Demo of a expanding/contracting monorepo for mortals

This repo is a fork of https://github.com/google/guava - with no intention of merging back. This is about demonstrating how Google uses a "sparse checkout" (Git and Subversion language) with their gigantic Monorepo (86TB of history, 9 million unique files).

Guava uses Maven - which is why I chose it. (you can do expanding/contracting monorepos with Maven too). Google uses Blaze internally (which was open sourced as Bazel - with the expand/contract feature missing).

• Main blog entry, documenting this: Maven In A Google Style Monorepo (2017)
• Google knowhow for the edification of the masses Googlers Subset their Trunk (2014)
• On the piece left out of Bazel: Turning Bazel back into Blaze for monorepo nirvana (2015)
• A bigger (more convincing) version of this demo: Further Experiments With Expanding/Contracting Monorepos (2017)
• The monorepos page on the site I put together with friends: trunkbaseddevelopment.com/monorepos/
• Same site, but the expandable/contractable page: trunkbaseddevelopment.com/expanding-contracting-monorepos

Doing a 'quick' experiment with this repo/branch

Say that you goal is to only build/test 'guava-testlib' and not any of the other sub-modules that Maven were to recurse to by habit if run from the root level:

Initial setup:

git clone git@github.com:paul-hammant/googles-monorepo-demo.git
cd googles-monorepo-demo

To run the experiment:

git config core.sparsecheckout true
echo '/mr' > .git/info/sparse-checkout
echo '/README.md' >> .git/info/sparse-checkout
echo '/pom*' >> .git/info/sparse-checkout
echo '/guava/' >> .git/info/sparse-checkout
echo '/guava-testlib/' >> .git/info/sparse-checkout
mr/checkout.sh
mvn install

The huge 'samples' directory isn't in the checkout (yes yes, it is in the clone, relax). It isn't in the root POM's modules either - which is what we wanted.

Making your own Maven setup like this

In your repo, all pom.xml files need to be renamed to pom-template.xml:

find . -name pom.xml -type f | while read a; do n=$(echo $a | sed -e 's/pom.xml/pom-template.xml/'); git mv $a $n; done

You'll need to checkin the mr directory we have above. You'll also want to add pom.xml to .gitignore - they're not under source control any more, pom-template.xml is instead.