build(rust): vendor rnix parser crate

third_party/crates/rnix-0.14.0/README.md

@@ -0,0 +1,88 @@
+# rnix-parser [![Crates.io](https://img.shields.io/crates/v/rnix.svg)](http://crates.io/crates/rnix) [![Chat on Matrix](https://matrix.to/img/matrix-badge.svg)](https://matrix.to/#/#rnix-lsp:matrix.org)
+
+rnix is a parser for the [Nix language](https://nixos.org/nix/) written in Rust.
+
+This can be used to manipulate the Nix AST and can for example be used for:
+
+- Interactively render Nix on a GUI
+- Formatting Nix code
+- Rename identifiers
+
+and a lot more!
+
+rnix nowadays uses [@matklad](https://github.com/matklad)'s
+[rowan](https://crates.io/crates/rowan) crate to ensure:
+
+- all span information is preserved, meaning you can use the AST to for
+  example apply highlighting
+- printing out the AST prints out 100% the original code. This is not an
+  over-exaggeration, even completely invalid nix code such as this README can
+  be intact after a parsing session (though the AST will mark errnous nodes)
+- easy ways to walk the tree without resorting to recursion
+
+## Demo
+
+Examples can be found in the `examples/` directory. 
+
+You may also want to see
+[nix-explorer](https://gitlab.com/jD91mZM2/nix-explorer): An example
+that highlights AST nodes in Nix code. This demonstrates how
+whitespaces and commands are preserved.
+
+## Hacking
+
+Tests can be run with `cargo test`.
+
+In order to update all `.expect`-files to the currently expected results,
+you may run `UPDATE_TESTS=1 cargo test`.
+
+You can parse Nix expressions from standard input using the `from-stdin` example.
+To try that, run the following in your shell:
+
+```sh
+echo "[hello nix]" | cargo run --quiet --example from-stdin
+```
+
+## Release Checklist
+
+* Ensure that all PRs that were scheduled for the release are merged (or optionally move
+  them to another milestone).
+* Close the milestone for the release (if any).
+* Run `cargo test` on `master` (or the branch to release from) with all changes being pulled in.
+* Apply the following patch to [nixpkgs-fmt](https://github.com/nix-community/nixpkgs-fmt):
+  ```diff
+  diff --git a/Cargo.toml b/Cargo.toml
+  index 0891350..edad471 100644
+  --- a/Cargo.toml
+  +++ b/Cargo.toml
+  @@ -13,6 +13,9 @@ repository = "https://github.com/nix-community/nixpkgs-fmt"
+   [workspace]
+   members = [ "./wasm" ]
+   
+  +[patch.crates-io]
+  +rnix = { path = "/home/ma27/Projects/rnix-parser" }
+  +
+   [dependencies]
+   rnix = "0.9.0"
+   smol_str = "0.1.17"
+  ```
+
+  and run `cargo test`.
+
+  While it's planned to add [fuzzing to `rnix-parser` as well](https://github.com/nix-community/rnix-parser/issues/32),
+  `nixpkgs-fmt` has a decent test-suite that would've helped to catch regressions in the past.
+
+  __Note:__ API changes are OK (and fixes should be contributed to `nixpkgs-fmt`), behavioral changes
+  are not unless explicitly discussed before.
+* Update the [CHANGELOG.md](https://github.com/nix-community/rnix-parser/blob/master/CHANGELOG.md).
+* Bump the version number in [Cargo.toml](https://github.com/nix-community/rnix-parser/blob/master/Cargo.toml) & re-run `cargo build` to refresh the lockfile.
+* Commit & run `nix build`.
+* Tag the release and push everything.
+* As soon as the CI has completed, run `cargo publish`.
+
+# RIP jd91mzm2
+
+Sadly, the original author of this project, [@jD91mZM2 has passed
+away](https://www.redox-os.org/news/open-source-mental-health/). His online
+presence was anonymous and what we have left is his code. This is but one of
+his many repos that he contributed to.