Allow custom publish scripts to complete without a Changesets output file

.changeset/calm-files-warn.md

@@ -0,0 +1,5 @@
+---
+"@changesets/action": patch
+---
+
+Allow custom publish scripts to complete without a Changesets output file, warning that GitHub releases and git tags cannot be created when that file is missing.

src/run.test.ts

@@ -1,10 +1,11 @@
 import path from "node:path";
+import * as core from "@actions/core";
 import type { Changeset } from "@changesets/types";
 import { writeChangeset } from "@changesets/write";
 import { createFixture } from "fs-fixture";
-import { beforeEach, describe, expect, it, vi } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { GitHub } from "./github.ts";
-import { runVersion } from "./run.ts";
+import { runPublish, runVersion } from "./run.ts";
 
 vi.mock("@actions/github", () => ({
   context: {
@@ -20,6 +21,10 @@ vi.mock("@actions/github", () => ({
     graphql: mockedGraphql,
   }),
 }));
+vi.mock("@actions/core", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@actions/core")>()),
+  warning: vi.fn(),
+}));
 vi.mock("@changesets/ghcommit");
 
 let mockedGithubMethods = {
@@ -102,6 +107,59 @@ beforeEach(() => {
   vi.clearAllMocks();
 });
 
+afterEach(() => {
+  vi.unstubAllEnvs();
+});
+
+describe("publish", () => {
+  it("warns when a custom publish script does not create the output file", async () => {
+    await using fixture = await createSimpleProjectFixture();
+    const cwd = fixture.path;
+    vi.stubEnv("RUNNER_TEMP", cwd);
+
+    const result = await runPublish({
+      script: 'node -e "void 0"',
+      github: createGithub(cwd),
+      createGithubReleases: true,
+      pushGitTags: true,
+      cwd,
+    });
+
+    expect(result).toEqual({ published: false, exitCode: 0 });
+    expect(core.warning).toHaveBeenCalledWith(
+      expect.stringContaining(
+        "GitHub releases and git tags cannot be created without this output",
+      ),
+    );
+  });
+
+  it("throws when the built-in publish command does not create the output file", async () => {
+    await using fixture = await createFixture({
+      "node_modules/@changesets/cli/package.json": JSON.stringify({
+        name: "@changesets/cli",
+        type: "module",
+      }),
+      "node_modules/@changesets/cli/bin.js": "",
+      "package.json": JSON.stringify({
+        name: "simple-project",
+        version: "1.0.0",
+      }),
+      "package-lock.json": "",
+    });
+    const cwd = fixture.path;
+    vi.stubEnv("RUNNER_TEMP", cwd);
+
+    await expect(
+      runPublish({
+        github: createGithub(cwd),
+        createGithubReleases: true,
+        pushGitTags: true,
+        cwd,
+      }),
+    ).rejects.toThrow("Failed to read changesets output at");
+  });
+});
+
 describe("version", () => {
   it("creates simple PR", async () => {
     await using fixture = await createSimpleProjectFixture();

src/run.ts

@@ -79,6 +79,8 @@ type ChangesetsOutputEvent = {
   packageName: string;
 };
 
+class ChangesetsOutputReadError extends Error {}
+
 type PublishResult =
   | {
       published: true;
@@ -113,9 +115,10 @@ async function readChangesetsOutput(outputPath: string) {
   try {
     rawOutput = await fs.readFile(outputPath, "utf8");
   } catch (err) {
-    throw new Error(`Failed to read changesets output at ${outputPath}`, {
-      cause: err,
-    });
+    throw new ChangesetsOutputReadError(
+      `Failed to read changesets output at ${outputPath}`,
+      { cause: err },
+    );
   }
 
   const events: ChangesetsOutputEvent[] = [];
@@ -195,7 +198,18 @@ export async function runPublish({
 
   let { packages, tool } = await getPackages(cwd);
   let packagesByName = new Map(packages.map((x) => [x.packageJson.name, x]));
-  let output = await readChangesetsOutput(outputFile);
+  let output: ChangesetsOutputEvent[];
+  try {
+    output = await readChangesetsOutput(outputFile);
+  } catch (err) {
+    if (!script || !(err instanceof ChangesetsOutputReadError)) {
+      throw err;
+    }
+    core.warning(
+      `${err.message}. GitHub releases and git tags cannot be created without this output. Ensure the custom publish script passes CHANGESETS_OUTPUT to the Changesets CLI.`,
+    );
+    output = [];
+  }
   let releases = output.map((event) => {
     let pkg = packagesByName.get(event.packageName);
     if (pkg === undefined) {