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-rw-r--r--compiler/rustc_lint/src/unused.rs1197
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diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
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+++ b/compiler/rustc_lint/src/unused.rs
@@ -0,0 +1,1197 @@
+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::{fluent, pluralize, Applicability, MultiSpan};
+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_span::symbol::Symbol;
+use rustc_span::symbol::{kw, sym};
+use rustc_span::{BytePos, Span, DUMMY_SP};
+
+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| {
+ lint.build(fluent::lint::unused_op)
+ .set_arg("op", must_use_op)
+ .span_label(expr.span, fluent::lint::label)
+ .span_suggestion_verbose(
+ expr.span.shrink_to_lo(),
+ fluent::lint::suggestion,
+ "let _ = ",
+ Applicability::MachineApplicable,
+ )
+ .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(fluent::lint::unused_result).set_arg("ty", ty).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 comps = if let hir::ExprKind::Tup(comps) = expr.kind {
+ debug_assert_eq!(comps.len(), tys.len());
+ comps
+ } else {
+ &[]
+ };
+ for (i, ty) in tys.iter().enumerate() {
+ let descr_post = &format!(" in tuple element {}", i);
+ let e = comps.get(i).unwrap_or(expr);
+ let span = e.span;
+ if check_must_use_ty(cx, ty, e, 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| {
+ // FIXME(davidtwco): this isn't properly translatable becauses of the
+ // pre/post strings
+ lint.build(fluent::lint::unused_closure)
+ .set_arg("count", plural_len)
+ .set_arg("pre", descr_pre)
+ .set_arg("post", descr_post)
+ .note(fluent::lint::note)
+ .emit();
+ });
+ true
+ }
+ ty::Generator(..) => {
+ cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
+ // FIXME(davidtwco): this isn't properly translatable becauses of the
+ // pre/post strings
+ lint.build(fluent::lint::unused_generator)
+ .set_arg("count", plural_len)
+ .set_arg("pre", descr_pre)
+ .set_arg("post", descr_post)
+ .note(fluent::lint::note)
+ .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 {
+ if let Some(attr) = cx.tcx.get_attr(def_id, sym::must_use) {
+ cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
+ // FIXME(davidtwco): this isn't properly translatable becauses of the pre/post
+ // strings
+ let mut err = lint.build(fluent::lint::unused_def);
+ err.set_arg("pre", descr_pre_path);
+ err.set_arg("post", descr_post_path);
+ err.set_arg("def", cx.tcx.def_path_str(def_id));
+ // check for #[must_use = "..."]
+ if let Some(note) = attr.value_str() {
+ err.note(note.as_str());
+ }
+ err.emit();
+ });
+ true
+ } else {
+ 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(fluent::lint::path_statement_drop);
+ if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) {
+ lint.span_suggestion(
+ s.span,
+ fluent::lint::suggestion,
+ format!("drop({});", snippet),
+ Applicability::MachineApplicable,
+ );
+ } else {
+ lint.span_help(s.span, fluent::lint::suggestion);
+ }
+ lint.emit();
+ } else {
+ lint.build(fluent::lint::path_statement_no_effect).emit();
+ }
+ });
+ }
+ }
+ }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+enum UnusedDelimsCtx {
+ FunctionArg,
+ MethodArg,
+ AssignedValue,
+ AssignedValueLetElse,
+ IfCond,
+ WhileCond,
+ ForIterExpr,
+ MatchScrutineeExpr,
+ ReturnValue,
+ BlockRetValue,
+ LetScrutineeExpr,
+ ArrayLenExpr,
+ AnonConst,
+ MatchArmExpr,
+}
+
+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",
+ }
+ }
+}
+
+/// 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,
+ _ => {}
+ }
+ }
+
+ // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`
+ let lhs_needs_parens = {
+ let mut innermost = inner;
+ loop {
+ innermost = match &innermost.kind {
+ ExprKind::Binary(_, lhs, _rhs) => lhs,
+ ExprKind::Call(fn_, _params) => fn_,
+ ExprKind::Cast(expr, _ty) => expr,
+ ExprKind::Type(expr, _ty) => expr,
+ ExprKind::Index(base, _subscript) => base,
+ _ => break false,
+ };
+ if !classify::expr_requires_semi_to_be_stmt(innermost) {
+ break true;
+ }
+ }
+ };
+
+ lhs_needs_parens
+ || (followed_by_block
+ && match &inner.kind {
+ ExprKind::Ret(_) | ExprKind::Break(..) | ExprKind::Yield(..) => true,
+ ExprKind::Range(_lhs, Some(rhs), _limits) => {
+ matches!(rhs.kind, ExprKind::Block(..))
+ }
+ _ => 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 spans = match value.kind {
+ ast::ExprKind::Block(ref block, None) if block.stmts.len() > 0 => {
+ let start = block.stmts[0].span;
+ let end = block.stmts[block.stmts.len() - 1].span;
+ if value.span.from_expansion() || start.from_expansion() || end.from_expansion() {
+ (
+ value.span.with_hi(value.span.lo() + BytePos(1)),
+ value.span.with_lo(value.span.hi() - BytePos(1)),
+ )
+ } else {
+ (value.span.with_hi(start.lo()), value.span.with_lo(end.hi()))
+ }
+ }
+ ast::ExprKind::Paren(ref expr) => {
+ if value.span.from_expansion() || expr.span.from_expansion() {
+ (
+ value.span.with_hi(value.span.lo() + BytePos(1)),
+ value.span.with_lo(value.span.hi() - BytePos(1)),
+ )
+ } else {
+ (value.span.with_hi(expr.span.lo()), value.span.with_lo(expr.span.hi()))
+ }
+ }
+ _ => return,
+ };
+ 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, spans, ctx.into(), keep_space);
+ }
+
+ fn emit_unused_delims(
+ &self,
+ cx: &EarlyContext<'_>,
+ spans: (Span, Span),
+ msg: &str,
+ keep_space: (bool, bool),
+ ) {
+ // FIXME(flip1995): Quick and dirty fix for #70814. This should be fixed in rustdoc
+ // properly.
+ if spans.0 == DUMMY_SP || spans.1 == DUMMY_SP {
+ return;
+ }
+
+ cx.struct_span_lint(self.lint(), MultiSpan::from(vec![spans.0, spans.1]), |lint| {
+ let replacement = vec![
+ (spans.0, if keep_space.0 { " ".into() } else { "".into() }),
+ (spans.1, if keep_space.1 { " ".into() } else { "".into() }),
+ ];
+ lint.build(fluent::lint::unused_delim)
+ .set_arg("delim", Self::DELIM_STR)
+ .set_arg("item", msg)
+ .multipart_suggestion(
+ fluent::lint::suggestion,
+ replacement,
+ Applicability::MachineApplicable,
+ )
+ .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((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(.., 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 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"
+}
+
+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) => {
+ 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,
+ ) {
+ 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 spans = if value.span.from_expansion() || inner.span.from_expansion() {
+ (
+ value.span.with_hi(value.span.lo() + BytePos(1)),
+ value.span.with_lo(value.span.hi() - BytePos(1)),
+ )
+ } else {
+ (value.span.with_hi(inner.span.lo()), value.span.with_lo(inner.span.hi()))
+ };
+ self.emit_unused_delims(cx, spans, "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;
+ }
+ 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::*};
+ 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, &param.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 spans = if ty.span.from_expansion() || r.span.from_expansion() {
+ (
+ ty.span.with_hi(ty.span.lo() + BytePos(1)),
+ ty.span.with_lo(ty.span.hi() - BytePos(1)),
+ )
+ } else {
+ (ty.span.with_hi(r.span.lo()), ty.span.with_lo(r.span.hi()))
+ };
+ self.emit_unused_delims(cx, spans, "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, false)
+ && (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(fluent::lint::unused_import_braces).set_arg("node", 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| {
+ lint.build(match m {
+ adjustment::AutoBorrowMutability::Not => fluent::lint::unused_allocation,
+ adjustment::AutoBorrowMutability::Mut { .. } => {
+ fluent::lint::unused_allocation_mut
+ }
+ })
+ .emit();
+ });
+ }
+ }
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-12 07:38:44 +0000