at least + // at the time of this writing) and is being shipped to us via a side + // channel of the tcx. There may have been extra expansion phases, + // however, which ended up removing the `def_id` *after* expansion. + // + // As a result we need to verify that `def_id` is indeed still valid for + // our AST and actually present in the HIR map. If it's not there then + // there's safely nothing to warn about, and otherwise we carry on with + // our execution. + // + // Note that if we carry through to the `extern_mod_stmt_cnum` query + // below it'll cause a panic because `def_id` is actually bogus at this + // point in time otherwise. + if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() { + return false; + } + true + }) + .filter(|&&(def_id, _)| { + tcx.extern_mod_stmt_cnum(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) + }) + }) + .cloned() + .collect(); + + // Collect all the extern crates (in a reliable order). + let mut crates_to_lint = vec![]; + + for id in tcx.hir().items() { + if matches!(tcx.def_kind(id.def_id), DefKind::ExternCrate) { + let item = tcx.hir().item(id); + if let hir::ItemKind::ExternCrate(orig_name) = item.kind { + crates_to_lint.push(ExternCrateToLint { + def_id: item.def_id.to_def_id(), + span: item.span, + orig_name, + warn_if_unused: !item.ident.as_str().starts_with('_'), + }); + } + } + } + + let extern_prelude = &tcx.resolutions(()).extern_prelude; + + for extern_crate in &crates_to_lint { + let def_id = extern_crate.def_id.expect_local(); + let item = tcx.hir().expect_item(def_id); + + // If the crate is fully unused, we suggest removing it altogether. + // We do this in any edition. + if extern_crate.warn_if_unused { + if let Some(&span) = unused_extern_crates.get(&def_id) { + // Removal suggestion span needs to include attributes (Issue #54400) + let id = tcx.hir().local_def_id_to_hir_id(def_id); + let span_with_attrs = tcx + .hir() + .attrs(id) + .iter() + .map(|attr| attr.span) + .fold(span, |acc, attr_span| acc.to(attr_span)); + + tcx.emit_spanned_lint(lint, id, span, UnusedExternCrate { span: span_with_attrs }); + continue; + } + } + + // If we are not in Rust 2018 edition, then we don't make any further + // suggestions. + if !tcx.sess.rust_2018() { + continue; + } + + // If the extern crate isn't in the extern prelude, + // there is no way it can be written as a `use`. + let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name); + if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) { + 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.orig_name.is_some() { + continue; + } + + let id = tcx.hir().local_def_id_to_hir_id(def_id); + // 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 !tcx.hir().attrs(id).is_empty() { + continue; + } + + let base_replacement = match extern_crate.orig_name { + Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name), + None => format!("use {};", item.ident.name), + }; + let vis = tcx.sess.source_map().span_to_snippet(item.vis_span).unwrap_or_default(); + let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) }; + tcx.emit_spanned_lint( + lint, + id, + extern_crate.span, + ExternCrateNotIdiomatic { + span: extern_crate.span, + msg_code: add_vis("use".to_string()), + suggestion_code: add_vis(base_replacement), + }, + ); + } +} + +struct ExternCrateToLint { + /// `DefId` of the extern crate + def_id: DefId, + + /// span from the item + span: Span, + + /// if `Some`, then this is renamed (`extern crate orig_name as + /// crate_name`), and -- perhaps surprisingly -- this stores the + /// *original* name (`item.name` will contain the new name) + orig_name: Option<Symbol>, + + /// if `false`, the original name started with `_`, so we shouldn't lint + /// about it going unused (but we should still emit idiom lints). + warn_if_unused: bool, +} |