procutil: make stream detection in make_line_buffered more correct and strict In make_line_buffered(), we don’t want to wrap the stream if we know that lines get flushed to the underlying raw stream already. Previously, the heuristic was too optimistic. It assumed that any stream which is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there are buffered streams that aren’t instances of io.BufferedIOBase, like Mercurial’s own winstdout. The new logic is different in two ways: First, only for the check, if unwraps any combination of WriteAllWrapper and winstdout. Second, it skips wrapping the stream only if it is an instance of io.RawIOBase (or already wrapped). If it is an instance of io.BufferedIOBase, it gets wrapped. In any other case, the function raises an exception. This ensures that, if an unknown stream is passed or we add another wrapper in the future, we don’t wrap the stream if it’s already line buffered or not wrap the stream if it’s not line buffered. In fact, this was already helpful during development of this change. Without it, I possibly would have forgot that WriteAllWrapper needs to be ignored for the check, leading to unnecessary wrapping if stdout is unbuffered. The alternative would have been to always wrap unknown streams. However, I don’t think that anyone would benefit from being less strict. We can expect streams from the standard library to be subclassing either io.RawIOBase or io.BufferedIOBase, so running Mercurial in the standard way should not regress by this change. Py2exe might replace sys.stdout and sys.stderr, but that currently breaks Mercurial anyway and also these streams don’t claim to be interactive, so this function is not called for them.

  $ cat <<EOF >> $HGRCPATH
  > [extensions]
  > hooklib =
  > 
  > [phases]
  > publish = False
  > EOF
  $ hg init a
  $ hg --cwd a debugbuilddag '.:parent.*parent'
  $ hg --cwd a log -G
  o  changeset:   2:fa942426a6fd
  |  tag:         tip
  |  parent:      0:1ea73414a91b
  |  user:        debugbuilddag
  |  date:        Thu Jan 01 00:00:02 1970 +0000
  |  summary:     r2
  |
  | o  changeset:   1:66f7d451a68b
  |/   user:        debugbuilddag
  |    date:        Thu Jan 01 00:00:01 1970 +0000
  |    summary:     r1
  |
  o  changeset:   0:1ea73414a91b
     tag:         parent
     user:        debugbuilddag
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     r0
  
  $ hg init b
  $ cat <<EOF >> b/.hg/hgrc
  > [hooks]
  > pretxnclose.reject_new_heads = \
  >   python:hgext.hooklib.reject_new_heads.hook
  > EOF
  $ hg --cwd b pull ../a
  pulling from ../a
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  error: pretxnclose.reject_new_heads hook failed: Changes on branch 'default' resulted in multiple heads
  transaction abort!
  rollback completed
  abort: Changes on branch 'default' resulted in multiple heads
  [255]
  $ hg --cwd b pull ../a -r 1ea73414a91b
  pulling from ../a
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files
  new changesets 1ea73414a91b (1 drafts)
  (run 'hg update' to get a working copy)