warn on duplicate entries in archives; #2619

tools/shared.py

@@ -1254,6 +1254,17 @@ def get_archive_contents(f):
         safe_ensure_dirs(temp_dir)
         os.chdir(temp_dir)
         contents = filter(lambda x: len(x) > 0, Popen([LLVM_AR, 't', f], stdout=PIPE).communicate()[0].split('\n'))
+        # llvm-ar appears to just use basenames inside archives. as a result, files with the same basename
+        # will trample each other when we extract them. to help warn of such situations, we warn if there
+        # are duplicate entries in the archive
+        if len(contents) != len(set(contents)):
+          logging.warning('loading from archive %s, which has duplicate entries (files with identical names). this is dangerous as only the last will be taken into account, and you may see surprising undefined symbols later. run |llvm-ar t archive.a| to see the list of entries' % f)
+          warned = set()
+          for i in range(len(contents)):
+            curr = contents[i]
+            if curr not in warned and curr in contents[i+1:]:
+              logging.warning('   duplicate: %s' % curr)
+              warned.add(curr)
         if len(contents) == 0:
           logging.debug('Archive %s appears to be empty (recommendation: link an .so instead of .a)' % f)
         else: