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use clippy_utils::diagnostics::span_lint;
use clippy_utils::higher;
use rustc_hir as hir;
use rustc_hir::intravisit;
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for instances of `mut mut` references.
///
/// ### Why is this bad?
/// Multiple `mut`s don't add anything meaningful to the
/// source. This is either a copy'n'paste error, or it shows a fundamental
/// misunderstanding of references.
///
/// ### Example
/// ```rust
/// # let mut y = 1;
/// let x = &mut &mut y;
/// ```
#[clippy::version = "pre 1.29.0"]
pub MUT_MUT,
pedantic,
"usage of double-mut refs, e.g., `&mut &mut ...`"
}
declare_lint_pass!(MutMut => [MUT_MUT]);
impl<'tcx> LateLintPass<'tcx> for MutMut {
fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
intravisit::walk_block(&mut MutVisitor { cx }, block);
}
fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>) {
use rustc_hir::intravisit::Visitor;
MutVisitor { cx }.visit_ty(ty);
}
}
pub struct MutVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
}
impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
if in_external_macro(self.cx.sess(), expr.span) {
return;
}
if let Some(higher::ForLoop { arg, body, .. }) = higher::ForLoop::hir(expr) {
// A `for` loop lowers to:
// ```rust
// match ::std::iter::Iterator::next(&mut iter) {
// // ^^^^
// ```
// Let's ignore the generated code.
intravisit::walk_expr(self, arg);
intravisit::walk_expr(self, body);
} else if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e) = expr.kind {
if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, _) = e.kind {
span_lint(
self.cx,
MUT_MUT,
expr.span,
"generally you want to avoid `&mut &mut _` if possible",
);
} else if let ty::Ref(_, ty, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() {
if ty.peel_refs().is_sized(self.cx.tcx, self.cx.param_env) {
span_lint(
self.cx,
MUT_MUT,
expr.span,
"this expression mutably borrows a mutable reference. Consider reborrowing",
);
}
}
}
}
fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
if in_external_macro(self.cx.sess(), ty.span) {
return;
}
if let hir::TyKind::Ref(
_,
hir::MutTy {
ty: pty,
mutbl: hir::Mutability::Mut,
},
) = ty.kind
{
if let hir::TyKind::Ref(
_,
hir::MutTy {
mutbl: hir::Mutability::Mut,
..
},
) = pty.kind
{
span_lint(
self.cx,
MUT_MUT,
ty.span,
"generally you want to avoid `&mut &mut _` if possible",
);
}
}
intravisit::walk_ty(self, ty);
}
}
|
