Give each fake eval its own URL

If we always add sourceURL even when we have source maps, the native stack gets source mapped. This is needed when looking up a source location from an error string where the engine doesn't have access to the native reference.

Async stacks are printed with native references but errors printed into the console are printed as strings and then reverse engineered back into source
mapped urls. This preserves each eval as its own id.

We use a separate protocol to exclude them from other Sources. Otherwise the real file and the fake file are listed right next to eachother.

Author: sebmarkbage

fixtures/flight/server/region.js

@@ -224,9 +224,10 @@ if (process.env.NODE_ENV === 'development') {
         // was already applied we also use this path.
         const sourceContent = await readFile(requestedFilePath, 'utf8');
         const lines = sourceContent.split('\n').length;
+        const sourceURL = requestedFilePath.startsWith('/') ? 'file://' + requestedFilePath : requestedFilePath;
         map = {
           version: 3,
-          sources: [requestedFilePath],
+          sources: [sourceURL],
           sourcesContent: [sourceContent],
           // Note: This approach to mapping each line only lets you jump to each line
           // not jump to a column within a line. To do that, you need a proper source map

packages/react-client/src/ReactFlightClient.js

@@ -1614,10 +1614,6 @@ function resolveErrorDev(
     } else {
       error = callStack();
     }
-    // Overriding the stack isn't really necessary at this point and maybe we should just
-    // leave the native one. However, the native one gets printed unsource mapped with
-    // reportError. If that's fixed it might be better to use the native one.
-    error.stack = stack;
   }
 
   (error: any).digest = digest;
@@ -1705,6 +1701,7 @@ const fakeFunctionCache: Map<string, FakeFunction<any>> = __DEV__
   ? new Map()
   : (null: any);
 
+let fakeFunctionIdx = 0;
 function createFakeFunction<T>(
   name: string,
   filename: string,
@@ -1723,20 +1720,29 @@ function createFakeFunction<T>(
   // point to the original source.
   let code;
   if (line <= 1) {
-    code = '_=>' + ' '.repeat(col < 4 ? 0 : col - 4) + '_()\n' + comment + '\n';
+    code = '_=>' + ' '.repeat(col < 4 ? 0 : col - 4) + '_()\n' + comment;
   } else {
     code =
       comment +
       '\n'.repeat(line - 2) +
       '_=>\n' +
       ' '.repeat(col < 1 ? 0 : col - 1) +
-      '_()\n';
+      '_()';
+  }
+
+  if (filename.startsWith('/')) {
+    // If the filename starts with `/` we assume that it is a file system file
+    // rather than relative to the current host. Since on the server fully qualified
+    // stack traces use the file path.
+    // TODO: What does this look like on Windows?
+    filename = 'file://' + filename;
   }
 
   if (sourceMap) {
-    code += '//# sourceMappingURL=' + sourceMap;
+    code += '\n//# sourceURL=rsc://server/' + filename + '?' + fakeFunctionIdx++;
+    code += '\n//# sourceMappingURL=' + sourceMap;
   } else if (filename) {
-    code += '//# sourceURL=' + filename;
+    code += '\n//# sourceURL=' + filename;
   }
 
   let fn: FakeFunction<T>;