The mirror manifest can be used to create a local mirror of official Android source repos using the following commands

$ mkdir -p /usr/local/aosp/mirror
$ cd /usr/local/aosp/mirror
$ repo init -u https://android.googlesource.com/mirror/manifest --mirror
$ repo sync

The local mirror can then be used like this

$ mkdir -p /usr/local/aosp/master
$ cd /usr/local/aosp/master
$ repo init -u /usr/local/aosp/mirror/platform/manifest.git
$ repo sync

The official mirror manifest contains all the projects that have been part of some Android release, even if they were removed in newer releases. This makes a complete mirror unnecessarily huge.

The downsized manifest file default.xml only contains projects used in Android Oreo (Android 8) and newer versions of Android. It was generated using the Python program prunemirrormanifest.py like this

$ python3 prunemirrormanifest.py
The following Android releases are available.

['2.2.3', '2.3.6', '2.3.7', '4.0.1', '4.0.2', '4.0.3', '4.0.4', '4.1.1', '4.1.2', '4.3.1', '4.4.1', '4.4.2', '4.4.3', '4.4.4', '5.0.0', '5.0.1', '5.0.2', '5.1.0', '5.1.1', '6.0.0', '6.0.1', '7.0.0', '7.1.0', '7.1.1', '7.1.2', '8.0.0', '8.1.0', '9.0.0']
Enter the oldest desired release : 8.0.0

To use this smaller mirror manifest just replace the URL https://android.googlesource.com/mirror/manifest with https://github.com/warraagal/android-mirror-manifest in the mirroring step above

If you also want to build Android releases older than Oreo, then fork this repository, choose an older release when running prunemirrormanifest.py