Add dependency cycle handing for plugins and config files.

packages/babel-core/src/config/loading/files/configuration.js

@@ -99,14 +99,31 @@ function readConfig(filepath) {
     : readConfigFile(filepath);
 }
 
+const LOADING_CONFIGS = new Set();
 const readConfigJS = makeStrongCache((filepath, cache) => {
   if (!fs.existsSync(filepath)) {
     cache.forever();
     return null;
   }
 
+  // The `require()` call below can make this code reentrant if a require hook like babel-register has been
+  // loaded into the system. That would cause Babel to attempt to compile the `.babelrc.js` file as it loads
+  // below. To cover this case, we auto-ignore re-entrant config processing.
+  if (LOADING_CONFIGS.has(filepath)) {
+    cache.never();
+
+    debug("Auto-ignoring usage of config %o.", filepath);
+    return {
+      filepath,
+      dirname: path.dirname(filepath),
+      options: {},
+    };
+  }
+
   let options;
   try {
+    LOADING_CONFIGS.add(filepath);
+
     // $FlowIssue
     const configModule = (require(filepath): mixed);
     options =
@@ -116,6 +133,8 @@ const readConfigJS = makeStrongCache((filepath, cache) => {
   } catch (err) {
     err.message = `${filepath}: Error while loading config - ${err.message}`;
     throw err;
+  } finally {
+    LOADING_CONFIGS.delete(filepath);
   }
 
   if (typeof options === "function") {

packages/babel-core/src/config/loading/files/plugins.js

@@ -35,7 +35,7 @@ export function loadPlugin(
     throw new Error(`Plugin ${name} not found relative to ${dirname}`);
   }
 
-  const value = requireModule(filepath);
+  const value = requireModule("plugin", filepath);
   debug("Loaded plugin %o from %o.", name, dirname);
 
   return { filepath, value };
@@ -50,7 +50,7 @@ export function loadPreset(
     throw new Error(`Preset ${name} not found relative to ${dirname}`);
   }
 
-  const value = requireModule(filepath);
+  const value = requireModule("preset", filepath);
 
   debug("Loaded preset %o from %o.", name, dirname);
 
@@ -63,7 +63,7 @@ export function loadParser(
 ): { filepath: string, value: Function } {
   const filepath = resolve.sync(name, { basedir: dirname });
 
-  const mod = requireModule(filepath);
+  const mod = requireModule("parser", filepath);
 
   if (!mod) {
     throw new Error(
@@ -91,7 +91,7 @@ export function loadGenerator(
 ): { filepath: string, value: Function } {
   const filepath = resolve.sync(name, { basedir: dirname });
 
-  const mod = requireModule(filepath);
+  const mod = requireModule("generator", filepath);
 
   if (!mod) {
     throw new Error(
@@ -195,7 +195,20 @@ function resolveStandardizedName(
   }
 }
 
-function requireModule(name: string): mixed {
-  // $FlowIssue
-  return require(name);
+const LOADING_MODULES = new Set();
+function requireModule(type: string, name: string): mixed {
+  if (LOADING_MODULES.has(name)) {
+    throw new Error(
+      // eslint-disable-next-line max-len
+      `Reentrant ${type} detected trying to load "${name}". This module is not ignored and is trying to load itself while compiling itself, leading to a dependency cycle. We recommend adding it to your "ignore" list in your babelrc, or to a .babelignore.`,
+    );
+  }
+
+  try {
+    LOADING_MODULES.add(name);
+    // $FlowIssue
+    return require(name);
+  } finally {
+    LOADING_MODULES.delete(name);
+  }
 }