regex-automata VS rust

I believe you're the second person to tell me they were confused by this, so there are probably several others confused but didn't say anything. I've added a warning to the top of regex-automata's README.

For anyone following along at home, we're having a very helpful discussion about the implementation I posted in my sibling comment here: https://github.com/BurntSushi/regex-automata/issues/30

My current technique only gets applied to alternations of simple literals. But the idea is generalizeable and I speculate that it is actually impactful to generalize it.

(I could use '_ => {}' instead of 'None' to save a few more.)

I do find the 'if let' variant to be a bit easier to read. It's optimizing for a particular and somewhat common case, so it does of course overlap with 'match'. But I don't find this particular overlap to be too bad. It's usually pretty clear when to use one vs the other.

But like I said, I could live without 'if let'. It is not a major quality of life enhancement to me. Neither will its impending extensions. i.e., 'if let pattern = foo && some_booolean_condition {'.

[1]: https://github.com/BurntSushi/regex-automata/blob/fbae906823...

[2]: https://github.com/BurntSushi/regex-automata/blob/fbae906823...

(The work on regex-automata 0.2 has been underway for over a year now.](https://github.com/BurntSushi/regex-automata/tree/ag/work) There's a lot done, but still a lot more to go. Once that's done, regex proper should be pretty close to a thin layer that glues regex-syntax, regex-automata, memchr and aho-corasick together. I don't currently expect regex to grow any more dependencies than that. And as it is, aho-corasick and memchr are both optional dependencies. Right now, regex-syntax is the only required dependency, but regex-automata will be added to that list.

For what it's worth, this is the script I'm using to build for our platform: build.ps1 / build.sh

Note that before I got the target triple upstream, I had to provide my own target json file. That's here: https://github.com/betrusted-io/rust/blob/1.53.0-xous/riscv32imac-unknown-xous-elf.json and you can adapt it as necessary. Simply creating the file in the correct path is enough. This is the code that does that: https://github.com/betrusted-io/rust/blob/e39344c5473d49a0cb4d45de119ad23713a00ed4/rebuild.ps1#L65

Everything you need to know to build for our platform is at https://github.com/betrusted-io/rust/ and maybe the scripts or patches there will be interesting to you.

Rust does use a Rust port of dlmalloc on platforms that don't provide malloc() and free(). We did port this to Xous, but ran into a feature bug that caused locking to be disabled. That was the source of weird and subtle bugs, which is how he discovered that fact about allocators.

This is correct.

When you tell someone to install Rust, they go to rustup.rs and install the latest version. Therefore, we need to have a libstd port for the latest version. Which effectively means we need to release libstd as soon as possible after the compiler is released. Our `sys` directory is at https://github.com/betrusted-io/rust/tree/1.61.0-xous/librar... and isn't too complicated. It's about 50 patches that need to be carried forward every six weeks.

Fortunately libstd doesn't change too much, at leaset not the parts we need. And I can usually pre-port the patches by applying them to `beta`, which means the patches against the release version usually apply cleanly.

It's still better than requiring nightly, which has absolutely no stability guarantees. By targeting stable, we don't run into issues of bitrot where we accidentally rely on features that have been removed. Rather than adjusting every service in the operating system, we just need to port one library: libstd

I've considered trying to upstream these, but I'm not sure how the rust team would feel about it.