I'm not always sure why rush change [-v] does, or does not, list a project. Occasionally, I would also like to see my commits, that caused rush to request a change file. You know, for due diligence :)

Under the hood

I had a look at the rush code to make sure I understand what's happening.

Included in "changed projects"

First, rush change [-v] calls git merge-base to find the target commit. This would be your last merge with the targetBranch.

libraries\rush-lib\src\logic\Git.ts

# getMergeBase() 
git --no-optional-locks merge-base -- HEAD ${targetBranch}

It then finds all changed files tracked by Git, which includes both, staged and committed changes.
libraries\package-deps-hash\src\getRepoState.ts

# getRepoChanges()
# revision: the mergeBase from the previous step
git --no-optional-locks diff-index --no-renames --no-commit-id `
--cached -z ${revision} --

Yes, staged changes also cause your project to be listed by rush change

NOT included in "changed projects"

Next, rush change validates if the newly added change files match the changed packages. It basically means that any project with a change file will be removed from the "changed projects" list and in effect, you will NOT be required to create a change file.

It does not matter, if you made any commits AFTER a change file was generated. The project will NOT require another change file.

rush whatchanged

rush whatchanged is a custom command that you can install using yeoman generator: yo rush-conventionalcommits

Wouldn't it be useful to see what is actually causing rush change to request a change file? Is it staged or committed changes? And if there are commits since the last merge, to easily browse through them?
If you are using conventional commits, a change type could be suggested, to spare you time deciding on something that is already "there"

Maybe it will make it to rush at some point (see here) but in the meantime, I'm using a custom rush command rush whatchanged.

When ran without parameters, it will display summary information.
You can see how many commits and staged files you have for each project. You also get a warning in case a change file already exists, because rush change will ignore this project.

rush whatchanges --showcommits

If a change file exists for a project, rush whatchanges --showcommits provides you with a history of commits done AFTER the latest change file was created.

shortlog

rush whatchanges --showcommits shortlog executes git shortlog and displays the output to the terminal.

full

In case you have many commits and it's not comfortable to read though them in a console, use rush whatchanges --showcommits full. It saves the commits history to a rush temp folder:

rush whatchanges --recommend-changetype

This command parses your commits and analyses them, following convenvtional commits convention.
If a change file already exists, only commits AFTER the latest change file are taken into account.

The script invokes git rev-list --count --grep with a regular expression to filter and count commit messages.

major

To detect and count commits that may require major change:

git rev-list --count --extended-regexp --grep "(^(feat|fix|docs|style|refactor|perf|test|build|ci|chore|revert)(.*?)?!:.*|^BREAKING CHANGE: )" -- "${projectFolder}"

minor

If no commits causing major change are found, the script searches for minor change commits:

git rev-list --count --extended-regexp --grep "^feat((.*?))?:" -- "${projectFolder}"

patch

And finally, if there are no major or minor changes, it will see if there are any commits causing patch bump:

git rev-list --count --extended-regexp --grep "^fix((.*?))?:" -- "${projectFolder}"

none

If no major/minor/patch changes are found, none change type is recommended. It may mean that you either didn't have changes causing version bump, or you don't use conventional commits =) I'm not differentiating between these two cases becase if the latter is true, you shouldn't be calling rush whatchanges --recommend-changetype =)

Resources

You can install the yeoman generator from npm
As always, the code is on github