Improve error reporting when failing to associate a companion template

packages/transform/__tests__/rewrite.test.ts

@@ -265,6 +265,68 @@ describe('rewriteModule', () => {
       `);
     });
 
+    test('with no default value export', () => {
+      let script = {
+        filename: 'test.ts',
+        contents: stripIndent`
+          import Component from '@glimmer/component';
+          export class MyComponent extends Component {}
+        `,
+      };
+
+      let template = {
+        filename: 'test.hbs',
+        contents: stripIndent``,
+      };
+
+      let transformedModule = rewriteModule({ script, template }, emberLooseEnvironment);
+
+      expect(transformedModule?.errors).toEqual([
+        {
+          message:
+            'Modules with an associated template must have a default export that is a class declaration or expression',
+          source: script,
+          location: {
+            start: 0,
+            end: script.contents.length,
+          },
+        },
+      ]);
+
+      expect(transformedModule?.getOriginalRange(0, script.contents.length)).toEqual({
+        source: script,
+        start: 0,
+        end: script.contents.length,
+      });
+    });
+
+    test('with an unresolvable default export', () => {
+      let script = {
+        filename: 'test.ts',
+        contents: stripIndent`
+          export default Foo;
+        `,
+      };
+
+      let template = {
+        filename: 'test.hbs',
+        contents: stripIndent``,
+      };
+
+      let transformedModule = rewriteModule({ script, template }, emberLooseEnvironment);
+
+      expect(transformedModule?.errors).toEqual([
+        {
+          message: 'Unable to resolve a class body to associate a template declaration to',
+          source: script,
+          location: {
+            start: script.contents.indexOf('Foo'),
+            end: script.contents.indexOf(';'),
+          },
+        },
+      ]);
+    });
+
     test('with a class with default export in module augmentation', () => {
       let script = {
         filename: 'test.ts',

packages/transform/src/index.ts

@@ -137,6 +137,7 @@ function calculateCorrelatedSpans(
 ): CorrelatedSpansResult {
   let errors: Array<TransformError> = [];
   let partialSpans: Array<PartialCorrelatedSpan> = [];
+  let defaultExportSeen = false;
 
   traverse(ast, {
     TaggedTemplateExpression(path) {
@@ -152,15 +153,25 @@ function calculateCorrelatedSpans(
     },
 
     ExportDefaultDeclaration(path) {
-      if (template) {
-        let result = calculateCompanionTemplateSpans(path, script, template, environment);
+      let declaration = path.get('declaration');
+      if (template && (declaration.isClass() || declaration.isExpression())) {
+        let result = calculateCompanionTemplateSpans(declaration, script, template, environment);
 
+        defaultExportSeen = true;
         errors.push(...result.errors);
         partialSpans.push(...result.partialSpans);
       }
     },
   });
 
+  if (template && !defaultExportSeen) {
+    errors.push({
+      message: `Modules with an associated template must have a default export that is a class declaration or expression`,
+      source: script,
+      location: { start: 0, end: script.contents.length },
+    });
+  }
+
   return { errors, partialSpans };
 }
 

packages/transform/src/inlining/companion-file.ts

@@ -9,7 +9,7 @@ import { assert } from '../util';
 const STANDALONE_TEMPLATE_FIELD = `'~template'`;
 
 export function calculateCompanionTemplateSpans(
-  path: NodePath<t.ExportDefaultDeclaration>,
+  path: NodePath<t.Class> | NodePath<t.Expression>,
   script: SourceFile,
   template: SourceFile,
   environment: GlintEnvironment
@@ -30,9 +30,12 @@ export function calculateCompanionTemplateSpans(
   let targetPath = findCompanionTemplateTarget(path);
   if (!targetPath) {
     errors.push({
+      message: `Unable to resolve a class body to associate a template declaration to`,
       source: script,
-      location: { start: 0, end: script.contents.length },
-      message: `Modules with an associated template must have a default export`,
+      location: {
+        start: path.node.start ?? 0,
+        end: path.node.end ?? script.contents.length,
+      },
     });
 
     return { errors, partialSpans };
@@ -124,11 +127,10 @@ export function calculateCompanionTemplateSpans(
 type CompanionTemplateTarget = NodePath<t.Class> | NodePath<t.Expression> | null;
 
 function findCompanionTemplateTarget(
-  path: NodePath<t.ExportDefaultDeclaration>
+  declaration: NodePath<t.Class> | NodePath<t.Expression>
 ): CompanionTemplateTarget {
-  let declaration = path.get('declaration');
   let value = declaration.isIdentifier()
-    ? path.scope.getBinding(declaration.node.name)?.path
+    ? declaration.scope.getBinding(declaration.node.name)?.path
     : declaration;
 
   if (value?.isClass() || value?.isExpression()) {

packages/transform/src/transformed-module.ts

@@ -81,7 +81,10 @@ export default class TransformedModule {
     let startInfo = this.determineOriginalOffsetAndSpan(transformedStart);
     let endInfo = this.determineOriginalOffsetAndSpan(transformedEnd);
 
-    assert(startInfo.correlatedSpan.originalFile === endInfo.correlatedSpan.originalFile);
+    assert(
+      startInfo.correlatedSpan.originalFile === endInfo.correlatedSpan.originalFile,
+      'Attempted to transform a range across two different files'
+    );
 
     let source = startInfo.correlatedSpan.originalFile;
     let start = startInfo.originalOffset;