This change improves our output formatting by generally adding
fewer prefixes. As shown in pulumi/pulumi#359, we were being
excessively verbose in many places, including prefixing every
console.out with "langhost[nodejs].stdout: ", displaying full
stack traces for simple errors like missing configuration, etc.
Overall, this change includes the following:
* Don't prefix stdout and stderr output from the program, other
than the standard "info:" prefix. I experimented with various
schemes here, but they all felt gratuitous. Simply emitting
the output seems fine, especially as it's closer to what would
happen if you just ran the program under node.
* Do NOT make writes to stderr fail the plan/deploy. Previously
we assumed that any console.errors, for instance, meant that
the overall program should fail. This simply isn't how stderr
is treated generally and meant you couldn't use certain
logging techniques and libraries, among other things.
* Do make sure that stderr writes in the program end up going to
stderr in the Pulumi CLI output, however, so that redirection
works as it should. This required a new Infoerr log level.
* Make a small fix to the planning logic so we don't attempt to
print the summary if an error occurs.
* Finally, add a new error type, RunError, that when thrown and
uncaught does not result in a full stack trace being printed.
Anyone can use this, however, we currently use it for config
errors so that we can terminate with a pretty error message,
rather than the monstrosity shown in pulumi/pulumi#359.
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