BTreeMap: bring back the key slice for immutable lookup

[ssomers]

Pave the way for binary search, by reverting a bit of #73971, which banned keys for misbehaving while it was defined for every BorrowType. Adding some debug_asserts along the way.

r? @Mark-Simulacrum

[Mark-Simulacrum]

@bors r+ rollup=never in case it has perf effects

[bors]

📌 Commit c0e8075 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit c0e8075 with merge 20c4653b12095750b2282a23e242eb1d15bae307...

[rust-log-analyzer]

The job dist-x86_64-linux failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking crates-io v0.31.1 (/tmp/cargo/crates/crates-io)
error[E0283]: type annotations needed
   --> src/cargo/util/config/de.rs:530:63
    |
530 |                 seed.deserialize(Tuple2Deserializer(1i32, env.as_ref()))
    |                                                           |   |
    |                                                           |   |
    |                                                           |   cannot infer type for type parameter `T` declared on the trait `AsRef`
    |                                                           this method call resolves to `&T`
    |
    = note: cannot satisfy `std::string::String: AsRef<_>`
help: use the fully qualified path for the potential candidates
    |
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<OsStr>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<std::path::Path>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<str>>::as_ref(env)))
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 |                 seed.deserialize(Tuple2Deserializer(1i32, <std::string::String as AsRef<[u8]>>::as_ref(env)))

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.

[bors]

💔 Test failed - checks-actions

[Mark-Simulacrum]

@bors retry - cargo lockfile not pinned for pgo

[bors]

⌛ Testing commit c0e8075 with merge 7907345...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 7907345 to master...