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.

     1

  $ hg init a

     2

  $ cd a

     3

  $ touch empty1

     4

  $ hg add empty1

     5

  $ hg commit -m 'add empty1'

     6

     7

  $ touch empty2

     8

  $ hg add empty2

     9

  $ hg commit -m 'add empty2'

    10

    11

  $ hg up -C 0

    12

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

    13

  $ touch empty3

    14

  $ hg add empty3

    15

  $ hg commit -m 'add empty3'

    16

  created new head

    17

    18

  $ hg heads

    19

  changeset:   2:a1cb177e0d44

    20

  tag:         tip

    21

  parent:      0:1e1d9c4e5b64

    22

  user:        test

    23

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

    24

  summary:     add empty3

    25

    26

  changeset:   1:097d2b0e17f6

    27

  user:        test

    28

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

    29

  summary:     add empty2

    30

    31

    32

  $ hg merge 1

    33

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

    34

  (branch merge, don't forget to commit)

    35

    36

Before changeset 05257fd28591, we didn't notice the

    37

empty file that came from rev 1:

    38

    39

  $ hg status

    40

  M empty2

    41

  $ hg commit -m merge

    42

  $ hg manifest --debug tip

    43

  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty1

    44

  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty2

    45

  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty3

    46

    47

  $ cd ..