Make firebase a peer dependency of @angular/fire #3804

AngularFire lists firebase under dependencies, so an app that requests a different firebase version than AngularFire does gets a second copy of the SDK nested under node_modules/@angular/fire/node_modules/firebase. The two copies reject each other's objects at runtime. That is the mechanism behind #3684, #3681 and #3682 on 21.0.0-rc.0, and the same failure is in older reports such as #3245 and #3442.

Proposal

Make firebase a peer dependency in AngularFire 22, so the app owns the single copy of the SDK:

• firebase ^12.18.0 moves from dependencies to peerDependencies in the published package.json.
• A migration-v22 for ng update adds firebase to the app's package.json when it is missing, and aligns an existing entry that is outside the range. ng update itself updates a peer the app already declares but never adds one. The migration reuses the alignment ng add already runs.
• The v22 upgrade guide documents the change and the install-time error it produces.

What would change for apps

• On npm, a firebase outside the supported range fails to install with ERESOLVE, which says which two versions conflict, instead of installing a second copy that fails at runtime.
• On pnpm and Yarn, an out-of-range firebase installs as one copy with a peer warning. Yarn installs no peer dependencies at all, so an app that never declared firebase has to add it, which the migration does.
• The ng add warning for two installed firebase versions stays. Under a peer dependency, two copies appear only when another package bundles its own firebase.

History

AngularFire 2.0 made firebase a peer dependency for this exact reason (#749, 2016), and 7.3.0 moved it back to dependencies (#3159, 2022). Seven of nine comparable wrapper libraries, including rxfire, reactfire and vuefire, list the SDK as a peer.

This is a breaking change, for 22.0.0.