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github-desktop/docs/technical/packaging.md

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Building and Packaging Desktop

This document outlines how Desktop is currently packaged for all platforms - there are some parts in common but then each platform has it's own quirks.

webpack

GitHub Desktop use webpack to transpile and bundle its application resources. The configuration files that webpack uses are found under app/:

  • app/webpack.common.ts - base config and settings
  • app/webpack.development.ts - additional changes to base config for building and running Desktop in development mode
  • app/webpack.production.ts - additional changes to base config for building and running the app in production mode

The webpack configuration files organize the source files into these targets:

  • main.js - logic in the main process in Electron
  • renderer.js - logic in the renderer process in Electron
  • crash.js - specialised UI for displaying an error that crashed the app
  • highlighter.js - logic for syntax highlighting, which runs in a web worker
  • cli.js - logic for the github command line interface

Webpack also handles these steps:

  • placeholders in source for platform-specific values are now replaced, using app/app-info.ts and the values of the platform the build is being performed on
  • SCSS stylesheets under app/styles/ are transpiled to CSS and emitted
  • source maps are generated to help with correlating runtime errors to the corresponding TypeScript source

The output from webpack is stored in the out directory, and this folder is ignored in version control.

app/package.json

The version attribute in app/package.json is the canonical reference for the version number you see in the About view of GitHub Desktop.

changelog.json

This file is used to track user-facing changes associated with each Desktop release. This can include new features, bug fixes, improvements or even removed features.

script/build.ts

After webpack the next component in the pipeline is script/build.ts which handles moving app resources into place and launching electron-packager, which merges the application resources and Electron runtime for the current platform into an executable program.

This script is responsible for:

  • merging additional static resources into the output directory
  • generating a license bundle from the projects that Desktop uses, which are accessible from the About GitHub Desktop dialog
  • generating license metadata from the choosealicense.com source repository, so the user can add a suitable license to their new repository when creating a repository in Desktop

electron-packager is also responsible for code-signing on macOS at this stage, and if you do not have this configured you will likely see an error like this:

Packaging app for platform darwin x64 using electron v2.0.9
WARNING: Code sign failed; please retry manually. Error: No identity found for signing.

This is fine for development purposes, but code-signing is highly recommended when distributing Desktop to end users.

script/package.ts

After the build is the final step is to package the application for distribution to end users, and this is where much of the platform-specific variations occur.

macOS

macOS does not need any additional work, as the previous step generated an application bundle and performed the required code-signing.

The generated app is compressed into a .zip archive, reducing the download size by ~60%.

Windows

Desktop uses electron-winstaller to generate two installers:

  • a Squirrel-based .exe that does not require elevated permissions to install
  • an installer based on Windows Installer that supports being installed by administrators. Please note that this is a partial solution and this still leverages %LOCALAPPDATA% when each users runs the app for the first time. See #1086 for an ongoing discussion about alternatives.

Other things to note about the Windows packaging process:

  • electron-winstaller is responsible for signing these installers
  • Squirrel supports generating delta packages (representing the difference between this version and the previous version) to avoid downloading bytes that haven't changed. This has been enabled for Desktop, and requires downloading the previous version from Central to generate the delta package.

Linux

Refer to the shiftkey/desktop fork for packaging details about Linux.

script/publish.ts

This script uploads the packaging artifacts to our S3 bucket, which is then verified before the build is made available to users.