documentation for new portfile with git HEAD no tarball

[gaming-hacker (G Alexander)]

the documentation ​https://guide.macports.org/#development.creating-portfile

is lacking a decent example of how to create a new portfile from a git repo, HEAD, not a released/stable tarball

1. there is no indication of how to create a sha256 checksum/hash
2. there is no indication of how to pass CMAKE macro definitions when there is no configure

[gaming-hacker (G Alexander)]

forgot to add for item 1. especially if i need to use multiple git commands to pull source from main repo and cherry-pick fromm others or include PRs not merged in master

[ryandesign (Ryan Carsten Schmidt)]

We never create ports that fetch from the HEAD of a repository. They should always fetch from a specific repeatable commit. Ports for software that is hosted on github usually want to use the github portgroup. Read the documentation in the comments at the top of that portgroup file.

The ​guide shows a method for computing checksums.

Ports for software that uses cmake usually want to use the cmake portgroup. You can look at other ports that use that portgroup for help on how to pass "configure flags" to cmake.

Please ask on the macports-dev mailing list if you need help with this or other portfile development topics.