From edbd08745a21bde1a1bf0fe304e09cba6ce7e142 Mon Sep 17 00:00:00 2001
From: Vitali Zaidman <vzaidman@meta.com>
Date: Thu, 12 Sep 2024 06:15:48 -0700
Subject: [PATCH] Fix source mapping for codegenNativeCommands (#46452)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/46452

`babel-plugin-codegen` transforms `codegenNativeComponent`s by expending it with a whole set of many commands (~40 lines) that don't have a good equivalent on the source file.

Currently these lines are pointing to random parts of the due to a bug that causes the source maps to be incorrect and confusing.

Instead, I point all these generated lines of code to the default export as the only line that can represent them.

This way, if an error is thrown from that generated code it would point to that export.

If the users are confused by how it works, there's a comment in the function that is used in the default export in these that explains it:
```
// If this function runs then that means the view configs were not
// generated at build time using `GenerateViewConfigJs.js`. Thus
// we need to `requireNativeComponent` to get the view configs from view managers.
// `requireNativeComponent` is not available in Bridgeless mode.
// e.g. This function runs at runtime if `codegenNativeComponent` was not called
// from a file suffixed with NativeComponent.js.
function codegenNativeComponent<Props>(
  componentName: string,
  options?: Options,
): NativeComponentType<Props> {
```

The transformation is from all the types and exports after the imports:
[`MyNativeViewNativeComponent` for example](https://github.com/facebook/react-native/blob/773a02ad5d3cc38e0f5837b42ba9a5e05a206bf9/packages/rn-tester/NativeComponentExample/js/MyNativeViewNativeComponent.js#L4)
Which is roughly (ignoring all typing):
```
// types and exports
export const Commands: NativeCommands = codegenNativeCommands<NativeCommands>({
  supportedCommands: [
    'callNativeMethodToChangeBackgroundColor',
    'callNativeMethodToAddOverlays',
    'callNativeMethodToRemoveOverlays',
    'fireLagacyStyleEvent',
  ],
});

export default (codegenNativeComponent<NativeProps>(
  'RNTMyNativeView',
): MyNativeViewType);

```
to roughly:
```
  var React = require('react');
  var nativeComponentName = 'RNTMyNativeView';
  var __INTERNAL_VIEW_CONFIG = {
    uiViewClassName: 'RNTMyNativeView',
    bubblingEventTypes: {
      topIntArrayChanged: { /* */ },
      topAlternativeLegacyName: { /* */ },
    },
    validAttributes: {
      opacity: true,
      values: true,
      ...require('ViewConfigIgnore').ConditionallyIgnoredEventHandlers({
        onIntArrayChanged: true,
        onLegacyStyleEvent: true
      })
    }
  };
  var _default = require('NativeComponentRegistry').get(nativeComponentName, () => __INTERNAL_VIEW_CONFIG);
  var Commands = {
    callNativeMethodToChangeBackgroundColor(ref, color) {
      require('RendererProxy').dispatchCommand(ref, "callNativeMethodToChangeBackgroundColor", [color]);
    },
    callNativeMethodToAddOverlays(ref, overlayColors) {
     require('RendererProxy').dispatchCommand(ref, "callNativeMethodToAddOverlays", [overlayColors]);
    },
    callNativeMethodToRemoveOverlays(ref) {
      require('RendererProxy').dispatchCommand(ref, "callNativeMethodToRemoveOverlays", []);
    },
    fireLagacyStyleEvent(ref) {
     require('RendererProxy').dispatchCommand(ref, "fireLagacyStyleEvent", []);
    }
  };
  exports.default = _default;
  exports.__INTERNAL_VIEW_CONFIG = __INTERNAL_VIEW_CONFIG;
  exports.Commands = Commands;
```

Differential Revision: D62443699
---
 packages/babel-plugin-codegen/index.js     | 31 +++++++++++++++++-----
 packages/babel-plugin-codegen/package.json |  1 +
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/packages/babel-plugin-codegen/index.js b/packages/babel-plugin-codegen/index.js
index 77de6b77b33ad7..6dc382c4d2258f 100644
--- a/packages/babel-plugin-codegen/index.js
+++ b/packages/babel-plugin-codegen/index.js
@@ -12,6 +12,7 @@
 let FlowParser, TypeScriptParser, RNCodegen;
 
 const {basename} = require('path');
+const {cheap: traverseCheap} = require('@babel/traverse').default;
 
 try {
   FlowParser =
@@ -168,16 +169,32 @@ module.exports = function ({parse, types: t}) {
         exit(path) {
           if (this.defaultExport) {
             const viewConfig = generateViewConfig(this.filename, this.code);
-            this.defaultExport.replaceWithMultiple(
-              parse(viewConfig, {
-                babelrc: false,
-                browserslistConfigFile: false,
-                configFile: false,
-              }).program.body,
-            );
+
+            const ast = parse(viewConfig, {
+              babelrc: false,
+              browserslistConfigFile: false,
+              configFile: false,
+            });
+
+            // Almost the whole file is replaced with the viewConfig generated code that doesn't
+            // have a clear equivalent code on the source file when the user debugs, so we point
+            // it to the location of the default export that in that file, which is the closest
+            // to representing the code that is being generated.
+            // This is mostly useful when that generated code throws an error.
+            traverseCheap(ast, node => {
+              if (node?.loc) {
+                node.loc = this.defaultExport.node.loc;
+                node.start = this.defaultExport.node.start;
+                node.end = this.defaultExport.node.end;
+              }
+            });
+
+            this.defaultExport.replaceWithMultiple(ast.program.body);
+
             if (this.commandsExport != null) {
               this.commandsExport.remove();
             }
+
             this.codeInserted = true;
           }
         },
diff --git a/packages/babel-plugin-codegen/package.json b/packages/babel-plugin-codegen/package.json
index 57e7fc4854fdda..a2eae7dc7dc7d7 100644
--- a/packages/babel-plugin-codegen/package.json
+++ b/packages/babel-plugin-codegen/package.json
@@ -25,6 +25,7 @@
     "index.js"
   ],
   "dependencies": {
+    "@babel/traverse": "^7.25.3",
     "@react-native/codegen": "0.76.0-main"
   },
   "devDependencies": {