Aapt2 ValueTransformer
For future macro support, aapt2 must be able to convert Reference
values into other Value types. Currently a DescendingValueVisitor is
used to visit all of the References in a ResourceTable or a compiled
XML file to set their resource ids during the link phase. This was fine
since we were only mutating the resource id of the visited Reference.
A macro may reference a String, BinaryPrimitive, or any other Item
type. During the link phase, we will need to transform references to
macros into the values of the macros.
The only parameter in the methods of the ValueVisitor interface is a
raw pointer to the type being visited. The visitor interface does not
support reassigning the visited type to a different type.
ValueTransformer is a new interface for consuming a Value type and
transforming it into a compatible Value type. This change refactors
Value::Clone to use this interface.
Bug: 175616308
Test: aapt2_tests
Change-Id: Ic1b9d718b932c208764114cd9c74d880e189ccb0
diff --git a/tools/aapt2/ValueTransformer.h b/tools/aapt2/ValueTransformer.h
new file mode 100644
index 0000000..6925111
--- /dev/null
+++ b/tools/aapt2/ValueTransformer.h
@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2021 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 AAPT_VALUE_TRANSFORMER_H
+#define AAPT_VALUE_TRANSFORMER_H
+
+#include <memory>
+
+#include "StringPool.h"
+
+namespace aapt {
+
+class Value;
+struct Item;
+struct Reference;
+struct Id;
+struct RawString;
+struct String;
+struct StyledString;
+struct FileReference;
+struct BinaryPrimitive;
+struct Attribute;
+struct Style;
+struct Array;
+struct Plural;
+struct Styleable;
+
+#define AAPT_TRANSFORM_VALUE(T) \
+ virtual std::unique_ptr<T> TransformDerived(const T* value) = 0; \
+ virtual std::unique_ptr<Value> TransformValue(const T* value);
+
+#define AAPT_TRANSFORM_ITEM(T) \
+ virtual std::unique_ptr<Item> TransformItem(const T* value); \
+ AAPT_TRANSFORM_VALUE(T)
+
+/**
+ * An interface for consuming a Value type and transforming it into another Value.
+ *
+ * The interface defines 2 methods for each type (T) that inherits from TransformableValue:
+ * std::unique_ptr<T> TransformDerived(const T*)
+ * std::unique_ptr<Value> TransformValue(const T*)
+ *
+ * The interface defines 3 method for each type (T) that inherits from TransformableItem:
+ * std::unique_ptr<T> TransformDerived(const T*)
+ * std::unique_ptr<Item> TransformItem(const T*)
+ * std::unique_ptr<Value> TransformValue(const T*)
+ *
+ * TransformDerived is invoked when Transform is invoked on the derived type T.
+ * TransformItem is invoked when Transform is invoked on an Item type.
+ * TransformValue is invoked when Transform is invoked on a Value type.
+ *
+ * ValueTransformerImpl transformer(&string_pool);
+ * T* derived = ...;
+ * std::unique_ptr<T> new_type = derived->Transform(transformer); // Invokes TransformDerived
+ *
+ * Item* item = derived;
+ * std::unique_ptr<Item> new_item = item->TransformItem(transformer); // Invokes TransformItem
+ *
+ * Value* value = item;
+ * std::unique_ptr<Value> new_value = value->TransformValue(transformer); // Invokes TransformValue
+ *
+ * For types that inherit from AbstractTransformableItem, the default implementation of
+ * TransformValue invokes TransformItem which invokes TransformDerived.
+ *
+ * For types that inherit from AbstractTransformableValue, the default implementation of
+ * TransformValue invokes TransformDerived.
+ */
+struct ValueTransformer {
+ // `new_pool` is the new StringPool that newly created Values should use for string storing string
+ // values.
+ explicit ValueTransformer(StringPool* new_pool);
+ virtual ~ValueTransformer() = default;
+
+ AAPT_TRANSFORM_ITEM(Id);
+ AAPT_TRANSFORM_ITEM(Reference);
+ AAPT_TRANSFORM_ITEM(RawString);
+ AAPT_TRANSFORM_ITEM(String);
+ AAPT_TRANSFORM_ITEM(StyledString);
+ AAPT_TRANSFORM_ITEM(FileReference);
+ AAPT_TRANSFORM_ITEM(BinaryPrimitive);
+
+ AAPT_TRANSFORM_VALUE(Attribute);
+ AAPT_TRANSFORM_VALUE(Style);
+ AAPT_TRANSFORM_VALUE(Array);
+ AAPT_TRANSFORM_VALUE(Plural);
+ AAPT_TRANSFORM_VALUE(Styleable);
+
+ protected:
+ StringPool* const pool_;
+};
+
+#undef AAPT_TRANSFORM_VALUE
+#undef AAPT_TRANSFORM_ITEM
+
+template <typename Derived, typename Base>
+struct TransformableValue : public Base {
+ // Transform this Derived into another Derived using the transformer.
+ std::unique_ptr<Derived> Transform(ValueTransformer& transformer) const;
+
+ private:
+ Value* TransformValueImpl(ValueTransformer& transformer) const override;
+};
+
+template <typename Derived, typename Base>
+struct TransformableItem : public TransformableValue<Derived, Base> {
+ private:
+ Item* TransformItemImpl(ValueTransformer& transformer) const override;
+};
+
+} // namespace aapt
+
+// Implementation
+#include "ValueTransformer_inline.h"
+
+#endif // AAPT_VALUE_TRANSFORMER_H
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