chore: add guideline how deprecations shall be handled (GetStream#1676)

commitlint.config.js

@@ -1,3 +1,23 @@
 module.exports = {
-  extends: ['@commitlint/config-conventional']
+  extends: ['@commitlint/config-conventional'],
+  rules: {
+    'type-enum': [
+      2,
+      'always',
+      [
+        'build',
+        'chore',
+        'ci',
+        'docs',
+        'feat',
+        'fix',
+        'perf',
+        'refactor',
+        'revert',
+        'style',
+        'test',
+        'deprecate',
+      ],
+    ],
+  },
 };

developers/COMMIT.md

@@ -1,4 +1,4 @@
-We follow [Angular's Commit Messag Format rules](https://github.com/angular/angular/blob/master/CONTRIBUTING.md#-commit-message-format). Even though these are curated sets of rules, the following represent our additions to them:
+We follow [Angular's Commit Message Format rules](https://github.com/angular/angular/blob/master/CONTRIBUTING.md#-commit-message-format). Even though these are curated sets of rules, the following represent our additions to them:
 
 ## Commit message type
 
@@ -21,3 +21,4 @@ It must be one of the following:
 * **refactor**: A code change that neither fixes a bug nor adds a feature
 * **style**: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
 * **test**: Adding missing tests or correcting existing tests
+* **deprecate**: Certain parts or APIs are deprecated and scheduled for a removal in a newer major version

developers/DEPRECATIONS.md

@@ -0,0 +1,25 @@
+## Deprecations
+
+You can deprecate a feature or a component once:
+1. an alternative exists.
+2. the support for the given functionality is scheduled for termination
+
+The deprecated component should be marked as follows:
+
+```typescript jsx
+/**
+ * @deprecated - This UI component will be removed in the next major release. This component is deprecated because <XY>.
+ * For more information see [docs link](https://....)
+ *
+ * FixedHeightMessage - This component renders a single message.
+ * It uses fixed height elements to make sure it works well in VirtualizedMessageList
+ */
+```
+
+### How to deprecate?
+
+1. Deprecated component:
+   1. does not receive an alternative -> update the documentation on how to implement the deprecated feature.
+   2. receives an alternative -> update the documentation on how to use the introduced alternative solution.
+2. Commit the changes under `deprecate` commit type, with commit description stating the reasons for deprecation.
+3. Create an issue, so it can be scheduled for removal in foreseeable future. Tag the issue with the label `breaking`.