decodetree: Open files with encoding='utf-8'

When decodetree.py was added in commit 568ae7efae7, QEMU was
using Python 2 which happily reads UTF-8 files in text mode.
Python 3 requires either UTF-8 locale or an explicit encoding
passed to open(). Now that Python 3 is required, explicit
UTF-8 encoding for decodetree source files.

To avoid further problems with the user locale, also explicit
UTF-8 encoding for the generated C files.

Explicit both input/output are plain text by using the 't' mode.

This fixes:

  $ /usr/bin/python3 scripts/decodetree.py test.decode
  Traceback (most recent call last):
    File "scripts/decodetree.py", line 1397, in <module>
      main()
    File "scripts/decodetree.py", line 1308, in main
      parse_file(f, toppat)
    File "scripts/decodetree.py", line 994, in parse_file
      for line in f:
    File "/usr/lib/python3.6/encodings/ascii.py", line 26, in decode
      return codecs.ascii_decode(input, self.errors)[0]
  UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 80:
  ordinal not in range(128)

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Suggested-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210110000240.761122-1-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

scripts/decodetree.py

@@ -20,6 +20,7 @@
 # See the syntax and semantics in docs/devel/decodetree.rst.
 #
 
+import io
 import os
 import re
 import sys
@@ -1304,7 +1305,7 @@ def main():
 
     for filename in args:
         input_file = filename
-        f = open(filename, 'r')
+        f = open(filename, 'rt', encoding='utf-8')
         parse_file(f, toppat)
         f.close()
 
@@ -1324,9 +1325,11 @@ def main():
         prop_size(stree)
 
     if output_file:
-        output_fd = open(output_file, 'w')
+        output_fd = open(output_file, 'wt', encoding='utf-8')
     else:
-        output_fd = sys.stdout
+        output_fd = io.TextIOWrapper(sys.stdout.buffer,
+                                     encoding=sys.stdout.encoding,
+                                     errors="ignore")
 
     output_autogen()
     for n in sorted(arguments.keys()):