Improve linker_verbose_tracking.py

tools/win/linker_verbose_tracking.py

 # Copyright (c) 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 This script parses the /verbose output from the VC++ linker and uses it to
 explain why a particular object file is being linked in. It parses records
 like these:
 
       Found "public: static void * __cdecl SkTLS::Get(void * (__cdecl*)(void)...
@@ skipping 32 matching lines @@
 
 stream_decoder.obj pulled in for symbol "_FLAC__stream_decoder_new" by
         stream_encoder.obj
 bitwriter.obj pulled in for symbol "_FLAC__bitwriter_new" by
         stream_encoder.obj
 
 stream_encoder.obj pulled in for symbol "_FLAC__stream_encoder_new" by
         Command-line obj file: audio_encoder.obj
 """
 
+import io
 import pdb
 import re
 import sys
 
 def ParseVerbose(input_file):
   # This matches line like this:
   #   Referenced in skia.lib(SkError.obj)
   # with the groups()[0] referring to the object file name without the file
   # extension.
   obj_match = re.compile('.*\((.*)\.obj\)')
   # Prefix used for symbols that are referenced:
   found_prefix = '      Found'
 
   cross_refs = {}
   cross_refed_symbols = {}
 
   references = None
-  for line in open(input_file):
-    if line.startswith(found_prefix):
-      references = []
-      # Grab the symbol name
-      symbol = line[len(found_prefix):].strip()
-      if symbol[0] == '"':
-        # Strip off leading and trailing quotes if present.
-        symbol = symbol[1:-1]
-      continue
-    if type(references) == type([]):
-      sub_line = line.strip()
-      match = obj_match.match(sub_line)
-      # See if the line is part of the list of places where this symbol was
-      # referenced
-      if sub_line.count('Referenced ') > 0:
-        if match:
-          # This indicates a match that is xxx.lib(yyy.obj), so a referencing
-          # .obj file that was itself inside of a library. We discard the
-          # library name.
-          reference = match.groups()[0]
-        else:
-          # This indicates a match that is just a pure .obj file name
-          # I think this means that the .obj file was specified on the linker
-          # command line.
-          reference = ('Command-line obj file: ' +
-                       sub_line[len('Referenced in '): -len('.obj')])
-        references.append(reference)
-      elif sub_line.count('Loaded ') > 0:
-        if match:
-          loaded = match.groups()[0]
-          cross_refs[loaded] = references
-          cross_refed_symbols[loaded] = symbol
-        references = None
-    if line.startswith('Finished pass 1'):
-      # Stop now because the remaining 90% of the verbose output is
-      # not of interest. Could probably use /VERBOSE:REF to trim out
-      # boring information.
-      break
+  # When you redirect the linker output to a file from a command prompt the
+  # result will be a utf-8 (or ASCII?) output file. However if you do the same
+  # thing from PowerShell you get a utf-16 file. So, we need to handle both
+  # options. Only the first BOM option (\xff\xfe) has been tested, but it seems
+  # appropriate to handle the other as well.
+  file_encoding = 'utf-8'
+  with open(input_file) as file_handle:
+    header = file_handle.read(2)
+    if header == '\xff\xfe' or header == '\xfe\xff':
+      file_encoding = 'utf-16'
+  with io.open(input_file, encoding=file_encoding) as file_handle:
+    for line in file_handle:
+      if line.startswith(found_prefix):
+        references = []
+        # Grab the symbol name
+        symbol = line[len(found_prefix):].strip()
+        if symbol[0] == '"':
+          # Strip off leading and trailing quotes if present.
+          symbol = symbol[1:-1]
+        continue
+      if type(references) == type([]):
+        sub_line = line.strip()
+        match = obj_match.match(sub_line)
+        # See if the line is part of the list of places where this symbol was
+        # referenced
+        if sub_line.count('Referenced ') > 0:
+          if match:
+            # This indicates a match that is xxx.lib(yyy.obj), so a referencing
+            # .obj file that was itself inside of a library. We discard the
+            # library name.
+            reference = match.groups()[0]
+          else:
+            # This indicates a match that is just a pure .obj file name
+            # I think this means that the .obj file was specified on the linker
+            # command line.
+            reference = ('Command-line obj file: ' +
+                         sub_line[len('Referenced in '): -len('.obj')])
+          references.append(reference)
+        elif sub_line.count('Loaded ') > 0:
+          if match:
+            loaded = match.groups()[0]
+            cross_refs[loaded] = references
+            cross_refed_symbols[loaded] = symbol
+          references = None
+      if line.startswith('Finished pass 1'):
+        # Stop now because the remaining 90% of the verbose output is
+        # not of interest. Could probably use /VERBOSE:REF to trim out
+        # boring information.
+        break
   return cross_refs, cross_refed_symbols
 
 
 def TrackObj(cross_refs, cross_refed_symbols, obj_name):
   if obj_name.lower().endswith('.obj'):
     obj_name = obj_name[:-len('.obj')]
 
   # Keep track of which references we've already followed.
   tracked = {}
 
@@ skipping 10 matching lines @@
           printed = True
           print '%s.obj pulled in for symbol "%s" by' % (target, symbol)
           for ref in cross_refs[target]:
             print '\t%s.obj' % ref
             new_targets[ref] = True
     if len(new_targets) == 0:
       break
     print
     targets = new_targets.keys()
   if not printed:
-    print 'No references to %s.obj found.' % obj_name
+    print ('No references to %s.obj found. Directly specified in sources or a '
+          'source_set?' % obj_name)
 
 
 def main():
   if len(sys.argv) < 3:
     print r'Usage: %s <verbose_output_file> <objfile>' % sys.argv[0]
     print r'Sample: %s chrome_dll_verbose.txt SkTLS' % sys.argv[0]
     return 0
   cross_refs, cross_refed_symbols = ParseVerbose(sys.argv[1])
   print 'Database loaded - %d xrefs found' % len(cross_refs)
+  if not len(cross_refs):
+    print 'No data found to analyze. Exiting'
+    return 0
   TrackObj(cross_refs, cross_refed_symbols, sys.argv[2])
 
 if __name__ == '__main__':
   sys.exit(main())