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.

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Initial setup.

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  $ hg init repo

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  $ cd repo

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  $ touch thefile

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  $ hg ci -A -m 'Initial commit.'

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  adding thefile

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Create a tag.

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  $ hg tag branchortag

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Create a branch with the same name as the tag.

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  $ hg branch branchortag

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  marked working directory as branch branchortag

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  (branches are permanent and global, did you want a bookmark?)

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  $ hg ci -m 'Create a branch with the same name as a tag.'

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This is what we have:

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  $ hg log

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  changeset:   2:10519b3f489a

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  branch:      branchortag

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  tag:         tip

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Create a branch with the same name as a tag.

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  changeset:   1:2635c45ca99b

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Added tag branchortag for changeset f57387372b5d

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  changeset:   0:f57387372b5d

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  tag:         branchortag

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Initial commit.

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Update to the tag:

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  $ hg up 'tag(branchortag)'

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  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

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  $ hg parents

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  changeset:   0:f57387372b5d

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  tag:         branchortag

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Initial commit.

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Updating to the branch:

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  $ hg up 'branch(branchortag)'

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  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

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  $ hg parents

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  changeset:   2:10519b3f489a

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  branch:      branchortag

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  tag:         tip

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Create a branch with the same name as a tag.

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  $ cd ..