Support environment variable replacement in manifest value fields

[WillNeill]

User Story

As a developer, when I'm building for multiple environments (dev, staging, prod) and multiple platform targets, I want to define environment variables for replacement in the manifest, so I can dynamically change the name, icons and other properties based on the build requirements.

Example

When building for staging, we make the following changes to our manifest:

• add -staging to our app name
• change favicon to a custom staging variant
• change homepage_url to the staging site (for integration testing)

And, based on semver commits, we also calculate and set out version number automatically when running builds in our ci. We don't get this from package.json, so we also need to update the manifest version number with the correct calculated version.

Potential implementation

Webpack WebExtension Plugin includes this capability by using a similar syntax to vendor keys:

For example:

In JS

process.env.APP_NAME

In Manifest

{
  "name": "__APP_NAME__",
}