Show callstack in browser upon REPL crashes

scripts/test-runner.js

@@ -286,6 +286,7 @@ function runTest(name, code, options: PrepackOptions, args) {
   options.invariantLevel = code.includes("// omit invariants") || args.verbose ? 0 : 99;
   if (code.includes("// emit concrete model")) options.emitConcreteModel = true;
   if (code.includes("// exceeds stack limit")) options.maxStackDepth = 10;
+  if (code.includes("// heapGraph")) options.heapGraphFormat = "VISJS";
   if (code.includes("// react")) {
     options.reactEnabled = true;
     options.reactOutput = "jsx";

src/serializer/serializer.js

@@ -175,6 +175,17 @@ export class Serializer {
         );
 
         if (this.options.heapGraphFormat) {
+          if (additionalFunctionValuesAndEffects.size > 0) {
+            let diagnostic = new CompilerDiagnostic(
+              "Using __optimize with --heapGraphFilePath flag is not currently supported",
+              undefined,
+              "N/A",
+              "FatalError"
+            );
+            this.realm.handleError(diagnostic);
+            throw new FatalError("Using __optimize with --heapGraphFilePath flag is not currently supported");
+          }
+
           const heapRefCounter = new ResidualHeapRefCounter(
             this.realm,
             this.logger,

src/utils/generator.js

@@ -253,9 +253,15 @@ class ModifiedBindingEntry extends GeneratorEntry {
       containingGenerator === this.containingGenerator,
       "This entry requires effects to be applied and may not be moved"
     );
-    invariant(this.modifiedBinding.value === this.newValue);
+    invariant(
+      this.modifiedBinding.value === this.newValue,
+      "ModifiedBinding's value has been changed since last visit."
+    );
     let [residualBinding, newValue] = context.visitModifiedBinding(this.modifiedBinding);
-    invariant(this.residualFunctionBinding === undefined || this.residualFunctionBinding === residualBinding);
+    invariant(
+      this.residualFunctionBinding === undefined || this.residualFunctionBinding === residualBinding,
+      "ResidualFunctionBinding has been changed since last visit."
+    );
     this.residualFunctionBinding = residualBinding;
     this.newValue = newValue;
     return true;