Here's the fastgron printer if you want to compare:

https://github.com/adamritter/fastgron/blob/main/src/print_g...

Why?

It appears to be so it can sort the lines. Not sure how useful that is however.

An ironic near-miss on the UNIX philosophy. There's a great UNIX tool that will handle sorting arbitrarily large files!

It will mess up array indices, though.

Wouldn’t “sort -n” work with indices?

It's tricky to specify the sorting criterium: you have to indicate the column. Gron's output looks like this:

a.b[0].c.d[0]: ... a.b[0].e[0].f: ...

It shouldn't need to buffer the output to do that, right?

Correct.