Poor's man way to debug font-lock matcher functions?

Question

I was told on Reddit that font-lock-studio will help me debug a matcher I was working on, however, I find myself with one more problem than before as I need to learn edebug and also grasp how to debug my font-lock keywords with font-lock-studio.

Thus, I thought maybe setting up something like behavioral tests on the matcher function to help me with the debugging and testing of the matcher itself as I don't exactly know what am I doing (doing right or wrong, to be honest).

At some point, the matcher use set-match-data for the resulting matches, I was wondering if there was a way to get that data in order to compare it with the results I'm looking (match-data is the way to go? Because I eval it after executing manually the matcher function and the values I see makes no sense to me), and also a way to setup a test for the matcher function that can be run at a command.

Answer 1

You can use font-lock-studio to visualize the match data. If you step the matcher function using, say space, the parts of the source buffer that corresponds to the match data is highlighted. The different matches are highlighted in different colors.

If you would like to call your function directly, you can call match-data to get a list that represents the matches. In your case, it should contains eight elements, as in (BEG0 END0 BEG1 END1 etc.).

Edebug isn't hard. You can enable it by evaluating the function using C-u M-C-x and then call it. Execution will stop at the beginning of the function and you can single step though it using space. I would start with the simpler functions, making sure amzn-font-lock-skip-whitespace-etc work as intended (the regexp in looking-at looks suspicious).

If you want to write regression tests, you can use the built-in ert package.

To write regression tests for font-lock packages you can use the package faceup.