Fix an issue where LLDB would run out of stack space trying to decide if a deeply nested child can be updated in the face of an invalid execution context

The issue is that a child can't really ask the root object, since this decision could actually hinge on whether a dynamic and/or synthetic value is present
To do this, make values vote lazily for whether they are willing to allow this, so that we can navigate up the chain without recursively invoking ourselves

Tentative fix for rdar://21949558

llvm-svn: 243077

lldb/include/lldb/Core/ValueObject.h

@@ -861,7 +861,7 @@ public:
     bool
     NeedsUpdating ()
     {
-        const bool accept_invalid_exe_ctx = CanUpdateWithInvalidExecutionContext();
+        const bool accept_invalid_exe_ctx = (CanUpdateWithInvalidExecutionContext() == eLazyBoolYes);
         return m_update_point.NeedsUpdating(accept_invalid_exe_ctx);
     }
     
@@ -1172,10 +1172,10 @@ protected:
     virtual bool
     UpdateValue () = 0;
 
-    virtual bool
+    virtual LazyBool
     CanUpdateWithInvalidExecutionContext ()
     {
-        return false;
+        return eLazyBoolCalculate;
     }
     
     virtual void

lldb/include/lldb/Core/ValueObjectChild.h

@@ -84,7 +84,7 @@ protected:
     virtual bool
     UpdateValue ();
     
-    virtual bool
+    virtual LazyBool
     CanUpdateWithInvalidExecutionContext ();
 
     virtual ClangASTType

lldb/include/lldb/Core/ValueObjectDynamicValue.h

@@ -109,10 +109,10 @@ protected:
     virtual bool
     UpdateValue ();
     
-    virtual bool
+    virtual LazyBool
     CanUpdateWithInvalidExecutionContext ()
     {
-        return true;
+        return eLazyBoolYes;
     }
     
     virtual lldb::DynamicValueType

lldb/include/lldb/Core/ValueObjectSyntheticFilter.h

@@ -156,10 +156,10 @@ protected:
     virtual bool
     UpdateValue ();
     
-    virtual bool
+    virtual LazyBool
     CanUpdateWithInvalidExecutionContext ()
     {
-        return true;
+        return eLazyBoolYes;
     }
     
     virtual ClangASTType

lldb/source/Core/ValueObjectChild.cpp

@@ -109,12 +109,14 @@ ValueObjectChild::GetDisplayTypeName()
     return display_name;
 }
 
-bool
+LazyBool
 ValueObjectChild::CanUpdateWithInvalidExecutionContext ()
 {
-    if (m_parent)
-        return m_parent->CanUpdateWithInvalidExecutionContext();
-    return this->ValueObject::CanUpdateWithInvalidExecutionContext();
+    ValueObject* opinionated_ancestor = FollowParentChain([] (ValueObject* vo) -> bool {
+        return (vo->CanUpdateWithInvalidExecutionContext() == eLazyBoolCalculate);
+    });
+    
+    return opinionated_ancestor ? opinionated_ancestor->CanUpdateWithInvalidExecutionContext() : this->ValueObject::CanUpdateWithInvalidExecutionContext();
 }
 
 bool