rust-lang/rust · error

unsafe binders are not implemented yet

Error message

unsafe binders are not implemented yet

What it means

Clippy's author lint (clippy_lints::utils::author) prints Rust patterns that mirror the AST a lint author wants to match. It walks HIR expressions but has no handling for ExprKind::UnsafeBinderCast (the unstable unsafe_binders cast node), so it panics with unimplemented!("unsafe binders are not implemented yet") at author.rs:718.

Source

Thrown at src/tools/clippy/clippy_lints/src/utils/author.rs:718

                    self.expr(field!(field.expr));
                });
                base.if_some(|e| self.expr(e));
            },
            ExprKind::ConstBlock(_) => kind!("ConstBlock(_)"),
            ExprKind::Repeat(value, length) => {
                bind!(self, value, length);
                kind!("Repeat({value}, {length})");
                self.expr(value);
                self.const_arg(length);
            },
            ExprKind::Err(_) => kind!("Err(_)"),
            ExprKind::DropTemps(expr) => {
                bind!(self, expr);
                kind!("DropTemps({expr})");
                self.expr(expr);
            },
            ExprKind::UnsafeBinderCast(..) => {
                unimplemented!("unsafe binders are not implemented yet");
            },
        }
    }

    fn block(&self, block: &Binding<&hir::Block<'_>>) {
        self.slice(field!(block.stmts), |stmt| self.stmt(stmt));
        self.option(field!(block.expr), "trailing_expr", |expr| {
            self.expr(expr);
        });
    }

    fn body(&self, body_id: &Binding<hir::BodyId>) {
        let expr = self.cx.tcx.hir_body(body_id.value).value;
        bind!(self, expr);
        chain!(self, "{expr} = &cx.tcx.hir_body({body_id}).value");
        self.expr(expr);
    }

View on GitHub (pinned to 7088e4b63a)

Solutions

  1. Do not run the author lint on code containing UnsafeBinderCast expressions.
  2. Remove/comment out the unsafe binder cast before invoking CLIPPY_AUTHOR.
  3. Isolate the snippet you want to learn about and author-lint only that part without the binder cast.
  4. Upstream an author.rs branch that emits the UnsafeBinderCast pattern.

Example fix

// before
#![feature(unsafe_binders)]
$ CLIPPY_AUTHOR=1 cargo clippy   // hits UnsafeBinderCast -> panic

// after: drop the binder cast before author-linting
let v: &T = unsafe { value }; // ordinary expression, then author-lint
Defensive patterns

Strategy: validation

Validate before calling

// Do not run the author lint on code with UnsafeBinderCast nodes.
// Strip the #![feature(unsafe_binders)] cast expressions before CLIPPY_AUTHOR=1.

Prevention

When it happens

Trigger: Running clippy with the author lint (-A clippy::author or CLIPPY_AUTHOR=...) on code that contains an unsafe binder cast expression (#![feature(unsafe_binders)] using the wrap/unwrap cast syntax).

Common situations: Lint authors experimenting with unsafe_binders code while using the author lint to learn the AST shape; running clippy author over a crate that enables the unstable feature.

Related errors

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/f4bf6746b69f90d7. Report an issue: GitHub.