Compile time error if name is used before variable is declared

runtime/vm/scopes.cc

 // 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.
 
 #include "vm/scopes.h"
 
 #include "vm/ast.h"
 #include "vm/bit_vector.h"
 #include "vm/object.h"
 #include "vm/parser.h"
@@ skipping 12 matching lines @@
     : parent_(parent),
       child_(NULL),
       sibling_(NULL),
       function_level_(function_level),
       loop_level_(loop_level),
       context_level_(LocalScope::kUnitializedContextLevel),
       num_context_variables_(0),
       begin_token_pos_(0),
       end_token_pos_(0),
       variables_(),
-      labels_() {
+      labels_(),
+      referenced_() {
   // Hook this node into the children of the parent, unless the parent has a
   // different function_level, since the local scope of a nested function can
   // be discarded after it has been parsed.
   if ((parent != NULL) && (parent->function_level() == function_level)) {
     sibling_ = parent->child_;
     parent->child_ = this;
   }
 }
 
 
@@ skipping 31 matching lines @@
   labels_.Add(label);
   if (label->owner() == NULL) {
     // Labels must be added to their owner scope first. Subsequent calls
     // to 'add' treat the label as an alias.
     label->set_owner(this);
   }
   return true;
 }
 
 
+NameReference* LocalScope::FindReference(const String& name) const {
+  intptr_t num_references = referenced_.length();
+  for (intptr_t i = 0; i < num_references; i++) {
+    if (name.Equals(referenced_[i]->name())) {
+      return referenced_[i];
+    }
+  }
+  return NULL;
+}
+
+
+void LocalScope::AddReferencedName(intptr_t token_pos,
+                                   const String& name) {
+  if (LocalLookupVariable(name) != NULL) {
+    return;
+  }
+  NameReference* ref = FindReference(name);
+  if (ref != NULL) {
+    ref->set_token_pos(token_pos);

[Ivan Posva, 2013/11/01 16:35:12]

Is it your intent to show the last reference when printing the possible error?

[hausner, 2013/11/01 16:42:51]

Yes.

+    return;
+  }
+  ref = new NameReference(token_pos, name);
+  referenced_.Add(ref);
+  // Add name reference in innermost enclosing scopes that do not
+  // define a local variable with this name.
+  LocalScope* scope = this->parent();
+  while (scope != NULL && (scope->LocalLookupVariable(name) == NULL)) {
+    scope->referenced_.Add(ref);
+    scope = scope->parent();
+  }
+}
+
+
+intptr_t LocalScope::PreviousReferencePos(const String& name) const {
+  NameReference* ref = FindReference(name);
+  if (ref != NULL) {
+    return ref->token_pos();
+  }
+  return -1;
+}
+
+
 void LocalScope::AllocateContextVariable(LocalVariable* variable,
                                          LocalScope** context_owner) {
   ASSERT(variable->is_captured());
   ASSERT(variable->owner()->loop_level() == loop_level());
   if (num_context_variables_ == 0) {
     // This scope will allocate and chain a new context.
     int new_context_level = ((*context_owner) == NULL) ?
         1 : (*context_owner)->context_level() + 1;
     // This scope becomes the current context owner.
     *context_owner = this;
@@ skipping 505 matching lines @@
     return fixed_parameter_count - (index() - kParamEndSlotFromFp);
   } else {
     // Shift negative indexes so that the lowest one is 0 (they are still
     // non-positive).
     return fixed_parameter_count - (index() - kFirstLocalSlotFromFp);
   }
 }
 
 
 }  // namespace dart