system('foo &', 'bar'): Show error, don't crash.

Closes #3529
Closes #5241

In Vim,
    :echo system('cat - &', 'foo')
works because for both system() and :! Vim writes input to a temp file and uses
shell syntax to redirect the file to the backgrounded `cat` (get_cmd_output()
.. make_filter_cmd()).

In Nvim,
    :echo system('cat - &', 'foo')
fails because we write the input directly via pipes (shell.c:do_os_system()),
but (per POSIX[1]) backgrounded process input stream is redirected from
/dev/null (unless overridden by shell redirection; supported only by some shells
[2]), so our writes are ignored, the process exits quickly, and if we are
writing data larger than the buffer size we'll see EPIPE.

This still works:
    :%w !tee > foo1358.txt &
but this does not:
    :%w !tee foo1358.txt &
though it *should* (why doesn't it?) because we still do the temp file dance
in do_bang() .. do_filter().

[1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_03_02
[2] http://unix.stackexchange.com/a/71218

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/event/rstream.c b/src/nvim/event/rstream.c
index 5126dfd84e..92efc9fa2e 100644
--- a/src/nvim/event/rstream.c
+++ b/src/nvim/event/rstream.c
@@ -112,8 +112,8 @@ static void read_cb(uv_stream_t *uvstream, ssize_t cnt, const uv_buf_t *buf)
         // to `alloc_cb` will return the same unused pointer(`rbuffer_produced`
         // won't be called)
         && cnt != 0) {
-      DLOG("Closing Stream(%p) because of %s(%zd)", stream,
-           uv_strerror((int)cnt), cnt);
+      DLOG("Closing Stream (%p): %s (%s)", stream,
+           uv_err_name((int)cnt), os_strerror((int)cnt));
       // Read error or EOF, either way stop the stream and invoke the callback
       // with eof == true
       uv_read_stop(uvstream);