Do not include types in JS blueprints

For the fallback case, where Ember's blueprints are being executed by a
version of Ember CLI earlier than 4.3.0, the emitted blueprints *must
not* include any TypeScript types, since the CLI will not be able to
remove the types. Accordingly:

1.  Return a boolean flag from the `maybePolyfillTypeScriptBlueprints`
    helper, indicating whether the blueprint is in a mode where it can
    reliably *emit* types.

2.  Use that new helper in the component blueprint so that it can avoid
    emitting a signature type, and specifically can avoid emitting it
    as a type parameter on the class or function default export.

Author: chriskrycho

blueprints/-maybe-polyfill-typescript-blueprints.js

@@ -8,10 +8,12 @@ function canEmitTypeScript() {
 }
 
 module.exports = function (context) {
-  if (canEmitTypeScript()) {
+  let canUseTypeScript = canEmitTypeScript();
+  if (canUseTypeScript) {
     typescriptBlueprintPolyfill(context);
   } else {
     // Use the plain old JS templates from before
     context.path = context.path.replace('blueprints', 'blueprints-js');
   }
+  return canUseTypeScript;
 };

blueprints/component/index.js

@@ -53,9 +53,17 @@ module.exports = {
     },
   ],
 
+  /**
+    Flag to let us correctly handle the case where we are running against a
+    version of Ember CLI which does not support TS-based emit, and where we
+    therefore *must* not emit a `defaultExport` local which includes a type
+    parameter in the exported function call or class definition.
+   */
+  _isUsingTS: false,
+
   init() {
     this._super && this._super.init.apply(this, arguments);
-    maybePolyfillTypeScriptBlueprints(this);
+    this._isUsingTS = maybePolyfillTypeScriptBlueprints(this);
     let isOctane = has('octane');
 
     this.availableOptions.forEach((option) => {
@@ -264,13 +272,21 @@ module.exports = {
         break;
       case '@glimmer/component':
         importComponent = `import Component from '@glimmer/component';`;
-        componentSignature = signatureFor(classifiedModuleName);
-        defaultExport = `class ${classifiedModuleName}Component extends Component<${classifiedModuleName}Signature> {}`;
+        if (this._isUsingTS) {
+          componentSignature = signatureFor(classifiedModuleName);
+          defaultExport = `class ${classifiedModuleName}Component extends Component<${classifiedModuleName}Signature> {}`;
+        } else {
+          defaultExport = `class ${classifiedModuleName}Component extends Component {}`;
+        }
         break;
       case '@ember/component/template-only':
         importComponent = `import templateOnly from '@ember/component/template-only';`;
-        componentSignature = signatureFor(classifiedModuleName);
-        defaultExport = `templateOnly<${classifiedModuleName}Signature>();`;
+        if (this._isUsingTS) {
+          componentSignature = signatureFor(classifiedModuleName);
+          defaultExport = `templateOnly<${classifiedModuleName}Signature>();`;
+        } else {
+          defaultExport = `templateOnly();`;
+        }
         break;
     }