1. Install Xcode (directly from https://developer.apple.com/download/more or using the App Store).
2. Clone the project from GitHub:

git clone --recursive -j8 git@github.com:BoykoMihail/Telegram-iOS.git

3. Adjust configuration parameters (from project folder)

mkdir -p $HOME/telegram-configuration
mkdir -p $HOME/telegram-provisioning
cp build-system/appstore-configuration.json $HOME/telegram-configuration/configuration.json
cp -R build-system/fake-codesigning $HOME/telegram-provisioning/ 

• Modify the values in configuration.json ("enable_siri": false, "enable_icloud": false)

4. (Optional) Create a build cache directory to speed up rebuilds. (need to install bazel: brew install bazel)

mkdir -p "$HOME/telegram-bazel-cache"

5. Build the app

python3 build-system/Make/Make.py \
    --cacheDir="$HOME/telegram-bazel-cache" \
    generateProject \
    --configurationPath="$HOME/telegram-configuration/configuration.json" \
    --codesigningInformationPath=$HOME/telegram-provisioning/fake-codesigning \
    --disableExtensions \
    --disableProvisioningProfiles

Tip: use --disableExtensions when developing to speed up development by not building application extensions and the WatchOS app.

Bazel is used to build the app. To simplify the development setup a helper script is provided (build-system/Make/Make.py). See help:

python3 build-system/Make/Make.py --help
python3 build-system/Make/Make.py build --help
python3 build-system/Make/Make.py generateProject --help

Bazel is automatically downloaded when running Make.py for the first time. If you wish to use your own build of Bazel, pass --bazel=path-to-bazel. If your Bazel version differs from that in versions.json, you may use --overrideBazelVersion to skip the version check.

Each release is built using specific Xcode and Bazel versions (see versions.json). The helper script checks the versions of installed software and reports an error if they don't match the ones specified in versions.json. There are flags that allow to bypass these checks:

python3 build-system/Make/Make.py --overrideBazelVersion build ... # Don't check the version of Bazel
python3 build-system/Make/Make.py --overrideXcodeVersion build ... # Don't check the version of Xcode