[LLVMdev] Behaviour of outs()?

[Reid Kleckner]

We've had this argument before. IMO LLVM should not be in the business of
closing stdout, and no code in lib/ should print to stdout because users
may expect output there (-o -).

On Fri, Jan 23, 2015 at 10:20 AM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> > On 2015-Jan-23, at 09:52, mats petersson <mats at planetcatfish.com> wrote:
> >
> > I was just fixing a bug that was caused by `stdout` being closed
> > before the runtime has done `fflush(stdout)` [or however this is
> > implemented in the runtime].
> >
> > The cause of this seems to be that `outs()` returns a static object
> > created from `raw_fd_stream(STDOUT_FILENO, true)` - the `true` being
> > the `shouldClose` parameter.
> >
> > Surely LLVM is not supposed to close `stdout` as part of its operations?
>
> Looks like this was added in r111643:
>
> commit 5d56d9df928c48571980efe8d4205de8ab557b7c
> Author: Dan Gohman <gohman at apple.com>
> Date:   Fri Aug 20 16:44:56 2010 +0000
>
>     Make outs() close its file when its stream is destructed, so that
>     pending output errors are detected.
>
>
>     git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111643
> 91177308-0d34-0410-b5e6-96231b3b80d8
>
> Certainly looks intentional.  Comment in the code is:
>
>     // Delete the file descriptor when the program exits, forcing error
>     // detection. If you don't want this behavior, don't use outs().
>
> I don't really have an opinion on whether this is a good idea, but it
> does suggest that any use of `outs()` in `lib/` is a bug.
>
> $ git grep -l 'outs()' -- lib/
> lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp
> lib/IR/GCOV.cpp
> lib/Support/CommandLine.cpp
> lib/Support/FormattedStream.cpp
> lib/Support/TargetRegistry.cpp
> lib/Support/raw_ostream.cpp
> lib/Target/CppBackend/CPPBackend.cpp
>
> All of these cases seem to be for outputting help text of some sort.  But
> probably they should be passed a reference to a `raw_ostream`, so that the
> caller gets to choose whether or not to use `outs()`.
>
> Were you hitting one of these?
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