Throw proper error when there are circular dependencies between harmony extensions

src/app.ts

@@ -6,6 +6,7 @@ import { BitCliExt } from './extensions/cli';
 import defaultHandleError from './cli/default-error-handler';
 import { logErrAndExit } from './cli/command-registry';
 import { BitExt } from './extensions/bit';
+import HarmonyError from './harmony/exceptions/harmony-error';
 
 process.env.MEMFS_DONT_WARN = 'true'; // suppress fs experimental warnings from memfs
 
@@ -23,17 +24,22 @@ const config = {
     components: '*'
   }
 };
-
-const harmony = Harmony.load([BitCliExt, BitExt], config);
-harmony
-  .run()
-  .then(() => {
-    const cli = harmony.get('BitCli');
-    // @ts-ignore
-    if (cli && cli.instance) return cli.instance.run([], harmony);
-    throw new Error('failed to load CLI');
-  })
-  .catch(err => {
-    const handledError = defaultHandleError(err.originalError);
-    logErrAndExit(handledError || err, process.argv[1] || '');
-  });
+try {
+  const harmony = Harmony.load([BitCliExt, BitExt], config);
+  harmony
+    .run()
+    .then(() => {
+      const cli = harmony.get('BitCli');
+      // @ts-ignore
+      if (cli && cli.instance) return cli.instance.run([], harmony);
+      throw new Error('failed to load CLI');
+    })
+    .catch(err => {
+      const handledError = defaultHandleError(err.originalError);
+      logErrAndExit(handledError || err, process.argv[1] || '');
+    });
+  // Catching errors from the load phase
+} catch (err) {
+  const handledError = err instanceof HarmonyError ? err.toString() : err;
+  logErrAndExit(handledError, process.argv[1] || '');
+}

src/harmony/exceptions/extension-potential-circular.ts

@@ -0,0 +1,25 @@
+import chalk from 'chalk';
+import { Extension } from '../extension';
+import HarmonyError from './harmony-error';
+
+export default class ExtensionPotentialCircular extends HarmonyError {
+  constructor(
+    /**
+     * failed extension
+     */
+    private extension: Extension,
+
+    /**
+     * valid extensions dependencies names
+     */
+    private validDeps: string[]
+  ) {
+    super();
+  }
+
+  toString() {
+    return `Failed to load the dependencies for extension ${chalk.bold(this.extension.name)}. 
+This may result from a wrong import or from circular dependencies in imports. 
+The following dependencies succeeded loading: ${chalk.bold(this.validDeps.join(', '))}`;
+  }
+}

src/harmony/exceptions/harmony-error.ts

@@ -0,0 +1 @@
+export default class HarmonyError extends Error {}

src/harmony/exceptions/index.ts

@@ -1,2 +1,3 @@
 export { default as ExtensionLoadError } from './extension-load-error';
+export { default as ExtensionPotentialCircular } from './extension-potential-circular';
 export { HarmonyAlreadyRunning } from './harmony-already-running';

src/harmony/extension-graph/from-extension.ts

@@ -2,6 +2,7 @@ import { Vertex, Edge } from 'cleargraph';
 import { AnyExtension } from '../types';
 import { ExtensionManifest } from '../extension-manifest';
 import { extensionFactory } from '../factory';
+import ExtensionPotentialCircular from '../exceptions/extension-potential-circular';
 
 /**
  * build vertices and edges from the given extension
@@ -15,8 +16,11 @@ export function fromExtension(extension: ExtensionManifest) {
     if (vertices[id]) return;
 
     const instance = extensionFactory(root);
+    const validDeps = instance.dependencies.filter(dep => dep).map(dep => dep.name);
+    if (instance.dependencies.length > validDeps.length) {
+      throw new ExtensionPotentialCircular(instance, validDeps);
+    }
     vertices[id] = new Vertex<AnyExtension>(id, instance);
-
     const newEdges = instance.dependencies.map(dep => {
       return Edge.fromObject({
         srcId: id,