No field: left on nodes of kind Call/Comment

[jasper-easics]

sylver version 0.3.4

Running the following command:
sylver ruleset run --files="**/*.py" --rulesets="https://github.com/sylver-dev/rulesets#python_comprehensions.yaml"

gives the output:
❗️No field: left on nodes of kind Call
or
❗️No field: left on nodes of kind Comment
probably depending on which rule happens to be triggered first.

The rulesets python_base.yaml and python_bugbear.yaml are working.

[jasper-easics]

Starting the REPL
sylver query --files="**/*.py" --language=python

and executing the SYLQ query:
match l@ListComprehension when l.body.text == l.children[1].left.text && no l.children match IfClause;

gives:
No field: left on nodes of kind Comment

All other queries in the python_comprehensions.yaml ruleset seem to run without error.
I have not encountered the No field: left on nodes of kind Call error when going through them.

[jasper-easics]

Is there an easy way to check which file and which line causes the error?

[jasper-easics]

The problem was due to a comment line inside a list comprehension, see the example below.

foo = [
    # Some comment at the start.
    i
    for i in range(10)
]

This results in the following ast:

ListComprehension {
. ● body: Comment { # Some comment at the start. }
. Identifier { i }
. ForInClause {
. . ● left: Identifier { i }
. . ● right: Call {
. . . ● function: Identifier { range }
. . . ● arguments: ArgumentList {
. . . . Integer { 10 }
. . . }
. . }
. }
}

Which causes sylver to crash when evaluating the expression l.children[1].left.text from the python_comprehensions.yaml ruleset.

I added an extra check to that rule in PR #2 to prevent sylver from crashing.

This PR does not fix that the redundant list comprehension above is not detected,
because it can also be written as foo = list(range(10)).
Nor would it be detected if the comment was in the middle, e.g.:

foo = [
    i
    # Some comment in the middle.
    for i in range(10)
]

I tried making a more general rule, but ran into issues. Maybe because I am not yet familiar with sylver queries.
Creating a general rule would be easier if the ast of ListComprehension had a field clauses which could contain a list of ForInClauses.
Also, in the ast above the body field should probably contain the Identifier instead of the Comment.

[jasper-easics]

Thanks for accepting the pull request.
Is it possible to improve the error message if a field is missing, or more generally if there is an error when evaluating a query,
so it gives an indication of which lines and which file of parsed code caused the issue?
This would help finding the root cause in the future.
Now I just tried different --files arguments to find which file contained the problematic code.

[geoffreycopin]

Adding the file and position to error messages is a geat idea!
I'll implement it

[jasper-easics]

Great, thanks! Once the implementation is committed to the repository I will close this issue.