view tests/test-merge-local.t @ 20742:3681de20b0a7

parsers: fail fast if Python has wrong minor version (issue4110)

This change causes an informative ImportError to be raised when importing
the parsers extension module if the minor version of the currently-running
Python interpreter doesn't match that of the Python used when compiling
the extension module.

This change also exposes a parsers.versionerrortext constant in the
C implementation of the module.  Its presence can be used to determine
whether this behavior is present in a version of the module.  The value
of the constant is the leading text of the ImportError raised and is set
to "Python minor version mismatch".

Here is an example of what the new error looks like:

  Traceback (most recent call last):
    File "test.py", line 1, in <module>
      import mercurial.parsers
  ImportError: Python minor version mismatch: The Mercurial extension
  modules were compiled with Python 2.7.6, but Mercurial is currently using
  Python with sys.hexversion=33883888: Python 2.5.6
  (r256:88840, Nov 18 2012, 05:37:10)
  [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))]
   at: /opt/local/Library/Frameworks/Python.framework/Versions/2.5/Resources/
    Python.app/Contents/MacOS/Python

The reason for raising an error in this scenario is that Python's C API
is known not to be compatible from minor version to minor version, even
if sys.api_version is the same.  See for example this Python bug report
about incompatibilities between 2.5 and 2.6+:

  http://bugs.python.org/issue8118

These incompatibilities can cause Mercurial to break in mysterious,
unforeseen ways.  For example, when Mercurial compiled with Python 2.7 was
run with 2.5, the following crash occurred when running "hg status":

  http://bz.selenic.com/show_bug.cgi?id=4110

After this crash was fixed, running with Python 2.5 no longer crashes, but
the following puzzling behavior still occurs:

    $ hg status
      ...
      File ".../mercurial/changelog.py", line 123, in __init__
        revlog.revlog.__init__(self, opener, "00changelog.i")
      File ".../mercurial/revlog.py", line 251, in __init__
        d = self._io.parseindex(i, self._inline)
      File ".../mercurial/revlog.py", line 158, in parseindex
        index, cache = parsers.parse_index2(data, inline)
    TypeError: data is not a string

which can be reproduced more simply with:

    import mercurial.parsers as parsers
    parsers.parse_index2("", True)

Both the crash and the TypeError occurred because the Python C API's
PyString_Check() returns the wrong value when the C header files from
Python 2.7 are run with Python 2.5.  This is an example of an
incompatibility of the sort mentioned in the Python bug report above.

Failing fast with an informative error message results in a better user
experience in cases like the above.  The information in the ImportError
also simplifies troubleshooting for those on Mercurial mailing lists, the
bug tracker, etc.

This patch only adds the version check to parsers.c, which is sufficient
to affect command-line commands like "hg status" and "hg summary".
An idea for a future improvement is to move the version-checking C code
to a more central location, and have it run when importing all
Mercurial extension modules and not just parsers.c.

  $ hg init

Revision 0:

  $ echo "unchanged" > unchanged
  $ echo "remove me" > remove
  $ echo "copy me" > copy
  $ echo "move me" > move
  $ for i in 1 2 3 4 5 6 7 8 9; do
  >     echo "merge ok $i" >> zzz1_merge_ok
  > done
  $ echo "merge bad" > zzz2_merge_bad
  $ hg ci -Am "revision 0"
  adding copy
  adding move
  adding remove
  adding unchanged
  adding zzz1_merge_ok
  adding zzz2_merge_bad

Revision 1:

  $ hg rm remove
  $ hg mv move moved
  $ hg cp copy copied
  $ echo "added" > added
  $ hg add added
  $ echo "new first line" > zzz1_merge_ok
  $ hg cat zzz1_merge_ok >> zzz1_merge_ok
  $ echo "new last line" >> zzz2_merge_bad
  $ hg ci -m "revision 1"

Local changes to revision 0:

  $ hg co 0
  4 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ echo "new last line" >> zzz1_merge_ok
  $ echo "another last line" >> zzz2_merge_bad

  $ hg diff --nodates | grep "^[+-][^<>]"
  --- a/zzz1_merge_ok
  +++ b/zzz1_merge_ok
  +new last line
  --- a/zzz2_merge_bad
  +++ b/zzz2_merge_bad
  +another last line

  $ hg st
  M zzz1_merge_ok
  M zzz2_merge_bad

Local merge with bad merge tool:

  $ HGMERGE=false hg co
  merging zzz1_merge_ok
  merging zzz2_merge_bad
  merging zzz2_merge_bad failed!
  3 files updated, 1 files merged, 2 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg co 0
  merging zzz1_merge_ok
  merging zzz2_merge_bad
  warning: conflicts during merge.
  merging zzz2_merge_bad incomplete! (edit conflicts, then use 'hg resolve --mark')
  2 files updated, 1 files merged, 3 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg diff --nodates | grep "^[+-][^<>]"
  --- a/zzz1_merge_ok
  +++ b/zzz1_merge_ok
  +new last line
  --- a/zzz2_merge_bad
  +++ b/zzz2_merge_bad
  +another last line
  +=======

  $ hg st
  M zzz1_merge_ok
  M zzz2_merge_bad
  ? zzz2_merge_bad.orig

Local merge with conflicts:

  $ hg co
  merging zzz1_merge_ok
  merging zzz2_merge_bad
  warning: conflicts during merge.
  merging zzz2_merge_bad incomplete! (edit conflicts, then use 'hg resolve --mark')
  3 files updated, 1 files merged, 2 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg co 0
  merging zzz1_merge_ok
  merging zzz2_merge_bad
  warning: conflicts during merge.
  merging zzz2_merge_bad incomplete! (edit conflicts, then use 'hg resolve --mark')
  2 files updated, 1 files merged, 3 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg diff --nodates | grep "^[+-][^<>]"
  --- a/zzz1_merge_ok
  +++ b/zzz1_merge_ok
  +new last line
  --- a/zzz2_merge_bad
  +++ b/zzz2_merge_bad
  +another last line
  +=======
  +=======
  +new last line
  +=======

  $ hg st
  M zzz1_merge_ok
  M zzz2_merge_bad
  ? zzz2_merge_bad.orig

Local merge without conflicts:

  $ hg revert zzz2_merge_bad

  $ hg co
  merging zzz1_merge_ok
  4 files updated, 1 files merged, 2 files removed, 0 files unresolved

  $ hg diff --nodates | grep "^[+-][^<>]"
  --- a/zzz1_merge_ok
  +++ b/zzz1_merge_ok
  +new last line

  $ hg st
  M zzz1_merge_ok
  ? zzz2_merge_bad.orig