fix(@schematics/angular): better error message when finding only routing modules (#11994)

Closes #11961

Author: alan-agius4

packages/schematics/angular/utility/find-module.ts

@@ -28,7 +28,7 @@ export function findModuleFromOptions(host: Tree, options: ModuleOptions): Path
 
   if (!options.module) {
     const pathToCheck = (options.path || '')
-                      + (options.flat ? '' : '/' + strings.dasherize(options.name));
+      + (options.flat ? '' : '/' + strings.dasherize(options.name));
 
     return normalize(findModule(host, pathToCheck));
   } else {
@@ -59,21 +59,30 @@ export function findModule(host: Tree, generateDir: string): Path {
   const moduleRe = /\.module\.ts$/;
   const routingModuleRe = /-routing\.module\.ts/;
 
+  let foundRoutingModule = false;
+
   while (dir) {
-    const matches = dir.subfiles.filter(p => moduleRe.test(p) && !routingModuleRe.test(p));
+    const allMatches = dir.subfiles.filter(p => moduleRe.test(p));
+    const filteredMatches = allMatches.filter(p => !routingModuleRe.test(p));
+
+    foundRoutingModule = foundRoutingModule || allMatches.length !== filteredMatches.length;
 
-    if (matches.length == 1) {
-      return join(dir.path, matches[0]);
-    } else if (matches.length > 1) {
+    if (filteredMatches.length == 1) {
+      return join(dir.path, filteredMatches[0]);
+    } else if (filteredMatches.length > 1) {
       throw new Error('More than one module matches. Use skip-import option to skip importing '
         + 'the component into the closest module.');
     }
 
     dir = dir.parent;
   }
 
-  throw new Error('Could not find an NgModule. Use the skip-import '
-    + 'option to skip importing in NgModule.');
+  const errorMsg = foundRoutingModule ? 'Could not find a non Routing NgModule.'
+    + '\nModules with suffix \'-routing.module\' are strictly reserved for routing.'
+    + '\nUse the skip-import option to skip importing in NgModule.'
+    : 'Could not find an NgModule. Use the skip-import option to skip importing in NgModule.';
+
+  throw new Error(errorMsg);
 }
 
 /**

packages/schematics/angular/utility/find-module_spec.ts

@@ -53,6 +53,18 @@ describe('find-module', () => {
       }
     });
 
+    it('should throw if only routing modules were found', () => {
+      host = new EmptyTree();
+      host.create('/foo/src/app/anything-routing.module.ts', 'anything routing module');
+
+      try {
+        findModule(host, 'foo/src/app/anything-routing');
+        throw new Error('Succeeded, should have failed');
+      } catch (err) {
+        expect(err.message).toMatch(/Could not find a non Routing NgModule/);
+      }
+    });
+
     it('should throw if two modules found', () => {
       try {
         host = new EmptyTree();