123 lines
3.4 KiB
Rust
123 lines
3.4 KiB
Rust
use rustc::hir;
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use rustc::hir::intravisit;
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use rustc::lint::*;
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use rustc::ty;
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use utils::{higher, in_external_macro, span_lint};
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/// **What it does:** Checks for instances of `mut mut` references.
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///
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/// **Why is this bad?** 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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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let x = &mut &mut y;
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/// ```
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declare_lint! {
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pub MUT_MUT,
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Allow,
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"usage of double-mut refs, e.g. `&mut &mut ...`"
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}
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#[derive(Copy, Clone)]
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pub struct MutMut;
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impl LintPass for MutMut {
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fn get_lints(&self) -> LintArray {
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lint_array!(MUT_MUT)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutMut {
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fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) {
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intravisit::walk_block(&mut MutVisitor { cx: cx }, block);
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}
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fn check_ty(&mut self, cx: &LateContext<'a, 'tcx>, ty: &'tcx hir::Ty) {
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use rustc::hir::intravisit::Visitor;
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MutVisitor { cx: cx }.visit_ty(ty);
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}
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}
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pub struct MutVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, '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, expr.span) {
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return;
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}
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if let Some((_, arg, body)) = higher::for_loop(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::ExprAddrOf(hir::MutMutable, ref e) = expr.node {
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if let hir::ExprAddrOf(hir::MutMutable, _) = e.node {
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span_lint(
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self.cx,
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MUT_MUT,
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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::TyRef(
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_,
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ty::TypeAndMut {
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mutbl: hir::MutMutable,
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..
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},
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) = self.cx.tables.expr_ty(e).sty
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{
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span_lint(
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self.cx,
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MUT_MUT,
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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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fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
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if let hir::TyRptr(
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_,
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hir::MutTy {
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ty: ref pty,
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mutbl: hir::MutMutable,
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},
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) = ty.node
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{
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if let hir::TyRptr(
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_,
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hir::MutTy {
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mutbl: hir::MutMutable,
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..
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},
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) = pty.node
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{
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span_lint(
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self.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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intravisit::walk_ty(self, ty);
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}
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fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
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intravisit::NestedVisitorMap::None
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}
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}
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