Compile time error if name is used before variable is declared

runtime/vm/scopes.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SCOPES_H_
 #define VM_SCOPES_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/growable_array.h"
@@ skipping 99 matching lines @@
                       // in the stack frame.
   bool is_invisible_;
   int index_;  // Allocation index in words relative to frame pointer (if not
                // captured), or relative to the context pointer (if captured).
 
   friend class LocalScope;
   DISALLOW_COPY_AND_ASSIGN(LocalVariable);
 };
 
 
+class NameReference : public ZoneAllocated {
+ public:
+  NameReference(intptr_t token_pos, const String& name)
+    : token_pos_(token_pos),
+      name_(name) {
+  }
+  const String& name() const { return name_; }
+  intptr_t token_pos() const { return token_pos_; }
+  void set_token_pos(intptr_t value) { token_pos_ = value; }
+ private:
+  intptr_t token_pos_;
+  const String& name_;
+};
+
+
 class SourceLabel : public ZoneAllocated {
  public:
   enum Kind {
     kFor,
     kWhile,
     kDoWhile,
     kSwitch,
     kCase,
     kTry,
     kCatch,
@@ skipping 169 matching lines @@
   intptr_t num_variables() const { return variables_.length(); }
   LocalVariable* VariableAt(intptr_t index) const {
     ASSERT((index >= 0) && (index < variables_.length()));
     return variables_[index];
   }
 
   // Count the captured variables belonging to outer scopes and referenced in
   // this local scope.
   int NumCapturedVariables() const;
 
+  // Add a reference to the given name into this scope and the enclosing
+  // scopes that do not have a local variable declaration for this name
+  // already.
+  void AddReferencedName(intptr_t token_pos, const String& name);
+  intptr_t PreviousReferencePos(const String& name) const;
+
   // Allocate both captured and non-captured variables declared in this scope
   // and in its children scopes of the same function level. Allocating means
   // assigning a frame slot index or a context slot index.
   // Parameters to be allocated in the frame must all appear in the top scope
   // and not in its children (we do not yet handle register parameters).
   // Locals must be listed after parameters in top scope and in its children.
   // Two locals in different sibling scopes may share the same frame slot.
   // Return the index of the next available frame slot.
   int AllocateVariables(int first_parameter_index,
                         int num_parameters,
@@ skipping 28 matching lines @@
   // Allocate the variable in the current context, possibly updating the current
   // context owner scope, if the variable is the first one to be allocated at
   // this loop level.
   // The variable may belong to this scope or to any of its children, but at the
   // same loop level.
   void AllocateContextVariable(LocalVariable* variable,
                                LocalScope** context_owner);
 
   void CollectLocalVariables(GrowableArray<VarDesc>* vars, int16_t* scope_id);
 
+  NameReference* FindReference(const String& name) const;
+
   static const int kUnitializedContextLevel = INT_MIN;
   LocalScope* parent_;
   LocalScope* child_;
   LocalScope* sibling_;
   int function_level_;  // Reflects the nesting level of local functions.
   int loop_level_;      // Reflects the loop nesting level.
   int context_level_;   // Reflects the level of the runtime context.
   int num_context_variables_;   // Only set if this scope is a context owner.
   intptr_t begin_token_pos_;  // Token index of beginning of scope.
   intptr_t end_token_pos_;    // Token index of end of scope.
   GrowableArray<LocalVariable*> variables_;
   GrowableArray<SourceLabel*> labels_;
 
+  // List of names referenced in this scope and its children that
+  // are not resolved to local variables.
+  GrowableArray<NameReference*> referenced_;
+
   DISALLOW_COPY_AND_ASSIGN(LocalScope);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCOPES_H_