Parser error position

[sabelka]

This PR adds a new parser_error exception which contains the error location, i.e. the position of the last token parsed.
With this information it is possible to count the line number where the error happened (which would fix also #10)

[pantor]

Sorry for the late response, and thanks so much for your initiative! I've added the calculation of the exact text position in line numbers and column offsets. What do you think about that?

[sabelka]

Hi, thanks for considering my pull request! I had a quick look in you additions: I appreciate the calculation of lines/columns. (In my application had to do this after catching the exception anyways, so this makes things simpler). However, now the position is only available in the text of the error message and I think there is no way to get it programmatically (without parsing the error message, which I'd like to avoid). In my case, I'd need the exact location of the error because I want to draw squiggles in a template editor.

[pantor]

Ah, I haven't thought about your use case. I've updated my code so you can get the location programmatically.

[sabelka]

@pantor : Hi, finally I got time to integrate the new version of the line numbers patch back into my project - thanks for merging!
However, I noticed a small problem with the error locations which is best explained with an example. Consider the following template:

{{
aaa
bbb
ccc
ddd
eee
fff

Here, I would expect an error at the end of line 2 or beginning of line 3 because {{ aaa is valid, but then the closing '}}' are missing. However, I get:

[inja.exception.parser_error] (at 4:2) expected expression close, got 'bbb'

So, instead of 4:2 I would expect 3:1.

There is probably something wrong in Lexer::current_position() but I'm mot sure if I understand this function. Can you have a look?