[res] Simplify XmlPullParser::FindAttribute() and StringPool::Sort

1. FindAttribute used to do lots of work that C++17 does
   automatically

2. Use function_ref for a more efficient callback passing

Test: aapt2_tests
Flag: EXEMPT minor refactor
Change-Id: I4f172cca16c05422992b107e347ed01479fff898

4 files changed, 33 insertions, 45 deletions

diff --git a/libs/androidfw/StringPool.cpp b/libs/androidfw/StringPool.cpp
index ad445c042e63..629f14683b19 100644
--- a/libs/androidfw/StringPool.cpp
+++ b/libs/androidfw/StringPool.cpp
@@ -297,24 +297,22 @@ void StringPool::Prune() {
 template <typename E>
 static void SortEntries(
     std::vector<std::unique_ptr<E>>& entries,
-    const std::function<int(const StringPool::Context&, const StringPool::Context&)>& cmp) {
+    base::function_ref<int(const StringPool::Context&, const StringPool::Context&)> cmp) {
   using UEntry = std::unique_ptr<E>;
+  std::sort(entries.begin(), entries.end(), [cmp](const UEntry& a, const UEntry& b) -> bool {
+    int r = cmp(a->context, b->context);
+    if (r == 0) {
+      r = a->value.compare(b->value);
+    }
+    return r < 0;
+  });
+}
 
-  if (cmp != nullptr) {
-    std::sort(entries.begin(), entries.end(), [&cmp](const UEntry& a, const UEntry& b) -> bool {
-      int r = cmp(a->context, b->context);
-      if (r == 0) {
-        r = a->value.compare(b->value);
-      }
-      return r < 0;
-    });
-  } else {
-    std::sort(entries.begin(), entries.end(),
-              [](const UEntry& a, const UEntry& b) -> bool { return a->value < b->value; });
-  }
+void StringPool::Sort() {
+  Sort([](auto&&, auto&&) { return 0; });
 }
 
-void StringPool::Sort(const std::function<int(const Context&, const Context&)>& cmp) {
+void StringPool::Sort(base::function_ref<int(const Context&, const Context&)> cmp) {
   SortEntries(styles_, cmp);
   SortEntries(strings_, cmp);
   ReAssignIndices();
diff --git a/libs/androidfw/include/androidfw/StringPool.h b/libs/androidfw/include/androidfw/StringPool.h
index 0190ab57bf23..9b2c72a29f48 100644
--- a/libs/androidfw/include/androidfw/StringPool.h
+++ b/libs/androidfw/include/androidfw/StringPool.h
@@ -17,7 +17,6 @@
 #ifndef _ANDROID_STRING_POOL_H
 #define _ANDROID_STRING_POOL_H
 
-#include <functional>
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ -25,6 +24,7 @@
 
 #include "BigBuffer.h"
 #include "IDiagnostics.h"
+#include "android-base/function_ref.h"
 #include "android-base/macros.h"
 #include "androidfw/ConfigDescription.h"
 #include "androidfw/StringPiece.h"
@@ -205,7 +205,8 @@ class StringPool {
   // Sorts the strings according to their Context using some comparison function.
   // Equal Contexts are further sorted by string value, lexicographically.
   // If no comparison function is provided, values are only sorted lexicographically.
-  void Sort(const std::function<int(const Context&, const Context&)>& cmp = nullptr);
+  void Sort();
+  void Sort(base::function_ref<int(const Context&, const Context&)> cmp);
 
   // Removes any strings that have no references.
   void Prune();
diff --git a/tools/aapt2/xml/XmlPullParser.cpp b/tools/aapt2/xml/XmlPullParser.cpp
index 203832d2dbe8..8abc26d67c1f 100644
--- a/tools/aapt2/xml/XmlPullParser.cpp
+++ b/tools/aapt2/xml/XmlPullParser.cpp
@@ -14,11 +14,13 @@
  * limitations under the License.
  */
 
-#include <iostream>
+#include "xml/XmlPullParser.h"
+
+#include <algorithm>
 #include <string>
+#include <tuple>
 
 #include "util/Util.h"
-#include "xml/XmlPullParser.h"
 #include "xml/XmlUtil.h"
 
 using ::android::InputStream;
@@ -325,5 +327,18 @@ std::optional<StringPiece> FindNonEmptyAttribute(const XmlPullParser* parser, St
   return {};
 }
 
+XmlPullParser::const_iterator XmlPullParser::FindAttribute(android::StringPiece namespace_uri,
+                                                           android::StringPiece name) const {
+  const auto end_iter = end_attributes();
+  const auto iter = std::lower_bound(begin_attributes(), end_iter, std::tuple(namespace_uri, name),
+                                     [](const Attribute& attr, const auto& rhs) {
+                                       return std::tie(attr.namespace_uri, attr.name) < rhs;
+                                     });
+  if (iter != end_iter && namespace_uri == iter->namespace_uri && name == iter->name) {
+    return iter;
+  }
+  return end_iter;
+}
+
 }  // namespace xml
 }  // namespace aapt
diff --git a/tools/aapt2/xml/XmlPullParser.h b/tools/aapt2/xml/XmlPullParser.h
index 655e6dc93e75..64274d032c61 100644
--- a/tools/aapt2/xml/XmlPullParser.h
+++ b/tools/aapt2/xml/XmlPullParser.h
@@ -19,8 +19,7 @@
 
 #include <expat.h>
 
-#include <algorithm>
-#include <istream>
+#include <optional>
 #include <ostream>
 #include <queue>
 #include <stack>
@@ -302,31 +301,6 @@ inline bool XmlPullParser::Attribute::operator!=(const Attribute& rhs) const {
   return compare(rhs) != 0;
 }
 
-inline XmlPullParser::const_iterator XmlPullParser::FindAttribute(
-    android::StringPiece namespace_uri, android::StringPiece name) const {
-  const auto end_iter = end_attributes();
-  const auto iter = std::lower_bound(
-      begin_attributes(), end_iter,
-      std::pair<android::StringPiece, android::StringPiece>(namespace_uri, name),
-      [](const Attribute& attr,
-         const std::pair<android::StringPiece, android::StringPiece>& rhs) -> bool {
-        int cmp = attr.namespace_uri.compare(
-            0, attr.namespace_uri.size(), rhs.first.data(), rhs.first.size());
-        if (cmp < 0) return true;
-        if (cmp > 0) return false;
-        cmp = attr.name.compare(0, attr.name.size(), rhs.second.data(),
-                                rhs.second.size());
-        if (cmp < 0) return true;
-        return false;
-      });
-
-  if (iter != end_iter && namespace_uri == iter->namespace_uri &&
-      name == iter->name) {
-    return iter;
-  }
-  return end_iter;
-}
-
 }  // namespace xml
 }  // namespace aapt