[ylluminate]

py2v file.py printed nothing and exited 1 when the Python frontend failed, for example on a file with a syntax error or a path that doesn't exist. The frontend does print a message, but os.exec_opt returns an error when the command exits non-zero, and main handled that with or { exit(1) }, so the block right below it that prints the output was never reached.

Now the error is printed:

$ py2v missing.py
Error running Python frontend:
Error: File 'missing.py' does not exist.

and a syntax error prints SyntaxError in 'bad.py': invalid syntax (bad.py, line 1) the same way. --package already reported a syntax error in a file it translates.

Fixes #5. That issue is only a title, "Add error handling", and this silent exit is what I found missing when I went through py2v's failure paths for it.

Test plan

• Two new checks in tests/run_tests.vsh, a file with a syntax error and a file that doesn't exist: both fail with master's py2v and pass with this change.
• v tests/run_tests.vsh: 174 passed, 0 failed (172 before, plus the two checks).