Up until early 2019, anyone contributing to Asterisk probably came across a change that required an addition to the CHANGES or UPGRADE.txt files. If you're one of those people, then you probably also know how frustrating it was having to deal with merge conflicts if another person had touched this file in one of their reviews. Because of this, a new process has been added that will ease the pains of having to document something in these files.
A couple of things. You no longer need to add anything to the CHANGES and UPGRADE.txt files themselves. By removing this, there should not be any merge conflicts (at least, none relating to these files!). Instead, two new directories have been created under the doc/ directory: CHANGES-staging and UPGRADE-staging. Any code you add that is considered a new feature or an enhancement of an existing feature should be documented in the CHANGES-staging directory. Changes that would break existing behavior should be documented under the UPGRADE-staging directory. The format is similar to how things were done in the past, but you no longer need to worry about typing out dashes and asterisks to separate things. That's all done for you!
The release process is what handles updating the CHANGES and UPGRADE.txt files now. Whenever a release is being made, everything in the staging directories is taken and added to the beginning of the corresponding file. Everything that has the same subject (e.g, "res_pjsip") will be grouped under one section and separated by asterisks, exactly how it has been done in the past. These directories will then be cleaned up and the commit will be pushed in along with everything else. Easy as that!
Here's an example of what one of these directories might look like before a release:
Inside of one of these files (say, the first one), it should follow the format of subject line, blank line, then a description of the change. It could look something like this:
Viola! That's all there is to it. One thing to not is that changes will be sorted alphabetically, and then sorted by commit timestamp (in epoch). The reasoning will be explained below.
Mainline Branches vs Master
Releases from mainline branches (16.2.0 -> 16.3.0) work as expected following the above rules. The changes are fetched from the staging directory, put in their individual categories, and then sorted. This is all fine until we get to master. Master does not get a release for 16.2.0 -> 16.3.0. Because of this, things need to be done a little differently. Ordinarily when a release was done, the changes would be cherry picked to the master CHANGES and UPGRADE.txt files as well, and upon doing a release of a new version of Asterisk from master, a new UPGRADE.txt file would be created. Now, there will only be one UPGRADE.txt file. When releasing 17, there will be 2 new sections added to the file: a "new in 17" section and a "changes from 16 to 17" section. CHANGES will behave in a similar way.