emit metro raw source maps for older RN versions

Author: David Sheldrick

.gitignore

@@ -56,3 +56,4 @@ jspm_packages/
 
 dist
 package
+*.tar.gz

src/composeSourceMaps.ts

@@ -32,6 +32,26 @@ export function convertMetroRawSourceMapToStandardSourceMap(
   return outputMap.toString()
 }
 
+export function convertStandardSourceMapToMetroRawSourceMap(
+  map: RawSourceMap | string,
+) {
+  const consumer = new SourceMapConsumer(map as any) // upstream types are wrong
+
+  const outputMap: MetroRawSourceMap = []
+
+  consumer.eachMapping(mapping => {
+    outputMap.push([
+      mapping.generatedLine,
+      mapping.generatedColumn,
+      mapping.originalLine,
+      mapping.originalColumn,
+      mapping.name,
+    ])
+  })
+
+  return outputMap
+}
+
 export function composeSourceMaps(
   sourceMap: string | RawSourceMap,
   targetMap: string | RawSourceMap,

src/getMetroTransformer.ts

@@ -1,7 +1,10 @@
 import { Node } from "babel-core"
 import { RawSourceMap, SourceMapConsumer } from "source-map"
 import * as semver from "semver"
-import { MetroRawSourceMap } from "./composeSourceMaps"
+import {
+  MetroRawSourceMap,
+  convertStandardSourceMapToMetroRawSourceMap,
+} from "./composeSourceMaps"
 import * as babylon from "babylon"
 import traverse from "babel-traverse"
 
@@ -56,9 +59,10 @@ export interface ReactNativeObfuscatingTransformerDefaultResult {
 }
 
 export function maybeTransformMetroResult(
+  upstreamResult: MetroTransformerResult,
   { code, map }: ReactNativeObfuscatingTransformerDefaultResult,
   reactNativeMinorVersion: number = getReactNativeMinorVersion(),
-): ReactNativeObfuscatingTransformerDefaultResult | { ast: Node } {
+): MetroTransformerResult {
   if (reactNativeMinorVersion >= 52) {
     // convert code and map to ast
     const ast = babylon.parse(code, {
@@ -82,6 +86,8 @@ export function maybeTransformMetroResult(
     })
 
     return { ast }
+  } else if (Array.isArray(upstreamResult.map)) {
+    return { code, map: convertStandardSourceMapToMetroRawSourceMap(map) }
   } else {
     return { code, map }
   }

src/obfuscatingTransformer.ts

@@ -91,6 +91,7 @@ export function obfuscatingTransformer({
         }
 
         return maybeTransformMetroResult(
+          result,
           obfuscateCodePreservingSourceMap(
             code,
             map,