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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Corrupt an hg repo with two pulls.

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create one repo with a long history

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  $ hg init source1

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  $ cd source1

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  $ touch foo

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  $ hg add foo

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  $ for i in 1 2 3 4 5 6 7 8 9 10; do

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  >     echo $i >> foo

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  >     hg ci -m $i

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  > done

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  $ cd ..

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create one repo with a shorter history

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  $ hg clone -r 0 source1 source2

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  adding changesets

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  adding manifests

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  adding file changes

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  added 1 changesets with 1 changes to 1 files

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  new changesets 495a0ec48aaf

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  updating to branch default

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

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  $ cd source2

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  $ echo a >> foo

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  $ hg ci -m a

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  $ cd ..

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create a third repo to pull both other repos into it

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  $ hg init corrupted

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  $ cd corrupted

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use a hook to make the second pull start while the first one is still running

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  $ echo '[hooks]' >> .hg/hgrc

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  $ echo 'prechangegroup = sleep 5' >> .hg/hgrc

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start a pull...

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  $ hg pull ../source1 > pull.out 2>&1 &

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... and start another pull before the first one has finished

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  $ sleep 1

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  $ hg pull ../source2 2>/dev/null

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  pulling from ../source2

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  searching for changes

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  adding changesets

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  adding manifests

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  adding file changes

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  added 1 changesets with 1 changes to 1 files (+1 heads)

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  new changesets ca3c05af513e

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  (run 'hg heads' to see heads, 'hg merge' to merge)

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  $ cat pull.out

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  pulling from ../source1

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  requesting all changes

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  adding changesets

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  adding manifests

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  adding file changes

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  added 10 changesets with 10 changes to 1 files

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  new changesets 495a0ec48aaf:1e7b6c812ca8

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  (run 'hg update' to get a working copy)

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see the result

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  $ wait

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  $ hg verify

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  checking changesets

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  checking manifests

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  crosschecking files in changesets and manifests

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  checking files

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  checked 11 changesets with 11 changes to 1 files

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  $ cd ..