| use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext}; |
| use rustc::ty::adjustment; |
| use rustc::ty::{self, Ty}; |
| use rustc_ast::ast; |
| use rustc_ast::attr; |
| use rustc_ast::util::parser; |
| use rustc_ast_pretty::pprust; |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_errors::{pluralize, Applicability}; |
| use rustc_feature::{AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP}; |
| use rustc_hir as hir; |
| use rustc_hir::def::{DefKind, Res}; |
| use rustc_hir::def_id::DefId; |
| use rustc_session::lint::builtin::UNUSED_ATTRIBUTES; |
| use rustc_span::symbol::Symbol; |
| use rustc_span::symbol::{kw, sym}; |
| use rustc_span::{BytePos, Span}; |
| |
| use log::debug; |
| |
| declare_lint! { |
| pub UNUSED_MUST_USE, |
| Warn, |
| "unused result of a type flagged as `#[must_use]`", |
| report_in_external_macro |
| } |
| |
| declare_lint! { |
| pub UNUSED_RESULTS, |
| Allow, |
| "unused result of an expression in a statement" |
| } |
| |
| declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults { |
| fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt<'_>) { |
| let expr = match s.kind { |
| hir::StmtKind::Semi(ref expr) => &**expr, |
| _ => return, |
| }; |
| |
| if let hir::ExprKind::Ret(..) = expr.kind { |
| return; |
| } |
| |
| let ty = cx.tables.expr_ty(&expr); |
| let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "", "", 1); |
| |
| let mut fn_warned = false; |
| let mut op_warned = false; |
| let maybe_def_id = match expr.kind { |
| hir::ExprKind::Call(ref callee, _) => { |
| match callee.kind { |
| hir::ExprKind::Path(ref qpath) => { |
| match cx.tables.qpath_res(qpath, callee.hir_id) { |
| Res::Def(DefKind::Fn, def_id) | Res::Def(DefKind::Method, def_id) => { |
| Some(def_id) |
| } |
| // `Res::Local` if it was a closure, for which we |
| // do not currently support must-use linting |
| _ => None, |
| } |
| } |
| _ => None, |
| } |
| } |
| hir::ExprKind::MethodCall(..) => cx.tables.type_dependent_def_id(expr.hir_id), |
| _ => None, |
| }; |
| if let Some(def_id) = maybe_def_id { |
| fn_warned = check_must_use_def(cx, def_id, s.span, "return value of ", ""); |
| } else if type_permits_lack_of_use { |
| // We don't warn about unused unit or uninhabited types. |
| // (See https://github.com/rust-lang/rust/issues/43806 for details.) |
| return; |
| } |
| |
| let must_use_op = match expr.kind { |
| // Hardcoding operators here seemed more expedient than the |
| // refactoring that would be needed to look up the `#[must_use]` |
| // attribute which does exist on the comparison trait methods |
| hir::ExprKind::Binary(bin_op, ..) => match bin_op.node { |
| hir::BinOpKind::Eq |
| | hir::BinOpKind::Lt |
| | hir::BinOpKind::Le |
| | hir::BinOpKind::Ne |
| | hir::BinOpKind::Ge |
| | hir::BinOpKind::Gt => Some("comparison"), |
| hir::BinOpKind::Add |
| | hir::BinOpKind::Sub |
| | hir::BinOpKind::Div |
| | hir::BinOpKind::Mul |
| | hir::BinOpKind::Rem => Some("arithmetic operation"), |
| hir::BinOpKind::And | hir::BinOpKind::Or => Some("logical operation"), |
| hir::BinOpKind::BitXor |
| | hir::BinOpKind::BitAnd |
| | hir::BinOpKind::BitOr |
| | hir::BinOpKind::Shl |
| | hir::BinOpKind::Shr => Some("bitwise operation"), |
| }, |
| hir::ExprKind::Unary(..) => Some("unary operation"), |
| _ => None, |
| }; |
| |
| if let Some(must_use_op) = must_use_op { |
| cx.struct_span_lint(UNUSED_MUST_USE, expr.span, |lint| { |
| lint.build(&format!("unused {} that must be used", must_use_op)).emit() |
| }); |
| op_warned = true; |
| } |
| |
| if !(type_permits_lack_of_use || fn_warned || op_warned) { |
| cx.struct_span_lint(UNUSED_RESULTS, s.span, |lint| lint.build("unused result").emit()); |
| } |
| |
| // Returns whether an error has been emitted (and thus another does not need to be later). |
| fn check_must_use_ty<'tcx>( |
| cx: &LateContext<'_, 'tcx>, |
| ty: Ty<'tcx>, |
| expr: &hir::Expr<'_>, |
| span: Span, |
| descr_pre: &str, |
| descr_post: &str, |
| plural_len: usize, |
| ) -> bool { |
| if ty.is_unit() || cx.tcx.is_ty_uninhabited_from(cx.tcx.parent_module(expr.hir_id), ty) |
| { |
| return true; |
| } |
| |
| let plural_suffix = pluralize!(plural_len); |
| |
| match ty.kind { |
| ty::Adt(..) if ty.is_box() => { |
| let boxed_ty = ty.boxed_ty(); |
| let descr_pre = &format!("{}boxed ", descr_pre); |
| check_must_use_ty(cx, boxed_ty, expr, span, descr_pre, descr_post, plural_len) |
| } |
| ty::Adt(def, _) => check_must_use_def(cx, def.did, span, descr_pre, descr_post), |
| ty::Opaque(def, _) => { |
| let mut has_emitted = false; |
| for (predicate, _) in cx.tcx.predicates_of(def).predicates { |
| if let ty::Predicate::Trait(ref poly_trait_predicate, _) = predicate { |
| let trait_ref = poly_trait_predicate.skip_binder().trait_ref; |
| let def_id = trait_ref.def_id; |
| let descr_pre = |
| &format!("{}implementer{} of ", descr_pre, plural_suffix,); |
| if check_must_use_def(cx, def_id, span, descr_pre, descr_post) { |
| has_emitted = true; |
| break; |
| } |
| } |
| } |
| has_emitted |
| } |
| ty::Dynamic(binder, _) => { |
| let mut has_emitted = false; |
| for predicate in binder.skip_binder().iter() { |
| if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate { |
| let def_id = trait_ref.def_id; |
| let descr_post = |
| &format!(" trait object{}{}", plural_suffix, descr_post,); |
| if check_must_use_def(cx, def_id, span, descr_pre, descr_post) { |
| has_emitted = true; |
| break; |
| } |
| } |
| } |
| has_emitted |
| } |
| ty::Tuple(ref tys) => { |
| let mut has_emitted = false; |
| let spans = if let hir::ExprKind::Tup(comps) = &expr.kind { |
| debug_assert_eq!(comps.len(), tys.len()); |
| comps.iter().map(|e| e.span).collect() |
| } else { |
| vec![] |
| }; |
| for (i, ty) in tys.iter().map(|k| k.expect_ty()).enumerate() { |
| let descr_post = &format!(" in tuple element {}", i); |
| let span = *spans.get(i).unwrap_or(&span); |
| if check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, plural_len) |
| { |
| has_emitted = true; |
| } |
| } |
| has_emitted |
| } |
| ty::Array(ty, len) => match len.try_eval_usize(cx.tcx, cx.param_env) { |
| // If the array is definitely non-empty, we can do `#[must_use]` checking. |
| Some(n) if n != 0 => { |
| let descr_pre = &format!("{}array{} of ", descr_pre, plural_suffix,); |
| check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, n as usize + 1) |
| } |
| // Otherwise, we don't lint, to avoid false positives. |
| _ => false, |
| }, |
| _ => false, |
| } |
| } |
| |
| // Returns whether an error has been emitted (and thus another does not need to be later). |
| // FIXME: Args desc_{pre,post}_path could be made lazy by taking Fn() -> &str, but this |
| // would make calling it a big awkward. Could also take String (so args are moved), but |
| // this would still require a copy into the format string, which would only be executed |
| // when needed. |
| fn check_must_use_def( |
| cx: &LateContext<'_, '_>, |
| def_id: DefId, |
| span: Span, |
| descr_pre_path: &str, |
| descr_post_path: &str, |
| ) -> bool { |
| for attr in cx.tcx.get_attrs(def_id).iter() { |
| if attr.check_name(sym::must_use) { |
| cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| { |
| let msg = format!( |
| "unused {}`{}`{} that must be used", |
| descr_pre_path, |
| cx.tcx.def_path_str(def_id), |
| descr_post_path |
| ); |
| let mut err = lint.build(&msg); |
| // check for #[must_use = "..."] |
| if let Some(note) = attr.value_str() { |
| err.note(¬e.as_str()); |
| } |
| err.emit(); |
| }); |
| return true; |
| } |
| } |
| false |
| } |
| } |
| } |
| |
| declare_lint! { |
| pub PATH_STATEMENTS, |
| Warn, |
| "path statements with no effect" |
| } |
| |
| declare_lint_pass!(PathStatements => [PATH_STATEMENTS]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements { |
| fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt<'_>) { |
| if let hir::StmtKind::Semi(ref expr) = s.kind { |
| if let hir::ExprKind::Path(_) = expr.kind { |
| cx.struct_span_lint(PATH_STATEMENTS, s.span, |lint| { |
| lint.build("path statement with no effect").emit() |
| }); |
| } |
| } |
| } |
| } |
| |
| #[derive(Copy, Clone)] |
| pub struct UnusedAttributes { |
| builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>, |
| } |
| |
| impl UnusedAttributes { |
| pub fn new() -> Self { |
| UnusedAttributes { builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP } |
| } |
| } |
| |
| impl_lint_pass!(UnusedAttributes => [UNUSED_ATTRIBUTES]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes { |
| fn check_attribute(&mut self, cx: &LateContext<'_, '_>, attr: &ast::Attribute) { |
| debug!("checking attribute: {:?}", attr); |
| |
| if attr.is_doc_comment() { |
| return; |
| } |
| |
| let attr_info = attr.ident().and_then(|ident| self.builtin_attributes.get(&ident.name)); |
| |
| if let Some(&&(name, ty, ..)) = attr_info { |
| match ty { |
| AttributeType::Whitelisted => { |
| debug!("{:?} is Whitelisted", name); |
| return; |
| } |
| _ => (), |
| } |
| } |
| |
| if !attr::is_used(attr) { |
| debug!("emitting warning for: {:?}", attr); |
| cx.struct_span_lint(UNUSED_ATTRIBUTES, attr.span, |lint| { |
| lint.build("unused attribute").emit() |
| }); |
| // Is it a builtin attribute that must be used at the crate level? |
| if attr_info.map_or(false, |(_, ty, ..)| ty == &AttributeType::CrateLevel) { |
| cx.struct_span_lint(UNUSED_ATTRIBUTES, attr.span, |lint| { |
| let msg = match attr.style { |
| ast::AttrStyle::Outer => { |
| "crate-level attribute should be an inner attribute: add an exclamation \ |
| mark: `#![foo]`" |
| } |
| ast::AttrStyle::Inner => "crate-level attribute should be in the root module", |
| }; |
| lint.build(msg).emit() |
| }); |
| } |
| } else { |
| debug!("Attr was used: {:?}", attr); |
| } |
| } |
| } |
| |
| declare_lint! { |
| pub(super) UNUSED_PARENS, |
| Warn, |
| "`if`, `match`, `while` and `return` do not need parentheses" |
| } |
| |
| declare_lint_pass!(UnusedParens => [UNUSED_PARENS]); |
| |
| impl UnusedParens { |
| fn is_expr_parens_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool { |
| followed_by_block |
| && match inner.kind { |
| ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true, |
| _ => parser::contains_exterior_struct_lit(&inner), |
| } |
| } |
| |
| fn check_unused_parens_expr( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Expr, |
| msg: &str, |
| followed_by_block: bool, |
| left_pos: Option<BytePos>, |
| right_pos: Option<BytePos>, |
| ) { |
| match value.kind { |
| ast::ExprKind::Paren(ref inner) => { |
| if !Self::is_expr_parens_necessary(inner, followed_by_block) |
| && value.attrs.is_empty() |
| && !value.span.from_expansion() |
| { |
| let expr_text = |
| if let Ok(snippet) = cx.sess().source_map().span_to_snippet(value.span) { |
| snippet |
| } else { |
| pprust::expr_to_string(value) |
| }; |
| let keep_space = ( |
| left_pos.map(|s| s >= value.span.lo()).unwrap_or(false), |
| right_pos.map(|s| s <= value.span.hi()).unwrap_or(false), |
| ); |
| Self::remove_outer_parens(cx, value.span, &expr_text, msg, keep_space); |
| } |
| } |
| ast::ExprKind::Let(_, ref expr) => { |
| // FIXME(#60336): Properly handle `let true = (false && true)` |
| // actually needing the parenthesis. |
| self.check_unused_parens_expr( |
| cx, |
| expr, |
| "`let` head expression", |
| followed_by_block, |
| None, |
| None, |
| ); |
| } |
| _ => {} |
| } |
| } |
| |
| fn check_unused_parens_pat( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Pat, |
| avoid_or: bool, |
| avoid_mut: bool, |
| ) { |
| use ast::{BindingMode, Mutability, PatKind}; |
| |
| if let PatKind::Paren(inner) = &value.kind { |
| match inner.kind { |
| // The lint visitor will visit each subpattern of `p`. We do not want to lint |
| // any range pattern no matter where it occurs in the pattern. For something like |
| // `&(a..=b)`, there is a recursive `check_pat` on `a` and `b`, but we will assume |
| // that if there are unnecessary parens they serve a purpose of readability. |
| PatKind::Range(..) => return, |
| // Avoid `p0 | .. | pn` if we should. |
| PatKind::Or(..) if avoid_or => return, |
| // Avoid `mut x` and `mut x @ p` if we should: |
| PatKind::Ident(BindingMode::ByValue(Mutability::Mut), ..) if avoid_mut => return, |
| // Otherwise proceed with linting. |
| _ => {} |
| } |
| |
| let pattern_text = |
| if let Ok(snippet) = cx.sess().source_map().span_to_snippet(value.span) { |
| snippet |
| } else { |
| pprust::pat_to_string(value) |
| }; |
| Self::remove_outer_parens(cx, value.span, &pattern_text, "pattern", (false, false)); |
| } |
| } |
| |
| fn remove_outer_parens( |
| cx: &EarlyContext<'_>, |
| span: Span, |
| pattern: &str, |
| msg: &str, |
| keep_space: (bool, bool), |
| ) { |
| cx.struct_span_lint(UNUSED_PARENS, span, |lint| { |
| let span_msg = format!("unnecessary parentheses around {}", msg); |
| let mut err = lint.build(&span_msg); |
| let mut ate_left_paren = false; |
| let mut ate_right_paren = false; |
| let parens_removed = pattern.trim_matches(|c| match c { |
| '(' => { |
| if ate_left_paren { |
| false |
| } else { |
| ate_left_paren = true; |
| true |
| } |
| } |
| ')' => { |
| if ate_right_paren { |
| false |
| } else { |
| ate_right_paren = true; |
| true |
| } |
| } |
| _ => false, |
| }); |
| |
| let replace = { |
| let mut replace = if keep_space.0 { |
| let mut s = String::from(" "); |
| s.push_str(parens_removed); |
| s |
| } else { |
| String::from(parens_removed) |
| }; |
| |
| if keep_space.1 { |
| replace.push(' '); |
| } |
| replace |
| }; |
| |
| err.span_suggestion_short( |
| span, |
| "remove these parentheses", |
| replace, |
| Applicability::MachineApplicable, |
| ); |
| err.emit(); |
| }); |
| } |
| } |
| |
| impl EarlyLintPass for UnusedParens { |
| fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { |
| use rustc_ast::ast::ExprKind::*; |
| let (value, msg, followed_by_block, left_pos, right_pos) = match e.kind { |
| Let(ref pat, ..) => { |
| self.check_unused_parens_pat(cx, pat, false, false); |
| return; |
| } |
| |
| If(ref cond, ref block, ..) => { |
| let left = e.span.lo() + rustc_span::BytePos(2); |
| let right = block.span.lo(); |
| (cond, "`if` condition", true, Some(left), Some(right)) |
| } |
| |
| While(ref cond, ref block, ..) => { |
| let left = e.span.lo() + rustc_span::BytePos(5); |
| let right = block.span.lo(); |
| (cond, "`while` condition", true, Some(left), Some(right)) |
| } |
| |
| ForLoop(ref pat, ref cond, ref block, ..) => { |
| self.check_unused_parens_pat(cx, pat, false, false); |
| (cond, "`for` head expression", true, None, Some(block.span.lo())) |
| } |
| |
| Match(ref head, _) => { |
| let left = e.span.lo() + rustc_span::BytePos(5); |
| (head, "`match` head expression", true, Some(left), None) |
| } |
| |
| Ret(Some(ref value)) => { |
| let left = e.span.lo() + rustc_span::BytePos(3); |
| (value, "`return` value", false, Some(left), None) |
| } |
| |
| Assign(_, ref value, _) => (value, "assigned value", false, None, None), |
| AssignOp(.., ref value) => (value, "assigned value", false, None, None), |
| // either function/method call, or something this lint doesn't care about |
| ref call_or_other => { |
| let (args_to_check, call_kind) = match *call_or_other { |
| Call(_, ref args) => (&args[..], "function"), |
| // first "argument" is self (which sometimes needs parens) |
| MethodCall(_, ref args) => (&args[1..], "method"), |
| // actual catch-all arm |
| _ => { |
| return; |
| } |
| }; |
| // Don't lint if this is a nested macro expansion: otherwise, the lint could |
| // trigger in situations that macro authors shouldn't have to care about, e.g., |
| // when a parenthesized token tree matched in one macro expansion is matched as |
| // an expression in another and used as a fn/method argument (Issue #47775) |
| if e.span.ctxt().outer_expn_data().call_site.from_expansion() { |
| return; |
| } |
| let msg = format!("{} argument", call_kind); |
| for arg in args_to_check { |
| self.check_unused_parens_expr(cx, arg, &msg, false, None, None); |
| } |
| return; |
| } |
| }; |
| self.check_unused_parens_expr(cx, &value, msg, followed_by_block, left_pos, right_pos); |
| } |
| |
| fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat) { |
| use ast::{Mutability, PatKind::*}; |
| match &p.kind { |
| // Do not lint on `(..)` as that will result in the other arms being useless. |
| Paren(_) |
| // The other cases do not contain sub-patterns. |
| | Wild | Rest | Lit(..) | Mac(..) | Range(..) | Ident(.., None) | Path(..) => return, |
| // These are list-like patterns; parens can always be removed. |
| TupleStruct(_, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps { |
| self.check_unused_parens_pat(cx, p, false, false); |
| }, |
| Struct(_, fps, _) => for f in fps { |
| self.check_unused_parens_pat(cx, &f.pat, false, false); |
| }, |
| // Avoid linting on `i @ (p0 | .. | pn)` and `box (p0 | .. | pn)`, #64106. |
| Ident(.., Some(p)) | Box(p) => self.check_unused_parens_pat(cx, p, true, false), |
| // Avoid linting on `&(mut x)` as `&mut x` has a different meaning, #55342. |
| // Also avoid linting on `& mut? (p0 | .. | pn)`, #64106. |
| Ref(p, m) => self.check_unused_parens_pat(cx, p, true, *m == Mutability::Not), |
| } |
| } |
| |
| fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) { |
| use ast::StmtKind::*; |
| |
| match s.kind { |
| Local(ref local) => { |
| self.check_unused_parens_pat(cx, &local.pat, false, false); |
| |
| if let Some(ref value) = local.init { |
| self.check_unused_parens_expr(cx, &value, "assigned value", false, None, None); |
| } |
| } |
| Expr(ref expr) => { |
| self.check_unused_parens_expr(cx, &expr, "block return value", false, None, None); |
| } |
| _ => {} |
| } |
| } |
| |
| fn check_param(&mut self, cx: &EarlyContext<'_>, param: &ast::Param) { |
| self.check_unused_parens_pat(cx, ¶m.pat, true, false); |
| } |
| |
| fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) { |
| self.check_unused_parens_pat(cx, &arm.pat, false, false); |
| } |
| |
| fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) { |
| if let &ast::TyKind::Paren(ref r) = &ty.kind { |
| match &r.kind { |
| &ast::TyKind::TraitObject(..) => {} |
| &ast::TyKind::ImplTrait(_, ref bounds) if bounds.len() > 1 => {} |
| _ => { |
| let pattern_text = |
| if let Ok(snippet) = cx.sess().source_map().span_to_snippet(ty.span) { |
| snippet |
| } else { |
| pprust::ty_to_string(ty) |
| }; |
| |
| Self::remove_outer_parens(cx, ty.span, &pattern_text, "type", (false, false)); |
| } |
| } |
| } |
| } |
| |
| fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { |
| use ast::ItemKind::*; |
| |
| if let Const(.., Some(expr)) | Static(.., Some(expr)) = &item.kind { |
| self.check_unused_parens_expr(cx, expr, "assigned value", false, None, None); |
| } |
| } |
| } |
| |
| declare_lint! { |
| UNUSED_IMPORT_BRACES, |
| Allow, |
| "unnecessary braces around an imported item" |
| } |
| |
| declare_lint_pass!(UnusedImportBraces => [UNUSED_IMPORT_BRACES]); |
| |
| impl UnusedImportBraces { |
| fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) { |
| if let ast::UseTreeKind::Nested(ref items) = use_tree.kind { |
| // Recursively check nested UseTrees |
| for &(ref tree, _) in items { |
| self.check_use_tree(cx, tree, item); |
| } |
| |
| // Trigger the lint only if there is one nested item |
| if items.len() != 1 { |
| return; |
| } |
| |
| // Trigger the lint if the nested item is a non-self single item |
| let node_name = match items[0].0.kind { |
| ast::UseTreeKind::Simple(rename, ..) => { |
| let orig_ident = items[0].0.prefix.segments.last().unwrap().ident; |
| if orig_ident.name == kw::SelfLower { |
| return; |
| } |
| rename.unwrap_or(orig_ident).name |
| } |
| ast::UseTreeKind::Glob => Symbol::intern("*"), |
| ast::UseTreeKind::Nested(_) => return, |
| }; |
| |
| cx.struct_span_lint(UNUSED_IMPORT_BRACES, item.span, |lint| { |
| lint.build(&format!("braces around {} is unnecessary", node_name)).emit() |
| }); |
| } |
| } |
| } |
| |
| impl EarlyLintPass for UnusedImportBraces { |
| fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { |
| if let ast::ItemKind::Use(ref use_tree) = item.kind { |
| self.check_use_tree(cx, use_tree, item); |
| } |
| } |
| } |
| |
| declare_lint! { |
| pub(super) UNUSED_ALLOCATION, |
| Warn, |
| "detects unnecessary allocations that can be eliminated" |
| } |
| |
| declare_lint_pass!(UnusedAllocation => [UNUSED_ALLOCATION]); |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation { |
| fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr<'_>) { |
| match e.kind { |
| hir::ExprKind::Box(_) => {} |
| _ => return, |
| } |
| |
| for adj in cx.tables.expr_adjustments(e) { |
| if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind { |
| cx.struct_span_lint(UNUSED_ALLOCATION, e.span, |lint| { |
| let msg = match m { |
| adjustment::AutoBorrowMutability::Not => { |
| "unnecessary allocation, use `&` instead" |
| } |
| adjustment::AutoBorrowMutability::Mut { .. } => { |
| "unnecessary allocation, use `&mut` instead" |
| } |
| }; |
| lint.build(msg).emit() |
| }); |
| } |
| } |
| } |
| } |