Use automatic CHANGELOG management

[nicoddemus]

As suggested by @RonnyPfannschmidt, we want to adopt an automatic CHANGELOG file management to remove/reduce merge conflicts due to changes in the CHANGELOG file (which are quite common).

towncrier has been suggested as a good tool for this.

Here's what's needed:

• Configure towncrier according to the instructions in its README;
• Update instructions in CONTRIBUTING.rst related to the CHANGELOG;
• Update instructions in .github/PULL_REQUEST_TEMPLATE.md;

Ideally we should tackle this right after the upcoming 3.1 release.

@RonnyPfannschmidt, you mentioned you wanted to do this?

[RonnyPfannschmidt]

@nicoddemus correct

[nicoddemus]

Nice. I suggest we also adopt invoke to have well named tasks in place. You could introduce invoke and the first new task, generate_news or so (similar to what pip does in https://github.com/pypa/pip/blob/master/tasks/generate.py).

[RonnyPfannschmidt]

@nicoddemus we first have to agree on some formatting tho - if we keep doing changelogs as is towncrier as is will be a pain

[nicoddemus]

Looking at pip's changelog, the only difference I see is the fact that it doesn't generate links to the issues; that could be suggested upstream or even contributed by us.

If that's the only reason, I'm not against just using towncrier as is; I think switching to towncrier will be a huge maintenance improvement for us, so it out weights this small drawback.

[fschulze]

We looked into towncrier for devpi and it was too opinionated for us. Your milage may vary. I'm currently throwing together an alternative after I didn't find anything else that matches what we would like.

[RonnyPfannschmidt]

@nicoddemus hence wanting to agree on formatting, not open up big cans of worm

[RonnyPfannschmidt]

@fschulze, can you show me where it was too opinionated?

[nicoddemus]

I looked at pip's NEWS.rst file and it looks good to me. I would like to contribute linking the issues automatically though, but I'm fine with starting using it now and enjoying the links later.

[nicoddemus]

can you show me where it was too opinionated?

I'm curious as well. 😁

[fschulze]

Turns out, it was just lacking documentation. After I looked again into how pip uses towncrier, I found the title_format and template options, which allow me to remove the opinionated stuff. Now there is only a small bug preventing towncrier to work with the template option on Python 3.x. Reporting it ...

[fschulze]

And the issue is already fixed in 17.4.0 twisted/towncrier@c48a58f

[nicoddemus]

@RonnyPfannschmidt with 3.1.0 being out, now it would be a good time to tackle this! 👍