How much did the verification cost on top? how did you gate it? was it a Go test suite you ran against the Rust or what? I always wonder how ppl are testing these rewrites, rewriting the tests can also lead to bug. I really wonder how reliable are rewrites like that, a 65k lines you didn't actually read. How did you confirm the semantic equivalence, same behaviour?

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aka-rider 4 days ago | parent | next [-]

All very good questions.

Agents are actively destroy QA gates in many ways, usually by cheating ("the test is buggy, not my changes" — changes the test), or just rot QA slowly by writing buggy overcomplicated tests

What works for me 10/10 is fuzzing and my own constant usage. For this project specifically (text editor), I asked LLM to create human-like fuzzing session, it sends keystrokes like: "the user is searching for a file, editing, <ordering a lizard>, saves changes".

On top of it, I run https://mutants.rs/ which is kind of tests fuzzing. It flips random switches in the app itself, and if tests are silent - they missed a bug.

The downside of this, is I usually find bugs after 1-2 hours of running. I use local Qwen to babysit these sessions, to make initial investigation, a repro case, and file a ticket.

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metaltyphoon 4 days ago | parent [-]

Why are you just pasting LLM answers :(? I see this constantly in Slack DMs to every day from work. It hurts

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tensegrist 4 days ago | parent | next [-]

this is not llm writing. there's no need to startle at the sight of an em-dash

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aka-rider 4 days ago | parent | prev [-]

This is genuinely how I write :'(

It is probably because I read tons and tons of LLM output.

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orwin 4 days ago | parent [-]

It's ok, it is slightly llm-like but not in the worst way, like it was edited after. You aren't Claude at least.

	▲	aka-rider 4 days ago \| parent [-]
		>You aren't Claude at least. I absorbed so many different models at this point :) Thank you for the kind words.

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aka-rider 4 days ago | parent | prev | next [-]

I realized that I haven't answered the question. These $400 also include the tests. Fable ported "human fuzzing session" (the best bug hunter) from Go to Rust and used it to validate everything else. I used hierarchical state machines, so a lot of my QA gates were encoded into the implementation — impossible states are, well, impossible.

(I ported first 80% practically in one shot, planning and then leaving Fable overnight to orchestrate). Then I added a bunch of features, so at the end I ported more like 150% of the original code, I added tree-sitter, and a bunch of syntaxes highlighters. At the end with all that, price went up to ~$650

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coder-pm 4 days ago | parent [-]

This is impressive but it again led me to questions. Porting the fuzzer from Go to Rust to validate Rust is a bit circular, isn’t it^^? Porting a fuzzer bug will hide the same class bug in the code it’s checking, who fuzzes the fuzzer / setup / harness:)? A good standard for rewrites is a differential testing, feed the same input to the old Go app and the new Rust then diff the outputs. Did you do that?

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aka-rider 3 days ago | parent [-]

>feed the same input to the old Go app and the new Rust then diff the outputs.

Yes, I completely forgot to mention, this is exactly my case. Rune is a TUI editor, so I feeded the same terminal sequences to the old and new apps.

It didn't translate 1:1 (I ported core editor first, there were side panels, and different chrome elements) so I instructed LLM to use ttyd (tty -> browser render), Fable then could open both apps with playwright, make and compare screenshots.

To rephrase, one critical component is to establish a feedback loop for the model. This new generation of models: Opus 5, Fable, GLM-5.2, even Qwen3.8-27B can self-correct, provided they know whether they are progressing or not.

A month ago, especially smaller model would fall into a rabbit hole it dug for itself and would never recover. This generation can sometimes run tens of hours without losing track.

I still wouldn't trust a model after 70% context window, but the progress is noticeable.

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coder-pm 3 days ago | parent [-]

The ttyd and playwright is a clever differential way, personally I’m doing the same when it’s about to compare the views (or fix something related to rendering). Good job on that!

A TUI editor’s real output is the bytes stored on disk, while rendering can look identical the saved files might diverge (encoding, line endings, trailing new lines etc). Did you manage to diff that?

Totally agree on the overnight roadmap runs I have the same experience here. The agents have to know how to self-correct and if it’s progressing, otherwise it’s failing!

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aka-rider 3 days ago | parent [-]

>files might diverge

The way rune works with files minimizes chances of silent corruption. I keep original byte blobs immutable, separately there is a journal (kinda WAL) of positional deltas (inserts and deletes).

So I only need to validate that blob + deltas = snapshot.

Disk IO is encapsulated through VFS, and writes are atomics (write to a temp file, then rename).

Separate virtual rendering buffer is built on top of that. Rune, like Obsidian, renders markdown preview inline, so the same chunk could be rendered as "Header" as well as `## Header` when under the cursor.

All of that makes it quite easy to work with text. The core function is to translate offset in a byte array to line and column and back, which is pure math and relatively easy to test.

Another trick that helped a lot is to use sqlite extensively: blobs, deltas, vfs, redo and undo history graph are all sqlite tables.

I noticed that LLMs make stupid decisions when it comes to data structures, but they understand CRUD and SQL, so I turned all Rune's internals into dumb CRUD.

	▲	coder-pm 3 days ago \| parent [-]
		Nice trick with the structures, good for agent legibility! I will try it out on the right occasion:)

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doc_ick 4 days ago | parent | prev [-]

Well the author “cannot simply dye my hair blue” so maybe they can’t confirm semantic equivalence or behavior? Poke aside (and unserious intro?) seems like a general and loose question of if the conversion can happen.

*be me over eager

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aka-rider 4 days ago | parent [-]

I consider a wig. I'm still on a fence with Rust at this point. see comments above

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doc_ick 3 days ago | parent [-]

Llm rewrite or llm boosted dev aside, I’m still on the fence about rust too. My main issue is deployment as I hop different os’s casually and makes rust a non-starter.

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aka-rider 2 days ago | parent [-]

I don’t know about Windows but between MacOS and Linux mine experience is smooth. I can even cross compile from Linux to MacOS.

	▲	doc_ick 2 days ago \| parent [-]
		How? Is there a working example? I ended up switching to go before I started digging down the rabbit hole of vagrant based builds