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use clippy_utils::diagnostics::span_lint;
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use std::iter;
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 mutable reference rules out all other references to
/// the value. Also the code misleads about the intent of the call site.
///
/// ### Example
/// ```rust
/// # let mut vec = Vec::new();
/// # let mut value = 5;
/// vec.push(&mut value);
/// ```
///
/// Use instead:
/// ```rust
/// # let mut vec = Vec::new();
/// # let value = 5;
/// vec.push(&value);
/// ```
#[clippy::version = "pre 1.29.0"]
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(fn_expr, arguments) => {
if let ExprKind::Path(ref path) = fn_expr.kind {
check_arguments(
cx,
arguments.iter().collect(),
cx.typeck_results().expr_ty(fn_expr),
&rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false)),
"function",
);
}
},
ExprKind::MethodCall(path, receiver, arguments, _) => {
let def_id = cx.typeck_results().type_dependent_def_id(e.hir_id).unwrap();
let substs = cx.typeck_results().node_substs(e.hir_id);
let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
check_arguments(
cx,
std::iter::once(receiver).chain(arguments.iter()).collect(),
method_type,
path.ident.as_str(),
"method",
);
},
_ => (),
}
}
}
fn check_arguments<'tcx>(
cx: &LateContext<'tcx>,
arguments: Vec<&Expr<'_>>,
type_definition: Ty<'tcx>,
name: &str,
fn_kind: &str,
) {
match type_definition.kind() {
ty::FnDef(..) | ty::FnPtr(_) => {
let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
for (argument, parameter) in iter::zip(arguments, parameters) {
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 {fn_kind} `{name}` doesn't need a mutable reference"),
);
}
},
_ => (),
}
}
},
_ => (),
}
}
|
