rust-clippy/src/mut_mut.rs

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use rustc::lint::*;
use rustc_front::hir::*;
use rustc::middle::ty::{TypeAndMut, TyRef};
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use utils::{in_external_macro, span_lint};
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declare_lint!(pub MUT_MUT, Allow,
"usage of double-mut refs, e.g. `&mut &mut ...` (either copy'n'paste error, \
or shows a fundamental misunderstanding of references)");
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#[derive(Copy,Clone)]
pub struct MutMut;
impl LintPass for MutMut {
fn get_lints(&self) -> LintArray {
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lint_array!(MUT_MUT)
}
}
impl LateLintPass for MutMut {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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check_expr_mut(cx, expr)
}
fn check_ty(&mut self, cx: &LateContext, ty: &Ty) {
unwrap_mut(ty).and_then(unwrap_mut).map_or((), |_| span_lint(cx, MUT_MUT,
ty.span, "generally you want to avoid `&mut &mut _` if possible"))
}
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}
fn check_expr_mut(cx: &LateContext, expr: &Expr) {
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if in_external_macro(cx, expr.span) { return; }
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fn unwrap_addr(expr: &Expr) -> Option<&Expr> {
match expr.node {
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ExprAddrOf(MutMutable, ref e) => Some(e),
_ => None
}
}
unwrap_addr(expr).map_or((), |e| {
unwrap_addr(e).map_or_else(
|| {
if let TyRef(_, TypeAndMut{ty: _, mutbl: MutMutable}) =
cx.tcx.expr_ty(e).sty {
span_lint(cx, MUT_MUT, expr.span,
"this expression mutably borrows a mutable reference. \
Consider reborrowing")
}
},
|_| {
span_lint(cx, MUT_MUT, expr.span,
"generally you want to avoid `&mut &mut _` if possible")
}
)
})
}
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fn unwrap_mut(ty: &Ty) -> Option<&Ty> {
match ty.node {
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TyRptr(_, MutTy{ ty: ref pty, mutbl: MutMutable }) => Some(pty),
_ => None
}
}