[FEATURE] generate Signature in component blueprints

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/files/__root__/__path__/__name__.ts

@@ -1,3 +1,4 @@
 <%= importComponent %>
 <%= importTemplate %>
+<%= componentSignature %>
 export default <%= defaultExport %>

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) => {
@@ -227,15 +235,8 @@ module.exports = {
   },
 
   locals(options) {
-    let sanitizedModuleName = options.entity.name.replace(/\//g, '-');
-    let classifiedModuleName = stringUtil.classify(sanitizedModuleName);
-
-    let templatePath = '';
-    let importComponent = '';
-    let importTemplate = '';
-    let defaultExport = '';
-
     // if we're in an addon, build import statement
+    let templatePath = '';
     if (options.project.isEmberCLIAddon() || (options.inRepoAddon && !options.inDummy)) {
       if (options.pod) {
         templatePath = './template';
@@ -251,6 +252,14 @@ module.exports = {
       ? options.componentClass
       : '@ember/component';
 
+    let sanitizedModuleName = options.entity.name.replace(/\//g, '-');
+    let classifiedModuleName = stringUtil.classify(sanitizedModuleName);
+
+    let importComponent = '';
+    let importTemplate = '';
+    let defaultExport = '';
+    let componentSignature = '';
+
     switch (componentClass) {
       case '@ember/component':
         importComponent = `import Component from '@ember/component';`;
@@ -263,20 +272,53 @@ module.exports = {
         break;
       case '@glimmer/component':
         importComponent = `import Component from '@glimmer/component';`;
-        defaultExport = `class ${classifiedModuleName}Component extends Component {}`;
+        if (this._isUsingTS) {
+          componentSignature = signatureFor(classifiedModuleName);
+          defaultExport = `class ${classifiedModuleName}Component extends Component<${classifiedModuleName}Signature> {}`;
+        } else {
+          defaultExport = `class ${classifiedModuleName}Component extends Component {}`;
+        }
         break;
       case '@ember/component/template-only':
         importComponent = `import templateOnly from '@ember/component/template-only';`;
-        defaultExport = `templateOnly();`;
+        if (this._isUsingTS) {
+          componentSignature = signatureFor(classifiedModuleName);
+          defaultExport = `templateOnly<${classifiedModuleName}Signature>();`;
+        } else {
+          defaultExport = `templateOnly();`;
+        }
         break;
     }
 
     return {
       importTemplate,
       importComponent,
+      componentSignature,
       defaultExport,
       path: getPathOption(options),
       componentClass: options.componentClass,
     };
   },
 };
+
+function signatureFor(classifiedModuleName) {
+  let args = `  // The arguments accepted by the component${EOL}  Args: {};`;
+
+  let blocks =
+    `  // Any blocks yielded by the component${EOL}` +
+    `  Blocks: {${EOL}` +
+    `    default: []${EOL}` +
+    `  };`;
+
+  let element =
+    `  // The element to which \`...attributes\` is applied in the component template${EOL}` +
+    `  Element: null;`;
+
+  return (
+    `interface ${classifiedModuleName}Signature {${EOL}` +
+    `${args}${EOL}` +
+    `${blocks}${EOL}` +
+    `${element}${EOL}` +
+    `}${EOL}`
+  );
+}