inline blockly sourcemaps in development builds

gulpfile.js

@@ -336,6 +336,14 @@ function runUglify() {
     return Promise.resolve();
 }
 
+function inlineBlocklySourcemaps() {
+    if (process.env.PXT_ENV === 'production') {
+        return;
+    }
+
+    return exec("node ./scripts/inlineBlocklySourceMaps.js");
+}
+
 
 
 /********************************************************
@@ -733,7 +741,7 @@ function getMochaExecutable() {
 const buildAll = gulp.series(
     updatestrings,
     maybeUpdateWebappStrings(),
-    gulp.parallel(copyTypescriptServices, copyBlocklyMedia),
+    gulp.parallel(copyTypescriptServices, copyBlocklyMedia, inlineBlocklySourcemaps),
     gulp.parallel(pxtlib, pxtweb),
     gulp.parallel(pxtcompiler, pxtsim, backendutils),
     pxtpy,

scripts/inlineBlocklySourceMaps.js

@@ -0,0 +1,21 @@
+const fs = require("fs");
+const path = require("path");
+
+const blocklyRoot = path.resolve(__dirname, "..", "node_modules", "blockly");
+
+const files = [
+    "blockly_compressed.js",
+    "blocks_compressed.js"
+];
+
+for (const file of files) {
+    const fullPath = path.join(blocklyRoot, file);
+    const source = fs.readFileSync(fullPath, "utf8");
+    const maps = fs.readFileSync(fullPath + ".map", "utf8");
+
+    const dataUri = "data:application/json;charset=utf-8;base64," + Buffer.from(maps).toString("base64");
+
+    const patched = source.replace(/\/\/# sourceMappingURL=.*/, `//# sourceMappingURL=${dataUri}`);
+
+    fs.writeFileSync(fullPath, patched, "utf8");
+}