[view-compiler] Add layout validation

Layout validation walks over a layout resource and verifies that the layout only
uses features the layout compiler supports.

Currently this means we reject layouts that use any of the following tags:
  * include
  * fragment
  * merge
  * view

In the future, we will extend the layout compiler to handle these, but for now
we want to be liberal in what we reject.

Bug: 111895153
Test: atest view-compiler-tests
Change-Id: I8dca30c035a83b6763497a36fc60c68438fa1b0c

1 files changed, 46 insertions, 0 deletions

diff --git a/startop/view_compiler/layout_validation.h b/startop/view_compiler/layout_validation.h
new file mode 100644
index 000000000000..bed34bb38e5e
--- /dev/null
+++ b/startop/view_compiler/layout_validation.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef LAYOUT_VALIDATION_H_
+#define LAYOUT_VALIDATION_H_
+
+#include "dex_builder.h"
+
+#include <string>
+
+namespace startop {
+
+// This visitor determines whether a layout can be compiled. Since we do not currently support all
+// features, such as includes and merges, we need to pre-validate the layout before we start
+// compiling.
+class LayoutValidationVisitor {
+ public:
+  void VisitStartDocument() const {}
+  void VisitEndDocument() const {}
+  void VisitStartTag(const std::u16string& name);
+  void VisitEndTag() const {}
+
+  const std::string& message() const { return message_; }
+  bool can_compile() const { return can_compile_; }
+
+ private:
+  std::string message_{"Okay"};
+  bool can_compile_{true};
+};
+
+}  // namespace startop
+
+#endif  // LAYOUT_VALIDATION_H_