Make release asset guard idempotent

.github/workflows/release.yml

@@ -194,36 +194,41 @@ jobs:
           ./scripts/sparkle_generate_appcast.sh cmux-macos.dmg "$GITHUB_REF_NAME" appcast.xml
 
       - name: Guard immutable release assets
+        id: guard_release_assets
         uses: actions/github-script@v7
         with:
           script: |
+            const { evaluateReleaseAssetGuard } = require('./scripts/release_asset_guard');
             const tag = context.ref.replace('refs/tags/', '');
-            const requiredAssets = ['cmux-macos.dmg', 'appcast.xml'];
             try {
               const release = await github.rest.repos.getReleaseByTag({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
                 tag,
               });
-              const assetNames = new Set((release.data.assets || []).map((asset) => asset.name));
-              const conflicts = requiredAssets.filter((asset) => assetNames.has(asset));
-              if (conflicts.length > 0) {
-                core.setFailed(
+              const existingAssetNames = (release.data.assets || []).map((asset) => asset.name);
+              const { conflicts, shouldSkipUpload } = evaluateReleaseAssetGuard({ existingAssetNames });
+              if (shouldSkipUpload) {
+                core.notice(
                   `Release ${tag} already contains immutable assets (${conflicts.join(', ')}). ` +
-                  'Refusing to overwrite signed artifacts for an existing tag.'
+                  'Skipping upload to preserve existing signed artifacts.'
                 );
+                core.setOutput('skip_upload', 'true');
                 return;
               }
               core.notice(`Release ${tag} exists but does not contain conflicting assets.`);
+              core.setOutput('skip_upload', 'false');
             } catch (error) {
               if (error.status === 404) {
                 core.notice(`Release ${tag} does not exist yet; safe to publish assets.`);
+                core.setOutput('skip_upload', 'false');
                 return;
               }
               throw error;
             }
 
       - name: Upload release asset
+        if: steps.guard_release_assets.outputs.skip_upload != 'true'
         uses: softprops/action-gh-release@v2
         with:
           files: |

scripts/release_asset_guard.js

@@ -0,0 +1,17 @@
+"use strict";
+
+const IMMUTABLE_RELEASE_ASSETS = ["cmux-macos.dmg", "appcast.xml"];
+
+function evaluateReleaseAssetGuard({ existingAssetNames, immutableAssetNames = IMMUTABLE_RELEASE_ASSETS }) {
+  const existing = new Set(existingAssetNames || []);
+  const conflicts = immutableAssetNames.filter((assetName) => existing.has(assetName));
+  return {
+    conflicts,
+    shouldSkipUpload: conflicts.length > 0,
+  };
+}
+
+module.exports = {
+  IMMUTABLE_RELEASE_ASSETS,
+  evaluateReleaseAssetGuard,
+};

scripts/release_asset_guard.test.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const test = require("node:test");
+const assert = require("node:assert/strict");
+
+const {
+  IMMUTABLE_RELEASE_ASSETS,
+  evaluateReleaseAssetGuard,
+} = require("./release_asset_guard");
+
+test("skips upload when immutable assets already exist", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["cmux-macos.dmg", "appcast.xml", "notes.txt"],
+  });
+
+  assert.deepEqual(result.conflicts, IMMUTABLE_RELEASE_ASSETS);
+  assert.equal(result.shouldSkipUpload, true);
+});
+
+test("allows upload when immutable assets are not present", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["notes.txt", "checksums.txt"],
+  });
+
+  assert.deepEqual(result.conflicts, []);
+  assert.equal(result.shouldSkipUpload, false);
+});
+
+test("skips upload when any immutable asset would conflict", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["appcast.xml"],
+  });
+
+  assert.deepEqual(result.conflicts, ["appcast.xml"]);
+  assert.equal(result.shouldSkipUpload, true);
+});