1199 lines
43 KiB
Rust
1199 lines
43 KiB
Rust
use crate::Lint;
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use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
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use rustc_ast as ast;
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use rustc_ast::util::parser;
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use rustc_ast::{ExprKind, StmtKind};
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use rustc_ast_pretty::pprust;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_errors::{pluralize, Applicability};
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use rustc_feature::{AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
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use rustc_hir as hir;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::def_id::DefId;
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use rustc_middle::ty::adjustment;
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use rustc_middle::ty::{self, Ty};
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use rustc_session::lint::builtin::UNUSED_ATTRIBUTES;
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use rustc_span::symbol::Symbol;
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use rustc_span::symbol::{kw, sym};
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use rustc_span::{BytePos, Span, DUMMY_SP};
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use tracing::debug;
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declare_lint! {
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/// The `unused_must_use` lint detects unused result of a type flagged as
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/// `#[must_use]`.
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///
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/// ### Example
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///
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/// ```rust
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/// fn returns_result() -> Result<(), ()> {
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/// Ok(())
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/// }
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///
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/// fn main() {
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/// returns_result();
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/// }
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// The `#[must_use]` attribute is an indicator that it is a mistake to
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/// ignore the value. See [the reference] for more details.
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///
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/// [the reference]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
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pub UNUSED_MUST_USE,
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Warn,
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"unused result of a type flagged as `#[must_use]`",
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report_in_external_macro
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}
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declare_lint! {
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/// The `unused_results` lint checks for the unused result of an
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/// expression in a statement.
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///
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/// ### Example
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///
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/// ```rust,compile_fail
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/// #![deny(unused_results)]
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/// fn foo<T>() -> T { panic!() }
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///
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/// fn main() {
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/// foo::<usize>();
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/// }
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// Ignoring the return value of a function may indicate a mistake. In
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/// cases were it is almost certain that the result should be used, it is
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/// recommended to annotate the function with the [`must_use` attribute].
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/// Failure to use such a return value will trigger the [`unused_must_use`
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/// lint] which is warn-by-default. The `unused_results` lint is
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/// essentially the same, but triggers for *all* return values.
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///
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/// This lint is "allow" by default because it can be noisy, and may not be
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/// an actual problem. For example, calling the `remove` method of a `Vec`
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/// or `HashMap` returns the previous value, which you may not care about.
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/// Using this lint would require explicitly ignoring or discarding such
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/// values.
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///
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/// [`must_use` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
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/// [`unused_must_use` lint]: warn-by-default.html#unused-must-use
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pub UNUSED_RESULTS,
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Allow,
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"unused result of an expression in a statement"
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}
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declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]);
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impl<'tcx> LateLintPass<'tcx> for UnusedResults {
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fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
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let expr = match s.kind {
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hir::StmtKind::Semi(ref expr) => &**expr,
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_ => return,
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};
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if let hir::ExprKind::Ret(..) = expr.kind {
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return;
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}
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let ty = cx.typeck_results().expr_ty(&expr);
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let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "", "", 1);
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let mut fn_warned = false;
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let mut op_warned = false;
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let maybe_def_id = match expr.kind {
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hir::ExprKind::Call(ref callee, _) => {
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match callee.kind {
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hir::ExprKind::Path(ref qpath) => {
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match cx.qpath_res(qpath, callee.hir_id) {
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Res::Def(DefKind::Fn | DefKind::AssocFn, def_id) => Some(def_id),
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// `Res::Local` if it was a closure, for which we
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// do not currently support must-use linting
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_ => None,
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}
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}
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_ => None,
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}
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}
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hir::ExprKind::MethodCall(..) => cx.typeck_results().type_dependent_def_id(expr.hir_id),
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_ => None,
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};
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if let Some(def_id) = maybe_def_id {
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fn_warned = check_must_use_def(cx, def_id, s.span, "return value of ", "");
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} else if type_permits_lack_of_use {
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// We don't warn about unused unit or uninhabited types.
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// (See https://github.com/rust-lang/rust/issues/43806 for details.)
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return;
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}
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let must_use_op = match expr.kind {
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// Hardcoding operators here seemed more expedient than the
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// refactoring that would be needed to look up the `#[must_use]`
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// attribute which does exist on the comparison trait methods
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hir::ExprKind::Binary(bin_op, ..) => match bin_op.node {
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hir::BinOpKind::Eq
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| hir::BinOpKind::Lt
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| hir::BinOpKind::Le
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| hir::BinOpKind::Ne
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| hir::BinOpKind::Ge
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| hir::BinOpKind::Gt => Some("comparison"),
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hir::BinOpKind::Add
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| hir::BinOpKind::Sub
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| hir::BinOpKind::Div
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| hir::BinOpKind::Mul
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| hir::BinOpKind::Rem => Some("arithmetic operation"),
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hir::BinOpKind::And | hir::BinOpKind::Or => Some("logical operation"),
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hir::BinOpKind::BitXor
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| hir::BinOpKind::BitAnd
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| hir::BinOpKind::BitOr
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| hir::BinOpKind::Shl
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| hir::BinOpKind::Shr => Some("bitwise operation"),
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},
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hir::ExprKind::Unary(..) => Some("unary operation"),
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_ => None,
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};
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if let Some(must_use_op) = must_use_op {
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cx.struct_span_lint(UNUSED_MUST_USE, expr.span, |lint| {
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lint.build(&format!("unused {} that must be used", must_use_op)).emit()
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});
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op_warned = true;
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}
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if !(type_permits_lack_of_use || fn_warned || op_warned) {
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cx.struct_span_lint(UNUSED_RESULTS, s.span, |lint| lint.build("unused result").emit());
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}
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// Returns whether an error has been emitted (and thus another does not need to be later).
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fn check_must_use_ty<'tcx>(
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cx: &LateContext<'tcx>,
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ty: Ty<'tcx>,
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expr: &hir::Expr<'_>,
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span: Span,
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descr_pre: &str,
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descr_post: &str,
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plural_len: usize,
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) -> bool {
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if ty.is_unit()
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|| cx.tcx.is_ty_uninhabited_from(
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cx.tcx.parent_module(expr.hir_id).to_def_id(),
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ty,
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cx.param_env,
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)
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{
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return true;
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}
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let plural_suffix = pluralize!(plural_len);
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match *ty.kind() {
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ty::Adt(..) if ty.is_box() => {
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let boxed_ty = ty.boxed_ty();
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let descr_pre = &format!("{}boxed ", descr_pre);
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check_must_use_ty(cx, boxed_ty, expr, span, descr_pre, descr_post, plural_len)
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}
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ty::Adt(def, _) => check_must_use_def(cx, def.did, span, descr_pre, descr_post),
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ty::Opaque(def, _) => {
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let mut has_emitted = false;
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for &(predicate, _) in cx.tcx.explicit_item_bounds(def) {
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// We only look at the `DefId`, so it is safe to skip the binder here.
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if let ty::PredicateAtom::Trait(ref poly_trait_predicate, _) =
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predicate.skip_binders()
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{
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let def_id = poly_trait_predicate.trait_ref.def_id;
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let descr_pre =
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&format!("{}implementer{} of ", descr_pre, plural_suffix,);
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if check_must_use_def(cx, def_id, span, descr_pre, descr_post) {
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has_emitted = true;
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break;
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}
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}
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}
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has_emitted
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}
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ty::Dynamic(binder, _) => {
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let mut has_emitted = false;
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for predicate in binder.iter() {
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if let ty::ExistentialPredicate::Trait(ref trait_ref) =
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predicate.skip_binder()
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{
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let def_id = trait_ref.def_id;
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let descr_post =
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&format!(" trait object{}{}", plural_suffix, descr_post,);
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if check_must_use_def(cx, def_id, span, descr_pre, descr_post) {
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has_emitted = true;
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break;
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}
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}
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}
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has_emitted
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}
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ty::Tuple(ref tys) => {
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let mut has_emitted = false;
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let spans = if let hir::ExprKind::Tup(comps) = &expr.kind {
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debug_assert_eq!(comps.len(), tys.len());
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comps.iter().map(|e| e.span).collect()
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} else {
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vec![]
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};
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for (i, ty) in tys.iter().map(|k| k.expect_ty()).enumerate() {
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let descr_post = &format!(" in tuple element {}", i);
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let span = *spans.get(i).unwrap_or(&span);
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if check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, plural_len)
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{
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has_emitted = true;
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}
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}
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has_emitted
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}
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ty::Array(ty, len) => match len.try_eval_usize(cx.tcx, cx.param_env) {
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// If the array is empty we don't lint, to avoid false positives
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Some(0) | None => false,
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// If the array is definitely non-empty, we can do `#[must_use]` checking.
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Some(n) => {
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let descr_pre = &format!("{}array{} of ", descr_pre, plural_suffix,);
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check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, n as usize + 1)
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}
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},
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ty::Closure(..) => {
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cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
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let mut err = lint.build(&format!(
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"unused {}closure{}{} that must be used",
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descr_pre, plural_suffix, descr_post,
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));
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err.note("closures are lazy and do nothing unless called");
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err.emit();
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});
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true
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}
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ty::Generator(..) => {
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cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
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let mut err = lint.build(&format!(
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"unused {}generator{}{} that must be used",
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descr_pre, plural_suffix, descr_post,
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));
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err.note("generators are lazy and do nothing unless resumed");
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err.emit();
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});
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true
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}
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_ => false,
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}
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}
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// Returns whether an error has been emitted (and thus another does not need to be later).
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// FIXME: Args desc_{pre,post}_path could be made lazy by taking Fn() -> &str, but this
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// would make calling it a big awkward. Could also take String (so args are moved), but
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// this would still require a copy into the format string, which would only be executed
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// when needed.
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fn check_must_use_def(
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cx: &LateContext<'_>,
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def_id: DefId,
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span: Span,
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descr_pre_path: &str,
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descr_post_path: &str,
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) -> bool {
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for attr in cx.tcx.get_attrs(def_id).iter() {
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if cx.sess().check_name(attr, sym::must_use) {
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cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
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let msg = format!(
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"unused {}`{}`{} that must be used",
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descr_pre_path,
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cx.tcx.def_path_str(def_id),
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descr_post_path
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);
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let mut err = lint.build(&msg);
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// check for #[must_use = "..."]
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if let Some(note) = attr.value_str() {
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err.note(¬e.as_str());
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}
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err.emit();
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});
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return true;
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}
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}
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false
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}
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}
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}
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declare_lint! {
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/// The `path_statements` lint detects path statements with no effect.
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///
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/// ### Example
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///
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/// ```rust
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/// let x = 42;
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///
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/// x;
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// It is usually a mistake to have a statement that has no effect.
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pub PATH_STATEMENTS,
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Warn,
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"path statements with no effect"
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}
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declare_lint_pass!(PathStatements => [PATH_STATEMENTS]);
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impl<'tcx> LateLintPass<'tcx> for PathStatements {
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fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
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if let hir::StmtKind::Semi(expr) = s.kind {
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if let hir::ExprKind::Path(_) = expr.kind {
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cx.struct_span_lint(PATH_STATEMENTS, s.span, |lint| {
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let ty = cx.typeck_results().expr_ty(expr);
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if ty.needs_drop(cx.tcx, cx.param_env) {
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let mut lint = lint.build("path statement drops value");
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if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) {
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lint.span_suggestion(
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s.span,
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"use `drop` to clarify the intent",
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format!("drop({});", snippet),
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Applicability::MachineApplicable,
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);
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} else {
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lint.span_help(s.span, "use `drop` to clarify the intent");
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}
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lint.emit()
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} else {
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lint.build("path statement with no effect").emit()
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}
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});
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}
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}
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}
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}
|
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|
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#[derive(Copy, Clone)]
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pub struct UnusedAttributes {
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builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>,
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}
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impl UnusedAttributes {
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pub fn new() -> Self {
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UnusedAttributes { builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP }
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}
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}
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|
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impl_lint_pass!(UnusedAttributes => [UNUSED_ATTRIBUTES]);
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|
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impl<'tcx> LateLintPass<'tcx> for UnusedAttributes {
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fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
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debug!("checking attribute: {:?}", attr);
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|
|
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if attr.is_doc_comment() {
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return;
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}
|
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|
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let attr_info = attr.ident().and_then(|ident| self.builtin_attributes.get(&ident.name));
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|
|
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if let Some(&&(name, ty, ..)) = attr_info {
|
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if let AttributeType::AssumedUsed = ty {
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debug!("{:?} is AssumedUsed", name);
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return;
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}
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}
|
|
|
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if !cx.sess().is_attr_used(attr) {
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debug!("emitting warning for: {:?}", attr);
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cx.struct_span_lint(UNUSED_ATTRIBUTES, attr.span, |lint| {
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lint.build("unused attribute").emit()
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});
|
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// Is it a builtin attribute that must be used at the crate level?
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if attr_info.map_or(false, |(_, ty, ..)| ty == &AttributeType::CrateLevel) {
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cx.struct_span_lint(UNUSED_ATTRIBUTES, attr.span, |lint| {
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let msg = match attr.style {
|
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ast::AttrStyle::Outer => {
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"crate-level attribute should be an inner attribute: add an exclamation \
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mark: `#![foo]`"
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|
}
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ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
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};
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lint.build(msg).emit()
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});
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}
|
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} else {
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debug!("Attr was used: {:?}", attr);
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}
|
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}
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
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enum UnusedDelimsCtx {
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FunctionArg,
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MethodArg,
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AssignedValue,
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|
IfCond,
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WhileCond,
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ForIterExpr,
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MatchScrutineeExpr,
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ReturnValue,
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BlockRetValue,
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LetScrutineeExpr,
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ArrayLenExpr,
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AnonConst,
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}
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|
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impl From<UnusedDelimsCtx> for &'static str {
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fn from(ctx: UnusedDelimsCtx) -> &'static str {
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|
match ctx {
|
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UnusedDelimsCtx::FunctionArg => "function argument",
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UnusedDelimsCtx::MethodArg => "method argument",
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UnusedDelimsCtx::AssignedValue => "assigned value",
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UnusedDelimsCtx::IfCond => "`if` condition",
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UnusedDelimsCtx::WhileCond => "`while` condition",
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UnusedDelimsCtx::ForIterExpr => "`for` iterator expression",
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UnusedDelimsCtx::MatchScrutineeExpr => "`match` scrutinee expression",
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UnusedDelimsCtx::ReturnValue => "`return` value",
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UnusedDelimsCtx::BlockRetValue => "block return value",
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UnusedDelimsCtx::LetScrutineeExpr => "`let` scrutinee expression",
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UnusedDelimsCtx::ArrayLenExpr | UnusedDelimsCtx::AnonConst => "const expression",
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}
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}
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}
|
|
|
|
/// 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(|s| s >= value.span.lo()).unwrap_or(false),
|
|
right_pos.map(|s| s <= value.span.hi()).unwrap_or(false),
|
|
);
|
|
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) {
|
|
if let ExprKind::Let(ref pat, ..) | ExprKind::ForLoop(ref pat, ..) = e.kind {
|
|
self.check_unused_parens_pat(cx, pat, false, false);
|
|
}
|
|
|
|
<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, false, false);
|
|
}
|
|
|
|
<Self as UnusedDelimLint>::check_stmt(self, cx, s)
|
|
}
|
|
|
|
fn check_param(&mut self, cx: &EarlyContext<'_>, param: &ast::Param) {
|
|
self.check_unused_parens_pat(cx, ¶m.pat, true, false);
|
|
}
|
|
|
|
fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
|
|
self.check_unused_parens_pat(cx, &arm.pat, false, false);
|
|
}
|
|
|
|
fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) {
|
|
if let &ast::TyKind::Paren(ref r) = &ty.kind {
|
|
match &r.kind {
|
|
&ast::TyKind::TraitObject(..) => {}
|
|
&ast::TyKind::ImplTrait(_, ref bounds) if bounds.len() > 1 => {}
|
|
&ast::TyKind::Array(_, ref 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) => {
|
|
// FIXME(#60336): Properly handle `let true = (false && true)`
|
|
// actually needing the parenthesis.
|
|
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()
|
|
});
|
|
}
|
|
}
|
|
}
|
|
}
|