| use crate::lints::{ |
| PathStatementDrop, PathStatementDropSub, PathStatementNoEffect, UnusedAllocationDiag, |
| UnusedAllocationMutDiag, UnusedClosure, UnusedDef, UnusedDefSuggestion, UnusedDelim, |
| UnusedDelimSuggestion, UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedResult, |
| }; |
| use crate::Lint; |
| use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext}; |
| use rustc_ast as ast; |
| use rustc_ast::util::{classify, parser}; |
| use rustc_ast::{ExprKind, StmtKind}; |
| use rustc_errors::{pluralize, MultiSpan}; |
| use rustc_hir as hir; |
| use rustc_hir::def::{DefKind, Res}; |
| use rustc_hir::def_id::DefId; |
| use rustc_infer::traits::util::elaborate; |
| use rustc_middle::ty::adjustment; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_span::symbol::Symbol; |
| use rustc_span::symbol::{kw, sym}; |
| use rustc_span::{BytePos, Span}; |
| use std::iter; |
| |
| declare_lint! { |
| /// The `unused_must_use` lint detects unused result of a type flagged as |
| /// `#[must_use]`. |
| /// |
| /// ### Example |
| /// |
| /// ```rust |
| /// fn returns_result() -> Result<(), ()> { |
| /// Ok(()) |
| /// } |
| /// |
| /// fn main() { |
| /// returns_result(); |
| /// } |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// The `#[must_use]` attribute is an indicator that it is a mistake to |
| /// ignore the value. See [the reference] for more details. |
| /// |
| /// [the reference]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute |
| pub UNUSED_MUST_USE, |
| Warn, |
| "unused result of a type flagged as `#[must_use]`", |
| report_in_external_macro |
| } |
| |
| declare_lint! { |
| /// The `unused_results` lint checks for the unused result of an |
| /// expression in a statement. |
| /// |
| /// ### Example |
| /// |
| /// ```rust,compile_fail |
| /// #![deny(unused_results)] |
| /// fn foo<T>() -> T { panic!() } |
| /// |
| /// fn main() { |
| /// foo::<usize>(); |
| /// } |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// Ignoring the return value of a function may indicate a mistake. In |
| /// cases were it is almost certain that the result should be used, it is |
| /// recommended to annotate the function with the [`must_use` attribute]. |
| /// Failure to use such a return value will trigger the [`unused_must_use` |
| /// lint] which is warn-by-default. The `unused_results` lint is |
| /// essentially the same, but triggers for *all* return values. |
| /// |
| /// This lint is "allow" by default because it can be noisy, and may not be |
| /// an actual problem. For example, calling the `remove` method of a `Vec` |
| /// or `HashMap` returns the previous value, which you may not care about. |
| /// Using this lint would require explicitly ignoring or discarding such |
| /// values. |
| /// |
| /// [`must_use` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute |
| /// [`unused_must_use` lint]: warn-by-default.html#unused-must-use |
| pub UNUSED_RESULTS, |
| Allow, |
| "unused result of an expression in a statement" |
| } |
| |
| declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]); |
| |
| impl<'tcx> LateLintPass<'tcx> for UnusedResults { |
| fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) { |
| let hir::StmtKind::Semi(expr) = s.kind else { return; }; |
| |
| if let hir::ExprKind::Ret(..) = expr.kind { |
| return; |
| } |
| |
| if let hir::ExprKind::Match(await_expr, _arms, hir::MatchSource::AwaitDesugar) = expr.kind |
| && let ty = cx.typeck_results().expr_ty(&await_expr) |
| && let ty::Alias(ty::Opaque, ty::AliasTy { def_id: future_def_id, .. }) = ty.kind() |
| && cx.tcx.ty_is_opaque_future(ty) |
| && let async_fn_def_id = cx.tcx.parent(*future_def_id) |
| && matches!(cx.tcx.def_kind(async_fn_def_id), DefKind::Fn | DefKind::AssocFn) |
| // Check that this `impl Future` actually comes from an `async fn` |
| && cx.tcx.asyncness(async_fn_def_id).is_async() |
| && check_must_use_def( |
| cx, |
| async_fn_def_id, |
| expr.span, |
| "output of future returned by ", |
| "", |
| ) |
| { |
| // We have a bare `foo().await;` on an opaque type from an async function that was |
| // annotated with `#[must_use]`. |
| return; |
| } |
| |
| let ty = cx.typeck_results().expr_ty(&expr); |
| |
| let must_use_result = is_ty_must_use(cx, ty, &expr, expr.span); |
| let type_lint_emitted_or_suppressed = match must_use_result { |
| Some(path) => { |
| emit_must_use_untranslated(cx, &path, "", "", 1, false); |
| true |
| } |
| None => false, |
| }; |
| |
| let fn_warned = check_fn_must_use(cx, expr); |
| |
| if !fn_warned && type_lint_emitted_or_suppressed { |
| // 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::AddrOf(..) => Some("borrow"), |
| hir::ExprKind::Unary(..) => Some("unary operation"), |
| _ => None, |
| }; |
| |
| let mut op_warned = false; |
| |
| if let Some(must_use_op) = must_use_op { |
| cx.emit_spanned_lint( |
| UNUSED_MUST_USE, |
| expr.span, |
| UnusedOp { |
| op: must_use_op, |
| label: expr.span, |
| suggestion: expr.span.shrink_to_lo(), |
| }, |
| ); |
| op_warned = true; |
| } |
| |
| if !(type_lint_emitted_or_suppressed || fn_warned || op_warned) { |
| cx.emit_spanned_lint(UNUSED_RESULTS, s.span, UnusedResult { ty }); |
| } |
| |
| fn check_fn_must_use(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool { |
| let maybe_def_id = match expr.kind { |
| hir::ExprKind::Call(ref callee, _) => { |
| match callee.kind { |
| hir::ExprKind::Path(ref qpath) => { |
| match cx.qpath_res(qpath, callee.hir_id) { |
| Res::Def(DefKind::Fn | DefKind::AssocFn, 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.typeck_results().type_dependent_def_id(expr.hir_id) |
| } |
| _ => None, |
| }; |
| if let Some(def_id) = maybe_def_id { |
| check_must_use_def(cx, def_id, expr.span, "return value of ", "") |
| } else { |
| false |
| } |
| } |
| |
| /// A path through a type to a must_use source. Contains useful info for the lint. |
| #[derive(Debug)] |
| enum MustUsePath { |
| /// Suppress must_use checking. |
| Suppressed, |
| /// The root of the normal must_use lint with an optional message. |
| Def(Span, DefId, Option<Symbol>), |
| Boxed(Box<Self>), |
| Opaque(Box<Self>), |
| TraitObject(Box<Self>), |
| TupleElement(Vec<(usize, Self)>), |
| Array(Box<Self>, u64), |
| /// The root of the unused_closures lint. |
| Closure(Span), |
| /// The root of the unused_generators lint. |
| Generator(Span), |
| } |
| |
| #[instrument(skip(cx, expr), level = "debug", ret)] |
| fn is_ty_must_use<'tcx>( |
| cx: &LateContext<'tcx>, |
| ty: Ty<'tcx>, |
| expr: &hir::Expr<'_>, |
| span: Span, |
| ) -> Option<MustUsePath> { |
| if ty.is_unit() |
| || !ty.is_inhabited_from( |
| cx.tcx, |
| cx.tcx.parent_module(expr.hir_id).to_def_id(), |
| cx.param_env, |
| ) |
| { |
| return Some(MustUsePath::Suppressed); |
| } |
| |
| match *ty.kind() { |
| ty::Adt(..) if ty.is_box() => { |
| let boxed_ty = ty.boxed_ty(); |
| is_ty_must_use(cx, boxed_ty, expr, span) |
| .map(|inner| MustUsePath::Boxed(Box::new(inner))) |
| } |
| ty::Adt(def, _) => is_def_must_use(cx, def.did(), span), |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, .. }) => { |
| elaborate(cx.tcx, cx.tcx.explicit_item_bounds(def).subst_identity_iter_copied()) |
| // We only care about self bounds for the impl-trait |
| .filter_only_self() |
| .find_map(|(pred, _span)| { |
| // We only look at the `DefId`, so it is safe to skip the binder here. |
| if let ty::PredicateKind::Clause(ty::Clause::Trait( |
| ref poly_trait_predicate, |
| )) = pred.kind().skip_binder() |
| { |
| let def_id = poly_trait_predicate.trait_ref.def_id; |
| |
| is_def_must_use(cx, def_id, span) |
| } else { |
| None |
| } |
| }) |
| .map(|inner| MustUsePath::Opaque(Box::new(inner))) |
| } |
| ty::Dynamic(binders, _, _) => binders.iter().find_map(|predicate| { |
| if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() |
| { |
| let def_id = trait_ref.def_id; |
| is_def_must_use(cx, def_id, span) |
| .map(|inner| MustUsePath::TraitObject(Box::new(inner))) |
| } else { |
| None |
| } |
| }), |
| ty::Tuple(tys) => { |
| let elem_exprs = if let hir::ExprKind::Tup(elem_exprs) = expr.kind { |
| debug_assert_eq!(elem_exprs.len(), tys.len()); |
| elem_exprs |
| } else { |
| &[] |
| }; |
| |
| // Default to `expr`. |
| let elem_exprs = elem_exprs.iter().chain(iter::repeat(expr)); |
| |
| let nested_must_use = tys |
| .iter() |
| .zip(elem_exprs) |
| .enumerate() |
| .filter_map(|(i, (ty, expr))| { |
| is_ty_must_use(cx, ty, expr, expr.span).map(|path| (i, path)) |
| }) |
| .collect::<Vec<_>>(); |
| |
| if !nested_must_use.is_empty() { |
| Some(MustUsePath::TupleElement(nested_must_use)) |
| } else { |
| None |
| } |
| } |
| ty::Array(ty, len) => match len.try_eval_target_usize(cx.tcx, cx.param_env) { |
| // If the array is empty we don't lint, to avoid false positives |
| Some(0) | None => None, |
| // If the array is definitely non-empty, we can do `#[must_use]` checking. |
| Some(len) => is_ty_must_use(cx, ty, expr, span) |
| .map(|inner| MustUsePath::Array(Box::new(inner), len)), |
| }, |
| ty::Closure(..) => Some(MustUsePath::Closure(span)), |
| ty::Generator(def_id, ..) => { |
| // async fn should be treated as "implementor of `Future`" |
| let must_use = if cx.tcx.generator_is_async(def_id) { |
| let def_id = cx.tcx.lang_items().future_trait().unwrap(); |
| is_def_must_use(cx, def_id, span) |
| .map(|inner| MustUsePath::Opaque(Box::new(inner))) |
| } else { |
| None |
| }; |
| must_use.or(Some(MustUsePath::Generator(span))) |
| } |
| _ => None, |
| } |
| } |
| |
| fn is_def_must_use(cx: &LateContext<'_>, def_id: DefId, span: Span) -> Option<MustUsePath> { |
| if let Some(attr) = cx.tcx.get_attr(def_id, sym::must_use) { |
| // check for #[must_use = "..."] |
| let reason = attr.value_str(); |
| Some(MustUsePath::Def(span, def_id, reason)) |
| } else { |
| None |
| } |
| } |
| |
| // Returns whether further errors should be suppressed because either a lint has been emitted or the type should be ignored. |
| fn check_must_use_def( |
| cx: &LateContext<'_>, |
| def_id: DefId, |
| span: Span, |
| descr_pre_path: &str, |
| descr_post_path: &str, |
| ) -> bool { |
| is_def_must_use(cx, def_id, span) |
| .map(|must_use_path| { |
| emit_must_use_untranslated( |
| cx, |
| &must_use_path, |
| descr_pre_path, |
| descr_post_path, |
| 1, |
| false, |
| ) |
| }) |
| .is_some() |
| } |
| |
| #[instrument(skip(cx), level = "debug")] |
| fn emit_must_use_untranslated( |
| cx: &LateContext<'_>, |
| path: &MustUsePath, |
| descr_pre: &str, |
| descr_post: &str, |
| plural_len: usize, |
| is_inner: bool, |
| ) { |
| let plural_suffix = pluralize!(plural_len); |
| |
| match path { |
| MustUsePath::Suppressed => {} |
| MustUsePath::Boxed(path) => { |
| let descr_pre = &format!("{}boxed ", descr_pre); |
| emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true); |
| } |
| MustUsePath::Opaque(path) => { |
| let descr_pre = &format!("{}implementer{} of ", descr_pre, plural_suffix); |
| emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true); |
| } |
| MustUsePath::TraitObject(path) => { |
| let descr_post = &format!(" trait object{}{}", plural_suffix, descr_post); |
| emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true); |
| } |
| MustUsePath::TupleElement(elems) => { |
| for (index, path) in elems { |
| let descr_post = &format!(" in tuple element {}", index); |
| emit_must_use_untranslated( |
| cx, path, descr_pre, descr_post, plural_len, true, |
| ); |
| } |
| } |
| MustUsePath::Array(path, len) => { |
| let descr_pre = &format!("{}array{} of ", descr_pre, plural_suffix); |
| emit_must_use_untranslated( |
| cx, |
| path, |
| descr_pre, |
| descr_post, |
| plural_len.saturating_add(usize::try_from(*len).unwrap_or(usize::MAX)), |
| true, |
| ); |
| } |
| MustUsePath::Closure(span) => { |
| cx.emit_spanned_lint( |
| UNUSED_MUST_USE, |
| *span, |
| UnusedClosure { count: plural_len, pre: descr_pre, post: descr_post }, |
| ); |
| } |
| MustUsePath::Generator(span) => { |
| cx.emit_spanned_lint( |
| UNUSED_MUST_USE, |
| *span, |
| UnusedGenerator { count: plural_len, pre: descr_pre, post: descr_post }, |
| ); |
| } |
| MustUsePath::Def(span, def_id, reason) => { |
| cx.emit_spanned_lint( |
| UNUSED_MUST_USE, |
| *span, |
| UnusedDef { |
| pre: descr_pre, |
| post: descr_post, |
| cx, |
| def_id: *def_id, |
| note: *reason, |
| suggestion: (!is_inner) |
| .then_some(UnusedDefSuggestion { span: span.shrink_to_lo() }), |
| }, |
| ); |
| } |
| } |
| } |
| } |
| } |
| |
| declare_lint! { |
| /// The `path_statements` lint detects path statements with no effect. |
| /// |
| /// ### Example |
| /// |
| /// ```rust |
| /// let x = 42; |
| /// |
| /// x; |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// It is usually a mistake to have a statement that has no effect. |
| pub PATH_STATEMENTS, |
| Warn, |
| "path statements with no effect" |
| } |
| |
| declare_lint_pass!(PathStatements => [PATH_STATEMENTS]); |
| |
| impl<'tcx> LateLintPass<'tcx> for PathStatements { |
| fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) { |
| if let hir::StmtKind::Semi(expr) = s.kind { |
| if let hir::ExprKind::Path(_) = expr.kind { |
| let ty = cx.typeck_results().expr_ty(expr); |
| if ty.needs_drop(cx.tcx, cx.param_env) { |
| let sub = if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) |
| { |
| PathStatementDropSub::Suggestion { span: s.span, snippet } |
| } else { |
| PathStatementDropSub::Help { span: s.span } |
| }; |
| cx.emit_spanned_lint(PATH_STATEMENTS, s.span, PathStatementDrop { sub }) |
| } else { |
| cx.emit_spanned_lint(PATH_STATEMENTS, s.span, PathStatementNoEffect); |
| } |
| } |
| } |
| } |
| } |
| |
| #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
| enum UnusedDelimsCtx { |
| FunctionArg, |
| MethodArg, |
| AssignedValue, |
| AssignedValueLetElse, |
| IfCond, |
| WhileCond, |
| ForIterExpr, |
| MatchScrutineeExpr, |
| ReturnValue, |
| BlockRetValue, |
| LetScrutineeExpr, |
| ArrayLenExpr, |
| AnonConst, |
| MatchArmExpr, |
| IndexExpr, |
| } |
| |
| impl From<UnusedDelimsCtx> for &'static str { |
| fn from(ctx: UnusedDelimsCtx) -> &'static str { |
| match ctx { |
| UnusedDelimsCtx::FunctionArg => "function argument", |
| UnusedDelimsCtx::MethodArg => "method argument", |
| UnusedDelimsCtx::AssignedValue | UnusedDelimsCtx::AssignedValueLetElse => { |
| "assigned value" |
| } |
| UnusedDelimsCtx::IfCond => "`if` condition", |
| UnusedDelimsCtx::WhileCond => "`while` condition", |
| UnusedDelimsCtx::ForIterExpr => "`for` iterator expression", |
| UnusedDelimsCtx::MatchScrutineeExpr => "`match` scrutinee expression", |
| UnusedDelimsCtx::ReturnValue => "`return` value", |
| UnusedDelimsCtx::BlockRetValue => "block return value", |
| UnusedDelimsCtx::LetScrutineeExpr => "`let` scrutinee expression", |
| UnusedDelimsCtx::ArrayLenExpr | UnusedDelimsCtx::AnonConst => "const expression", |
| UnusedDelimsCtx::MatchArmExpr => "match arm expression", |
| UnusedDelimsCtx::IndexExpr => "index expression", |
| } |
| } |
| } |
| |
| /// Used by both `UnusedParens` and `UnusedBraces` to prevent code duplication. |
| trait UnusedDelimLint { |
| const DELIM_STR: &'static str; |
| |
| /// Due to `ref` pattern, there can be a difference between using |
| /// `{ expr }` and `expr` in pattern-matching contexts. This means |
| /// that we should only lint `unused_parens` and not `unused_braces` |
| /// in this case. |
| /// |
| /// ```rust |
| /// let mut a = 7; |
| /// let ref b = { a }; // We actually borrow a copy of `a` here. |
| /// a += 1; // By mutating `a` we invalidate any borrows of `a`. |
| /// assert_eq!(b + 1, a); // `b` does not borrow `a`, so we can still use it here. |
| /// ``` |
| const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool; |
| |
| // this cannot be a constant is it refers to a static. |
| fn lint(&self) -> &'static Lint; |
| |
| fn check_unused_delims_expr( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Expr, |
| ctx: UnusedDelimsCtx, |
| followed_by_block: bool, |
| left_pos: Option<BytePos>, |
| right_pos: Option<BytePos>, |
| ); |
| |
| fn is_expr_delims_necessary( |
| inner: &ast::Expr, |
| followed_by_block: bool, |
| followed_by_else: bool, |
| ) -> bool { |
| if followed_by_else { |
| match inner.kind { |
| ast::ExprKind::Binary(op, ..) if op.node.lazy() => return true, |
| _ if classify::expr_trailing_brace(inner).is_some() => return true, |
| _ => {} |
| } |
| } |
| |
| // Check if LHS needs parens to prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`. |
| { |
| let mut innermost = inner; |
| loop { |
| innermost = match &innermost.kind { |
| ExprKind::Binary(_op, lhs, _rhs) => lhs, |
| ExprKind::Call(fn_, _params) => fn_, |
| ExprKind::Cast(expr, _ty) => expr, |
| ExprKind::Type(expr, _ty) => expr, |
| ExprKind::Index(base, _subscript) => base, |
| _ => break, |
| }; |
| if !classify::expr_requires_semi_to_be_stmt(innermost) { |
| return true; |
| } |
| } |
| } |
| |
| // Check if RHS needs parens to prevent false-positives in cases like `if (() == return) {}`. |
| if !followed_by_block { |
| return false; |
| } |
| let mut innermost = inner; |
| loop { |
| innermost = match &innermost.kind { |
| ExprKind::Unary(_op, expr) => expr, |
| ExprKind::Binary(_op, _lhs, rhs) => rhs, |
| ExprKind::AssignOp(_op, _lhs, rhs) => rhs, |
| ExprKind::Assign(_lhs, rhs, _span) => rhs, |
| |
| ExprKind::Ret(_) | ExprKind::Yield(..) | ExprKind::Yeet(..) => return true, |
| |
| ExprKind::Break(_label, None) => return false, |
| ExprKind::Break(_label, Some(break_expr)) => { |
| return matches!(break_expr.kind, ExprKind::Block(..)); |
| } |
| |
| ExprKind::Range(_lhs, Some(rhs), _limits) => { |
| return matches!(rhs.kind, ExprKind::Block(..)); |
| } |
| |
| _ => return parser::contains_exterior_struct_lit(&inner), |
| } |
| } |
| } |
| |
| fn emit_unused_delims_expr( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Expr, |
| ctx: UnusedDelimsCtx, |
| left_pos: Option<BytePos>, |
| right_pos: Option<BytePos>, |
| ) { |
| // If `value` has `ExprKind::Err`, unused delim lint can be broken. |
| // For example, the following code caused ICE. |
| // This is because the `ExprKind::Call` in `value` has `ExprKind::Err` as its argument |
| // and this leads to wrong spans. #104897 |
| // |
| // ``` |
| // fn f(){(print!(á |
| // ``` |
| use rustc_ast::visit::{walk_expr, Visitor}; |
| struct ErrExprVisitor { |
| has_error: bool, |
| } |
| impl<'ast> Visitor<'ast> for ErrExprVisitor { |
| fn visit_expr(&mut self, expr: &'ast ast::Expr) { |
| if let ExprKind::Err = expr.kind { |
| self.has_error = true; |
| return; |
| } |
| walk_expr(self, expr) |
| } |
| } |
| let mut visitor = ErrExprVisitor { has_error: false }; |
| visitor.visit_expr(value); |
| if visitor.has_error { |
| return; |
| } |
| let spans = match value.kind { |
| ast::ExprKind::Block(ref block, None) if block.stmts.len() == 1 => block.stmts[0] |
| .span |
| .find_ancestor_inside(value.span) |
| .map(|span| (value.span.with_hi(span.lo()), value.span.with_lo(span.hi()))), |
| ast::ExprKind::Paren(ref expr) => { |
| expr.span.find_ancestor_inside(value.span).map(|expr_span| { |
| (value.span.with_hi(expr_span.lo()), value.span.with_lo(expr_span.hi())) |
| }) |
| } |
| _ => return, |
| }; |
| let keep_space = ( |
| left_pos.is_some_and(|s| s >= value.span.lo()), |
| right_pos.is_some_and(|s| s <= value.span.hi()), |
| ); |
| self.emit_unused_delims(cx, value.span, spans, ctx.into(), keep_space); |
| } |
| |
| fn emit_unused_delims( |
| &self, |
| cx: &EarlyContext<'_>, |
| value_span: Span, |
| spans: Option<(Span, Span)>, |
| msg: &str, |
| keep_space: (bool, bool), |
| ) { |
| let primary_span = if let Some((lo, hi)) = spans { |
| if hi.is_empty() { |
| // do not point at delims that do not exist |
| return; |
| } |
| MultiSpan::from(vec![lo, hi]) |
| } else { |
| MultiSpan::from(value_span) |
| }; |
| let suggestion = spans.map(|(lo, hi)| { |
| let sm = cx.sess().source_map(); |
| let lo_replace = |
| if keep_space.0 && |
| let Ok(snip) = sm.span_to_prev_source(lo) && !snip.ends_with(' ') { |
| " " |
| } else { |
| "" |
| }; |
| |
| let hi_replace = |
| if keep_space.1 && |
| let Ok(snip) = sm.span_to_next_source(hi) && !snip.starts_with(' ') { |
| " " |
| } else { |
| "" |
| }; |
| UnusedDelimSuggestion { |
| start_span: lo, |
| start_replace: lo_replace, |
| end_span: hi, |
| end_replace: hi_replace, |
| } |
| }); |
| cx.emit_spanned_lint( |
| self.lint(), |
| primary_span, |
| UnusedDelim { delim: Self::DELIM_STR, item: msg, suggestion }, |
| ); |
| } |
| |
| fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { |
| use rustc_ast::ExprKind::*; |
| let (value, ctx, followed_by_block, left_pos, right_pos) = match e.kind { |
| // Do not lint `unused_braces` in `if let` expressions. |
| If(ref cond, ref block, _) |
| if !matches!(cond.kind, Let(_, _, _)) |
| || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => |
| { |
| let left = e.span.lo() + rustc_span::BytePos(2); |
| let right = block.span.lo(); |
| (cond, UnusedDelimsCtx::IfCond, true, Some(left), Some(right)) |
| } |
| |
| // Do not lint `unused_braces` in `while let` expressions. |
| While(ref cond, ref block, ..) |
| if !matches!(cond.kind, Let(_, _, _)) |
| || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => |
| { |
| let left = e.span.lo() + rustc_span::BytePos(5); |
| let right = block.span.lo(); |
| (cond, UnusedDelimsCtx::WhileCond, true, Some(left), Some(right)) |
| } |
| |
| ForLoop(_, ref cond, ref block, ..) => { |
| (cond, UnusedDelimsCtx::ForIterExpr, true, None, Some(block.span.lo())) |
| } |
| |
| Match(ref head, _) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => { |
| let left = e.span.lo() + rustc_span::BytePos(5); |
| (head, UnusedDelimsCtx::MatchScrutineeExpr, true, Some(left), None) |
| } |
| |
| Ret(Some(ref value)) => { |
| let left = e.span.lo() + rustc_span::BytePos(3); |
| (value, UnusedDelimsCtx::ReturnValue, false, Some(left), None) |
| } |
| |
| Index(_, ref value) => (value, UnusedDelimsCtx::IndexExpr, false, None, None), |
| |
| Assign(_, ref value, _) | AssignOp(.., ref value) => { |
| (value, UnusedDelimsCtx::AssignedValue, false, None, None) |
| } |
| // either function/method call, or something this lint doesn't care about |
| ref call_or_other => { |
| let (args_to_check, ctx) = match *call_or_other { |
| Call(_, ref args) => (&args[..], UnusedDelimsCtx::FunctionArg), |
| MethodCall(ref call) => (&call.args[..], UnusedDelimsCtx::MethodArg), |
| // 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; |
| } |
| for arg in args_to_check { |
| self.check_unused_delims_expr(cx, arg, ctx, false, None, None); |
| } |
| return; |
| } |
| }; |
| self.check_unused_delims_expr(cx, &value, ctx, followed_by_block, left_pos, right_pos); |
| } |
| |
| fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) { |
| match s.kind { |
| StmtKind::Local(ref local) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => { |
| if let Some((init, els)) = local.kind.init_else_opt() { |
| let ctx = match els { |
| None => UnusedDelimsCtx::AssignedValue, |
| Some(_) => UnusedDelimsCtx::AssignedValueLetElse, |
| }; |
| self.check_unused_delims_expr(cx, init, ctx, false, None, None); |
| } |
| } |
| StmtKind::Expr(ref expr) => { |
| self.check_unused_delims_expr( |
| cx, |
| &expr, |
| UnusedDelimsCtx::BlockRetValue, |
| false, |
| None, |
| None, |
| ); |
| } |
| _ => {} |
| } |
| } |
| |
| fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { |
| use ast::ItemKind::*; |
| |
| if let Const(box ast::ConstItem { expr: Some(expr), .. }) |
| | Static(box ast::StaticItem { expr: Some(expr), .. }) = &item.kind |
| { |
| self.check_unused_delims_expr( |
| cx, |
| expr, |
| UnusedDelimsCtx::AssignedValue, |
| false, |
| None, |
| None, |
| ); |
| } |
| } |
| } |
| |
| declare_lint! { |
| /// The `unused_parens` lint detects `if`, `match`, `while` and `return` |
| /// with parentheses; they do not need them. |
| /// |
| /// ### Examples |
| /// |
| /// ```rust |
| /// if(true) {} |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// The parentheses are not needed, and should be removed. This is the |
| /// preferred style for writing these expressions. |
| pub(super) UNUSED_PARENS, |
| Warn, |
| "`if`, `match`, `while` and `return` do not need parentheses" |
| } |
| |
| pub struct UnusedParens { |
| with_self_ty_parens: bool, |
| } |
| |
| impl UnusedParens { |
| pub fn new() -> Self { |
| Self { with_self_ty_parens: false } |
| } |
| } |
| |
| impl_lint_pass!(UnusedParens => [UNUSED_PARENS]); |
| |
| impl UnusedDelimLint for UnusedParens { |
| const DELIM_STR: &'static str = "parentheses"; |
| |
| const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = true; |
| |
| fn lint(&self) -> &'static Lint { |
| UNUSED_PARENS |
| } |
| |
| fn check_unused_delims_expr( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Expr, |
| ctx: UnusedDelimsCtx, |
| followed_by_block: bool, |
| left_pos: Option<BytePos>, |
| right_pos: Option<BytePos>, |
| ) { |
| match value.kind { |
| ast::ExprKind::Paren(ref inner) => { |
| let followed_by_else = ctx == UnusedDelimsCtx::AssignedValueLetElse; |
| if !Self::is_expr_delims_necessary(inner, followed_by_block, followed_by_else) |
| && value.attrs.is_empty() |
| && !value.span.from_expansion() |
| && (ctx != UnusedDelimsCtx::LetScrutineeExpr |
| || !matches!(inner.kind, ast::ExprKind::Binary( |
| rustc_span::source_map::Spanned { node, .. }, |
| _, |
| _, |
| ) if node.lazy())) |
| { |
| self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos) |
| } |
| } |
| ast::ExprKind::Let(_, ref expr, _) => { |
| self.check_unused_delims_expr( |
| cx, |
| expr, |
| UnusedDelimsCtx::LetScrutineeExpr, |
| followed_by_block, |
| None, |
| None, |
| ); |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| impl UnusedParens { |
| fn check_unused_parens_pat( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Pat, |
| avoid_or: bool, |
| avoid_mut: bool, |
| keep_space: (bool, bool), |
| ) { |
| use ast::{BindingAnnotation, 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(BindingAnnotation::MUT, ..) if avoid_mut => { |
| return; |
| } |
| // Otherwise proceed with linting. |
| _ => {} |
| } |
| let spans = inner |
| .span |
| .find_ancestor_inside(value.span) |
| .map(|inner| (value.span.with_hi(inner.lo()), value.span.with_lo(inner.hi()))); |
| self.emit_unused_delims(cx, value.span, spans, "pattern", keep_space); |
| } |
| } |
| } |
| |
| impl EarlyLintPass for UnusedParens { |
| #[inline] |
| fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { |
| match e.kind { |
| ExprKind::Let(ref pat, _, _) | ExprKind::ForLoop(ref pat, ..) => { |
| self.check_unused_parens_pat(cx, pat, false, false, (true, true)); |
| } |
| // We ignore parens in cases like `if (((let Some(0) = Some(1))))` because we already |
| // handle a hard error for them during AST lowering in `lower_expr_mut`, but we still |
| // want to complain about things like `if let 42 = (42)`. |
| ExprKind::If(ref cond, ref block, ref else_) |
| if matches!(cond.peel_parens().kind, ExprKind::Let(..)) => |
| { |
| self.check_unused_delims_expr( |
| cx, |
| cond.peel_parens(), |
| UnusedDelimsCtx::LetScrutineeExpr, |
| true, |
| None, |
| None, |
| ); |
| for stmt in &block.stmts { |
| <Self as UnusedDelimLint>::check_stmt(self, cx, stmt); |
| } |
| if let Some(e) = else_ { |
| <Self as UnusedDelimLint>::check_expr(self, cx, e); |
| } |
| return; |
| } |
| ExprKind::Match(ref _expr, ref arm) => { |
| for a in arm { |
| self.check_unused_delims_expr( |
| cx, |
| &a.body, |
| UnusedDelimsCtx::MatchArmExpr, |
| false, |
| None, |
| None, |
| ); |
| } |
| } |
| _ => {} |
| } |
| |
| <Self as UnusedDelimLint>::check_expr(self, cx, e) |
| } |
| |
| fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat) { |
| use ast::{Mutability, PatKind::*}; |
| let keep_space = (false, false); |
| 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(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) => {}, |
| // 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, keep_space); |
| }, |
| Struct(_, _, fps, _) => for f in fps { |
| self.check_unused_parens_pat(cx, &f.pat, false, false, keep_space); |
| }, |
| // 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, keep_space), |
| // 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, keep_space), |
| } |
| } |
| |
| fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) { |
| if let StmtKind::Local(ref local) = s.kind { |
| self.check_unused_parens_pat(cx, &local.pat, true, false, (false, false)); |
| } |
| |
| <Self as UnusedDelimLint>::check_stmt(self, cx, s) |
| } |
| |
| fn check_param(&mut self, cx: &EarlyContext<'_>, param: &ast::Param) { |
| self.check_unused_parens_pat(cx, ¶m.pat, true, false, (false, false)); |
| } |
| |
| fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) { |
| self.check_unused_parens_pat(cx, &arm.pat, false, false, (false, false)); |
| } |
| |
| fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) { |
| match &ty.kind { |
| ast::TyKind::Array(_, len) => { |
| self.check_unused_delims_expr( |
| cx, |
| &len.value, |
| UnusedDelimsCtx::ArrayLenExpr, |
| false, |
| None, |
| None, |
| ); |
| } |
| ast::TyKind::Paren(r) => { |
| match &r.kind { |
| ast::TyKind::TraitObject(..) => {} |
| ast::TyKind::BareFn(b) |
| if self.with_self_ty_parens && b.generic_params.len() > 0 => {} |
| ast::TyKind::ImplTrait(_, bounds) if bounds.len() > 1 => {} |
| _ => { |
| let spans = r |
| .span |
| .find_ancestor_inside(ty.span) |
| .map(|r| (ty.span.with_hi(r.lo()), ty.span.with_lo(r.hi()))); |
| |
| self.emit_unused_delims(cx, ty.span, spans, "type", (false, false)); |
| } |
| } |
| self.with_self_ty_parens = false; |
| } |
| _ => {} |
| } |
| } |
| |
| fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { |
| <Self as UnusedDelimLint>::check_item(self, cx, item) |
| } |
| |
| fn enter_where_predicate(&mut self, _: &EarlyContext<'_>, pred: &ast::WherePredicate) { |
| use rustc_ast::{WhereBoundPredicate, WherePredicate}; |
| if let WherePredicate::BoundPredicate(WhereBoundPredicate { |
| bounded_ty, |
| bound_generic_params, |
| .. |
| }) = pred && |
| let ast::TyKind::Paren(_) = &bounded_ty.kind && |
| bound_generic_params.is_empty() { |
| self.with_self_ty_parens = true; |
| } |
| } |
| |
| fn exit_where_predicate(&mut self, _: &EarlyContext<'_>, _: &ast::WherePredicate) { |
| assert!(!self.with_self_ty_parens); |
| } |
| } |
| |
| declare_lint! { |
| /// The `unused_braces` lint detects unnecessary braces around an |
| /// expression. |
| /// |
| /// ### Example |
| /// |
| /// ```rust |
| /// if { true } { |
| /// // ... |
| /// } |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// The braces are not needed, and should be removed. This is the |
| /// preferred style for writing these expressions. |
| pub(super) UNUSED_BRACES, |
| Warn, |
| "unnecessary braces around an expression" |
| } |
| |
| declare_lint_pass!(UnusedBraces => [UNUSED_BRACES]); |
| |
| impl UnusedDelimLint for UnusedBraces { |
| const DELIM_STR: &'static str = "braces"; |
| |
| const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = false; |
| |
| fn lint(&self) -> &'static Lint { |
| UNUSED_BRACES |
| } |
| |
| fn check_unused_delims_expr( |
| &self, |
| cx: &EarlyContext<'_>, |
| value: &ast::Expr, |
| ctx: UnusedDelimsCtx, |
| followed_by_block: bool, |
| left_pos: Option<BytePos>, |
| right_pos: Option<BytePos>, |
| ) { |
| match value.kind { |
| ast::ExprKind::Block(ref inner, None) |
| if inner.rules == ast::BlockCheckMode::Default => |
| { |
| // emit a warning under the following conditions: |
| // |
| // - the block does not have a label |
| // - the block is not `unsafe` |
| // - the block contains exactly one expression (do not lint `{ expr; }`) |
| // - `followed_by_block` is true and the internal expr may contain a `{` |
| // - the block is not multiline (do not lint multiline match arms) |
| // ``` |
| // match expr { |
| // Pattern => { |
| // somewhat_long_expression |
| // } |
| // // ... |
| // } |
| // ``` |
| // - the block has no attribute and was not created inside a macro |
| // - if the block is an `anon_const`, the inner expr must be a literal |
| // not created by a macro, i.e. do not lint on: |
| // ``` |
| // struct A<const N: usize>; |
| // let _: A<{ 2 + 3 }>; |
| // let _: A<{produces_literal!()}>; |
| // ``` |
| // FIXME(const_generics): handle paths when #67075 is fixed. |
| if let [stmt] = inner.stmts.as_slice() { |
| if let ast::StmtKind::Expr(ref expr) = stmt.kind { |
| if !Self::is_expr_delims_necessary(expr, followed_by_block, false) |
| && (ctx != UnusedDelimsCtx::AnonConst |
| || (matches!(expr.kind, ast::ExprKind::Lit(_)) |
| && !expr.span.from_expansion())) |
| && !cx.sess().source_map().is_multiline(value.span) |
| && value.attrs.is_empty() |
| && !value.span.from_expansion() |
| && !inner.span.from_expansion() |
| { |
| self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos) |
| } |
| } |
| } |
| } |
| ast::ExprKind::Let(_, ref expr, _) => { |
| self.check_unused_delims_expr( |
| cx, |
| expr, |
| UnusedDelimsCtx::LetScrutineeExpr, |
| followed_by_block, |
| None, |
| None, |
| ); |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| impl EarlyLintPass for UnusedBraces { |
| fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) { |
| <Self as UnusedDelimLint>::check_stmt(self, cx, s) |
| } |
| |
| #[inline] |
| fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { |
| <Self as UnusedDelimLint>::check_expr(self, cx, e); |
| |
| if let ExprKind::Repeat(_, ref anon_const) = e.kind { |
| self.check_unused_delims_expr( |
| cx, |
| &anon_const.value, |
| UnusedDelimsCtx::AnonConst, |
| false, |
| None, |
| None, |
| ); |
| } |
| } |
| |
| fn check_generic_arg(&mut self, cx: &EarlyContext<'_>, arg: &ast::GenericArg) { |
| if let ast::GenericArg::Const(ct) = arg { |
| self.check_unused_delims_expr( |
| cx, |
| &ct.value, |
| UnusedDelimsCtx::AnonConst, |
| false, |
| None, |
| None, |
| ); |
| } |
| } |
| |
| fn check_variant(&mut self, cx: &EarlyContext<'_>, v: &ast::Variant) { |
| if let Some(anon_const) = &v.disr_expr { |
| self.check_unused_delims_expr( |
| cx, |
| &anon_const.value, |
| UnusedDelimsCtx::AnonConst, |
| false, |
| None, |
| None, |
| ); |
| } |
| } |
| |
| fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) { |
| match ty.kind { |
| ast::TyKind::Array(_, ref len) => { |
| self.check_unused_delims_expr( |
| cx, |
| &len.value, |
| UnusedDelimsCtx::ArrayLenExpr, |
| false, |
| None, |
| None, |
| ); |
| } |
| |
| ast::TyKind::Typeof(ref anon_const) => { |
| self.check_unused_delims_expr( |
| cx, |
| &anon_const.value, |
| UnusedDelimsCtx::AnonConst, |
| false, |
| None, |
| None, |
| ); |
| } |
| |
| _ => {} |
| } |
| } |
| |
| fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { |
| <Self as UnusedDelimLint>::check_item(self, cx, item) |
| } |
| } |
| |
| declare_lint! { |
| /// The `unused_import_braces` lint catches unnecessary braces around an |
| /// imported item. |
| /// |
| /// ### Example |
| /// |
| /// ```rust,compile_fail |
| /// #![deny(unused_import_braces)] |
| /// use test::{A}; |
| /// |
| /// pub mod test { |
| /// pub struct A; |
| /// } |
| /// # fn main() {} |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// If there is only a single item, then remove the braces (`use test::A;` |
| /// for example). |
| /// |
| /// This lint is "allow" by default because it is only enforcing a |
| /// stylistic choice. |
| 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 (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.emit_spanned_lint( |
| UNUSED_IMPORT_BRACES, |
| item.span, |
| UnusedImportBracesDiag { node: node_name }, |
| ); |
| } |
| } |
| } |
| |
| 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! { |
| /// The `unused_allocation` lint detects unnecessary allocations that can |
| /// be eliminated. |
| /// |
| /// ### Example |
| /// |
| /// ```rust |
| /// fn main() { |
| /// let a = Box::new([1, 2, 3]).len(); |
| /// } |
| /// ``` |
| /// |
| /// {{produces}} |
| /// |
| /// ### Explanation |
| /// |
| /// When a `box` expression is immediately coerced to a reference, then |
| /// the allocation is unnecessary, and a reference (using `&` or `&mut`) |
| /// should be used instead to avoid the allocation. |
| pub(super) UNUSED_ALLOCATION, |
| Warn, |
| "detects unnecessary allocations that can be eliminated" |
| } |
| |
| declare_lint_pass!(UnusedAllocation => [UNUSED_ALLOCATION]); |
| |
| impl<'tcx> LateLintPass<'tcx> for UnusedAllocation { |
| fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) { |
| match e.kind { |
| hir::ExprKind::Call(path_expr, [_]) |
| if let hir::ExprKind::Path(qpath) = &path_expr.kind |
| && let Some(did) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id() |
| && cx.tcx.is_diagnostic_item(sym::box_new, did) |
| => {} |
| _ => return, |
| } |
| |
| for adj in cx.typeck_results().expr_adjustments(e) { |
| if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind { |
| match m { |
| adjustment::AutoBorrowMutability::Not => { |
| cx.emit_spanned_lint(UNUSED_ALLOCATION, e.span, UnusedAllocationDiag); |
| } |
| adjustment::AutoBorrowMutability::Mut { .. } => { |
| cx.emit_spanned_lint(UNUSED_ALLOCATION, e.span, UnusedAllocationMutDiag); |
| } |
| }; |
| } |
| } |
| } |
| } |
