AAPT2: Allow merging of Style attributes from overlays

Previously style overlays would completely override an existing style.
To be compatible with AAPT, styles now merge with the overlay, allowing
the overlay's attributes and parent to take precedence.

Bug: 38355988
Test: make aapt2_tests
Change-Id: Id25c7240050a43e6a4a177c6e3d51e048d0cceb5

1 files changed, 32 insertions, 0 deletions

diff --git a/tools/aapt2/ResourceValues_test.cpp b/tools/aapt2/ResourceValues_test.cpp
index 692258003471..e154d93b6f85 100644
--- a/tools/aapt2/ResourceValues_test.cpp
+++ b/tools/aapt2/ResourceValues_test.cpp
@@ -148,4 +148,36 @@ TEST(ResourceValuesTest, StyleClone) {
   EXPECT_TRUE(a->Equals(b.get()));
 }
 
+TEST(ResourceValuesTest, StyleMerges) {
+  StringPool pool_a;
+  StringPool pool_b;
+
+  std::unique_ptr<Style> a =
+      test::StyleBuilder()
+          .SetParent("android:style/Parent")
+          .AddItem("android:attr/a", util::make_unique<String>(pool_a.MakeRef("FooA")))
+          .AddItem("android:attr/b", util::make_unique<String>(pool_a.MakeRef("FooB")))
+          .Build();
+
+  std::unique_ptr<Style> b =
+      test::StyleBuilder()
+          .SetParent("android:style/OverlayParent")
+          .AddItem("android:attr/c", util::make_unique<String>(pool_b.MakeRef("OverlayFooC")))
+          .AddItem("android:attr/a", util::make_unique<String>(pool_b.MakeRef("OverlayFooA")))
+          .Build();
+
+  a->MergeWith(b.get(), &pool_a);
+
+  StringPool pool;
+  std::unique_ptr<Style> expected =
+      test::StyleBuilder()
+          .SetParent("android:style/OverlayParent")
+          .AddItem("android:attr/a", util::make_unique<String>(pool.MakeRef("OverlayFooA")))
+          .AddItem("android:attr/b", util::make_unique<String>(pool.MakeRef("FooB")))
+          .AddItem("android:attr/c", util::make_unique<String>(pool.MakeRef("OverlayFooC")))
+          .Build();
+
+  EXPECT_TRUE(a->Equals(expected.get()));
+}
+
 } // namespace aapt