2016-01-21 17:19:23 -06:00
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[package]
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authors = ["The Rust Project Developers"]
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name = "core"
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version = "0.0.0"
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2021-02-20 12:18:01 -06:00
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license = "MIT OR Apache-2.0"
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repository = "https://github.com/rust-lang/rust.git"
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description = "The Rust Core Library"
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2018-05-10 13:02:19 -05:00
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autotests = false
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autobenches = false
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2019-04-14 21:23:21 -05:00
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edition = "2018"
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2016-01-21 17:19:23 -06:00
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[lib]
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test = false
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2016-11-25 15:13:59 -06:00
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bench = false
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2016-04-29 16:23:15 -05:00
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[[test]]
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2017-04-03 09:53:04 -05:00
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name = "coretests"
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2020-06-11 21:31:49 -05:00
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path = "tests/lib.rs"
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2016-11-25 15:13:59 -06:00
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2017-02-03 17:04:22 -06:00
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[[bench]]
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2017-02-06 04:38:47 -06:00
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name = "corebenches"
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2020-06-11 21:31:49 -05:00
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path = "benches/lib.rs"
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2020-06-08 11:09:21 -05:00
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test = true
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2018-02-26 11:07:16 -06:00
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[dev-dependencies]
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2019-08-04 07:27:48 -05:00
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rand = "0.7"
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2018-11-29 15:06:10 -06:00
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[features]
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# Make panics and failed asserts immediately abort without formatting any message
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panic_immediate_abort = []
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Add `debug-refcell` feature to libcore
See https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Attaching.20backtraces.20to.20RefCell/near/226273614
for some background discussion
This PR adds a new off-by-default feature `debug-refcell` to libcore.
When enabled, this feature stores additional debugging information in
`RefCell`. This information is included in the panic message when
`borrow()` or `borrow_mut()` panics, to make it easier to track down the
source of the issue.
Currently, we store the caller location for the earliest active borrow.
This has a number of advantages:
* There is only a constant amount of overhead per `RefCell`
* We don't need any heap memory, so it can easily be implemented in core
* Since we are storing the *earliest* active borrow, we don't need any
extra logic in the `Drop` implementation for `Ref` and `RefMut`
Limitations:
* We only store the caller location, not a full `Backtrace`. Until
we get support for `Backtrace` in libcore, this is the best tha we can
do.
* The captured location is only displayed when `borrow()` or
`borrow_mut()` panics. If a crate calls `try_borrow().unwrap()`
or `try_borrow_mut().unwrap()`, this extra information will be lost.
To make testing easier, I've enabled the `debug-refcell` feature by
default. I'm not sure how to write a test for this feature - we would
need to rebuild core from the test framework, and create a separate
sysroot.
Since this feature will be off-by-default, users will need to use
`xargo` or `cargo -Z build-std` to enable this feature. For users using
a prebuilt standard library, this feature will be disabled with zero
overhead.
I've created a simple test program:
```rust
use std::cell::RefCell;
fn main() {
let _ = std::panic::catch_unwind(|| {
let val = RefCell::new(true);
let _first = val.borrow();
let _second = val.borrow();
let _third = val.borrow_mut();
});
let _ = std::panic::catch_unwind(|| {
let val = RefCell::new(true);
let first = val.borrow_mut();
drop(first);
let _second = val.borrow_mut();
let _thid = val.borrow();
});
}
```
which produces the following output:
```
thread 'main' panicked at 'already borrowed: BorrowMutError { location: Location { file: "refcell_test.rs", line: 6, col: 26 } }', refcell_test.rs:8:26
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at 'already mutably borrowed: BorrowError { location: Location { file: "refcell_test.rs", line: 16, col: 27 } }', refcell_test.rs:18:25
```
2021-02-17 20:30:39 -06:00
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# Make `RefCell` store additional debugging information, which is printed out when
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# a borrow error occurs
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debug_refcell = []
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