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.
== New Features ==
* `hg purge` is now a core command using `--confirm` by default.
* The `rev-branch-cache` is now updated incrementally whenever changesets
are added.
* The new options `experimental.bundlecompthreads` and
`experimental.bundlecompthreads.<engine>` can be used to instruct
the compression engines for bundle operations to use multiple threads
for compression. The default is single threaded operation. Currently
only supported for zstd.
== Default Format Change ==
These changes affects newly created repositories (or new clone) done with
Mercurial 5.8.
* The `ZSTD` compression will now be used by default for new repositories
when available. This compression format was introduced in Mercurial 5.0,
released in May 2019. See `hg help config.format.revlog-compression` for
details.
* Mercurial installation built with the Rust parts will now use the
"persistent nodemap" feature by default. This feature was introduced in
Mercurial 5.4 (May 2020). However Mercurial instalation built without the
fast Rust implementation will refuse to interract with them by default.
This restriction can be lifted through configuration.
See `hg help config.format.use-persistent-nodemap` for details
== New Experimental Features ==
* There's a new `diff.merge` config option to show the changes
relative to an automerge for merge changesets. This makes it
easier to detect and review manual changes performed in merge
changesets. It is supported by `hg diff --change`, `hg log -p`
`hg incoming -p`, and `hg outgoing -p` so far.
== Bug Fixes ==
* gracefully recover from inconsistent persistent-nodemap data from disk.
== Backwards Compatibility Changes ==
* In normal repositories, the first parent of a changeset is not null,
unless both parents are null (like the first changeset). Some legacy
repositories violate this condition. The revlog code will now
silentely swap the parents if this condition is tested. This can
change the output of `hg log` when explicitly asking for first or
second parent. The changesets "nodeid" are not affected.
== Internal API Changes ==
* `changelog.branchinfo` is deprecated and will be removed after 5.8.
It is superseded by `changelogrevision.branchinfo`.
* Callbacks for revlog.addgroup and the changelog._nodeduplicatecallback hook
now get a revision number as argument instead of a node.
* revlog.addrevision returns the revision number instead of the node.
* `nodes.nullid` and related constants are being phased out as part of
the deprecation of SHA1. Repository instances and related classes
provide access via `nodeconstants` and in some cases `nullid` attributes.