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.
$ hg init repo
$ cd repo
$ echo line 1 > foo
$ hg ci -qAm 'add foo'
copy foo to bar and change both files
$ hg cp foo bar
$ echo line 2-1 >> foo
$ echo line 2-2 >> bar
$ hg ci -m 'cp foo bar; change both'
in another branch, change foo in a way that doesn't conflict with
the other changes
$ hg up -qC 0
$ echo line 0 > foo
$ hg cat foo >> foo
$ hg ci -m 'change foo'
created new head
we get conflicts that shouldn't be there
$ hg merge -P
changeset: 1:484bf6903104
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: cp foo bar; change both
$ hg merge --debug
unmatched files in other:
bar
all copies found (* = to merge, ! = divergent, % = renamed and deleted):
on remote side:
src: 'foo' -> dst: 'bar' *
checking for directory renames
resolving manifests
branchmerge: True, force: False, partial: False
ancestor: e6dc8efe11cc, local: 6a0df1dad128+, remote: 484bf6903104
starting 4 threads for background file closing (?)
preserving foo for resolve of bar
preserving foo for resolve of foo
bar: remote copied from foo -> m
picked tool ':merge' for bar (binary False symlink False changedelete False)
merging foo and bar to bar
my bar@6a0df1dad128+ other bar@484bf6903104 ancestor foo@e6dc8efe11cc
premerge successful
foo: versions differ -> m
picked tool ':merge' for foo (binary False symlink False changedelete False)
merging foo
my foo@6a0df1dad128+ other foo@484bf6903104 ancestor foo@e6dc8efe11cc
premerge successful
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
contents of foo
$ cat foo
line 0
line 1
line 2-1
contents of bar
$ cat bar
line 0
line 1
line 2-2
$ cd ..