tools/aapt2/optimize/ResourceDeduper.cpp

/*
 * Copyright (C) 2016 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.
 */

#include "optimize/ResourceDeduper.h"

#include <algorithm>

#include "DominatorTree.h"
#include "ResourceTable.h"
#include "trace/TraceBuffer.h"

using android::ConfigDescription;

namespace aapt {

namespace {

/**
 * Remove duplicated key-value entries from dominated resources.
 *
 * Based on the dominator tree, we can remove a value of an entry if:
 *
 * 1. The configuration for the entry's value is dominated by a configuration
 *    with an equivalent entry value.
 * 2. All compatible configurations for the entry (those not in conflict and
 *    unrelated by domination with the configuration for the entry's value) have
 *    an equivalent entry value.
 */
class DominatedKeyValueRemover : public DominatorTree::BottomUpVisitor {
 public:
  using Node = DominatorTree::Node;

  explicit DominatedKeyValueRemover(IAaptContext* context, ResourceEntry* entry)
      : context_(context), entry_(entry) {}

  void VisitConfig(Node* node) {
    Node* parent = node->parent();
    if (!parent) {
      return;
    }
    ResourceConfigValue* node_value = node->value();
    ResourceConfigValue* parent_value = parent->value();
    if (!node_value || !parent_value) {
      return;
    }
    if (!node_value->value->Equals(parent_value->value.get())) {
      return;
    }

    // It is not safe to remove a value when both screenWidthDp and screenHeightDp are defined on
    // the node unless they are the same width and height. This is because there could
    // be a third value C not in this hierarchy and there are values that should match the current
    // node but if we remove the value they will instead match C. This is because domination is
    // determined first by width and then height but runtime matching is both at the same time
    // (b/414775283). For example, say we had A with config w600dp-h800dp and value foo, B with
    // config w800dp-h1000dp and value foo, and C with config w500dp-h1200dp and value bar. A would
    // dominate B but C would neither dominate nor me dominated by either A or B. If we removed
    // the B value there would be some screen sizes like w800dp-h1200dp that should have gotten foo
    // but now get bar.
    if (node_value->config.screenWidthDp && node_value->config.screenHeightDp &&
        node_value->config.screenSizeDp != parent_value->config.screenSizeDp) {
      return;
    }

    // Compare compatible configs for this entry and ensure the values are
    // equivalent.
    const ConfigDescription& node_configuration = node_value->config;
    for (const auto& sibling : parent->children()) {
      ResourceConfigValue* sibling_value = sibling->value();
      if (!sibling_value->value) {
        // Sibling was already removed.
        continue;
      }
      if (node_configuration.IsCompatibleWith(sibling_value->config) &&
          !node_value->value->Equals(sibling_value->value.get())) {
        // The configurations are compatible, but the value is
        // different, so we can't remove this value.
        return;
      }
    }
    if (context_->IsVerbose()) {
      context_->GetDiagnostics()->Note(android::DiagMessage(node_value->value->GetSource())
                                       << "removing dominated duplicate resource with name \""
                                       << entry_->name << "\"");
      context_->GetDiagnostics()->Note(android::DiagMessage(parent_value->value->GetSource())
                                       << "dominated here");
    }
    node_value->value = {};
  }

 private:
  DISALLOW_COPY_AND_ASSIGN(DominatedKeyValueRemover);

  IAaptContext* context_;
  ResourceEntry* entry_;
};

static void DedupeEntry(IAaptContext* context, ResourceEntry* entry) {
  DominatorTree tree(entry->values);
  DominatedKeyValueRemover remover(context, entry);
  tree.Accept(&remover);

  // Erase the values that were removed.
  entry->values.erase(
      std::remove_if(
          entry->values.begin(), entry->values.end(),
          [](const std::unique_ptr<ResourceConfigValue>& val) -> bool {
            return val == nullptr || val->value == nullptr;
          }),
      entry->values.end());
}

}  // namespace

bool ResourceDeduper::Consume(IAaptContext* context, ResourceTable* table) {
  TRACE_CALL();
  for (auto& package : table->packages) {
    for (auto& type : package->types) {
      for (auto& entry : type->entries) {
        DedupeEntry(context, entry.get());
      }
    }
  }
  return true;
}

}  // namespace aapt