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108 lines
4.5 KiB
Markdown
108 lines
4.5 KiB
Markdown
# Feature flags
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When developing new features for Element, we use feature flags to give us more
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flexibility and control over when and where those features are enabled.
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For example, flags make the following things possible:
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* Extended testing of a feature via labs on develop
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* Enabling features when ready instead of the first moment the code is released
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* Testing a feature with a specific set of users (by enabling only on a specific
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Element instance)
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The size of the feature controlled by a feature flag may vary widely: it could
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be a large project like reactions or a smaller change to an existing algorithm.
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A large project might use several feature flags if it's useful to control the
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deployment of different portions independently.
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Everyone involved in a feature (engineering, design, product, reviewers) should
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think about its deployment plan up front as best as possible so we can have the
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right feature flags in place from the start.
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## Interaction with spec process
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Historically, we have often used feature flags to guard client features that
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depend on unstable spec features. Unfortunately, there was never clear agreement
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about how long such a flag should live for, when it should be removed, etc.
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Under the [new spec
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process](https://github.com/matrix-org/matrix-doc/pull/2324), server-side
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unstable features can be used by clients and enabled by default as long as
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clients commit to doing the associated clean up work once a feature stabilises.
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## Starting work on a feature
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When starting work on a feature, we should create a matching feature flag:
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1. Add a new
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[setting](https://github.com/matrix-org/matrix-react-sdk/blob/develop/src/settings/Settings.tsx)
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of the form:
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```js
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"feature_cats": {
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isFeature: true,
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displayName: _td("Adds cats everywhere"),
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supportedLevels: LEVELS_FEATURE,
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default: false,
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},
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```
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2. Check whether the feature is enabled as appropriate:
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```js
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SettingsStore.getValue("feature_cats")
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```
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3. Document the feature in the [labs documentation](https://github.com/vector-im/element-web/blob/develop/docs/labs.md)
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With these steps completed, the feature is disabled by default, but can be
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enabled on develop and nightly by interested users for testing.
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Different features may have different deployment plans for when to enable where.
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The following lists a few common options.
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## Enabling by default on develop and nightly
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Set the feature to `true` in the
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[develop](https://github.com/vector-im/element-web/blob/develop/element.io/develop/config.json)
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and
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[nightly](https://github.com/vector-im/element-desktop/blob/develop/element.io/nightly/config.json)
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configs:
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```json
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"features": {
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"feature_cats": true
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},
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```
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## Enabling by default on staging, app, and release
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Set the feature to `true` in the
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[staging / app](https://github.com/vector-im/element-web/blob/develop/element.io/app/config.json)
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and
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[release](https://github.com/vector-im/element-desktop/blob/develop/element.io/release/config.json)
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configs.
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**Note:** The above will only enable the feature for https://app.element.io and official Element
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Desktop builds. It will not be enabled for self-hosted installed, custom desktop builds, etc. To
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cover these cases, change the setting's `default` in `Settings.tsx` to `true`.
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## Feature deployed successfully
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Once we're confident that a feature is working well, we should remove or convert the flag.
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If the feature is meant to be turned off/on by the user:
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1. Remove `isFeature` from the [setting](https://github.com/matrix-org/matrix-react-sdk/blob/develop/src/settings/Settings.ts)
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2. Change the `default` to `true` (if desired).
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3. Remove the feature from the [labs documentation](https://github.com/vector-im/element-web/blob/develop/docs/labs.md)
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4. Celebrate! 🥳
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If the feature is meant to be forced on (non-configurable):
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1. Remove the [setting](https://github.com/matrix-org/matrix-react-sdk/blob/develop/src/settings/Settings.ts)
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2. Remove all `getValue` lines that test for the feature.
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3. Remove the feature from the [labs documentation](https://github.com/vector-im/element-web/blob/develop/docs/labs.md)
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4. If applicable, remove the feature state from
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[develop](https://github.com/vector-im/element-web/blob/develop/element.io/develop/config.json),
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[nightly](https://github.com/vector-im/element-desktop/blob/develop/element.io/nightly/config.json),
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[staging / app](https://github.com/vector-im/element-web/blob/develop/element.io/app/config.json),
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and
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[release](https://github.com/vector-im/element-desktop/blob/develop/element.io/release/config.json)
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configs
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5. Celebrate! 🥳
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