GN: Throw an error overwriting a nonempty scope.

tools/gn/scope.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_SCOPE_H_
 #define TOOLS_GN_SCOPE_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 107 matching lines @@
   const Scope* mutable_containing() const { return mutable_containing_; }
   const Scope* const_containing() const { return const_containing_; }
   const Scope* containing() const {
     return mutable_containing_ ? mutable_containing_ : const_containing_;
   }
 
   // Clears any references to containing scopes. This scope will now be
   // self-sufficient.
   void DetachFromContaining();
 
+  // Returns true if the scope has any values set. This does not check other
+  // things that may be set like templates or defaults.
+  //
+  // Currently this does not search nested scopes and this will assert if you
+  // want to search nested scopes. The enum is passed so the callers are
+  // unambiguous about nested scope handling. This can be added if needed.
+  bool HasValues(SearchNested search_nested) const;
+
   // Returns NULL if there's no such value.
   //
   // counts_as_used should be set if the variable is being read in a way that
   // should count for unused variable checking.
   const Value* GetValue(const base::StringPiece& ident,
                         bool counts_as_used);
   const Value* GetValue(const base::StringPiece& ident) const;
 
-  // If the value exists in the current scope, destrictively moves it into the
-  // return value. If it exists in a containing scope, copies it.
-  //
-  // This is for implementing modify-write operations where we want to read
-  // the existing value and plan to immediately overwrite it. If the value is
-  // in a containing scope, we never want to touch it (all writes go to the
-  // current scope), but if it's in the current scope, avoid the copy since it
-  // will be overwritten anyway.
-  //Value DestructiveMoveOut(const base::StringPiece& ident);
-
   // Returns the requested value as a mutable one if possible. If the value
   // is not found in a mutable scope, then returns null. Note that the value
   // could still exist in a const scope, so GetValue() could still return
   // non-null in this case.
   //
   // Say you have a local scope that then refers to the const root scope from
   // the master build config. You can't change the values from the master
   // build config (it's read-only so it can be read from multiple threads
   // without locking). Read-only operations would work on values from the root
   // scope, but write operations would only work on values in the derived
@@ skipping 215 matching lines @@
 
   typedef std::set<ProgrammaticProvider*> ProviderSet;
   ProviderSet programmatic_providers_;
 
   SourceDir source_dir_;
 
   DISALLOW_COPY_AND_ASSIGN(Scope);
 };
 
 #endif  // TOOLS_GN_SCOPE_H_