rust-clippy/clippy_lints/src/mut_mut.rs

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use crate::rustc::hir;
use crate::rustc::hir::intravisit;
use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass, in_external_macro, LintContext};
use crate::rustc::{declare_tool_lint, lint_array};
use crate::rustc::ty;
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use crate::utils::{higher, span_lint};
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/// **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.
///
/// **Known problems:** None.
///
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/// **Example:**
/// ```rust
/// let x = &mut &mut y;
/// ```
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declare_clippy_lint! {
pub MUT_MUT,
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pedantic,
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"usage of double-mut refs, e.g. `&mut &mut ...`"
}
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#[derive(Copy, Clone)]
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pub struct MutMut;
impl LintPass for MutMut {
fn get_lints(&self) -> LintArray {
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lint_array!(MUT_MUT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutMut {
fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) {
intravisit::walk_block(&mut MutVisitor { cx }, block);
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}
fn check_ty(&mut self, cx: &LateContext<'a, 'tcx>, ty: &'tcx hir::Ty) {
use crate::rustc::hir::intravisit::Visitor;
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MutVisitor { cx }.visit_ty(ty);
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}
}
pub struct MutVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
}
impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
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if in_external_macro(self.cx.sess(), expr.span) {
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return;
}
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if let Some((_, arg, body)) = higher::for_loop(expr) {
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// 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);
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} else if let hir::ExprKind::AddrOf(hir::MutMutable, ref e) = expr.node {
if let hir::ExprKind::AddrOf(hir::MutMutable, _) = e.node {
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span_lint(
self.cx,
MUT_MUT,
expr.span,
"generally you want to avoid `&mut &mut _` if possible",
);
} else if let ty::Ref(
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_,
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_,
hir::MutMutable,
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) = self.cx.tables.expr_ty(e).sty
{
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span_lint(
self.cx,
MUT_MUT,
expr.span,
"this expression mutably borrows a mutable reference. Consider reborrowing",
);
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}
}
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}
fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
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if let hir::TyKind::Rptr(
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_,
hir::MutTy {
ty: ref pty,
mutbl: hir::MutMutable,
},
) = ty.node
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{
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if let hir::TyKind::Rptr(
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_,
hir::MutTy {
mutbl: hir::MutMutable,
..
},
) = pty.node
{
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span_lint(
self.cx,
MUT_MUT,
ty.span,
"generally you want to avoid `&mut &mut _` if possible",
);
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}
}
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intravisit::walk_ty(self, ty);
}
fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
intravisit::NestedVisitorMap::None
}
}