Hoist core of changenotes.mts assemble into own function

pr-checks/changenotes.ts

@@ -50,6 +50,28 @@ function getChangenotes(): ChangenoteFile[] {
   });
 }
 
+/**
+ * Populates the '[UNRELEASED]' section of CHANGELOG.md with the contents
+ * of the changenotes in {@link CHANGENOTES_DIR} and then deletes those changenotes.
+ * @param contents The contents of CHANGELOG.md
+ * @returns The updated contents of CHANGELOG.md
+ */
+export function transferChangenotesToChangelog(contents: string): string {
+  const changenotes = getChangenotes();
+  const changenoteBodies = changenotes.map((c) => c.content);
+  const changenotePaths = changenotes.map((c) => c.absolutePath);
+
+  const changelog = parseChangelog(contents);
+  addBodyLinesToUnreleasedSection(changelog, changenoteBodies);
+  const updatedChangelog = renderChangelog(changelog);
+
+  for (const p of changenotePaths) {
+    fs.unlinkSync(p);
+  }
+
+  return updatedChangelog;
+}
+
 const entryPoint = process.argv[1];
 if (entryPoint && import.meta.url === pathToFileURL(entryPoint).href) {
   try {
@@ -91,26 +113,13 @@ function usage(): ExitCode {
 
 function assemble(): ExitCode {
   try {
-    const changenotes = getChangenotes();
-    const changenoteBodies = changenotes.map((c) => c.content);
-    const changenotePaths = changenotes.map((c) => c.absolutePath);
-
     withChangelog((contents) => {
-      const changelog = parseChangelog(contents);
-      addBodyLinesToUnreleasedSection(changelog, changenoteBodies);
-      return renderChangelog(changelog);
+      return transferChangenotesToChangelog(contents);
     }, {});
-
-    // Delete changenotes only after successful processing.
-    for (const p of changenotePaths) {
-      fs.unlinkSync(p);
-    }
-
     return ExitCode.Success;
   } catch (e) {
     console.error("Failed to assemble changenotes to 'CHANGELOG.md'", e);
   }
-
   return ExitCode.Failure;
 }