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