ci: Introduce backport workflow and compute-backport-targets script (#26518)

.github/scripts/compute-backport-targets.mjs

@@ -0,0 +1,74 @@
+// Creates backport PR's according to labels on merged PR
+
+import { readPrLabels, resolveRcBranchForTrack, writeGithubOutput } from './github-helpers.mjs';
+
+/** @type { Record<string, import('./github-helpers.mjs').ReleaseTrack> } */
+const BACKPORT_BY_TAG_MAP = {
+	'Backport to Beta': 'beta',
+	'Backport to Stable': 'stable',
+};
+
+const BACKPORT_BY_BRANCH_MAP = {
+	'Backport to v1': '1.x',
+};
+
+/**
+ * @param {Set<string>} labels
+ *
+ * @returns { Set<string> }
+ */
+export function labelsToReleaseCandidateBranches(labels) {
+	const targets = new Set();
+
+	// Backport by tag map includes mapping of label to git tag to resolve
+	for (const [label, tag] of Object.entries(BACKPORT_BY_TAG_MAP)) {
+		// Check if backport label is present
+		if (!labels.has(label)) {
+			continue;
+		}
+
+		const branch = resolveRcBranchForTrack(tag);
+		// Make sure our backport branch exists
+		if (!branch) {
+			continue;
+		}
+
+		targets.add(branch);
+	}
+
+	// Backport by branch map includes mapping of label to git branch. This is used for
+	// older versions of n8n. v1, etc.
+	for (const [label, branch] of Object.entries(BACKPORT_BY_BRANCH_MAP)) {
+		// Check if backport label is present
+		if (!labels.has(label)) {
+			continue;
+		}
+
+		targets.add(branch);
+	}
+
+	return targets;
+}
+
+async function main() {
+	const labels = new Set(readPrLabels());
+	if (!labels || labels.size === 0) {
+		console.log('No labels on PR. Exiting...');
+		return;
+	}
+
+	const backportBranches = labelsToReleaseCandidateBranches(labels);
+
+	if (backportBranches.size === 0) {
+		console.log('No backports needed. Exiting...');
+		return;
+	}
+
+	const target_branches = [...backportBranches].join(' '); // korthout/backport-action@v4 uses space-delimited branch list
+	writeGithubOutput({ target_branches });
+}
+
+// only run when executed directly, not when imported by tests
+if (import.meta.url === `file://${process.argv[1]}`) {
+	await main();
+}

.github/scripts/compute-backport-targets.test.mjs

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+import { describe, it, mock, before } from 'node:test';
+import assert from 'node:assert/strict';
+
+/**
+ * Run these tests by running
+ *
+ * node --test --experimental-test-module-mocks ./.github/scripts/compute-backport-targets.test.mjs
+ * */
+
+// mock.module must be called before the module under test is imported,
+// because static imports are hoisted and resolve before any code runs.
+mock.module('./github-helpers.mjs', {
+	namedExports: {
+		ensureEnvVar: () => {}, // no-op
+		readPrLabels: () => {}, // no-op
+		resolveRcBranchForTrack: mockResolveRcBranchForTrack,
+		writeGithubOutput: () => {}, //no-op
+	},
+});
+
+function mockResolveRcBranchForTrack(track) {
+	switch (track) {
+		case 'beta':
+			return 'release-candidate/2.10.1';
+		case 'stable':
+			return 'release-candidate/2.9.4';
+	}
+	return undefined;
+}
+
+let labelsToReleaseCandidateBranches;
+before(async () => {
+	({ labelsToReleaseCandidateBranches } = await import('./compute-backport-targets.mjs'));
+});
+
+describe('Compute backport targets', () => {
+	it('Finds backport branches for pointer tag labels', () => {
+		const labels = new Set(['Backport to Beta', 'Backport to Stable']);
+		/** @type { Set<string> } */
+		const result = labelsToReleaseCandidateBranches(labels);
+
+		assert.equal(result.size, 2);
+		assert.ok(result.has('release-candidate/2.10.1'));
+		assert.ok(result.has('release-candidate/2.9.4'));
+	});
+
+	it("Doesn't parse other labes to backport branches", () => {
+		const labels = new Set(['n8n team', 'release']);
+		/** @type { Set<string> } */
+		const result = labelsToReleaseCandidateBranches(labels);
+
+		assert.equal(result.size, 0);
+	});
+
+	it("Doesn't parse malformed backport labels", () => {
+		const labels = new Set(['Backport to Fork', 'Backport to my Home']);
+		/** @type { Set<string> } */
+		const result = labelsToReleaseCandidateBranches(labels);
+
+		assert.equal(result.size, 0);
+	});
+});