Python compiler needs a flag to return the full sequence of errors as json about prql

[max-sixty]

Yes, I could see a couple of approaches:

Another function — prql_to_sql

prql_to_sql function that is similar to compile, but raises an error as pure JSON. It would operate similarly to prql_to_pl, which gives a long string of JSON:

prql.prql_to_pl("^")


---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[12], line 1
----> 1 prql.prql_to_pl("^")

ValueError: {"inner":[{"kind":"Error","code":null,"reason":"unexpected ^","hints":[],"span":"1:0-1","display":"Error: \n   ╭─[:1:1]\n   │\n 1 │ ^\n   │ ┬  \n   │ ╰── unexpected ^
\n───╯\n","location":{"start":[0,0],"end":[0,1]}}]}

...rather than a nice Error message:

prql.compile("frm artists")


Traceback (most recent call last):

  File /opt/homebrew/lib/python3.9/site-packages/IPython/core/interactiveshell.py:3508 in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)

  Cell In[3], line 1
    prql.compile("frm artists")

  File <string>
SyntaxError: Error:
   ╭─[:1:1]
   │
 1 │ frm artists
   │ ─┬─
   │  ╰─── Unknown name
───╯

I think this could be a quite small PR.

Add the JSON onto the Exception

Browsing the PyO3 docs, I think we could return an exception which has a .json attribute which contains the JSON.

This would be the nicer approach but is a bit more work / requires a bit of work with PyO3...

Edit: I guess the even better thing would be a custom error type which contained the fields — rather than JSON — and then has a string representation with the full error message. But that's a bit more work yet.

---

Any thoughts from others?

[max-sixty]

The basic version of this is implemented in #4066; @brunorpinho let me know if that works for you.

I'll close, but we can come back when the next version of PyO3 is out and see if we can do this more elegantly.

[brunorpinho]

@max-sixty it absolutely works, all I would need for my use case is that json. Thank you!

Which version of prql am I expected to see this implemented?

[max-sixty]

Which version of prql am I expected to see this implemented?

It would be in the next release, which we could do quite soon if it'd be helpful. You can also use the version on main with pip install git+https://github.com/PRQL/prql#subdirectory=prqlc/bindings/python

[max-sixty]

@brunorpinho instead of doing that, use something like this:

try:
  x = prql_to_pl(query)
  x = pl_to_rq(x)
  x = rq_to_sql(x)
except Exception as e:
  json_exception = e

...and then in the future, we'll change compile to have the information on the object itself.

(I'm planning to revert prql_to_sql as it doesn't add much that's useful beyond the snippet above...)