Fixed handling of the npm 12 info output

.changeset/tidy-eyes-repair.md

@@ -0,0 +1,5 @@
+---
+"@changesets/cli": patch
+---
+
+Fixed already-published version detection with npm 12, which always wraps successful `npm info --json` output in an array. The unwrapped output made `changeset publish` treat every package as unpublished and fail attempting to republish existing versions.

packages/cli/src/commands/publish/__tests__/publishPackages.test.ts

@@ -109,6 +109,47 @@ describe("publishPackages", () => {
     ).toBe(false);
   });
 
+  it("detects already-published versions when npm 12 wraps info output in an array", async () => {
+    const cwd = await testdir({
+      "package.json": JSON.stringify({
+        private: true,
+        workspaces: ["packages/*"],
+      }),
+      "packages/pkg-a/package.json": JSON.stringify({
+        name: "pkg-a",
+        version: "1.0.0",
+      }),
+    });
+
+    mockSpawnImplementation((cmd, args) => {
+      if (cmd === "npm" && args?.[0] === "info") {
+        return spawnResult(
+          JSON.stringify([
+            {
+              name: "pkg-a",
+              version: "1.0.0",
+              versions: ["1.0.0"],
+            },
+          ])
+        );
+      }
+      return spawnResult("", 1);
+    });
+
+    const result = await publishPackages({
+      packages: (await getPackages(cwd)).packages,
+      access: "public",
+      preState: undefined,
+    });
+
+    expect(result).toEqual([]);
+    expect(
+      mockSpawn.mock.calls.some(
+        ([cmd, args]) => cmd === "npm" && args?.[0] === "publish"
+      )
+    ).toBe(false);
+  });
+
   it("publishes a new prerelease when exact version fallback also 404s", async () => {
     const cwd = await testdir({
       "package.json": JSON.stringify({

packages/cli/src/commands/publish/npm-utils.ts

@@ -153,6 +153,14 @@ export async function getTokenIsRequired() {
 //   queries return empty → no versions list → only-pre detection is not
 //   possible. Such packages (e.g. GitHub Packages with no auto-latest) are
 //   published with preState.tag rather than "latest".
+
+// npm 12 always wraps successful `npm info --json` output in an array.
+// Unwrap it so downstream consumers keep seeing a single manifest.
+function normalizeInfoJson(parsed: any) {
+  // given we query the implicit `latest` tag or an exact version, the resulting array should have at most one element
+  return Array.isArray(parsed) ? parsed[0] : parsed;
+}
+
 export function getPackageInfo(packageJson: PackageJSON) {
   return npmRequestQueue.add(async () => {
     info(`npm info ${packageJson.name}`);
@@ -189,7 +197,7 @@ export function getPackageInfo(packageJson: PackageJSON) {
         },
       };
     }
-    return jsonParse(result.stdout.toString());
+    return normalizeInfoJson(jsonParse(result.stdout.toString()));
   });
 }