An option for hy to *only* check syntax

[kozross]

I'm writing a syntax checker for Hy in Flycheck at the moment, and have hit a bit of a stumbling block. At the moment, the only (easy...) way to syntax-check Hy source code is to pump it through hy and hope it executes. This isn't very desirable in a Flycheck checker, as it means executing (again and again) code that may take a long time to run or have side effects we don't want.

Would it be possible to add a flag to hy (I suggest -c) which only checks it for syntactic validity? It would spew the same errors as hy does now if the code isn't syntactically valid (or it can't find the module or whatever), and do nothing but return success otherwise?

[paultag]

Yeah that sounds awesome! :D

Perhaps also machine readable lexer errors!

On Thu, Nov 20, 2014 at 2:02 PM, Koz Ross notifications@github.com wrote:

I'm writing a syntax checker for Hy in Flycheck at the moment, and have
hit a bit of a stumbling block. At the moment, the only (easy...) way to
syntax-check Hy source code is to pump it through hy and hope it
executes. This isn't very desirable in a Flycheck checker, as it means
executing (again and again) code that may take a long time to run or have
side effects we don't want.

Would it be possible to add a flag to hy (I suggest -c) which only checks
it for syntactic validity? It would spew the same errors as hy does now
if the code isn't syntactically valid (or it can't find the module or
whatever), and do nothing but return success otherwise?

—
Reply to this email directly or view it on GitHub
#689.

:wq

[refi64]

If you just want to check for syntatical/macro errors:

$ alias hycheck="python -c \"import hy.lex, hy.compiler, sys; hy.compiler.hy_compile(hy.lex.tokenize(sys.stdin.read()), '__console__')\""

From then on, you can just do:

$ hycheck < myfile.hy

[kozross]

@kirbyfan64 This will only check syntax - not invalid imports, undefined functions, etc. I guess that stuff is all done at runtime, which basically means that I'd have to write a linter for Hy if I wanted that stuff checked. Well, I guess I can do that - in Hy!

I have three ideas for names:

1. hylite (oh god, the puns, plz stop)
2. crazyrap (source)
3. back2school (source)

[rakete]

I would like to have error checking for hy with flycheck as well, so I tried to make pylint work with hy:
https://gist.github.com/rakete/2699be18d4218685c66d

This seems to actually work. Pylint just uses an python ast, and it takes one created by hy just fine. Some of the warnings don't make much sense though and I have not spend a lot of time playing with different (and more complex) hy sources yet. Basic things like getting told when I use an undefined variable or unused arguments and stuff like that are already a huge success for me.

[xificurC]

Is there anything done on this part? It's marked as good-first-bug but it seems like a bigger project (to write a full-blown linter)

[Kodiologist]

No, nobody has worked on this since. Presumably @berkerpeksag marked it good-first-bug on the assumption that you'd either use a method like Kirby suggested or use pylint. But in any case, I'd tend to think it's not a very good first bug.

[Kodiologist]

Beware that once we have reader macros, which seems likely to happen (#2242), syntactic correctness will become Turing-undecidable. That is, you'll have to compile and macroexpand everything in order to check the syntax, which can involve running arbitrary code. Perl has a similar problem due to BEGIN blocks.

[Kodiologist]

Yeah, considering that issue, this feature would probably not be very helpful, and it would be dangerous because people would probably use it not realizing that it can run arbitrary code. You could implement an approximation of some sort, like checking that code with no reader macros is syntactically correct in terms of what can be analyzed statically, but that's probably something best implemented as an external tool than a feature of Hy itself.