Auto merge of #137284 - matthiaskrgr:rollup-deuhk46, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #127793 (Added project-specific Zed IDE settings)
 - #134995 (Stabilize const_slice_flatten)
 - #136301 (Improve instant docs)
 - #136347 (Add a bullet point to `std::fs::copy`)
 - #136794 (Stabilize file_lock)
 - #137094 (x86_win64 ABI: do not use xmm0 with softfloat ABI)
 - #137227 (docs(dev): Update the feature-gate instructions)
 - #137232 (Don't mention `FromResidual` on bad `?`)
 - #137251 (coverage: Get hole spans from nested items without fully visiting them)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: src/building/suggested.md

@@ -154,6 +154,16 @@ You can run `./x setup editor` and select `helix`, which will prompt you to
 create `languages.toml` with the recommended configuration for Helix. The
 recommended settings live at [`src/etc/rust_analyzer_helix.toml`].
 
+### Zed
+
+Zed comes with built-in LSP and rust-analyzer support.
+It can be configured through `.zed/settings.json`, as described
+[here](https://zed.dev/docs/configuring-languages). Selecting `zed`
+in `./x setup editor` will prompt you to create a `.zed/settings.json`
+file which will configure Zed with the recommended configuration. The
+recommended `rust-analyzer` settings live
+at [`src/etc/rust_analyzer_zed.json`].
+
 ## Check, check, and check again
 
 When doing simple refactoring, it can be useful to run `./x check`
@@ -381,4 +391,5 @@ load this completion.
 [`src/etc/rust_analyzer_settings.json`]: https://github.com/rust-lang/rust/blob/master/src/etc/rust_analyzer_settings.json
 [`src/etc/rust_analyzer_eglot.el`]: https://github.com/rust-lang/rust/blob/master/src/etc/rust_analyzer_eglot.el
 [`src/etc/rust_analyzer_helix.toml`]: https://github.com/rust-lang/rust/blob/master/src/etc/rust_analyzer_helix.toml
+[`src/etc/rust_analyzer_zed.json`]: https://github.com/rust-lang/rust/blob/master/src/etc/rust_analyzer_zed.json
 [`src/etc/pre-push.sh`]: https://github.com/rust-lang/rust/blob/master/src/etc/pre-push.sh

Diff for: src/implementing_new_features.md

@@ -167,9 +167,7 @@ a new unstable feature:
 
 1. Prevent usage of the new feature unless the feature gate is set.
    You can check it in most places in the compiler using the
-   expression `tcx.features().$feature_name` (or
-   `sess.features_untracked().$feature_name` if the
-   tcx is unavailable)
+   expression `tcx.features().$feature_name()`
 
     If the feature gate is not set, you should either maintain
     the pre-feature behavior or raise an error, depending on