Rust Programming Language FOSDEM Rust Devroom 2018, 6 Feb 2018

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From YouTube: Pascal Hertleif - rustfix

Description

…and the journey to getting better code automatically

Rust programmers often seem happy to get compiler errors. Understandably so, the compiler is known to not just catch what would in other languages become a run time bug, but also to be quite helpful. On top of that, the clippy project adds more than 200 additional lints, to catch even more errors, but also help guide users towards writing more idiomatic code. This talk is about the dream of automatically fixing many of these errors (based on compiler-provided suggestions) with rustfix.

Pascal Hertleif has been writing code professionally for the last seven years and is active in the Rust community since 2014. He is the author of multiple open source libraries and co-organizer of Rust Cologne. Currently, he is studying computer science at the university of Bonn, Germany, as well as working as freelance software developer.

Rust devroom @ FOSDEM 2018
https://fosdem.org/2018/schedule/event/rust_rustfix_automatic_fixes/

These talks have been recorded at FOSDEM (https://fosdem.org/)
This work is licensed under the Creative Commons Attribution 2.0 Belgium Licence.
To view a copy of this licence, visit http://creativecommons.org/licenses/by/2.0/be/deed.en

A

What you're coming can you humans back all right? Let's get started with some quick questions who have you knows about the Clippy project who knew about the Clippy project yesterday, all right all right, it's still a very good numbers. Thank you! So much okay, so first things first hi I'm, Pascal I do rust since 2014 and if you ever happen to be in Cologne, please try to be there on a on the first once day of a month, because we do great Rashmi labs.

A

You can also follow me on Twitter and I write some stuff in my blog about Russ as well. So you might want to check that out soon, but let's start with something as absolutely everyone can agree with that. Russ programmers like compiler errors, yeah I'm, pretty sure that every one of you has seen a compiler error once in his or her lifetime, and you set yourself wow. This is this is really great. I won't have more of those.

A

This page, three words looks. It looks like it might be a bit small, but it's a very nice error format, and this is something that delivers the promise of rust safety, because the compiler is there to to help. You check your stuff, so you can be confident that your code actually works. Also, the errors are pretty, and it's not just errors or warnings to like. We have a warning that you have not used the result of a function like if you have a result type and you did not check it- was an error.

A

It was an error. If it's of any use, the compiler will tell you. This is not something that breaks your code, it's just something that finds in the direction of maybe a mistake you made, so your code gets even better and a my absolutely favorite length of all is missing documentation. If you're publishing your library and you activate this lint, it tells you which public items have no documentation this, not just so.

A

You can write documentation, but it's also very, very helpful to figure out which items are actually public and which items you did not want to be public and wanted to change later on, and maybe he publish a breaking change. So it's very, very useful for that and about two-thirds of you said you knew about clipping just for the other ones. Clippy is awesome. You should totally look it up. It's a collection of even more links. So, if you like the built in errors, you can get even more errors like yesterday, there were 208 additional lens.

A

I am pretty sure. If you check in next week's there will be two hundred and ten or twelve or something like that, and it goes more into the case of catching even more mace mistakes that you may have missed. For example, if you wrote the new Fidel's and both code blocks is the same. It's probably mistake on your part and you just copy pasted it from the results and forgot to check it later on on fix it. Clippy has a link for that as well.

A

It's it's very, very impish, aspra jecht and it's very, very awesome. Okay, a completely other aspect of Flint's and warnings is that you don't just want to catch warnings, but you also want to learn about new things. For example, I hope you can read it otherwise, I'll just read it out loud to you, so you have an iterator and you call the filter method on it and you give it a closure where you compare the items that you are iterating over with zero and then the result of that you call next on.

A

So basically, you have an iterator to get the next item that contains the number zero hmm it's an interesting way to write set. What what did you actually mean when you wrote that it's it could be anything it could be just a check for it. Is there any item that is zero? Why not find the item? And then you actually have explicitly stated in your code that you wanted to find an item that is 0 or.

A

It's a trivial example: let's go for something more, it's new statement that if the map M does not contain the key K, you insert K with the value D into M. Okay, it's all good. It's like how you insert stuff into a hash map in basically every language, but Russ can help you with that in a way that may be surprising, but will lead to very good code. Have you heard the good news about the entry API?

A

If you use dot entry instead of contains key and then insert you will do the hashing only once you ask the map is the arm. Entry was that map's to K, and if it's not there, you can insert it. This is very concise and very much not if-then do stuff, so you might not have even noticed that there is such an API and there's a link to tell you about it and afterwards, you'll be a bit more experienced in the crazy API. Is that raphson that library has to offer?

A

So this lens help you, when you're, basically almost using an API that you didn't know about, and if you happen to be bored some lazy afternoon, you can also just check the clip your documentation, because it has examples for basically every length with ok. This is what you wrote, and this is what you maybe have meant, and this is what you could also write so could read. I can recommend it.

A

Ok, ok, so I, don't know how many of you was there from a TS talk earlier this morning he talked about I, do mattock, rust and man. He told you all about how to do it yourself. Is it's a it's, a nice idea to actually fix your code yourself, but how about who makes us a bit more active okay? So the compiler already gives you suggestions.

A

If you wrote for AI in 10.0, you iterating over something that's never happening because ranges only work in the one direction and not counting down words. So you were looking for something. That's called a reverse loop. Basically, you wanted to say, 0.10 and then reverse it. You didn't know about it. Okay, it's totally fine I didn't know about it either, but the link didn't just tell you: okay here, you can't do this. No, no the length actually brought the code. You need to write to get good idea metric code.

A

So why fix it yourself?

A

This is from your perspective, for hope is totally from mine, but my perspective, the quote on the slides. If you can't read it, says: okay, I'm sold. These suggestions are great, but I, don't make me type, don't make me wait and just fix. My freaking code already enter Ross fix, so there is no magic and it's already happening you've seen the errors. You've seen the suggestions, the error messages and the Diagnostics can also be outputted as JSON instead of human readable text.

A

So let's just take this raisin and pass the suggestions and to a bit of certain replace, and you end up with better code. At least I hope you do it's actually, if you think about really trivial and so the rust fix there's a tool, that's called rust fix and it's a simple Scylla tool. You basically invoke it and it calls a compiler and asks hey. What do you say? What's a scout and for every single error message you would have gotten from the compiler rustics collects the arrows and shows you one by one hey.

A

So this is wrong or we can do better here. Would you like me to replace it with the red of the day, and you say yeah sure or yeah I don't know, or this is plain wrong- it's it's all in there and after you ran through all these errors, you say safe and it basically replaces the things you've thought totally to replace in your code and hopefully your code still compiles and it works better than before.

A

Big promises I know, but it's still not like. If you care you can do better like you need to manually call this tool like it's one step too many: okay, okay, what's better than like writing code and calling the compiler and making it tell us stuff and basically wrapping rustics around it. Well, obviously, let's do it in the editor. While we are typing, we want to have suggestions as well and luckily for us, people have already been working on that as well.

A

It's called the Ross language server and it exposes warnings, errors, suggestions to navitor that can consume the language server. The language server protocol, the most complete plugin for editor, is the one for a visual to decode and turns out. It can already fix our suggestions. So basically, why did we write this Eli? It just uses plugin, and so it turns out what clipping in this, like the rough language server doesn't know what clipping, why don't we make?

A

It know about clipping and I, had a horrible horrible hack that basically imported links from Clippy into the compiler that gets called by LS, and wasn't it wasn't pretty it really wasn't pretty so I was very glad to see minutes, and it was just this morning about hmm why not add cliffie as an optional feature to the last language server. So, thanks to Oliver who's here with us and whose talk is the one after Milan, you should totally stay for it. Well, clip is now optional feature in the Ross language.

A

Server and also five internet points for Nick Cameron, this already merged not released, but but much so if you are going to compile our ask yourself, you'll get this awesome bunch of additional links. So this is the time where I'll give you a demo. Well, I, don't I don't have my laptop, but that's no problem. I expected to not have my laptop because well, mine was too easy. So let's do a quick slideshow. This is what it looks like Jochen, visual studio code and basically writes these lines.

A

Let's enable basic, Clippy warnings right in main function, define a vector with the element. That's the number one and write an if statement assess. hmm What's the length is this length of the vector greater than zero? hmm What would you actually want to do here hmm length comparison to zero? It's a nice!

A

That's a nice overlay but also see there was a light, bulb: okay, yeah, let's fix it and three places if lengths play a greater zero which it's not empty, because that's what we actually wanted to express and also this is more performant, because collections collections that are not as trivial as vector can basically implement is empty in a more efficient ways and counting their elements. Okay, so we get a nice slap, oh forget a nice context menu and we can apply it and bam. It's done.

A

The plow surplus is absolutely not for me, like I, hope the people who actually made this work here are watching the stream sometime in the future, and this applause was for you, okay time for another demo, you wrote a live statement with a small boolean expression.

A

Just imagine it was like twice as long and not just something I came up with this morning. It can be simplified to what oh yeah, oh absolutely less than or equal sure we knew about that. Let's fix it, damn another thing done, but it's not all good like it's not all finished. It's not. Is this not one, not one, not Oh or anything near it and I want what I want you to take away from this is you can contribute?

A

This is a very nice length that tells you that if you wanted to write 3.14, you may have actually wanted to write the constant for pi. So why not use like the constant that actually defined? Okay, wait where's, our an ipod service. There is no light bulb because this suggestion does not exist. It's it's only their own message: okay, okay, so this was a demo. Thank you! So much I'm glad it works as well.

A

Let's talk a bit about how this actually works, like lots of zero lines of code, I committed just how it actually is working and linds our compiler plugins, basically, and if you've been here for the talk before mine nikita talked about sts and linds, basically are Naturals on particular ast structures. You try to find node and items of interest, and then you tell the compiler to basically annotate this piece of code with a suggestion or in health text or a warning, or what have you and the compiler then generates output?

A

This is a human readable as you've seen before, or machine readable, so rustics can't consume it. This is not that hard, as you like. This is actually rosin structure. I managed to do it. So if you wanted to look at some code and say hey, hmm maybe maybe I can actually fix this myself manually or by writing a length. You should totally not fix it yourself, because everyone can do that right, a lint.

A

We have a very interesting question still open, though, because what is actually auto fixable like we have these suggestions, and can we apply all of them? This is everything we get good codes that we can just search, replace yeah. A lot of it is actually like. I was surprised that I expected it to like, be very, very small percentage of all suggestions. We have that we could actually ought to apply, but it turns out. We can apply, Auto fix a lot.

A

We should totally make a list or actually how about we flag, approximate suggestions, so we know which ones are not all fixable and when I wrote these slides earlier last week the rosin was a PR open for the Ross compiler. This glorious pull request number forty, seven thousand five hundred and fourteen that acts at the simple flag to each suggestion. You write and passes this down to basically the JSON output as well, and it allows you to flag approximate suggestions.

A

Yeah I was going to talk about how this is good idea and how we could maybe do it, but actually that it got much already. So this stuff is changing rapidly like if you, if you look at this talking, agir I hope you already already be using it and everything I tell you would be totally unsurprising. So yeah, it's great progress, that's happening here and you should all contribute to it and with that. Thank you. So much.

A

And to recap, just so: I can leave the slide. Yeah search for us clipping, search for the good first issues and become a compiler hacker.

A

Yeah, let's start here and then go down.

B

A

Is basically a compiler plucking s? Pollens are so it would be very, very hard to stabilize compilers internal api's and not have them break ever so we don't want to do that, but actually Clippy will be shipped with rust up as a component. You can star just like rust format or LS, so you don't have to so. You can I sing ISM in the next release, or maybe in the the one. After that, then you can just write rest up component at clipping and get it on stable.

A

B

Okay, good good.

A

A

So the question was: if I have thought about fixes that introduce new errors, yeah, so a lot of suggestions and not yet they they introduced, maybe not errors, but but new suggestions- and this is a good case like we already producing codes that comprise but triggers new errors and yeah. It's it's. You could get into the way of thinking that, like okay, let's just recursively, run rust fix until it generates no more errors or it doesn't compile. This is this is a good solution, but not one.

A

That's that's working, quite as we intended it to so. I have I, have no solution to give you, except for calling it multiple times, but I'll be open to any suggestions.

A

Any more questions, yeah.

A

Maybe I don't know anyone I don't want to say yes, but maybe I, don't I, don't think so. I, don't think so, but yeah it's like do you want to do that.

C

A

You still have time for more questions. I guess.

B

A

Let's set actually the secret behind all my github contributions in the last year's.

A

No, no, no I've run it on personal codes. I have seen people run it on their code, but I have not yet started like doing pull requests automated by Russ fix. It might might be a good idea actually, but you should totally look into it.

A

A

The question was: if I have tried, or if I intended rustics to be a tool that can upgrade code. Basically, so once new rust features become available, that you can use rust fix to upgrade your code base to use them and I totally didn't think about this.

A

Until there was a discussion about introducing epochs to a box called actually into rust, because this year the rust team wants to basically compile a new version of the rust language itself and introduce breaking changes without breaking code, and they want to do that by actually versioning the compiler and the standard library in epochs.

A

So if you wanted to have a sink and the weight as a keyword in in random code, this was this was actually supposed. It would not work today, because you can't introduce new keywords, because people might already be using this for their variable names and epochs will sources, because in your cargo configuration file, you say: okay, let's use rust version 2018 instead of the implicit 2015 one, that's 1.0, and in this discussion people started talking about well.

A

Can we make all these changes in a way that they can be auto, applicable, reserve aspects and I was like? Yes, please, please do it, and if there are some limbs in Clippy that suggests using newer features or features that were not available in 1.0. So this already a bit of precedence for it and I'd be really happy to have the rust fix set. You can tell too low to lint groups, that's called upgrades to 2018 and get your code fixed.

A

Thank you. You.