The official PostGIS code repository is a git repository hosted on OSGeo ​Gitea instance (​​https://gitea.osgeo.org/postgis/postgis).

To get the source from main repo, and start a configure:

git clone https://gitea.osgeo.org/postgis/postgis.git
cd postgis
./autogen.sh
./configure

If you would like to submit pull requests via the main repo, you will first need an ​OSGeo LDAP ID

A number of CodeMirrors do exist for users and contributor's convenience.