diff options
| -rw-r--r-- | library/core/Cargo.toml | 3 | ||||
| -rw-r--r-- | library/core/src/cell.rs | 84 |
2 files changed, 76 insertions, 11 deletions
diff --git a/library/core/Cargo.toml b/library/core/Cargo.toml index 4a7dbb91822..b6aaf078cf0 100644 --- a/library/core/Cargo.toml +++ b/library/core/Cargo.toml @@ -28,3 +28,6 @@ rand = "0.7" [features] # Make panics and failed asserts immediately abort without formatting any message panic_immediate_abort = [] +# Make `RefCell` store additional debugging information, which is printed out when +# a borrow error occurs +debug_refcell = [] diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs index fa21a40e169..770169219aa 100644 --- a/library/core/src/cell.rs +++ b/library/core/src/cell.rs @@ -575,6 +575,12 @@ impl<T> Cell<[T]> { #[stable(feature = "rust1", since = "1.0.0")] pub struct RefCell<T: ?Sized> { borrow: Cell<BorrowFlag>, + // Stores the location of the earliest currently active borrow. + // This gets updated whenver we go from having zero borrows + // to having a single borrow. When a borrow occurs, this gets included + // in the generated `BorroeError/`BorrowMutError` + #[cfg(feature = "debug_refcell")] + borrowed_at: Cell<Option<&'static crate::panic::Location<'static>>>, value: UnsafeCell<T>, } @@ -582,12 +588,19 @@ pub struct RefCell<T: ?Sized> { #[stable(feature = "try_borrow", since = "1.13.0")] pub struct BorrowError { _private: (), + #[cfg(feature = "debug_refcell")] + location: &'static crate::panic::Location<'static>, } #[stable(feature = "try_borrow", since = "1.13.0")] impl Debug for BorrowError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("BorrowError").finish() + let mut builder = f.debug_struct("BorrowError"); + + #[cfg(feature = "debug_refcell")] + builder.field("location", self.location); + + builder.finish() } } @@ -602,12 +615,19 @@ impl Display for BorrowError { #[stable(feature = "try_borrow", since = "1.13.0")] pub struct BorrowMutError { _private: (), + #[cfg(feature = "debug_refcell")] + location: &'static crate::panic::Location<'static>, } #[stable(feature = "try_borrow", since = "1.13.0")] impl Debug for BorrowMutError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("BorrowMutError").finish() + let mut builder = f.debug_struct("BorrowMutError"); + + #[cfg(feature = "debug_refcell")] + builder.field("location", self.location); + + builder.finish() } } @@ -658,7 +678,12 @@ impl<T> RefCell<T> { #[rustc_const_stable(feature = "const_refcell_new", since = "1.24.0")] #[inline] pub const fn new(value: T) -> RefCell<T> { - RefCell { value: UnsafeCell::new(value), borrow: Cell::new(UNUSED) } + RefCell { + value: UnsafeCell::new(value), + borrow: Cell::new(UNUSED), + #[cfg(feature = "debug_refcell")] + borrowed_at: Cell::new(None), + } } /// Consumes the `RefCell`, returning the wrapped value. @@ -823,12 +848,29 @@ impl<T: ?Sized> RefCell<T> { /// ``` #[stable(feature = "try_borrow", since = "1.13.0")] #[inline] + #[cfg_attr(feature = "debug_refcell", track_caller)] pub fn try_borrow(&self) -> Result<Ref<'_, T>, BorrowError> { match BorrowRef::new(&self.borrow) { - // SAFETY: `BorrowRef` ensures that there is only immutable access - // to the value while borrowed. - Some(b) => Ok(Ref { value: unsafe { &*self.value.get() }, borrow: b }), - None => Err(BorrowError { _private: () }), + Some(b) => { + #[cfg(feature = "debug_refcell")] + { + // `borrowed_at` is always the *first* active borrow + if b.borrow.get() == 1 { + self.borrowed_at.set(Some(crate::panic::Location::caller())); + } + } + + // SAFETY: `BorrowRef` ensures that there is only immutable access + // to the value while borrowed. + Ok(Ref { value: unsafe { &*self.value.get() }, borrow: b }) + } + None => Err(BorrowError { + _private: (), + // If a borrow occured, then we must already have an outstanding borrow, + // so `borrowed_at` will be `Some` + #[cfg(feature = "debug_refcell")] + location: self.borrowed_at.get().unwrap(), + }), } } @@ -896,11 +938,25 @@ impl<T: ?Sized> RefCell<T> { /// ``` #[stable(feature = "try_borrow", since = "1.13.0")] #[inline] + #[cfg_attr(feature = "debug_refcell", track_caller)] pub fn try_borrow_mut(&self) -> Result<RefMut<'_, T>, BorrowMutError> { match BorrowRefMut::new(&self.borrow) { - // SAFETY: `BorrowRef` guarantees unique access. - Some(b) => Ok(RefMut { value: unsafe { &mut *self.value.get() }, borrow: b }), - None => Err(BorrowMutError { _private: () }), + Some(b) => { + #[cfg(feature = "debug_refcell")] + { + self.borrowed_at.set(Some(crate::panic::Location::caller())); + } + + // SAFETY: `BorrowRef` guarantees unique access. + Ok(RefMut { value: unsafe { &mut *self.value.get() }, borrow: b }) + } + None => Err(BorrowMutError { + _private: (), + // If a borrow occured, then we must already have an outstanding borrow, + // so `borrowed_at` will be `Some` + #[cfg(feature = "debug_refcell")] + location: self.borrowed_at.get().unwrap(), + }), } } @@ -1016,7 +1072,13 @@ impl<T: ?Sized> RefCell<T> { // and is thus guaranteed to be valid for the lifetime of `self`. Ok(unsafe { &*self.value.get() }) } else { - Err(BorrowError { _private: () }) + Err(BorrowError { + _private: (), + // If a borrow occured, then we must already have an outstanding borrow, + // so `borrowed_at` will be `Some` + #[cfg(feature = "debug_refcell")] + location: self.borrowed_at.get().unwrap(), + }) } } } |