…hpratt

Implement `str::copy_from_str`

Implements the accepted ACP rust-lang/libs-team#709: add `str::copy_from_str`, which copies a same-length `&str` into a mutable `str` in place, mirroring `<[T]>::copy_from_slice`.

The write is safe because UTF-8 is self-recovering: overwriting a `str` with a same-length `&str` cannot produce invalid UTF-8, and `copy_from_slice` enforces the length equality (panics otherwise).

The ACP accepted `copy_from_str` and rejected `copy_within`; `swap_with_str` was left out pending a use case, so this adds only the one method.

Tracking issue: rust-lang#159841

r? libs

…hpratt

Implement `str::copy_from_str`

Implements the accepted ACP rust-lang/libs-team#709: add `str::copy_from_str`, which copies a same-length `&str` into a mutable `str` in place, mirroring `<[T]>::copy_from_slice`.

The write is safe because UTF-8 is self-recovering: overwriting a `str` with a same-length `&str` cannot produce invalid UTF-8, and `copy_from_slice` enforces the length equality (panics otherwise).

The ACP accepted `copy_from_str` and rejected `copy_within`; `swap_with_str` was left out pending a use case, so this adds only the one method.

Tracking issue: rust-lang#159841

r? libs

…uwer

Rollup of 24 pull requests

Successful merges:

 - #159638 (bootstrap: Split the `Step` trait into multiple traits)
 - #159774 (rustc_trait_selection: fix trait solver hang caused by degenerate obligations)
 - #159837 (line-tables-only test: check that the line number matches the function name)
 - #159946 (Update Enzyme submodule to imporve llvm-cov)
 - #159617 (Fix up `#[linkage]` target checking)
 - #159733 (std: Switch implementations of `thread_local!` for WASI)
 - #159783 (Check unsafe impls on safe EIIs)
 - #159810 (Add tuple never coercion collection regression test)
 - #159821 (Update expect message using the recommended style in binary_heap module)
 - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate)
 - #159846 (Implement `str::copy_from_str`)
 - #159849 (rustc_parse: Stop returning `Option` from statement parsing)
 - #159853 (Updated expect messages for `CString` struct and method documentation)
 - #159875 (More cleanup in `rustc_attr_parsing`)
 - #159882 (Update expect messages in library/alloc/boxed.rs and library/alloc/string.rs to follow the style guide)
 - #159891 (Split multiline derives into std/rustc macros)
 - #159893 (Fix `find_attr` hygiene and `rustc_hir` cleanups)
 - #159895 (rustc-dev-guide subtree update)
 - #159902 (Clarify that the expected runtime symbols signature is for the current target only)
 - #159914 (Fix error in diagnostic on_unmatched_args)
 - #159917 (spare capacity mut constification)
 - #159918 (rename abort_unwind → abort_on_unwind)
 - #159936 (Minor `rustc_ast::ast` doc cleanups)
 - #159945 (Update expect messages in library/core/src/ptr/non_null.rs)

…uwer

Rollup of 24 pull requests

Successful merges:

 - #159638 (bootstrap: Split the `Step` trait into multiple traits)
 - #159774 (rustc_trait_selection: fix trait solver hang caused by degenerate obligations)
 - #159837 (line-tables-only test: check that the line number matches the function name)
 - #159946 (Update Enzyme submodule to imporve llvm-cov)
 - #159617 (Fix up `#[linkage]` target checking)
 - #159733 (std: Switch implementations of `thread_local!` for WASI)
 - #159783 (Check unsafe impls on safe EIIs)
 - #159810 (Add tuple never coercion collection regression test)
 - #159821 (Update expect message using the recommended style in binary_heap module)
 - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate)
 - #159846 (Implement `str::copy_from_str`)
 - #159849 (rustc_parse: Stop returning `Option` from statement parsing)
 - #159853 (Updated expect messages for `CString` struct and method documentation)
 - #159875 (More cleanup in `rustc_attr_parsing`)
 - #159882 (Update expect messages in library/alloc/boxed.rs and library/alloc/string.rs to follow the style guide)
 - #159891 (Split multiline derives into std/rustc macros)
 - #159893 (Fix `find_attr` hygiene and `rustc_hir` cleanups)
 - #159895 (rustc-dev-guide subtree update)
 - #159902 (Clarify that the expected runtime symbols signature is for the current target only)
 - #159914 (Fix error in diagnostic on_unmatched_args)
 - #159917 (spare capacity mut constification)
 - #159918 (rename abort_unwind → abort_on_unwind)
 - #159936 (Minor `rustc_ast::ast` doc cleanups)
 - #159945 (Update expect messages in library/core/src/ptr/non_null.rs)

…hpratt

Implement `str::copy_from_str`

Implements the accepted ACP rust-lang/libs-team#709: add `str::copy_from_str`, which copies a same-length `&str` into a mutable `str` in place, mirroring `<[T]>::copy_from_slice`.

The write is safe because UTF-8 is self-recovering: overwriting a `str` with a same-length `&str` cannot produce invalid UTF-8, and `copy_from_slice` enforces the length equality (panics otherwise).

The ACP accepted `copy_from_str` and rejected `copy_within`; `swap_with_str` was left out pending a use case, so this adds only the one method.

Tracking issue: rust-lang#159841

r? libs