Add an error message for when a changeset references a nonexistent pa…

…ckage (#1508)

* Add an error message for when a changeset references a nonexistent package

This can occur when a package with pending changesets is deleted.

* Add changeset

* Fix formatting

* Add tests

* Fix formatting

.changeset/sharp-impalas-jog.md

@@ -0,0 +1,5 @@
+---
+"@changesets/assemble-release-plan": patch
+---
+
+Add error-reporting for when a changeset references a non-existent package

packages/assemble-release-plan/src/index.test.ts

@@ -560,6 +560,28 @@ Mixed changesets that contain both ignored and not ignored packages are not allo
     expect(releases[1].newVersion).toEqual("1.0.0");
   });
 
+  it("should throw an error when a changeset contains a package that is not in the workspace", () => {
+    setup.addChangeset({
+      id: "big-cats-delight",
+      releases: [{ name: "pkg-a", type: "major" }],
+    });
+    setup.addChangeset({
+      id: "small-dogs-sad",
+      releases: [{ name: "pkg-z", type: "minor" }],
+    });
+
+    expect(() =>
+      assembleReleasePlan(
+        setup.changesets,
+        setup.packages,
+        defaultConfig,
+        undefined
+      )
+    ).toThrow(
+      "Found changeset small-dogs-sad for package pkg-z which is not in the workspace"
+    );
+  });
+
   describe("fixed packages", () => {
     it("should assemble release plan for fixed packages", () => {
       setup.addChangeset({

packages/assemble-release-plan/src/index.ts

@@ -276,8 +276,16 @@ function getRelevantChangesets(
     const skippedPackages = [];
     const notSkippedPackages = [];
     for (const release of changeset.releases) {
+      const packageByName = packagesByName.get(release.name);
+
+      if (!packageByName) {
+        throw new Error(
+          `Found changeset ${changeset.id} for package ${release.name} which is not in the workspace`
+        );
+      }
+
       if (
-        shouldSkipPackage(packagesByName.get(release.name)!, {
+        shouldSkipPackage(packageByName, {
           ignore: config.ignore,
           allowPrivatePackages: config.privatePackages.version,
         })