AAPT2: whitelist alphanums instead of blacklisting hyphens in package names.

BCP 47 uses plus signs for name mangling, and future qualifiers may
start using other reserved characters as well, so we might as well
futureproof the sanitizer.

Change-Id: I1be7ee4234f8e30bb0ea832372b4dc932d30550c
Fixes: 69134786
Test: UtilTest.SplitNamesAreSanitized
diff --git a/tools/aapt2/cmd/Util.cpp b/tools/aapt2/cmd/Util.cpp
index d39f43e..8b3a670 100644
--- a/tools/aapt2/cmd/Util.cpp
+++ b/tools/aapt2/cmd/Util.cpp
@@ -140,12 +140,27 @@
   return decl;
 }
 
+// Returns a copy of 'name' which conforms to the regex '[a-zA-Z]+[a-zA-Z0-9_]*' by
+// replacing nonconforming characters with underscores.
+//
+// See frameworks/base/core/java/android/content/pm/PackageParser.java which
+// checks this at runtime.
 static std::string MakePackageSafeName(const std::string &name) {
   std::string result(name);
+  bool first = true;
   for (char &c : result) {
-    if (c == '-') {
-      c = '_';
+    if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
+      first = false;
+      continue;
     }
+    if (!first) {
+      if (c >= '0' && c <= '9') {
+        continue;
+      }
+    }
+
+    c = '_';
+    first = false;
   }
   return result;
 }