Improve support for C-style for-loops

[skovhus]

Work in progress.

While browsing around in the known-errors (bash-it) I figured out that the C-style for-loops support has several bugs:

• does not support multiple variables assignments or updates (fixed)
• does not support spaces around variable assignments for ((x = 0 ; x <= 100 ; x++)); is not parsed as an assignment, but a command with an error (not fixed)

@maxbrunsfeld I'm not sure how I should approach the last issue. It seems variable assignment support inside for loops might be different than normal assignments. Do I have any control over white space parsing inside grammar.js?

See https://wiki-dev.bash-hackers.org/syntax/ccmd/c_for for context

[skovhus]

I see now that there is some overlap with #55

[skovhus]

@maxbrunsfeld Let me know if you have any comments.

[maxbrunsfeld]

It seems variable assignment support inside for loops might be different than normal assignments.

Yeah, it appears so. I think x = y will be handled currently by the binary_expression rule. Maybe we just need to add variable_assignment as an additional choice for the initializer (instead of replacing _expression with only variable_assignment).

Also, I don't think we should use repeat($._expression), because that would mean you could have multiple expressions immediately following one another, like i++ b++. In reality, there needs to be a comma in between.

[skovhus]

Thanks. I’ll have another look.