fixes rust-lang#125189

…ratt

Panic if `PathBuf::set_extension` would add a path separator

This is likely never intended and potentially a security vulnerability if it happens.

I'd guess that it's mostly literal strings that are passed to this function in practice, so I'm guessing this doesn't break anyone.

CC rust-lang#125060

… r=Mark-Simulacrum

tidy: stop special-casing tests/ui entry limit

It is genuinely more annoying to have this error, now that this value is below the general `ENTRY_LIMIT` cap, when one is trying to clean out tests from tests/ui! This code has served its purpose well, let it rest now rather than force it to continue haunting us.

…=Mark-Simulacrum

Create a triagebot ping group for Rust for Linux

Corresponding rustc-dev-guide PR [here](rust-lang/rustc-dev-guide#1984). Discussed on [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Testing.20Rust.20for.20Linux.20in.20our.20CI).

…, r=compiler-errors

drop region constraints for ambiguous goals

See the comment in `compute_external_query_constraints`. While the underlying issue is preexisting, this fixes a bug introduced by rust-lang#125343.

It slightly weakens the leak chec, even if we didn't have any test which was affected. I want to write such a test before merging this PR.

r? ``@compiler-errors``

A small diagnostic improvement for dropping_copy_types

For a value `m`  which implements `Copy` trait, `drop(m);` does nothing.
We now suggest user to ignore it by a abstract and general note: `let _ = ...`.
I think we can give a clearer note here: `let _ = m;`

fixes rust-lang#125189

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Stop SRoA'ing `DynMetadata` in MIR

Fixes rust-lang#125506

cleanup dependence of `ExtCtxt` in transcribe when macro expansion

part of rust-lang#125356
We can remove `transcribe`’s dependence on `ExtCtxt` to facilitate subsequent work (such as moving macro expansion into the incremental compilation system)

r? ``@petrochenkov``
Thanks for the reviewing!

…ific, r=Mark-Simulacrum

Also mention my-self for other check-cfg docs changes

This PR adds a mention for my-self for the recently added `src/doc/rustc/src/check-cfg` directory.

*I had to add a second mention just for the directory since [`Path::starts_with`](https://doc.rust-lang.org/std/path/struct.Path.html#method.starts_with) as used by [triagebot](https://github.com/rust-lang/triagebot/blob/48f29f351cae774caa90f555fbbc6d0df7dce80e/src/handlers/mentions.rs#L69), matches on path components and so can never return true for a file and directory at the same time.*