rust-clippy/clippy_lints/src/mut_reference.rs

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use rustc::lint::*;
use rustc::ty::{self, Ty};
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use rustc::ty::subst::Subst;
use rustc::hir::*;
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use crate::utils::span_lint;
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/// **What it does:** Detects giving a mutable reference to a function that only
/// requires an immutable reference.
///
/// **Why is this bad?** The immutable reference rules out all other references
/// to the value. Also the code misleads about the intent of the call site.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
/// my_vec.push(&mut value)
/// ```
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declare_clippy_lint! {
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pub UNNECESSARY_MUT_PASSED,
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style,
"an argument passed as a mutable reference although the callee only demands an \
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immutable reference"
}
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#[derive(Copy, Clone)]
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pub struct UnnecessaryMutPassed;
impl LintPass for UnnecessaryMutPassed {
fn get_lints(&self) -> LintArray {
lint_array!(UNNECESSARY_MUT_PASSED)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
match e.node {
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ExprKind::Call(ref fn_expr, ref arguments) => if let ExprKind::Path(ref path) = fn_expr.node {
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check_arguments(
cx,
arguments,
cx.tables.expr_ty(fn_expr),
&print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
);
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},
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ExprKind::MethodCall(ref path, _, ref arguments) => {
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let def_id = cx.tables.type_dependent_defs()[e.hir_id].def_id();
let substs = cx.tables.node_substs(e.hir_id);
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let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
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check_arguments(cx, arguments, method_type, &path.ident.as_str())
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},
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_ => (),
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}
}
}
fn check_arguments<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arguments: &[Expr], type_definition: Ty<'tcx>, name: &str) {
match type_definition.sty {
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ty::TyFnDef(..) | ty::TyFnPtr(_) => {
let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
match parameter.sty {
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ty::TyRef(
_,
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_,
MutImmutable,
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) |
ty::TyRawPtr(ty::TypeAndMut {
mutbl: MutImmutable,
..
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}) => if let ExprKind::AddrOf(MutMutable, _) = argument.node {
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span_lint(
cx,
UNNECESSARY_MUT_PASSED,
argument.span,
&format!("The function/method `{}` doesn't need a mutable reference", name),
);
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},
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_ => (),
}
}
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},
_ => (),
}
}