add build-babel.js to show missing sourcemaps

expo/build-babel.js

@@ -0,0 +1,31 @@
+// taken from: metro-babel-transformer
+// https://github.com/facebook/metro/blob/main/packages/metro-babel-transformer/src/index.js
+
+// TODO: see if a simpler source file results in source maps being correctly generated here
+
+const { transformSync, parseSync, transformFromAstSync } = require("@babel/core");
+
+const HermesParser = require("hermes-parser");
+
+const { generateFunctionMap } = require("metro-source-map");
+
+const fs = require('fs')
+
+
+const FILENAME = "target/index.js"
+
+const src = fs.readFileSync(FILENAME, 'utf8')
+
+const babelConfig = {
+  ast: true,
+  code: false,
+  filename: FILENAME,
+  sourceType: "module",
+  inputSourceMap: true,
+  sourceMaps: true,
+};
+
+const sourceAst = parseSync(src, babelConfig);
+const result = transformFromAstSync(sourceAst, src, babelConfig);
+
+console.log(result)