enforce peerDependencies for winglibs

apps/wing/fixtures/invalid6/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "invalid6",
+  "version": "0.0.0",
+  "description": "description",
+  "author": "author",
+  "license": "MIT",
+  "files": [
+    "**/*.ts"
+  ],
+  "dependencies": {
+    "some-dependency": "^1.0.0"
+  }
+}

apps/wing/fixtures/invalid6/util.ts

@@ -0,0 +1,3 @@
+export function add(x: number, y: number): number {
+  return x + y;
+}

apps/wing/src/commands/pack.test.ts

@@ -69,6 +69,21 @@ describe("wing pack", () => {
     await expectNoTarball(outdir);
   });
 
+  it("throws an error if package.json uses dependencies instead of peerDependencies", async () => {
+    // GIVEN
+    const projectDir = join(fixturesDir, "invalid6");
+    const outdir = await generateTmpDir();
+    process.chdir(projectDir);
+
+    // WHEN
+    await expect(pack({ outFile: join(outdir, "tarball.tgz") })).rejects.toThrow(
+      /Wing libraries should use "peerDependencies" instead of "dependencies" in package.json/
+    );
+
+    // THEN
+    await expectNoTarball(outdir);
+  });
+
   it("includes extra files specified by package.json", async () => {
     // valid1's package.json contains this:
     // {

apps/wing/src/commands/pack.ts

@@ -120,6 +120,13 @@ export async function pack(options: PackageOptions = {}): Promise<string> {
       }
     }
 
+    // check package.json has `dependencies`
+    if (pkgJson.dependencies) {
+      throw new Error(
+        `Wing libraries should use "peerDependencies" instead of "dependencies" in package.json.`
+      );
+    }
+
     // move compiler output
     await fs.rename(compilerOutputDir, path.join(workdir, compilerOutputFolder));