blob: 53341b6eba752a019c1c948312068a549b94d029 [file] [log] [blame]
use crate::utils::span_lint;
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::{self, Ty};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Detects passing 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:**
/// ```ignore
/// // Bad
/// my_vec.push(&mut value)
///
/// // Good
/// my_vec.push(&value)
/// ```
pub UNNECESSARY_MUT_PASSED,
style,
"an argument passed as a mutable reference although the callee only demands an immutable reference"
}
declare_lint_pass!(UnnecessaryMutPassed => [UNNECESSARY_MUT_PASSED]);
impl<'tcx> LateLintPass<'tcx> for UnnecessaryMutPassed {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
match e.kind {
ExprKind::Call(ref fn_expr, ref arguments) => {
if let ExprKind::Path(ref path) = fn_expr.kind {
check_arguments(
cx,
arguments,
cx.tables().expr_ty(fn_expr),
&rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false)),
);
}
},
ExprKind::MethodCall(ref path, _, ref arguments, _) => {
let def_id = cx.tables().type_dependent_def_id(e.hir_id).unwrap();
let substs = cx.tables().node_substs(e.hir_id);
let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
check_arguments(cx, arguments, method_type, &path.ident.as_str())
},
_ => (),
}
}
}
fn check_arguments<'tcx>(cx: &LateContext<'tcx>, arguments: &[Expr<'_>], type_definition: Ty<'tcx>, name: &str) {
match type_definition.kind {
ty::FnDef(..) | ty::FnPtr(_) => {
let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
match parameter.kind {
ty::Ref(_, _, Mutability::Not)
| ty::RawPtr(ty::TypeAndMut {
mutbl: Mutability::Not, ..
}) => {
if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _) = argument.kind {
span_lint(
cx,
UNNECESSARY_MUT_PASSED,
argument.span,
&format!("The function/method `{}` doesn't need a mutable reference", name),
);
}
},
_ => (),
}
}
},
_ => (),
}
}