Default feature flags as an object

[mstrasinskis]

When an expected flag is not provided by environment.featureFlags, the missing value is taken from a string that is supposed to contain all default values. The issue is that this approach cannot be verified, and it already omits some values, which could lead to a broken app state when environment constants are missing or outdated.

In cases where the featureFlags environment variable is empty or not provided, the dapp breaks with a dev console error: Uncaught (in promise) Error: Missing mandatory environment variables: featureFlags
This error is self-explanatory, so no changes are needed to handle this specific case.

However, when there are missing entries in the environment variable (e.g., record { 0="FEATURE_FLAGS"; 1="{}" };), the dapp also breaks with the error:Error: derived() expects stores as input, got a falsy value.
This happens because no derived store is created for the missing value(s). While we could modify the store creation mechanism to always initialize with the false value, I believe having explicitly set default values is a better solution.

Changes

• Add defaultFeatureFlagValues: FeatureFlags<boolean>.
• Replace missing flags with the entries from defaultFeatureFlagValues.

Tests

• Added a unit test to verify that the default flags are used.
• Tested manually: reproduced the issue with the current nns-dapp and missing flags, then confirmed that the updated version works with the default flags.

Todos

• Add entry to changelog (if necessary).
  Not necessary.