How to compile and install changes to Elementary?

Question

I just decided to switch over from Ubuntu 18.04 LTS to Elementary OS 5.1 (Hara) and like to tweak my desktop to hide the date/time in the top panel.

I found an answer to hiding the date in the top panel.

I went ahead and cloned the wingpanel-indicator-datetime GitHub repository to my system

@lemonslice nudges to ask a follow up question "how to compile a (debian) package?" so here I am :)

The answer refers to debuild (which I understand is for package creation) and the Elementary developer guide talks about using meson. I am a noob when it comes to front-end development.

Can someone explain or outline:

1. the difference between using both build tools to make and deploy a change
2. the recommended steps to rebuild wingpanel-indicator-datetime (after making desired changes to the source code)
3. the steps deploy it to my local instance of Elementary OS
4. the steps to rollback the changes (if there is an easier way than reverting the code and rebuilding/redeploying)

Answer 1

install Elementary SDK (this fix may work if you run into errors in 5.1 hera):

sudo apt install elementary-sdk

install a compiler:

sudo apt-get install cmake

assuming you have git already set up, clone the repository you want to work on (eg. wingpanel-datetime-panel):

git clone https://github.com/elementary/wingpanel-indicator-datetime.git

change into the directory and make whatever changes you want to make (eg. How to hide date in elementary top bar?)

cd wingpanel-indicator-datetime

read the README.md and install any dependencies not included with Elementary SDK (eg. libecal1.2-dev)

sudo apt install libecal1.2-dev

use meson to create your build environment (use --prefix=/usr if you want your changes to apply to all users on this computer):

meson build

fire off your build:

cd build
ninja

deploy your changes:

sudo ninja install

for a simple change to wingpanel in what is mocked above, it is sufficient to log out and log back in (no reboot needed)

presto!

if any of the above does not make sense, it is recommended you read the Elementary Developer Guide as it starts from square one (including setting up Git)