Add prepare-changelog.ts with tests

mbg · Jul 28, 2026 · Jul 24, 2026 · Jul 24, 2026 · Jul 24, 2026 · Jul 24, 2026
commit 85d157095f7ec93f7aa17909634728937fe6921d
@@ -0,0 +1,46 @@
+/**
+ * Tests for `prepare-changelog.ts`.
+ */
+
+import * as assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { afterEach, beforeEach, describe, it } from "node:test";
+
+import { EMPTY_CHANGELOG, NO_CHANGES_STR } from "./changelog";
+import { extractChangelogSnippet } from "./prepare-changelog";
+
+let testDir: string;
+
+beforeEach(() => {
+  // Set up a temporary directory for testing
+  testDir = fs.mkdtempSync(path.join(os.tmpdir(), "prepare-changelog-test-"));
+});
+
+afterEach(() => {
+  /** Clean up temporary directories. */
+  fs.rmSync(testDir, { recursive: true, force: true });
+});
+
+const testBody = `- Test change`;
+const testChangelog = `${EMPTY_CHANGELOG.replace(NO_CHANGES_STR, testBody)}
+
+## Another section
+
+- Other change`;
+
+describe("extractChangelogSnippet", async () => {
+  await it("returns the default body if the input doesn't exist", async () => {
+    const result = extractChangelogSnippet(path.join(testDir, "not-here.md"));
+    assert.deepEqual(result, NO_CHANGES_STR);
+  });
+
+  await it("returns the first section if the input exists", async () => {
+    const changelogPath = path.join(testDir, "test-readme.md");
+    fs.writeFileSync(changelogPath, testChangelog);
+
+    const result = extractChangelogSnippet(changelogPath);
+    assert.deepEqual(result, testBody);
+  });
+});
@@ -0,0 +1,96 @@
+#!/usr/bin/env npx tsx
+
+/**
+ * Extracts the body of the first changelog section and outputs it to either
+ * stdout or a file.
+ */
+
+import * as fs from "node:fs";
+import { parseArgs } from "node:util";
+
+import { getErrorMessage } from "../src/util";
+
+import { NO_CHANGES_STR } from "./changelog";
+import { CHANGELOG_FILE } from "./config";
+
+/**
+ * Prepare the changelog for the new release
+ * This function will extract the part of the changelog that
+ * we want to include in the new release.
+ *
+ * @param changelogPath The path to the changelog file.
+ */
+export function extractChangelogSnippet(changelogPath: string) {
+  try {
+    const lines = fs.readFileSync(changelogPath, "utf-8").split("\n");
+    const output: string[] = [];
+    let foundFirstSection = false;
+
+    // Extract the body of the first section in the changelog file.
+    for (const line of lines) {
+      if (line.startsWith("## ")) {
+        if (foundFirstSection) {
+          // This is the second section header we have found, which means that we have
+          // captured all lines in the first section in `output`. We can stop here.
+          break;
+        }
+
+        // We have discovered the first section header.
+        foundFirstSection = true;
+      } else if (foundFirstSection) {
+        // Add lines between the first section header (if any) and the next to the output.
+        output.push(line);
+      }
+    }
+
+    return output.join("\n").trim();
+  } catch (err) {
+    if (err instanceof Error && "code" in err && err.code === "ENOENT") {
+      console.error(`Changelog file at '${changelogPath}' does not exist.`);
+      return NO_CHANGES_STR;
+    } else {
+      throw Error(
+        `Failed to open changelog file at '${changelogPath}': ${getErrorMessage(err)}`,
+      );
+    }
+  }
+}
+
+function main() {
+  try {
+    const { values } = parseArgs({
+      options: {
+        changelog: {
+          type: "string",
+          short: "f",
+          default: CHANGELOG_FILE,
+        },
+        output: {
+          type: "string",
+          short: "o",
+        },
+      },
+      strict: true,
+    });
+
+    const body = extractChangelogSnippet(values.changelog);
+
+    // If no `output` argument was provided, output to stdout. Otherwise,
+    // write a file to the specified path.
+    if (values.output === undefined) {
+      console.info(body);
+    } else {
+      fs.writeFileSync(values.output, body);
+    }
+
+    return 0;
+  } catch (err) {
+    console.error(`Failed to prepare changelog: ${getErrorMessage(err)}`);
+    return -1;
+  }
+}
+
+// Only call `main` if this script was run directly.
+if (require.main === module) {
+  process.exit(main());
+}