- introduce new rules for the Category

- the rules can be used to match specified `Properties` with a `RegExp` (uses `test`) - to add them into a category
  - This allows more complex changelogs to be constructed, which for example want all `OPEN` PRs in one category

src/pullRequests.ts

@@ -2,7 +2,7 @@ import * as core from '@actions/core'
 import {Octokit, RestEndpointMethodTypes} from '@octokit/rest'
 import {Unpacked} from './utils'
 import moment from 'moment'
-import {Sort} from './configuration'
+import {Property, Sort} from './configuration'
 
 export interface PullRequestInfo {
   number: number
@@ -226,6 +226,22 @@ export function compare(a: PullRequestInfo, b: PullRequestInfo, sort: Sort): num
   }
 }
 
+/**
+ * Helper function to retrieve a property from the PullRequestInfo
+ */
+export function retrieveProperty(pr: PullRequestInfo, property: Property, useCase: string): string {
+  let value: string | Set<string> | string[] | undefined = pr[property]
+  if (value === undefined) {
+    core.warning(`⚠️ the provided property '${property}' for \`${useCase}\` is not valid. Fallback to 'body'`)
+    value = pr['body']
+  } else if (value instanceof Set) {
+    value = Array.from(value).join(',') // join into single string
+  } else if (Array.isArray(value)) {
+    value = value.join(',') // join into single string
+  }
+  return value
+}
+
 // helper function to add a special open label to prs not merged.
 function attachSpeciaLabels(status: 'open' | 'merged', labels: Set<string>): Set<string> {
   labels.add(`--rcba-${status}`)