Bug 857648 part 4. Add a formattedStack attribute on nsIStackFrame. r=khuey

dom/bindings/Exceptions.cpp

@@ -277,6 +277,7 @@ public:
   NS_IMETHOD GetFilename(nsAString& aFilename) MOZ_OVERRIDE;
   NS_IMETHOD GetName(nsAString& aFunction) MOZ_OVERRIDE;
   NS_IMETHOD GetCaller(nsIStackFrame** aCaller) MOZ_OVERRIDE;
+  NS_IMETHOD GetFormattedStack(nsAString& aStack) MOZ_OVERRIDE;
 
 protected:
   virtual bool IsJSFrame() const MOZ_OVERRIDE {
@@ -289,11 +290,13 @@ private:
   virtual ~JSStackFrame();
 
   JS::Heap<JSObject*> mStack;
+  nsString mFormattedStack;
 
   bool mFilenameInitialized;
   bool mFunnameInitialized;
   bool mLinenoInitialized;
   bool mCallerInitialized;
+  bool mFormattedStackInitialized;
 };
 
 JSStackFrame::JSStackFrame(JS::Handle<JSObject*> aStack)
@@ -302,6 +305,7 @@ JSStackFrame::JSStackFrame(JS::Handle<JSObject*> aStack)
   , mFunnameInitialized(false)
   , mLinenoInitialized(false)
   , mCallerInitialized(false)
+  , mFormattedStackInitialized(false)
 {
   MOZ_ASSERT(mStack);
 
@@ -495,6 +499,35 @@ NS_IMETHODIMP StackFrame::GetCaller(nsIStackFrame** aCaller)
   return NS_OK;
 }
 
+NS_IMETHODIMP JSStackFrame::GetFormattedStack(nsAString& aStack)
+{
+  if (!mFormattedStackInitialized) {
+    ThreadsafeAutoJSContext cx;
+    JS::Rooted<JS::Value> stack(cx, JS::ObjectValue(*mStack));
+    JS::ExposeObjectToActiveJS(mStack);
+    JSAutoCompartment ac(cx, mStack);
+    JS::Rooted<JSString*> formattedStack(cx, JS::ToString(cx, stack));
+    if (!formattedStack) {
+      return NS_ERROR_UNEXPECTED;
+    }
+    nsAutoJSString str;
+    if (!str.init(cx, formattedStack)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    mFormattedStack = str;
+    mFormattedStackInitialized = true;
+  }
+
+  aStack = mFormattedStack;
+  return NS_OK;
+}
+
+NS_IMETHODIMP StackFrame::GetFormattedStack(nsAString& aStack)
+{
+  aStack.Truncate();
+  return NS_OK;
+}
+
 /* AUTF8String toString (); */
 NS_IMETHODIMP StackFrame::ToString(nsACString& _retval)
 {

xpcom/base/nsIException.idl

@@ -10,7 +10,7 @@
 
 #include "nsISupports.idl"
 
-[scriptable, uuid(3bc4793f-e6be-44d6-b839-d6b9e85e5346)]
+[scriptable, uuid(13b75be1-f950-497b-81e4-a0214a14e5ae)]
 interface nsIStackFrame : nsISupports
 {
     // see nsIProgrammingLanguage for list of language consts
@@ -23,6 +23,11 @@ interface nsIStackFrame : nsISupports
     readonly attribute AUTF8String             sourceLine;
     readonly attribute nsIStackFrame           caller;
 
+    // Returns a formatted stack string that looks like the sort of
+    // string that would be returned by .stack on JS Error objects.
+    // Only works on JS-language stack frames.
+    readonly attribute AString                 formattedStack;
+
     AUTF8String toString();
 };