UB in From<String> for BoxedString #49
Description
I ran the existing test suite with miri, which encountered undefined behavior in From<String> for BoxedString. Specifically, the error is on the line:
unsafe { allocator.grow(ptr, old_layout, Self::layout_for(cap)) }And the output from miri is as follows:
test test::tests::fail ... error: Undefined Behavior: attempting a read access using <210053> at alloc55337[0x20], but that tag does not exist in the borrow stack for this location
--> /home/devin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:228:17
|
228 | ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| attempting a read access using <210053> at alloc55337[0x20], but that tag does not exist in the borrow stack for this location
| this error occurs as part of an access at alloc55337[0x0..0x21]
|
= help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <210053> was created by a SharedReadWrite retag at offsets [0x0..0x20]
--> src/boxed.rs:181:59
|
181 | let ptr = unsafe { NonNull::new_unchecked(s.as_mut_ptr()) };
| ^^^^^^^^^^^^^^
= note: BACKTRACE (of the first span):
= note: inside `std::alloc::Global::grow_impl` at /home/devin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:228:17: 228:87
= note: inside `<std::alloc::Global as std::alloc::Allocator>::grow` at /home/devin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:266:18: 266:68
note: inside `<boxed::BoxedString as std::convert::From<std::string::String>>::from`
--> src/boxed.rs:187:30
|
187 | unsafe { allocator.grow(ptr, old_layout, Self::layout_for(cap)) }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: inside `<std::string::String as std::convert::Into<boxed::BoxedString>>::into` at /home/devin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/convert/mod.rs:716:9: 716:22
note: inside `<SmartString<config::Compact> as std::convert::From<std::string::String>>::from`
--> src/lib.rs:679:30
|
679 | Self::from_boxed(string.into())
| ^^^^^^^^^^^^^
= note: inside `<std::string::String as std::convert::Into<SmartString<config::Compact>>>::into` at /home/devin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/convert/mod.rs:716:9: 716:22
note: inside `test::tests::fail`
--> src/test.rs:515:51
|
515 | let control_smart: SmartString<Compact> = control.into();
| ^^^^^^^^^^^^^^
note: inside closure
--> src/test.rs:509:15
|
508 | #[test]
| ------- in this procedural macro expansion
509 | fn fail() {
| ^
= note: this error originates in the attribute macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)