Extension reload breaks waitForExtension

[jpettitt]

When an extension depends on another extension for a service it ends up in waitForExtension if the provider hasn't yet loaded. We've been seeing timeouts from waitForExtension that shouldn't be happening.

This problem is that if v0.js detects a version mismatch (v0.js version differs from an extension version) it automatically loaded the correct version of the extension to match v0 9getExtensionScript_). When it does this it creates a new extension holder which leaves waitForExtension waiting on a load that will never happen.

This only happens on publisher sites due to the AMP cache automatically syncing versions and it only happens if the extension in cache mismatches v0.js.

See deletion of the extension holder https://github.com/ampproject/amphtml/blame/40fa29d8daacd92fbbcfda825f4b7f89dab25a34/src/service/extensions-impl.js#L255

[jpettitt]

cc @choumx @jridgewell @i-like-robots also tracked in Google b/143942489

force fail example https://github.com/i-like-robots/broken-amp-versions-test-case

[dvoytenko]

Got repro. I'm fixing this right now.

[dvoytenko]

I'm moving this to P0.

[dvoytenko]

/cc @erwinmombay

[dvoytenko]

The bug is in this line. The regex is too allowing and matches both amp-subscriptions-0.1 and amp-subscriptions-google-0.1. It was introduced by proxy in the #24730.

/cc @choumx

[dvoytenko]

The race condition indicated by @jpettitt is also an issue, but less likely to occur. Will be fixed in the same pull request.