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use crate::lints::{
PathStatementDrop, PathStatementDropSub, PathStatementNoEffect, UnusedAllocationDiag,
UnusedAllocationMutDiag, UnusedClosure, UnusedDef, UnusedDefSuggestion, UnusedDelim,
UnusedDelimSuggestion, UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedOpSuggestion,
UnusedResult,
};
use crate::Lint;
use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
use rustc_ast as ast;
use rustc_ast::util::{classify, parser};
use rustc_ast::{ExprKind, StmtKind};
use rustc_errors::{pluralize, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_infer::traits::util::elaborate;
use rustc_middle::ty::adjustment;
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::Symbol;
use rustc_span::symbol::{kw, sym};
use rustc_span::{BytePos, Span};
use std::iter;
declare_lint! {
/// The `unused_must_use` lint detects unused result of a type flagged as
/// `#[must_use]`.
///
/// ### Example
///
/// ```rust
/// fn returns_result() -> Result<(), ()> {
/// Ok(())
/// }
///
/// fn main() {
/// returns_result();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `#[must_use]` attribute is an indicator that it is a mistake to
/// ignore the value. See [the reference] for more details.
///
/// [the reference]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
pub UNUSED_MUST_USE,
Warn,
"unused result of a type flagged as `#[must_use]`",
report_in_external_macro
}
declare_lint! {
/// The `unused_results` lint checks for the unused result of an
/// expression in a statement.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_results)]
/// fn foo<T>() -> T { panic!() }
///
/// fn main() {
/// foo::<usize>();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Ignoring the return value of a function may indicate a mistake. In
/// cases were it is almost certain that the result should be used, it is
/// recommended to annotate the function with the [`must_use` attribute].
/// Failure to use such a return value will trigger the [`unused_must_use`
/// lint] which is warn-by-default. The `unused_results` lint is
/// essentially the same, but triggers for *all* return values.
///
/// This lint is "allow" by default because it can be noisy, and may not be
/// an actual problem. For example, calling the `remove` method of a `Vec`
/// or `HashMap` returns the previous value, which you may not care about.
/// Using this lint would require explicitly ignoring or discarding such
/// values.
///
/// [`must_use` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
/// [`unused_must_use` lint]: warn-by-default.html#unused-must-use
pub UNUSED_RESULTS,
Allow,
"unused result of an expression in a statement"
}
declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]);
impl<'tcx> LateLintPass<'tcx> for UnusedResults {
fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
let hir::StmtKind::Semi(mut expr) = s.kind else {
return;
};
let mut expr_is_from_block = false;
while let hir::ExprKind::Block(blk, ..) = expr.kind
&& let hir::Block { expr: Some(e), .. } = blk
{
expr = e;
expr_is_from_block = true;
}
if let hir::ExprKind::Ret(..) = expr.kind {
return;
}
if let hir::ExprKind::Match(await_expr, _arms, hir::MatchSource::AwaitDesugar) = expr.kind
&& let ty = cx.typeck_results().expr_ty(&await_expr)
&& let ty::Alias(ty::Opaque, ty::AliasTy { def_id: future_def_id, .. }) = ty.kind()
&& cx.tcx.ty_is_opaque_future(ty)
&& let async_fn_def_id = cx.tcx.parent(*future_def_id)
&& matches!(cx.tcx.def_kind(async_fn_def_id), DefKind::Fn | DefKind::AssocFn)
// Check that this `impl Future` actually comes from an `async fn`
&& cx.tcx.asyncness(async_fn_def_id).is_async()
&& check_must_use_def(
cx,
async_fn_def_id,
expr.span,
"output of future returned by ",
"",
expr_is_from_block,
)
{
// We have a bare `foo().await;` on an opaque type from an async function that was
// annotated with `#[must_use]`.
return;
}
let ty = cx.typeck_results().expr_ty(&expr);
let must_use_result = is_ty_must_use(cx, ty, &expr, expr.span);
let type_lint_emitted_or_suppressed = match must_use_result {
Some(path) => {
emit_must_use_untranslated(cx, &path, "", "", 1, false, expr_is_from_block);
true
}
None => false,
};
let fn_warned = check_fn_must_use(cx, expr, expr_is_from_block);
if !fn_warned && type_lint_emitted_or_suppressed {
// We don't warn about unused unit or uninhabited types.
// (See https://github.com/rust-lang/rust/issues/43806 for details.)
return;
}
let must_use_op = match expr.kind {
// Hardcoding operators here seemed more expedient than the
// refactoring that would be needed to look up the `#[must_use]`
// attribute which does exist on the comparison trait methods
hir::ExprKind::Binary(bin_op, ..) => match bin_op.node {
hir::BinOpKind::Eq
| hir::BinOpKind::Lt
| hir::BinOpKind::Le
| hir::BinOpKind::Ne
| hir::BinOpKind::Ge
| hir::BinOpKind::Gt => Some("comparison"),
hir::BinOpKind::Add
| hir::BinOpKind::Sub
| hir::BinOpKind::Div
| hir::BinOpKind::Mul
| hir::BinOpKind::Rem => Some("arithmetic operation"),
hir::BinOpKind::And | hir::BinOpKind::Or => Some("logical operation"),
hir::BinOpKind::BitXor
| hir::BinOpKind::BitAnd
| hir::BinOpKind::BitOr
| hir::BinOpKind::Shl
| hir::BinOpKind::Shr => Some("bitwise operation"),
},
hir::ExprKind::AddrOf(..) => Some("borrow"),
hir::ExprKind::Unary(..) => Some("unary operation"),
_ => None,
};
let mut op_warned = false;
if let Some(must_use_op) = must_use_op {
cx.emit_spanned_lint(
UNUSED_MUST_USE,
expr.span,
UnusedOp {
op: must_use_op,
label: expr.span,
suggestion: if expr_is_from_block {
UnusedOpSuggestion::BlockTailExpr {
before_span: expr.span.shrink_to_lo(),
after_span: expr.span.shrink_to_hi(),
}
} else {
UnusedOpSuggestion::NormalExpr { span: expr.span.shrink_to_lo() }
},
},
);
op_warned = true;
}
if !(type_lint_emitted_or_suppressed || fn_warned || op_warned) {
cx.emit_spanned_lint(UNUSED_RESULTS, s.span, UnusedResult { ty });
}
fn check_fn_must_use(
cx: &LateContext<'_>,
expr: &hir::Expr<'_>,
expr_is_from_block: bool,
) -> bool {
let maybe_def_id = match expr.kind {
hir::ExprKind::Call(ref callee, _) => {
match callee.kind {
hir::ExprKind::Path(ref qpath) => {
match cx.qpath_res(qpath, callee.hir_id) {
Res::Def(DefKind::Fn | DefKind::AssocFn, def_id) => Some(def_id),
// `Res::Local` if it was a closure, for which we
// do not currently support must-use linting
_ => None,
}
}
_ => None,
}
}
hir::ExprKind::MethodCall(..) => {
cx.typeck_results().type_dependent_def_id(expr.hir_id)
}
_ => None,
};
if let Some(def_id) = maybe_def_id {
check_must_use_def(
cx,
def_id,
expr.span,
"return value of ",
"",
expr_is_from_block,
)
} else {
false
}
}
/// A path through a type to a must_use source. Contains useful info for the lint.
#[derive(Debug)]
enum MustUsePath {
/// Suppress must_use checking.
Suppressed,
/// The root of the normal must_use lint with an optional message.
Def(Span, DefId, Option<Symbol>),
Boxed(Box<Self>),
Opaque(Box<Self>),
TraitObject(Box<Self>),
TupleElement(Vec<(usize, Self)>),
Array(Box<Self>, u64),
/// The root of the unused_closures lint.
Closure(Span),
/// The root of the unused_generators lint.
Generator(Span),
}
#[instrument(skip(cx, expr), level = "debug", ret)]
fn is_ty_must_use<'tcx>(
cx: &LateContext<'tcx>,
ty: Ty<'tcx>,
expr: &hir::Expr<'_>,
span: Span,
) -> Option<MustUsePath> {
if ty.is_unit()
|| !ty.is_inhabited_from(
cx.tcx,
cx.tcx.parent_module(expr.hir_id).to_def_id(),
cx.param_env,
)
{
return Some(MustUsePath::Suppressed);
}
match *ty.kind() {
ty::Adt(..) if ty.is_box() => {
let boxed_ty = ty.boxed_ty();
is_ty_must_use(cx, boxed_ty, expr, span)
.map(|inner| MustUsePath::Boxed(Box::new(inner)))
}
ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, .. }) => {
elaborate(
cx.tcx,
cx.tcx.explicit_item_bounds(def).instantiate_identity_iter_copied(),
)
// We only care about self bounds for the impl-trait
.filter_only_self()
.find_map(|(pred, _span)| {
// We only look at the `DefId`, so it is safe to skip the binder here.
if let ty::ClauseKind::Trait(ref poly_trait_predicate) =
pred.kind().skip_binder()
{
let def_id = poly_trait_predicate.trait_ref.def_id;
is_def_must_use(cx, def_id, span)
} else {
None
}
})
.map(|inner| MustUsePath::Opaque(Box::new(inner)))
}
ty::Dynamic(binders, _, _) => binders.iter().find_map(|predicate| {
if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder()
{
let def_id = trait_ref.def_id;
is_def_must_use(cx, def_id, span)
.map(|inner| MustUsePath::TraitObject(Box::new(inner)))
} else {
None
}
}),
ty::Tuple(tys) => {
let elem_exprs = if let hir::ExprKind::Tup(elem_exprs) = expr.kind {
debug_assert_eq!(elem_exprs.len(), tys.len());
elem_exprs
} else {
&[]
};
// Default to `expr`.
let elem_exprs = elem_exprs.iter().chain(iter::repeat(expr));
let nested_must_use = tys
.iter()
.zip(elem_exprs)
.enumerate()
.filter_map(|(i, (ty, expr))| {
is_ty_must_use(cx, ty, expr, expr.span).map(|path| (i, path))
})
.collect::<Vec<_>>();
if !nested_must_use.is_empty() {
Some(MustUsePath::TupleElement(nested_must_use))
} else {
None
}
}
ty::Array(ty, len) => match len.try_eval_target_usize(cx.tcx, cx.param_env) {
// If the array is empty we don't lint, to avoid false positives
Some(0) | None => None,
// If the array is definitely non-empty, we can do `#[must_use]` checking.
Some(len) => is_ty_must_use(cx, ty, expr, span)
.map(|inner| MustUsePath::Array(Box::new(inner), len)),
},
ty::Closure(..) => Some(MustUsePath::Closure(span)),
ty::Generator(def_id, ..) => {
// async fn should be treated as "implementor of `Future`"
let must_use = if cx.tcx.generator_is_async(def_id) {
let def_id = cx.tcx.lang_items().future_trait().unwrap();
is_def_must_use(cx, def_id, span)
.map(|inner| MustUsePath::Opaque(Box::new(inner)))
} else {
None
};
must_use.or(Some(MustUsePath::Generator(span)))
}
_ => None,
}
}
fn is_def_must_use(cx: &LateContext<'_>, def_id: DefId, span: Span) -> Option<MustUsePath> {
if let Some(attr) = cx.tcx.get_attr(def_id, sym::must_use) {
// check for #[must_use = "..."]
let reason = attr.value_str();
Some(MustUsePath::Def(span, def_id, reason))
} else {
None
}
}
// Returns whether further errors should be suppressed because either a lint has been emitted or the type should be ignored.
fn check_must_use_def(
cx: &LateContext<'_>,
def_id: DefId,
span: Span,
descr_pre_path: &str,
descr_post_path: &str,
expr_is_from_block: bool,
) -> bool {
is_def_must_use(cx, def_id, span)
.map(|must_use_path| {
emit_must_use_untranslated(
cx,
&must_use_path,
descr_pre_path,
descr_post_path,
1,
false,
expr_is_from_block,
)
})
.is_some()
}
#[instrument(skip(cx), level = "debug")]
fn emit_must_use_untranslated(
cx: &LateContext<'_>,
path: &MustUsePath,
descr_pre: &str,
descr_post: &str,
plural_len: usize,
is_inner: bool,
expr_is_from_block: bool,
) {
let plural_suffix = pluralize!(plural_len);
match path {
MustUsePath::Suppressed => {}
MustUsePath::Boxed(path) => {
let descr_pre = &format!("{descr_pre}boxed ");
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::Opaque(path) => {
let descr_pre = &format!("{descr_pre}implementer{plural_suffix} of ");
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::TraitObject(path) => {
let descr_post = &format!(" trait object{plural_suffix}{descr_post}");
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::TupleElement(elems) => {
for (index, path) in elems {
let descr_post = &format!(" in tuple element {index}");
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
}
MustUsePath::Array(path, len) => {
let descr_pre = &format!("{descr_pre}array{plural_suffix} of ");
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len.saturating_add(usize::try_from(*len).unwrap_or(usize::MAX)),
true,
expr_is_from_block,
);
}
MustUsePath::Closure(span) => {
cx.emit_spanned_lint(
UNUSED_MUST_USE,
*span,
UnusedClosure { count: plural_len, pre: descr_pre, post: descr_post },
);
}
MustUsePath::Generator(span) => {
cx.emit_spanned_lint(
UNUSED_MUST_USE,
*span,
UnusedGenerator { count: plural_len, pre: descr_pre, post: descr_post },
);
}
MustUsePath::Def(span, def_id, reason) => {
cx.emit_spanned_lint(
UNUSED_MUST_USE,
*span,
UnusedDef {
pre: descr_pre,
post: descr_post,
cx,
def_id: *def_id,
note: *reason,
suggestion: (!is_inner).then_some(if expr_is_from_block {
UnusedDefSuggestion::BlockTailExpr {
before_span: span.shrink_to_lo(),
after_span: span.shrink_to_hi(),
}
} else {
UnusedDefSuggestion::NormalExpr { span: span.shrink_to_lo() }
}),
},
);
}
}
}
}
}
declare_lint! {
/// The `path_statements` lint detects path statements with no effect.
///
/// ### Example
///
/// ```rust
/// let x = 42;
///
/// x;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to have a statement that has no effect.
pub PATH_STATEMENTS,
Warn,
"path statements with no effect"
}
declare_lint_pass!(PathStatements => [PATH_STATEMENTS]);
impl<'tcx> LateLintPass<'tcx> for PathStatements {
fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
if let hir::StmtKind::Semi(expr) = s.kind {
if let hir::ExprKind::Path(_) = expr.kind {
let ty = cx.typeck_results().expr_ty(expr);
if ty.needs_drop(cx.tcx, cx.param_env) {
let sub = if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span)
{
PathStatementDropSub::Suggestion { span: s.span, snippet }
} else {
PathStatementDropSub::Help { span: s.span }
};
cx.emit_spanned_lint(PATH_STATEMENTS, s.span, PathStatementDrop { sub })
} else {
cx.emit_spanned_lint(PATH_STATEMENTS, s.span, PathStatementNoEffect);
}
}
}
}
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum UnusedDelimsCtx {
FunctionArg,
MethodArg,
AssignedValue,
AssignedValueLetElse,
IfCond,
WhileCond,
ForIterExpr,
MatchScrutineeExpr,
ReturnValue,
BlockRetValue,
LetScrutineeExpr,
ArrayLenExpr,
AnonConst,
MatchArmExpr,
IndexExpr,
}
impl From<UnusedDelimsCtx> for &'static str {
fn from(ctx: UnusedDelimsCtx) -> &'static str {
match ctx {
UnusedDelimsCtx::FunctionArg => "function argument",
UnusedDelimsCtx::MethodArg => "method argument",
UnusedDelimsCtx::AssignedValue | UnusedDelimsCtx::AssignedValueLetElse => {
"assigned value"
}
UnusedDelimsCtx::IfCond => "`if` condition",
UnusedDelimsCtx::WhileCond => "`while` condition",
UnusedDelimsCtx::ForIterExpr => "`for` iterator expression",
UnusedDelimsCtx::MatchScrutineeExpr => "`match` scrutinee expression",
UnusedDelimsCtx::ReturnValue => "`return` value",
UnusedDelimsCtx::BlockRetValue => "block return value",
UnusedDelimsCtx::LetScrutineeExpr => "`let` scrutinee expression",
UnusedDelimsCtx::ArrayLenExpr | UnusedDelimsCtx::AnonConst => "const expression",
UnusedDelimsCtx::MatchArmExpr => "match arm expression",
UnusedDelimsCtx::IndexExpr => "index expression",
}
}
}
/// Used by both `UnusedParens` and `UnusedBraces` to prevent code duplication.
trait UnusedDelimLint {
const DELIM_STR: &'static str;
/// Due to `ref` pattern, there can be a difference between using
/// `{ expr }` and `expr` in pattern-matching contexts. This means
/// that we should only lint `unused_parens` and not `unused_braces`
/// in this case.
///
/// ```rust
/// let mut a = 7;
/// let ref b = { a }; // We actually borrow a copy of `a` here.
/// a += 1; // By mutating `a` we invalidate any borrows of `a`.
/// assert_eq!(b + 1, a); // `b` does not borrow `a`, so we can still use it here.
/// ```
const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool;
// this cannot be a constant is it refers to a static.
fn lint(&self) -> &'static Lint;
fn check_unused_delims_expr(
&self,
cx: &EarlyContext<'_>,
value: &ast::Expr,
ctx: UnusedDelimsCtx,
followed_by_block: bool,
left_pos: Option<BytePos>,
right_pos: Option<BytePos>,
is_kw: bool,
);
fn is_expr_delims_necessary(
inner: &ast::Expr,
followed_by_block: bool,
followed_by_else: bool,
) -> bool {
if followed_by_else {
match inner.kind {
ast::ExprKind::Binary(op, ..) if op.node.lazy() => return true,
_ if classify::expr_trailing_brace(inner).is_some() => return true,
_ => {}
}
}
// Check if LHS needs parens to prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`.
{
let mut innermost = inner;
loop {
innermost = match &innermost.kind {
ExprKind::Binary(_op, lhs, _rhs) => lhs,
ExprKind::Call(fn_, _params) => fn_,
ExprKind::Cast(expr, _ty) => expr,
ExprKind::Type(expr, _ty) => expr,
ExprKind::Index(base, _subscript, _) => base,
_ => break,
};
if !classify::expr_requires_semi_to_be_stmt(innermost) {
return true;
}
}
}
// Check if RHS needs parens to prevent false-positives in cases like `if (() == return) {}`.
if !followed_by_block {
return false;
}
// Check if we need parens for `match &( Struct { feild: }) {}`.
{
let mut innermost = inner;
loop {
innermost = match &innermost.kind {
ExprKind::AddrOf(_, _, expr) => expr,
_ => {
if parser::contains_exterior_struct_lit(&innermost) {
return true;
} else {
break;
}
}
}
}
}
let mut innermost = inner;
loop {
innermost = match &innermost.kind {
ExprKind::Unary(_op, expr) => expr,
ExprKind::Binary(_op, _lhs, rhs) => rhs,
ExprKind::AssignOp(_op, _lhs, rhs) => rhs,
ExprKind::Assign(_lhs, rhs, _span) => rhs,
ExprKind::Ret(_) | ExprKind::Yield(..) | ExprKind::Yeet(..) => return true,
ExprKind::Break(_label, None) => return false,
ExprKind::Break(_label, Some(break_expr)) => {
return matches!(break_expr.kind, ExprKind::Block(..));
}
ExprKind::Range(_lhs, Some(rhs), _limits) => {
return matches!(rhs.kind, ExprKind::Block(..));
}
_ => return parser::contains_exterior_struct_lit(&inner),
}
}
}
fn emit_unused_delims_expr(
&self,
cx: &EarlyContext<'_>,
value: &ast::Expr,
ctx: UnusedDelimsCtx,
left_pos: Option<BytePos>,
right_pos: Option<BytePos>,
is_kw: bool,
) {
// If `value` has `ExprKind::Err`, unused delim lint can be broken.
// For example, the following code caused ICE.
// This is because the `ExprKind::Call` in `value` has `ExprKind::Err` as its argument
// and this leads to wrong spans. #104897
//
// ```
// fn f(){(print!(á
// ```
use rustc_ast::visit::{walk_expr, Visitor};
struct ErrExprVisitor {
has_error: bool,
}
impl<'ast> Visitor<'ast> for ErrExprVisitor {
fn visit_expr(&mut self, expr: &'ast ast::Expr) {
if let ExprKind::Err = expr.kind {
self.has_error = true;
return;
}
walk_expr(self, expr)
}
}
let mut visitor = ErrExprVisitor { has_error: false };
visitor.visit_expr(value);
if visitor.has_error {
return;
}
let spans = match value.kind {
ast::ExprKind::Block(ref block, None) if block.stmts.len() == 1 => block.stmts[0]
.span
.find_ancestor_inside(value.span)
.map(|span| (value.span.with_hi(span.lo()), value.span.with_lo(span.hi()))),
ast::ExprKind::Paren(ref expr) => {
expr.span.find_ancestor_inside(value.span).map(|expr_span| {
(value.span.with_hi(expr_span.lo()), value.span.with_lo(expr_span.hi()))
})
}
_ => return,
};
let keep_space = (
left_pos.is_some_and(|s| s >= value.span.lo()),
right_pos.is_some_and(|s| s <= value.span.hi()),
);
self.emit_unused_delims(cx, value.span, spans, ctx.into(), keep_space, is_kw);
}
fn emit_unused_delims(
&self,
cx: &EarlyContext<'_>,
value_span: Span,
spans: Option<(Span, Span)>,
msg: &str,
keep_space: (bool, bool),
is_kw: bool,
) {
let primary_span = if let Some((lo, hi)) = spans {
if hi.is_empty() {
// do not point at delims that do not exist
return;
}
MultiSpan::from(vec![lo, hi])
} else {
MultiSpan::from(value_span)
};
let suggestion = spans.map(|(lo, hi)| {
let sm = cx.sess().source_map();
let lo_replace =
if (keep_space.0 || is_kw) &&
let Ok(snip) = sm.span_to_prev_source(lo) && !snip.ends_with(' ') {
" "
} else {
""
};
let hi_replace =
if keep_space.1 &&
let Ok(snip) = sm.span_to_next_source(hi) && !snip.starts_with(' ') {
" "
} else {
""
};
UnusedDelimSuggestion {
start_span: lo,
start_replace: lo_replace,
end_span: hi,
end_replace: hi_replace,
}
});
cx.emit_spanned_lint(
self.lint(),
primary_span,
UnusedDelim { delim: Self::DELIM_STR, item: msg, suggestion },
);
}
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
use rustc_ast::ExprKind::*;
let (value, ctx, followed_by_block, left_pos, right_pos, is_kw) = match e.kind {
// Do not lint `unused_braces` in `if let` expressions.
If(ref cond, ref block, _)
if !matches!(cond.kind, Let(..)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
{
let left = e.span.lo() + rustc_span::BytePos(2);
let right = block.span.lo();
(cond, UnusedDelimsCtx::IfCond, true, Some(left), Some(right), true)
}
// Do not lint `unused_braces` in `while let` expressions.
While(ref cond, ref block, ..)
if !matches!(cond.kind, Let(..)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
{
let left = e.span.lo() + rustc_span::BytePos(5);
let right = block.span.lo();
(cond, UnusedDelimsCtx::WhileCond, true, Some(left), Some(right), true)
}
ForLoop(_, ref cond, ref block, ..) => {
(cond, UnusedDelimsCtx::ForIterExpr, true, None, Some(block.span.lo()), true)
}
Match(ref head, _) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
let left = e.span.lo() + rustc_span::BytePos(5);
(head, UnusedDelimsCtx::MatchScrutineeExpr, true, Some(left), None, true)
}
Ret(Some(ref value)) => {
let left = e.span.lo() + rustc_span::BytePos(3);
(value, UnusedDelimsCtx::ReturnValue, false, Some(left), None, true)
}
Index(_, ref value, _) => (value, UnusedDelimsCtx::IndexExpr, false, None, None, false),
Assign(_, ref value, _) | AssignOp(.., ref value) => {
(value, UnusedDelimsCtx::AssignedValue, false, None, None, false)
}
// either function/method call, or something this lint doesn't care about
ref call_or_other => {
let (args_to_check, ctx) = match *call_or_other {
Call(_, ref args) => (&args[..], UnusedDelimsCtx::FunctionArg),
MethodCall(ref call) => (&call.args[..], UnusedDelimsCtx::MethodArg),
// actual catch-all arm
_ => {
return;
}
};
// Don't lint if this is a nested macro expansion: otherwise, the lint could
// trigger in situations that macro authors shouldn't have to care about, e.g.,
// when a parenthesized token tree matched in one macro expansion is matched as
// an expression in another and used as a fn/method argument (Issue #47775)
if e.span.ctxt().outer_expn_data().call_site.from_expansion() {
return;
}
for arg in args_to_check {
self.check_unused_delims_expr(cx, arg, ctx, false, None, None, false);
}
return;
}
};
self.check_unused_delims_expr(
cx,
&value,
ctx,
followed_by_block,
left_pos,
right_pos,
is_kw,
);
}
fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
match s.kind {
StmtKind::Local(ref local) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
if let Some((init, els)) = local.kind.init_else_opt() {
let ctx = match els {
None => UnusedDelimsCtx::AssignedValue,
Some(_) => UnusedDelimsCtx::AssignedValueLetElse,
};
self.check_unused_delims_expr(cx, init, ctx, false, None, None, false);
}
}
StmtKind::Expr(ref expr) => {
self.check_unused_delims_expr(
cx,
&expr,
UnusedDelimsCtx::BlockRetValue,
false,
None,
None,
false,
);
}
_ => {}
}
}
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
use ast::ItemKind::*;
if let Const(box ast::ConstItem { expr: Some(expr), .. })
| Static(box ast::StaticItem { expr: Some(expr), .. }) = &item.kind
{
self.check_unused_delims_expr(
cx,
expr,
UnusedDelimsCtx::AssignedValue,
false,
None,
None,
false,
);
}
}
}
declare_lint! {
/// The `unused_parens` lint detects `if`, `match`, `while` and `return`
/// with parentheses; they do not need them.
///
/// ### Examples
///
/// ```rust
/// if(true) {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The parentheses are not needed, and should be removed. This is the
/// preferred style for writing these expressions.
pub(super) UNUSED_PARENS,
Warn,
"`if`, `match`, `while` and `return` do not need parentheses"
}
pub struct UnusedParens {
with_self_ty_parens: bool,
/// `1 as (i32) < 2` parses to ExprKind::Lt
/// `1 as i32 < 2` parses to i32::<2[missing angle bracket]
parens_in_cast_in_lt: Vec<ast::NodeId>,
}
impl UnusedParens {
pub fn new() -> Self {
Self { with_self_ty_parens: false, parens_in_cast_in_lt: Vec::new() }
}
}
impl_lint_pass!(UnusedParens => [UNUSED_PARENS]);
impl UnusedDelimLint for UnusedParens {
const DELIM_STR: &'static str = "parentheses";
const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = true;
fn lint(&self) -> &'static Lint {
UNUSED_PARENS
}
fn check_unused_delims_expr(
&self,
cx: &EarlyContext<'_>,
value: &ast::Expr,
ctx: UnusedDelimsCtx,
followed_by_block: bool,
left_pos: Option<BytePos>,
right_pos: Option<BytePos>,
is_kw: bool,
) {
match value.kind {
ast::ExprKind::Paren(ref inner) => {
let followed_by_else = ctx == UnusedDelimsCtx::AssignedValueLetElse;
if !Self::is_expr_delims_necessary(inner, followed_by_block, followed_by_else)
&& value.attrs.is_empty()
&& !value.span.from_expansion()
&& (ctx != UnusedDelimsCtx::LetScrutineeExpr
|| !matches!(inner.kind, ast::ExprKind::Binary(
rustc_span::source_map::Spanned { node, .. },
_,
_,
) if node.lazy()))
{
self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos, is_kw)
}
}
ast::ExprKind::Let(_, ref expr, _, _) => {
self.check_unused_delims_expr(
cx,
expr,
UnusedDelimsCtx::LetScrutineeExpr,
followed_by_block,
None,
None,
false,
);
}
_ => {}
}
}
}
impl UnusedParens {
fn check_unused_parens_pat(
&self,
cx: &EarlyContext<'_>,
value: &ast::Pat,
avoid_or: bool,
avoid_mut: bool,
keep_space: (bool, bool),
) {
use ast::{BindingAnnotation, PatKind};
if let PatKind::Paren(inner) = &value.kind {
match inner.kind {
// The lint visitor will visit each subpattern of `p`. We do not want to lint
// any range pattern no matter where it occurs in the pattern. For something like
// `&(a..=b)`, there is a recursive `check_pat` on `a` and `b`, but we will assume
// that if there are unnecessary parens they serve a purpose of readability.
PatKind::Range(..) => return,
// Avoid `p0 | .. | pn` if we should.
PatKind::Or(..) if avoid_or => return,
// Avoid `mut x` and `mut x @ p` if we should:
PatKind::Ident(BindingAnnotation::MUT, ..) if avoid_mut => {
return;
}
// Otherwise proceed with linting.
_ => {}
}
let spans = inner
.span
.find_ancestor_inside(value.span)
.map(|inner| (value.span.with_hi(inner.lo()), value.span.with_lo(inner.hi())));
self.emit_unused_delims(cx, value.span, spans, "pattern", keep_space, false);
}
}
}
impl EarlyLintPass for UnusedParens {
#[inline]
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
if let ExprKind::Binary(op, lhs, _rhs) = &e.kind &&
(op.node == ast::BinOpKind::Lt || op.node == ast::BinOpKind::Shl) &&
let ExprKind::Cast(_expr, ty) = &lhs.kind &&
let ast::TyKind::Paren(_) = &ty.kind
{
self.parens_in_cast_in_lt.push(ty.id);
}
match e.kind {
ExprKind::Let(ref pat, _, _, _) | ExprKind::ForLoop(ref pat, ..) => {
self.check_unused_parens_pat(cx, pat, false, false, (true, true));
}
// We ignore parens in cases like `if (((let Some(0) = Some(1))))` because we already
// handle a hard error for them during AST lowering in `lower_expr_mut`, but we still
// want to complain about things like `if let 42 = (42)`.
ExprKind::If(ref cond, ref block, ref else_)
if matches!(cond.peel_parens().kind, ExprKind::Let(..)) =>
{
self.check_unused_delims_expr(
cx,
cond.peel_parens(),
UnusedDelimsCtx::LetScrutineeExpr,
true,
None,
None,
true,
);
for stmt in &block.stmts {
<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,
true,
);
}
}
_ => {}
}
<Self as UnusedDelimLint>::check_expr(self, cx, e)
}
fn check_expr_post(&mut self, _cx: &EarlyContext<'_>, e: &ast::Expr) {
if let ExprKind::Binary(op, lhs, _rhs) = &e.kind &&
(op.node == ast::BinOpKind::Lt || op.node == ast::BinOpKind::Shl) &&
let ExprKind::Cast(_expr, ty) = &lhs.kind &&
let ast::TyKind::Paren(_) = &ty.kind
{
let id = self.parens_in_cast_in_lt.pop().expect("check_expr and check_expr_post must balance");
assert_eq!(id, ty.id, "check_expr, check_ty, and check_expr_post are called, in that order, by the visitor");
}
}
fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat) {
use ast::{Mutability, PatKind::*};
let keep_space = (false, false);
match &p.kind {
// Do not lint on `(..)` as that will result in the other arms being useless.
Paren(_)
// The other cases do not contain sub-patterns.
| Wild | Rest | Lit(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) => {},
// These are list-like patterns; parens can always be removed.
TupleStruct(_, _, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
self.check_unused_parens_pat(cx, p, false, false, keep_space);
},
Struct(_, _, fps, _) => for f in fps {
self.check_unused_parens_pat(cx, &f.pat, false, false, keep_space);
},
// Avoid linting on `i @ (p0 | .. | pn)` and `box (p0 | .. | pn)`, #64106.
Ident(.., Some(p)) | Box(p) => self.check_unused_parens_pat(cx, p, true, false, keep_space),
// Avoid linting on `&(mut x)` as `&mut x` has a different meaning, #55342.
// Also avoid linting on `& mut? (p0 | .. | pn)`, #64106.
Ref(p, m) => self.check_unused_parens_pat(cx, p, true, *m == Mutability::Not, keep_space),
}
}
fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
if let StmtKind::Local(ref local) = s.kind {
self.check_unused_parens_pat(cx, &local.pat, true, false, (false, false));
}
<Self as UnusedDelimLint>::check_stmt(self, cx, s)
}
fn check_param(&mut self, cx: &EarlyContext<'_>, param: &ast::Param) {
self.check_unused_parens_pat(cx, ¶m.pat, true, false, (false, false));
}
fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
self.check_unused_parens_pat(cx, &arm.pat, false, false, (false, false));
}
fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) {
if let ast::TyKind::Paren(_) = ty.kind &&
Some(&ty.id) == self.parens_in_cast_in_lt.last()
{
return;
}
match &ty.kind {
ast::TyKind::Array(_, len) => {
self.check_unused_delims_expr(
cx,
&len.value,
UnusedDelimsCtx::ArrayLenExpr,
false,
None,
None,
false,
);
}
ast::TyKind::Paren(r) => {
match &r.kind {
ast::TyKind::TraitObject(..) => {}
ast::TyKind::BareFn(b)
if self.with_self_ty_parens && b.generic_params.len() > 0 => {}
ast::TyKind::ImplTrait(_, bounds) if bounds.len() > 1 => {}
_ => {
let spans = r
.span
.find_ancestor_inside(ty.span)
.map(|r| (ty.span.with_hi(r.lo()), ty.span.with_lo(r.hi())));
self.emit_unused_delims(cx, ty.span, spans, "type", (false, false), false);
}
}
self.with_self_ty_parens = false;
}
_ => {}
}
}
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
<Self as UnusedDelimLint>::check_item(self, cx, item)
}
fn enter_where_predicate(&mut self, _: &EarlyContext<'_>, pred: &ast::WherePredicate) {
use rustc_ast::{WhereBoundPredicate, WherePredicate};
if let WherePredicate::BoundPredicate(WhereBoundPredicate {
bounded_ty,
bound_generic_params,
..
}) = pred &&
let ast::TyKind::Paren(_) = &bounded_ty.kind &&
bound_generic_params.is_empty() {
self.with_self_ty_parens = true;
}
}
fn exit_where_predicate(&mut self, _: &EarlyContext<'_>, _: &ast::WherePredicate) {
assert!(!self.with_self_ty_parens);
}
}
declare_lint! {
/// The `unused_braces` lint detects unnecessary braces around an
/// expression.
///
/// ### Example
///
/// ```rust
/// if { true } {
/// // ...
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The braces are not needed, and should be removed. This is the
/// preferred style for writing these expressions.
pub(super) UNUSED_BRACES,
Warn,
"unnecessary braces around an expression"
}
declare_lint_pass!(UnusedBraces => [UNUSED_BRACES]);
impl UnusedDelimLint for UnusedBraces {
const DELIM_STR: &'static str = "braces";
const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = false;
fn lint(&self) -> &'static Lint {
UNUSED_BRACES
}
fn check_unused_delims_expr(
&self,
cx: &EarlyContext<'_>,
value: &ast::Expr,
ctx: UnusedDelimsCtx,
followed_by_block: bool,
left_pos: Option<BytePos>,
right_pos: Option<BytePos>,
is_kw: bool,
) {
match value.kind {
ast::ExprKind::Block(ref inner, None)
if inner.rules == ast::BlockCheckMode::Default =>
{
// emit a warning under the following conditions:
//
// - the block does not have a label
// - the block is not `unsafe`
// - the block contains exactly one expression (do not lint `{ expr; }`)
// - `followed_by_block` is true and the internal expr may contain a `{`
// - the block is not multiline (do not lint multiline match arms)
// ```
// match expr {
// Pattern => {
// somewhat_long_expression
// }
// // ...
// }
// ```
// - the block has no attribute and was not created inside a macro
// - if the block is an `anon_const`, the inner expr must be a literal
// not created by a macro, i.e. do not lint on:
// ```
// struct A<const N: usize>;
// let _: A<{ 2 + 3 }>;
// let _: A<{produces_literal!()}>;
// ```
// FIXME(const_generics): handle paths when #67075 is fixed.
if let [stmt] = inner.stmts.as_slice() {
if let ast::StmtKind::Expr(ref expr) = stmt.kind {
if !Self::is_expr_delims_necessary(expr, followed_by_block, false)
&& (ctx != UnusedDelimsCtx::AnonConst
|| (matches!(expr.kind, ast::ExprKind::Lit(_))
&& !expr.span.from_expansion()))
&& !cx.sess().source_map().is_multiline(value.span)
&& value.attrs.is_empty()
&& !value.span.from_expansion()
&& !inner.span.from_expansion()
{
self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos, is_kw)
}
}
}
}
ast::ExprKind::Let(_, ref expr, _, _) => {
self.check_unused_delims_expr(
cx,
expr,
UnusedDelimsCtx::LetScrutineeExpr,
followed_by_block,
None,
None,
false,
);
}
_ => {}
}
}
}
impl EarlyLintPass for UnusedBraces {
fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
<Self as UnusedDelimLint>::check_stmt(self, cx, s)
}
#[inline]
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
<Self as UnusedDelimLint>::check_expr(self, cx, e);
if let ExprKind::Repeat(_, ref anon_const) = e.kind {
self.check_unused_delims_expr(
cx,
&anon_const.value,
UnusedDelimsCtx::AnonConst,
false,
None,
None,
false,
);
}
}
fn check_generic_arg(&mut self, cx: &EarlyContext<'_>, arg: &ast::GenericArg) {
if let ast::GenericArg::Const(ct) = arg {
self.check_unused_delims_expr(
cx,
&ct.value,
UnusedDelimsCtx::AnonConst,
false,
None,
None,
false,
);
}
}
fn check_variant(&mut self, cx: &EarlyContext<'_>, v: &ast::Variant) {
if let Some(anon_const) = &v.disr_expr {
self.check_unused_delims_expr(
cx,
&anon_const.value,
UnusedDelimsCtx::AnonConst,
false,
None,
None,
false,
);
}
}
fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) {
match ty.kind {
ast::TyKind::Array(_, ref len) => {
self.check_unused_delims_expr(
cx,
&len.value,
UnusedDelimsCtx::ArrayLenExpr,
false,
None,
None,
false,
);
}
ast::TyKind::Typeof(ref anon_const) => {
self.check_unused_delims_expr(
cx,
&anon_const.value,
UnusedDelimsCtx::AnonConst,
false,
None,
None,
false,
);
}
_ => {}
}
}
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
<Self as UnusedDelimLint>::check_item(self, cx, item)
}
}
declare_lint! {
/// The `unused_import_braces` lint catches unnecessary braces around an
/// imported item.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_import_braces)]
/// use test::{A};
///
/// pub mod test {
/// pub struct A;
/// }
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If there is only a single item, then remove the braces (`use test::A;`
/// for example).
///
/// This lint is "allow" by default because it is only enforcing a
/// stylistic choice.
UNUSED_IMPORT_BRACES,
Allow,
"unnecessary braces around an imported item"
}
declare_lint_pass!(UnusedImportBraces => [UNUSED_IMPORT_BRACES]);
impl UnusedImportBraces {
fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) {
if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
// Recursively check nested UseTrees
for (tree, _) in items {
self.check_use_tree(cx, tree, item);
}
// Trigger the lint only if there is one nested item
if items.len() != 1 {
return;
}
// Trigger the lint if the nested item is a non-self single item
let node_name = match items[0].0.kind {
ast::UseTreeKind::Simple(rename) => {
let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
if orig_ident.name == kw::SelfLower {
return;
}
rename.unwrap_or(orig_ident).name
}
ast::UseTreeKind::Glob => Symbol::intern("*"),
ast::UseTreeKind::Nested(_) => return,
};
cx.emit_spanned_lint(
UNUSED_IMPORT_BRACES,
item.span,
UnusedImportBracesDiag { node: node_name },
);
}
}
}
impl EarlyLintPass for UnusedImportBraces {
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
if let ast::ItemKind::Use(ref use_tree) = item.kind {
self.check_use_tree(cx, use_tree, item);
}
}
}
declare_lint! {
/// The `unused_allocation` lint detects unnecessary allocations that can
/// be eliminated.
///
/// ### Example
///
/// ```rust
/// fn main() {
/// let a = Box::new([1, 2, 3]).len();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// When a `box` expression is immediately coerced to a reference, then
/// the allocation is unnecessary, and a reference (using `&` or `&mut`)
/// should be used instead to avoid the allocation.
pub(super) UNUSED_ALLOCATION,
Warn,
"detects unnecessary allocations that can be eliminated"
}
declare_lint_pass!(UnusedAllocation => [UNUSED_ALLOCATION]);
impl<'tcx> LateLintPass<'tcx> for UnusedAllocation {
fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
match e.kind {
hir::ExprKind::Call(path_expr, [_])
if let hir::ExprKind::Path(qpath) = &path_expr.kind
&& let Some(did) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::box_new, did)
=> {}
_ => return,
}
for adj in cx.typeck_results().expr_adjustments(e) {
if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
match m {
adjustment::AutoBorrowMutability::Not => {
cx.emit_spanned_lint(UNUSED_ALLOCATION, e.span, UnusedAllocationDiag);
}
adjustment::AutoBorrowMutability::Mut { .. } => {
cx.emit_spanned_lint(UNUSED_ALLOCATION, e.span, UnusedAllocationMutDiag);
}
};
}
}
}
}