[modules] Add --trace-module-status for printing status transitions.

This is for debugging only.

R=adamk@chromium.org

Bug: v8:1569
Change-Id: I6526d3a98e96bb1267f1850268c5dc83a64587a6
Reviewed-on: https://chromium-review.googlesource.com/586590
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46906}

src/flag-definitions.h

@@ -1080,6 +1080,8 @@ DEFINE_BOOL(print_global_handles, false, "report global handles after GC")
 DEFINE_BOOL(trace_turbo_escape, false, "enable tracing in escape analysis")
 
 // objects.cc
+DEFINE_BOOL(trace_module_status, false,
+            "Trace status transitions of ECMAScript modules")
 DEFINE_BOOL(trace_normalization, false,
             "prints when objects are turned into dictionaries.")
 

src/objects.cc

@@ -19662,10 +19662,27 @@ void Module::StoreVariable(Handle<Module> module, int cell_index,
   module->GetCell(cell_index)->set_value(*value);
 }
 
+#ifdef DEBUG
+void Module::PrintStatusTransition(Status new_status) {
+  if (FLAG_trace_module_status) {
+    OFStream os(stdout);
+    os << "Changing module status from " << status() << " to " << new_status
+       << " for ";
+    script()->GetNameOrSourceURL()->Print(os);
+#ifndef OBJECT_PRINT
+    os << "\n";
+#endif  // OBJECT_PRINT
+  }
+}
+#endif  // DEBUG
+
 void Module::SetStatus(Status new_status) {
   DisallowHeapAllocation no_alloc;
   DCHECK_LE(status(), new_status);
   DCHECK_NE(new_status, Module::kErrored);
+#ifdef DEBUG
+  PrintStatusTransition(new_status);
+#endif  // DEBUG
   set_status(new_status);
 }
 
@@ -19692,6 +19709,9 @@ void Module::RecordError() {
   set_code(info());
 
   DCHECK(exception()->IsTheHole(isolate));
+#ifdef DEBUG
+  PrintStatusTransition(Module::kErrored);
+#endif  // DEBUG
   set_status(Module::kErrored);
   set_exception(the_exception);
 }

src/objects.h

@@ -5057,6 +5057,11 @@ class Module : public Struct {
   void SetStatus(Status status);
   void RecordError();
 
+#ifdef DEBUG
+  // For --trace-module-status.
+  void PrintStatusTransition(Status new_status);
+#endif  // DEBUG
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Module);
 };