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Diffstat (limited to 'compiler/rustc_lint/src/unused.rs')
| -rw-r--r-- | compiler/rustc_lint/src/unused.rs | 1232 |
1 files changed, 1232 insertions, 0 deletions
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs new file mode 100644 index 00000000000..2b580452a60 --- /dev/null +++ b/compiler/rustc_lint/src/unused.rs @@ -0,0 +1,1232 @@ +use crate::Lint; +use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext}; +use rustc_ast as ast; +use rustc_ast::util::parser; +use rustc_ast::{ExprKind, StmtKind}; +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_middle::ty::adjustment; +use rustc_middle::ty::{self, Ty}; +use rustc_session::lint::builtin::UNUSED_ATTRIBUTES; +use rustc_span::symbol::Symbol; +use rustc_span::symbol::{kw, sym}; +use rustc_span::{BytePos, Span, DUMMY_SP}; + +use tracing::debug; + +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 expr = match s.kind { + hir::StmtKind::Semi(ref expr) => &**expr, + _ => return, + }; + + if let hir::ExprKind::Ret(..) = expr.kind { + return; + } + + let ty = cx.typeck_results().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.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 { + 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::AddrOf(..) => Some("borrow"), + 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| { + let mut lint = lint.build(&format!("unused {} that must be used", must_use_op)); + lint.span_label(expr.span, &format!("the {} produces a value", must_use_op)); + lint.span_suggestion_verbose( + expr.span.shrink_to_lo(), + "use `let _ = ...` to ignore the resulting value", + "let _ = ".to_string(), + Applicability::MachineApplicable, + ); + lint.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).to_def_id(), + ty, + cx.param_env, + ) + { + 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.explicit_item_bounds(def) { + // We only look at the `DefId`, so it is safe to skip the binder here. + if let ty::PredicateKind::Trait(ref poly_trait_predicate, _) = + predicate.kind().skip_binder() + { + let def_id = poly_trait_predicate.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.iter() { + if let ty::ExistentialPredicate::Trait(ref trait_ref) = + predicate.skip_binder() + { + 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 empty we don't lint, to avoid false positives + Some(0) | None => false, + // If the array is definitely non-empty, we can do `#[must_use]` checking. + Some(n) => { + 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) + } + }, + ty::Closure(..) => { + cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| { + let mut err = lint.build(&format!( + "unused {}closure{}{} that must be used", + descr_pre, plural_suffix, descr_post, + )); + err.note("closures are lazy and do nothing unless called"); + err.emit(); + }); + true + } + ty::Generator(..) => { + cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| { + let mut err = lint.build(&format!( + "unused {}generator{}{} that must be used", + descr_pre, plural_suffix, descr_post, + )); + err.note("generators are lazy and do nothing unless resumed"); + err.emit(); + }); + true + } + _ => 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 cx.sess().check_name(attr, 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! { + /// 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 { + cx.struct_span_lint(PATH_STATEMENTS, s.span, |lint| { + let ty = cx.typeck_results().expr_ty(expr); + if ty.needs_drop(cx.tcx, cx.param_env) { + let mut lint = lint.build("path statement drops value"); + if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) { + lint.span_suggestion( + s.span, + "use `drop` to clarify the intent", + format!("drop({});", snippet), + Applicability::MachineApplicable, + ); + } else { + lint.span_help(s.span, "use `drop` to clarify the intent"); + } + lint.emit() + } else { + 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<'tcx> LateLintPass<'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 { + if let AttributeType::AssumedUsed = ty { + debug!("{:?} is AssumedUsed", name); + return; + } + } + + if !cx.sess().is_attr_used(attr) { + debug!("emitting warning for: {:?}", attr); + cx.struct_span_lint(UNUSED_ATTRIBUTES, attr.span, |lint| { + // Mark as used to avoid duplicate warnings. + cx.sess().mark_attr_used(attr); + 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); + } + } +} + +#[derive(Copy, Clone, Debug, PartialEq, Eq)] +enum UnusedDelimsCtx { + FunctionArg, + MethodArg, + AssignedValue, + IfCond, + WhileCond, + ForIterExpr, + MatchScrutineeExpr, + ReturnValue, + BlockRetValue, + LetScrutineeExpr, + ArrayLenExpr, + AnonConst, +} + +impl From<UnusedDelimsCtx> for &'static str { + fn from(ctx: UnusedDelimsCtx) -> &'static str { + match ctx { + UnusedDelimsCtx::FunctionArg => "function argument", + UnusedDelimsCtx::MethodArg => "method argument", + UnusedDelimsCtx::AssignedValue => "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", + } + } +} + +/// 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) -> bool { + // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }` + let lhs_needs_parens = { + let mut innermost = inner; + loop { + if let ExprKind::Binary(_, lhs, _rhs) = &innermost.kind { + innermost = lhs; + if !rustc_ast::util::classify::expr_requires_semi_to_be_stmt(innermost) { + break true; + } + } else { + break false; + } + } + }; + + lhs_needs_parens + || (followed_by_block + && match inner.kind { + ExprKind::Ret(_) | ExprKind::Break(..) | ExprKind::Yield(..) => true, + _ => 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>, + ) { + 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_or(false, |s| s >= value.span.lo()), + right_pos.map_or(false, |s| s <= value.span.hi()), + ); + self.emit_unused_delims(cx, value.span, &expr_text, ctx.into(), keep_space); + } + + fn emit_unused_delims( + &self, + cx: &EarlyContext<'_>, + span: Span, + pattern: &str, + msg: &str, + keep_space: (bool, bool), + ) { + // FIXME(flip1995): Quick and dirty fix for #70814. This should be fixed in rustdoc + // properly. + if span == DUMMY_SP { + return; + } + + cx.struct_span_lint(self.lint(), span, |lint| { + let span_msg = format!("unnecessary {} around {}", Self::DELIM_STR, 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, + }) + .trim(); + + 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 + }; + + let suggestion = format!("remove these {}", Self::DELIM_STR); + + err.span_suggestion_short(span, &suggestion, replace, Applicability::MachineApplicable); + err.emit(); + }); + } + + 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) + } + + 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), + // first "argument" is self (which sometimes needs delims) + MethodCall(_, ref args, _) => (&args[1..], 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(ref value) = local.init { + self.check_unused_delims_expr( + cx, + &value, + UnusedDelimsCtx::AssignedValue, + 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(.., Some(expr)) | Static(.., 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 parenthesis 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" +} + +declare_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) => { + if !Self::is_expr_delims_necessary(inner, followed_by_block) + && 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, + ) { + 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.emit_unused_delims(cx, value.span, &pattern_text, "pattern", (false, false)); + } + } +} + +impl EarlyLintPass for UnusedParens { + 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); + } + // 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; + } + _ => {} + } + + <Self as UnusedDelimLint>::check_expr(self, cx, e) + } + + 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(..) | 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); + }, + 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) { + if let StmtKind::Local(ref local) = s.kind { + self.check_unused_parens_pat(cx, &local.pat, true, 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); + } + + 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(r) = &ty.kind { + match &r.kind { + ast::TyKind::TraitObject(..) => {} + ast::TyKind::ImplTrait(_, bounds) if bounds.len() > 1 => {} + ast::TyKind::Array(_, len) => { + self.check_unused_delims_expr( + cx, + &len.value, + UnusedDelimsCtx::ArrayLenExpr, + false, + None, + None, + ); + } + _ => { + let pattern_text = + if let Ok(snippet) = cx.sess().source_map().span_to_snippet(ty.span) { + snippet + } else { + pprust::ty_to_string(ty) + }; + + self.emit_unused_delims(cx, ty.span, &pattern_text, "type", (false, false)); + } + } + } + } + + fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) { + <Self as UnusedDelimLint>::check_item(self, cx, item) + } +} + +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 + // (do not lint `struct A<const N: usize>; let _: A<{ 2 + 3 }>;`) + // + // 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) + && (ctx != UnusedDelimsCtx::AnonConst + || matches!(expr.kind, ast::ExprKind::Lit(_))) + && !cx.sess().source_map().is_multiline(value.span) + && value.attrs.is_empty() + && !value.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) + } + + 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 &(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! { + /// The `unused_allocation` lint detects unnecessary allocations that can + /// be eliminated. + /// + /// ### Example + /// + /// ```rust + /// #![feature(box_syntax)] + /// fn main() { + /// let a = (box [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::Box(_) => {} + _ => return, + } + + for adj in cx.typeck_results().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() + }); + } + } + } +} |