Allow GN imports to be processed from imports.

tools/gn/scope_unittest.cc

+// 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.
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/input_file.h"
+#include "tools/gn/parse_tree.h"
+#include "tools/gn/scope.h"
+#include "tools/gn/test_with_scope.h"
+
+TEST(Scope, NonRecursiveMergeTo) {
+  TestWithScope setup;
+
+  // Make a pretend parse node with proper tracking that we can blame for the
+  // given value.
+  InputFile input_file(SourceFile("//foo"));
+  Token assignment_token(Location(&input_file, 1, 1), Token::STRING,
+      "\"hello\"");
+  LiteralNode assignment;
+  assignment.set_value(assignment_token);
+
+  Value old_value(&assignment, "hello");
+  setup.scope()->SetValue("v", old_value, &assignment);
+
+  // Detect collisions of values' values.
+  {
+    Scope new_scope(setup.settings());
+    Value new_value(&assignment, "goodbye");
+    new_scope.SetValue("v", new_value, &assignment);
+
+    Err err;
+    EXPECT_FALSE(new_scope.NonRecursiveMergeTo(
+        setup.scope(), &assignment, "error", &err));
+    EXPECT_TRUE(err.has_error());
+  }
+
+  // Don't flag values that technically collide but have the same value.
+  {
+    Scope new_scope(setup.settings());
+    Value new_value(&assignment, "hello");
+    new_scope.SetValue("v", new_value, &assignment);
+
+    Err err;
+    EXPECT_TRUE(new_scope.NonRecursiveMergeTo(
+        setup.scope(), &assignment, "error", &err));
+    EXPECT_FALSE(err.has_error());
+  }
+}