+/// How a local is captured by a closure
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CaptureKind {
+ Value,
+ Ref(Mutability),
+}
+impl CaptureKind {
+ pub fn is_imm_ref(self) -> bool {
+ self == Self::Ref(Mutability::Not)
+ }
+}
+impl std::ops::BitOr for CaptureKind {
+ type Output = Self;
+ fn bitor(self, rhs: Self) -> Self::Output {
+ match (self, rhs) {
+ (CaptureKind::Value, _) | (_, CaptureKind::Value) => CaptureKind::Value,
+ (CaptureKind::Ref(Mutability::Mut), CaptureKind::Ref(_))
+ | (CaptureKind::Ref(_), CaptureKind::Ref(Mutability::Mut)) => CaptureKind::Ref(Mutability::Mut),
+ (CaptureKind::Ref(Mutability::Not), CaptureKind::Ref(Mutability::Not)) => CaptureKind::Ref(Mutability::Not),
+ }
+ }
+}
+impl std::ops::BitOrAssign for CaptureKind {
+ fn bitor_assign(&mut self, rhs: Self) {
+ *self = *self | rhs;
+ }
+}
+
+/// Given an expression referencing a local, determines how it would be captured in a closure.
+/// Note as this will walk up to parent expressions until the capture can be determined it should
+/// only be used while making a closure somewhere a value is consumed. e.g. a block, match arm, or
+/// function argument (other than a receiver).
+pub fn capture_local_usage(cx: &LateContext<'tcx>, e: &Expr<'_>) -> CaptureKind {
+ fn pat_capture_kind(cx: &LateContext<'_>, pat: &Pat<'_>) -> CaptureKind {
+ let mut capture = CaptureKind::Ref(Mutability::Not);
+ pat.each_binding_or_first(&mut |_, id, span, _| match cx
+ .typeck_results()
+ .extract_binding_mode(cx.sess(), id, span)
+ .unwrap()
+ {
+ BindingMode::BindByValue(_) if !is_copy(cx, cx.typeck_results().node_type(id)) => {
+ capture = CaptureKind::Value;
+ },
+ BindingMode::BindByReference(Mutability::Mut) if capture != CaptureKind::Value => {
+ capture = CaptureKind::Ref(Mutability::Mut);
+ },
+ _ => (),
+ });
+ capture
+ }
+
+ debug_assert!(matches!(
+ e.kind,
+ ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(_), .. }))
+ ));
+
+ let mut child_id = e.hir_id;
+ let mut capture = CaptureKind::Value;
+ let mut capture_expr_ty = e;
+
+ for (parent_id, parent) in cx.tcx.hir().parent_iter(e.hir_id) {
+ if let [Adjustment {
+ kind: Adjust::Deref(_) | Adjust::Borrow(AutoBorrow::Ref(..)),
+ target,
+ }, ref adjust @ ..] = *cx
+ .typeck_results()
+ .adjustments()
+ .get(child_id)
+ .map_or(&[][..], |x| &**x)
+ {
+ if let rustc_ty::RawPtr(TypeAndMut { mutbl: mutability, .. }) | rustc_ty::Ref(_, _, mutability) =
+ *adjust.last().map_or(target, |a| a.target).kind()
+ {
+ return CaptureKind::Ref(mutability);
+ }
+ }
+
+ match parent {
+ Node::Expr(e) => match e.kind {
+ ExprKind::AddrOf(_, mutability, _) => return CaptureKind::Ref(mutability),
+ ExprKind::Index(..) | ExprKind::Unary(UnOp::Deref, _) => capture = CaptureKind::Ref(Mutability::Not),
+ ExprKind::Assign(lhs, ..) | ExprKind::Assign(_, lhs, _) if lhs.hir_id == child_id => {
+ return CaptureKind::Ref(Mutability::Mut);
+ },
+ ExprKind::Field(..) => {
+ if capture == CaptureKind::Value {
+ capture_expr_ty = e;
+ }
+ },
+ ExprKind::Let(pat, ..) => {
+ let mutability = match pat_capture_kind(cx, pat) {
+ CaptureKind::Value => Mutability::Not,
+ CaptureKind::Ref(m) => m,
+ };
+ return CaptureKind::Ref(mutability);
+ },
+ ExprKind::Match(_, arms, _) => {
+ let mut mutability = Mutability::Not;
+ for capture in arms.iter().map(|arm| pat_capture_kind(cx, arm.pat)) {
+ match capture {
+ CaptureKind::Value => break,
+ CaptureKind::Ref(Mutability::Mut) => mutability = Mutability::Mut,
+ CaptureKind::Ref(Mutability::Not) => (),
+ }
+ }
+ return CaptureKind::Ref(mutability);
+ },
+ _ => break,
+ },
+ Node::Local(l) => match pat_capture_kind(cx, l.pat) {
+ CaptureKind::Value => break,
+ capture @ CaptureKind::Ref(_) => return capture,
+ },
+ _ => break,
+ }
+
+ child_id = parent_id;
+ }
+
+ if capture == CaptureKind::Value && is_copy(cx, cx.typeck_results().expr_ty(capture_expr_ty)) {
+ // Copy types are never automatically captured by value.
+ CaptureKind::Ref(Mutability::Not)
+ } else {
+ capture
+ }
+}
+
+/// Checks if the expression can be moved into a closure as is. This will return a list of captures
+/// if so, otherwise, `None`.
+pub fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<HirIdMap<CaptureKind>> {