[cfe-dev] Test Modules/macro-undef-through-pch.m causes internal error in llvm-lit

[Nagurne, James via cfe-dev]

This test, and a few others, dump what is essentially binary data to stdout. This data trips up the cmake-detected Python interpreter (2.7.6) and causes the following error with a check-all build of LLVM:

Traceback (most recent call last):
  File "<path>/llvm-lit", line 37, in <module>
    main(builtin_parameters)
  File "llvm/utils/lit/lit/main.py", line 193, in main
    main_with_tmp(builtinParameters)
  File "llvm/utils/lit/lit/main.py", line 540, in main_with_tmp
    write_test_results(run, litConfig, testing_time, opts.output_path)
  File "llvm/utils/lit/lit/main.py", line 153, in write_test_results
    json.dump(data, f, indent=2, sort_keys=True)
  File "/usr/lib/python2.7/json/__init__.py", line 189, in dump
    for chunk in iterable:
  File "/usr/lib/python2.7/json/encoder.py", line 434, in _iterencode
    for chunk in _iterencode_dict(o, _current_indent_level):
  File "/usr/lib/python2.7/json/encoder.py", line 408, in _iterencode_dict
    for chunk in chunks:
  File "/usr/lib/python2.7/json/encoder.py", line 332, in _iterencode_list
    for chunk in chunks:
  File "/usr/lib/python2.7/json/encoder.py", line 390, in _iterencode_dict
    yield _encoder(value)
UnicodeDecodeError: 'utf8' codec can't decode byte 0xce in position 2685: invalid continuation byte
ninja: build stopped: subcommand failed.

This test has existed in a similar format since it was committed 4 years ago.
I can reproduce this with the following directed llvm-lit invocation:
/path/to/llvm/bin/llvm-lit --output=a.json /path/to/clang/ --filter=macro-undef

Has anyone run into this issue before? It seems unlikely that no one has tried to dump the output of this test to a JSON file in 4 years, so I'm open to suggestions as to what I might be doing wrong.
Since the test does not attempt to use the result of the RUN, I have been able to 'fix' the issue with the following minor patch:

diff --git a/test/Modules/macro-undef-through-pch.m b/test/Modules/macro-undef-through-pch.m
index fc32229bec..c4ea3fb98a 100644
--- a/test/Modules/macro-undef-through-pch.m
+++ b/test/Modules/macro-undef-through-pch.m
@@ -3,7 +3,7 @@
// RUN:            -I%S/Inputs/macro-undef-through-pch -emit-pch \
// RUN:            %S/Inputs/macro-undef-through-pch/foo.h -o %t.pch
// RUN: %clang_cc1 -x objective-c -fmodules -fimplicit-module-maps -fmodules-cache-path=%t \
-// RUN:            -I%S/Inputs/macro-undef-through-pch -emit-pch \
+// RUN:            -I%S/Inputs/macro-undef-through-pch -emit-pch -o %t.dummy.pch \
// RUN:            -include-pch %t.pch %s
 // PR19215

Regards,
J.B. Nagurne
Code Generation
Texas Instruments
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