Remove /system/etc/prop.default

Contents that were in /system/etc/prop.default are now in
/system/build.prop.

The content is placed at the top of build.prop to keep the existing
order between the two files.

Caveat #1: /prop.default still remains for non-Treble devices.

Caveat #2: ReadFileSymbolicLink test was changed to read /system/bin/ps
because /prop.default is no longer guaranteed to exist.

Bug: 117892318
Test: TH passes
Test: inspect  /system/build.prop and check if it has contents from
the old /system/etc/prop.default file

Change-Id: I0d3f96c1656dfe02bfa0e801680f7fa887afd1d9
diff --git a/init/property_service.cpp b/init/property_service.cpp
index 2fea8a3..f9a94d7 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -877,18 +877,19 @@
 }
 
 void PropertyLoadBootDefaults() {
-    // TODO(b/117892318): merge prop.default and build.prop files into one
     // We read the properties and their values into a map, in order to always allow properties
     // loaded in the later property files to override the properties in loaded in the earlier
     // property files, regardless of if they are "ro." properties or not.
     std::map<std::string, std::string> properties;
-    if (!load_properties_from_file("/system/etc/prop.default", nullptr, &properties)) {
-        // Try recovery path
-        if (!load_properties_from_file("/prop.default", nullptr, &properties)) {
-            // Try legacy path
-            load_properties_from_file("/default.prop", nullptr, &properties);
-        }
+
+    if (IsRecoveryMode()) {
+        load_properties_from_file("/prop.default", nullptr, &properties);
     }
+
+    // Try legacy (non-Treble) path. This file might not exist in most of the
+    // post-Oreo devices. Absence of the file is not an error.
+    load_properties_from_file("/default.prop", nullptr, &properties);
+
     load_properties_from_file("/system/build.prop", nullptr, &properties);
     load_properties_from_file("/system_ext/build.prop", nullptr, &properties);
 
diff --git a/init/util_test.cpp b/init/util_test.cpp
index 96a5b55..565e7d4 100644
--- a/init/util_test.cpp
+++ b/init/util_test.cpp
@@ -61,8 +61,8 @@
 
 TEST(util, ReadFileSymbolicLink) {
     errno = 0;
-    // lrw------- 1 root root 23 2008-12-31 19:00 default.prop -> system/etc/prop.default
-    auto file_contents = ReadFile("/default.prop");
+    // lrwxr-xr-x 1 root shell 6 2009-01-01 09:00 /system/bin/ps -> toybox
+    auto file_contents = ReadFile("/system/bin/ps");
     EXPECT_EQ(ELOOP, errno);
     ASSERT_FALSE(file_contents.ok());
     EXPECT_EQ("open() failed: Too many symbolic links encountered",