panic: GcCell<T> already borrowed

[langston-barrett]

This is an odd one! It actually seems to require a bunch of newlines.

Found with tree-splicer, reduced with treereduce.

list = [Number, Function];
ws = new WeakSet(list);   




ws = new WeakSet(new Set(list));

[ {
EPSILON: 2.220446049250313e-16,
MAX_SAFE_INTEGER: 9007199254740991,
MIN_SAFE_INTEGER: -9007199254740991,
MAX_VALUE: 1.7976931348623157e+308,
MIN_VALUE: 2.2250738585072014e-308,
NEGATIVE_INFINITY: -Infinity,
POSITIVE_INFINITY: Infinity,
 NaN: NaN,
parseInt: {
  length: 2,
    name: "parseInt"
    },
parseFloat: {
  length: 1,
    name: "parseFloat"
    },
isFinite: {
  length: 1,
    name: "isFinite"
    },
isNaN: {
  length: 1,
    name: "isNaN"
    },
isSafeInteger: {
  length: 1,
    name: "isSafeInteger"
    },
isInteger: {
  length: 1,
    name: "isInteger"
    },
prototype: {
toExponential: {
      length: 1,
        name: "toExponential"
        },
 toFixed: {
      length: 1,
        name: "toFixed"
        },
toLocaleString: {
      length: 0,
        name: "toLocaleString"
        },
toPrecision: {
      length: 1,
        name: "toPrecision"
        },
toString: {
      length: 1,
        name: "toString"
        },
 valueOf: {
      length: 0,
        name: "valueOf"
        },
constructor: [Cycle]
    },
length: 1,
name: "Number"
}, {
prototype: {
  length: 0,
    name: "",
   apply: {
      length: 2,
        name: "apply"
        },
    bind: {
      length: 1,
        name: "bind"
        },
    call: {
      length: 1,
        name: "call"
        },
toString: {
      length: 0,
        name: "toString"
        },
  caller: Getter & Setter,
arguments: Getter & Setter,
constructor: [Cycle],
Symbol(Symbol.hasInstance): {
      length: 1,
        name: "[Symbol.iterator]"
        }
    },
length: 1,
name: "Function"
} ]
{

}
undefined
undefined
undefined
undefined
thread 'main' panicked at 'GcCell<T> already borrowed', /home/langston/code/boa/boa_gc/src/cell.rs:167:23
stack backtrace:
   0: rust_begin_unwind
             at /rustc/2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74/library/core/src/panicking.rs:64:14
   2: core::panicking::panic_display
   3: <boa_gc::internals::weak_map_box::WeakMapBox<K,V> as boa_gc::internals::weak_map_box::ErasedWeakMapBox>::clear_dead_entries
   4: boa_gc::Allocator::manage_state
   5: boa_gc::pointers::weak::WeakGc<T>::new
   6: boa_gc::pointers::weak_map::WeakMap<K,V>::contains_key
   7: boa_engine::builtins::weak_set::WeakSet::add
   8: boa_engine::vm::code_block::<impl boa_engine::object::jsobject::JsObject>::call_internal
   9: boa_engine::object::internal_methods::function::function_call{{reify.shim}}
  10: <boa_engine::builtins::weak_set::WeakSet as boa_engine::builtins::BuiltInConstructor>::constructor
  11: boa_engine::object::internal_methods::function::function_construct{{reify.shim}}
  12: <boa_engine::vm::opcode::new::New as boa_engine::vm::opcode::Operation>::execute
  13: boa_engine::vm::<impl boa_engine::context::Context>::execute_instruction
  14: boa_engine::vm::<impl boa_engine::context::Context>::run
  15: boa_engine::context::Context::execute
  16: boa_engine::context::Context::eval_script
  17: boa::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Build environment (please complete the following information):

• OS: NixOS
• Target triple: x86_64-unknown-linux-gnu
• Rustc version: 1.68

[jedel1043]

Will close this in favour of #2732, since they seem to have the same root cause.