fix: get line numbers to be proper again

packages/bundle-source/demo/circular/b.js

@@ -5,5 +5,4 @@ import { foo } from './a';
  * --------->
  * <!-- foo as bar -->
  */
-console.error('here am I');
 export { foo as bar };

packages/bundle-source/src/index.js

@@ -88,20 +88,21 @@ export default async function bundleSource(
       // eslint-disable-next-line no-await-in-loop
       const consumer = await new SourceMapConsumer(chunk.map);
       const unmapped = new WeakSet();
-      let lastPos = ast.loc.start;
+      let lastPos = { ...ast.loc.start };
       unmapLoc = loc => {
         if (!loc || unmapped.has(loc)) {
           return;
         }
-        // Ensure we start in the right position... doesn't matter where we end.
-        loc.end = loc.start;
+        // Make sure things start at least at the right place.
+        loc.end = { ...loc.start };
         for (const pos of ['start', 'end']) {
           if (loc[pos]) {
             const newPos = consumer.originalPositionFor(loc[pos]);
             if (newPos.source !== null) {
-              lastPos = loc[pos];
-              lastPos.line = newPos.line;
-              lastPos.column = newPos.column;
+              lastPos = {
+                line: newPos.line,
+                column: newPos.column,
+              };
             }
             loc[pos] = lastPos;
           }

packages/bundle-source/test/circular.js

@@ -10,7 +10,7 @@ function evaluate(src, endowments) {
 
 test('circular export', async t => {
   try {
-    const { source: src1 } = await bundleSource(
+    const { source: src1, sourceMap: map1 } = await bundleSource(
       `${__dirname}/../demo/circular/a.js`,
       'nestedEvaluate',
     );
@@ -22,7 +22,7 @@ test('circular export', async t => {
       return evaluate(src, { require, nestedEvaluate });
     };
     // console.log(src1);
-    const srcMap1 = `(${src1})`;
+    const srcMap1 = `(${src1})\n${map1}`;
     const ex1 = nestedEvaluate(srcMap1)();
 
     // console.log(err.stack);