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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https://bz.mercurial-scm.org/522

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In the merge below, the file "foo" has the same contents in both

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parents, but if we look at the file-level history, we'll notice that

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the version in p1 is an ancestor of the version in p2. This test makes

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sure that we'll use the version from p2 in the manifest of the merge

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revision.

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  $ hg init

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  $ echo foo > foo

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  $ hg ci -qAm 'add foo'

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  $ echo bar >> foo

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  $ hg ci -m 'change foo'

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  $ hg backout -r tip -m 'backout changed foo'

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  reverting foo

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  changeset 2:4d9e78aaceee backs out changeset 1:b515023e500e

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  $ hg up -C 0

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

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  $ touch bar

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  $ hg ci -qAm 'add bar'

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  $ hg merge --debug

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  resolving manifests

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   branchmerge: True, force: False, partial: False

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   ancestor: bbd179dfa0a7, local: 71766447bdbb+, remote: 4d9e78aaceee

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   foo: remote is newer -> g

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  getting foo

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

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  (branch merge, don't forget to commit)

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  $ hg debugstate | grep foo

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  m   0         -2 unset               foo

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  $ hg st -A foo

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  M foo

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  $ hg ci -m 'merge'

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  $ hg manifest --debug | grep foo

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  c6fc755d7e68f49f880599da29f15add41f42f5a 644   foo

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  $ hg debugindex foo

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     rev linkrev       nodeid    p1-nodeid    p2-nodeid

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       0       0 2ed2a3912a0b 000000000000 000000000000

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       1       1 6f4310b00b9a 2ed2a3912a0b 000000000000

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       2       2 c6fc755d7e68 6f4310b00b9a 000000000000

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