What is package naming convention used in Dart?
This is documented on the name section of Pubspec Format documentation.
It should be all lowercase, with underscores to separate words,
just_like_this. Stick with basic Latin letters and Arabic digits:[a-z0-9_]and ensure that it’s a valid Dart identifier (i.e. doesn’t start with digits and isn’t a reserved word).Try to pick a name that is clear, terse, and not already in use.
There doesn't seem to be a convention for it, but most of the time, I see lowercase_words_with_underscore being used, both for libraries and packages.
For libraries inside packages, some people also use dots for grouping, for example my_package.lib_1 and my_package.lib_2.
It's all personal preference, I guess.
All the package conventions are documented on pub.dartlang.org. The package naming conventions in particular are documented on the pubspec format page.