use crate::lints::{ PathStatementDrop, PathStatementDropSub, PathStatementNoEffect, UnusedAllocationDiag, UnusedAllocationMutDiag, UnusedClosure, UnusedCoroutine, UnusedDef, UnusedDefSuggestion, UnusedDelim, UnusedDelimSuggestion, UnusedImportBracesDiag, UnusedOp, UnusedOpSuggestion, 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 { panic!() } /// /// fn main() { /// foo::(); /// } /// ``` /// /// {{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(mut expr) = s.kind else { return; }; let mut expr_is_from_block = false; while let hir::ExprKind::Block(blk, ..) = expr.kind && let hir::Block { expr: Some(e), .. } = blk { expr = e; expr_is_from_block = true; } 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 ", "", expr_is_from_block, ) { // 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, expr_is_from_block); true } None => false, }; let fn_warned = check_fn_must_use(cx, expr, expr_is_from_block); 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: if expr_is_from_block { UnusedOpSuggestion::BlockTailExpr { before_span: expr.span.shrink_to_lo(), after_span: expr.span.shrink_to_hi(), } } else { UnusedOpSuggestion::NormalExpr { span: 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<'_>, expr_is_from_block: bool, ) -> 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 ", "", expr_is_from_block, ) } 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), Boxed(Box), Opaque(Box), TraitObject(Box), TupleElement(Vec<(usize, Self)>), Array(Box, u64), /// The root of the unused_closures lint. Closure(Span), /// The root of the unused_coroutines lint. Coroutine(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 { 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).instantiate_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::ClauseKind::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::>(); 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::Coroutine(def_id, ..) => { // async fn should be treated as "implementor of `Future`" let must_use = if cx.tcx.coroutine_is_async(def_id) { let def_id = cx.tcx.lang_items().future_trait()?; is_def_must_use(cx, def_id, span) .map(|inner| MustUsePath::Opaque(Box::new(inner))) } else { None }; must_use.or(Some(MustUsePath::Coroutine(span))) } _ => None, } } fn is_def_must_use(cx: &LateContext<'_>, def_id: DefId, span: Span) -> Option { 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, expr_is_from_block: bool, ) -> 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, expr_is_from_block, ) }) .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, expr_is_from_block: bool, ) { let plural_suffix = pluralize!(plural_len); match path { MustUsePath::Suppressed => {} MustUsePath::Boxed(path) => { let descr_pre = &format!("{descr_pre}boxed "); emit_must_use_untranslated( cx, path, descr_pre, descr_post, plural_len, true, expr_is_from_block, ); } MustUsePath::Opaque(path) => { let descr_pre = &format!("{descr_pre}implementer{plural_suffix} of "); emit_must_use_untranslated( cx, path, descr_pre, descr_post, plural_len, true, expr_is_from_block, ); } 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, expr_is_from_block, ); } 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, expr_is_from_block, ); } } MustUsePath::Array(path, len) => { let descr_pre = &format!("{descr_pre}array{plural_suffix} of "); emit_must_use_untranslated( cx, path, descr_pre, descr_post, plural_len.saturating_add(usize::try_from(*len).unwrap_or(usize::MAX)), true, expr_is_from_block, ); } MustUsePath::Closure(span) => { cx.emit_spanned_lint( UNUSED_MUST_USE, *span, UnusedClosure { count: plural_len, pre: descr_pre, post: descr_post }, ); } MustUsePath::Coroutine(span) => { cx.emit_spanned_lint( UNUSED_MUST_USE, *span, UnusedCoroutine { 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(if expr_is_from_block { UnusedDefSuggestion::BlockTailExpr { before_span: span.shrink_to_lo(), after_span: span.shrink_to_hi(), } } else { UnusedDefSuggestion::NormalExpr { 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 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, right_pos: Option, is_kw: bool, ); 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; } // Check if we need parens for `match &( Struct { feild: }) {}`. { let mut innermost = inner; loop { innermost = match &innermost.kind { ExprKind::AddrOf(_, _, expr) => expr, _ => { if parser::contains_exterior_struct_lit(&innermost) { return true; } else { break; } } } } } 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, right_pos: Option, is_kw: bool, ) { // 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!(รก // ``` 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, is_kw); } fn emit_unused_delims( &self, cx: &EarlyContext<'_>, value_span: Span, spans: Option<(Span, Span)>, msg: &str, keep_space: (bool, bool), is_kw: 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 || is_kw) && 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, is_kw) = 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), true) } // 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), true) } ForLoop(_, ref cond, ref block, ..) => { (cond, UnusedDelimsCtx::ForIterExpr, true, None, Some(block.span.lo()), true) } 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, true) } Ret(Some(ref value)) => { let left = e.span.lo() + rustc_span::BytePos(3); (value, UnusedDelimsCtx::ReturnValue, false, Some(left), None, true) } Index(_, ref value, _) => (value, UnusedDelimsCtx::IndexExpr, false, None, None, false), Assign(_, ref value, _) | AssignOp(.., ref value) => { (value, UnusedDelimsCtx::AssignedValue, false, None, None, false) } // 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, false); } return; } }; self.check_unused_delims_expr( cx, &value, ctx, followed_by_block, left_pos, right_pos, is_kw, ); } 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, false); } } StmtKind::Expr(ref expr) => { self.check_unused_delims_expr( cx, &expr, UnusedDelimsCtx::BlockRetValue, false, None, None, false, ); } _ => {} } } 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, false, ); } } } 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, /// `1 as (i32) < 2` parses to ExprKind::Lt /// `1 as i32 < 2` parses to i32::<2[missing angle bracket] parens_in_cast_in_lt: Vec, } impl UnusedParens { pub fn new() -> Self { Self { with_self_ty_parens: false, parens_in_cast_in_lt: Vec::new() } } } 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, right_pos: Option, is_kw: bool, ) { 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, is_kw) } } ast::ExprKind::Let(_, ref expr, _, _) => { self.check_unused_delims_expr( cx, expr, UnusedDelimsCtx::LetScrutineeExpr, followed_by_block, None, None, false, ); } _ => {} } } } 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, false); } } } impl EarlyLintPass for UnusedParens { #[inline] fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { if let ExprKind::Binary(op, lhs, _rhs) = &e.kind && (op.node == ast::BinOpKind::Lt || op.node == ast::BinOpKind::Shl) && let ExprKind::Cast(_expr, ty) = &lhs.kind && let ast::TyKind::Paren(_) = &ty.kind { self.parens_in_cast_in_lt.push(ty.id); } 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, true, ); for stmt in &block.stmts { ::check_stmt(self, cx, stmt); } if let Some(e) = else_ { ::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, true, ); } } _ => {} } ::check_expr(self, cx, e) } fn check_expr_post(&mut self, _cx: &EarlyContext<'_>, e: &ast::Expr) { if let ExprKind::Binary(op, lhs, _rhs) = &e.kind && (op.node == ast::BinOpKind::Lt || op.node == ast::BinOpKind::Shl) && let ExprKind::Cast(_expr, ty) = &lhs.kind && let ast::TyKind::Paren(_) = &ty.kind { let id = self .parens_in_cast_in_lt .pop() .expect("check_expr and check_expr_post must balance"); assert_eq!( id, ty.id, "check_expr, check_ty, and check_expr_post are called, in that order, by the visitor" ); } } 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, (true, false)); } ::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) { if let ast::TyKind::Paren(_) = ty.kind && Some(&ty.id) == self.parens_in_cast_in_lt.last() { return; } match &ty.kind { ast::TyKind::Array(_, len) => { self.check_unused_delims_expr( cx, &len.value, UnusedDelimsCtx::ArrayLenExpr, false, None, None, false, ); } 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), false); } } self.with_self_ty_parens = false; } _ => {} } } fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { ::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, right_pos: Option, is_kw: bool, ) { 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; // 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, is_kw) } } } } ast::ExprKind::Let(_, ref expr, _, _) => { self.check_unused_delims_expr( cx, expr, UnusedDelimsCtx::LetScrutineeExpr, followed_by_block, None, None, false, ); } _ => {} } } } impl EarlyLintPass for UnusedBraces { fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) { ::check_stmt(self, cx, s) } #[inline] fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) { ::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, false, ); } } 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, false, ); } } 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, false, ); } } 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, false, ); } ast::TyKind::Typeof(ref anon_const) => { self.check_unused_delims_expr( cx, &anon_const.value, UnusedDelimsCtx::AnonConst, false, None, None, false, ); } _ => {} } } fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { ::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); } }; } } } }