$ buck build app
[-] PARSING BUILD FILES...FINISHED 0.2s
[+] BUILDING...0.6s
 |=> IDLE
 |=> IDLE
 |=> IDLE
 |=> IDLE
 |=> //apps/myapp:app#uber_r_dot_java...  0.6s (running dx[0.1s])
 |=> IDLE
Log:

trouble processing:
bad class file magic (cafebabe) or version (0033.0000)
...while parsing com/example/R$attr.class
...while processing com/example/R$attr.class

trouble processing:
bad class file magic (cafebabe) or version (0033.0000)
...while parsing com/example/R$string.class
...while processing com/example/R$string.class

trouble processing:
bad class file magic (cafebabe) or version (0033.0000)
...while parsing com/example/R.class
...while processing com/example/R.class
3 warnings
no classfiles specified
BUILD FAILED: //apps/myapp:app#uber_r_dot_java failed with exit code 1:
dx