add empty line before backtrace, to separate it from help text
I think this improves how things look, and makes it easier to see the help text (it currently kind of drowns next to the backtrace).
Before:
```
error: unsupported operation: Miri does not support threading
--> /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/thread.rs:68:19
|
68 | let ret = libc::pthread_create(&mut native, &attr, thread_start, &*p as *const _ as *mut _);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Miri does not support threading
|
= help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
= note: inside `std::sys::unix:🧵:Thread::new` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/thread.rs:68:19
= note: inside `std:🧵:Builder::spawn_unchecked::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:492:26
= note: inside `std:🧵:Builder::spawn::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:386:18
= note: inside `std:🧵:spawn::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:619:5
note: inside `main` at tests/compile-fail/thread-spawn.rs:6:5
--> tests/compile-fail/thread-spawn.rs:6:5
|
6 | thread::spawn(|| {});
| ^^^^^^^^^^^^^^^^^^^^
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:34
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:73
= note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<[closure@DefId(1:6030 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys_common/backtrace.rs:130:5
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:13
= note: inside `std::panicking::try::do_call::<[closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panicking.rs:331:40
= note: inside `std::panicking::try::<i32, [closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe]>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panicking.rs:274:15
= note: inside `std::panic::catch_unwind::<[closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panic.rs:394:14
= note: inside `std::rt::lang_start_internal` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:51:25
= note: inside `std::rt::lang_start::<()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:5
```
After:
```
error: unsupported operation: Miri does not support threading
--> /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/thread.rs:68:19
|
68 | let ret = libc::pthread_create(&mut native, &attr, thread_start, &*p as *const _ as *mut _);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Miri does not support threading
|
= help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
= note: inside `std::sys::unix:🧵:Thread::new` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys/unix/thread.rs:68:19
= note: inside `std:🧵:Builder::spawn_unchecked::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:492:26
= note: inside `std:🧵:Builder::spawn::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:386:18
= note: inside `std:🧵:spawn::<[closure@tests/compile-fail/thread-spawn.rs:6:19: 6:24], ()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/thread/mod.rs:619:5
note: inside `main` at tests/compile-fail/thread-spawn.rs:6:5
--> tests/compile-fail/thread-spawn.rs:6:5
|
6 | thread::spawn(|| {});
| ^^^^^^^^^^^^^^^^^^^^
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:34
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:73
= note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<[closure@DefId(1:6030 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys_common/backtrace.rs:130:5
= note: inside closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:13
= note: inside `std::panicking::try::do_call::<[closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panicking.rs:331:40
= note: inside `std::panicking::try::<i32, [closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe]>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panicking.rs:274:15
= note: inside `std::panic::catch_unwind::<[closure@DefId(1:6029 ~ std[2f86]::rt[0]::lang_start_internal[0]::{{closure}}[0]) 0:&&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/panic.rs:394:14
= note: inside `std::rt::lang_start_internal` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:51:25
= note: inside `std::rt::lang_start::<()>` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:5
```
What do you think?
Add shims for RwLock::try_read/RwLock::try_write
This implements proper locking so that we can check for reentrancy and implement the `try_*` methods.
Fixes https://github.com/rust-lang/miri/issues/781
Replace last_entry with last_key_value
Wondering why `last_entry` was introduced (in #1156) while the alternative is shorter and seems clearer to me.
Also, as the perpetrator of map_first_last, I now think that `first_entry`/`last_entry` are silly methods because they're supposed to be constant time (as opposed to `entry`), so there's no money to be made by doing multiple things with the entry.
