view tests/pdiff @ 29642:8960fcb76ca4 stable

demandimport: avoid infinite recursion at actual module importing (issue5304)

Before this patch, importing C module on Windows environment causes
infinite recursion call, if py2exe is used with -b2 option.

At importing C module "a.b", extra hooking by zipextimporter of py2exe
causes:

  0. assumption before accessing "b" of "a":

     - built-in module object is created for "a",
       (= "a" is actually imported)
     - _demandmod is created for "a.b" as a proxy object, and
       (= "a.b" is not yet imported)
     - an attribute "b" of "a" is initialized by the latter

  1. invocation of __import__ via _hgextimport() in _demandmod._load()
     for "a.b" implies _demandimport() for "a.b"

     This is unintentional, because _demandmod might be returned by
     _hgextimport() instead of built-in module object.

  2. _demandimport() at (1) is invoked with not context of "a", but
     context of zipextimporter

     Just after invocation of _hgextimport() in _demandimport(), an
     attribute "b" of the built-in module object for "a" is still
     bound to the proxy object for "a.b", because context of "a" isn't
     updated by actual importing "a.b". even though the built-in
     module object for "a.b" already appears in sys.modules.

     Therefore, chainmodules() returns _demandmod for "a.b", which is
     gotten from the attribute "b" of "a".

  3. processfromitem() on "a.b" causes _demandmod._load() for "a.b"
     again

     _demandimport() takes context of "a" in this case.

     Therefore, attributes below are bound to built-in module object
     for "a.b", as expected:

     - "b" of built-in module object for "a"
     - _module of _demandmod for "a.b"

  4. but _demandimport() invoked at (1) returns _demandmod object

     because _demandimport() just returns the object returned by
     chainmodules() at (3) above.

  5. then, _demandmod._load() causes infinite recursion call

     _demandimport() returns _demandmod for "a.b", and it is "self" at
     _demandmod._load().

To avoid infinite recursion at actual module importing, this patch
uses self._module, if _hgextimport() returns _demandmod itself. If
_demandmod._module isn't yet bound at this point, execution should be
aborted, because actual importing failed.

In this patch, _demandmod._module is examined not on _demandimport()
side, but on _demandmod._load() side, because:

  - the former has some exit points
  - only the latter uses _hgextimport(), except for _demandimport()

BTW, this issue occurs only in the code path for non .py/.pyc files in
zipextimporter (strictly speaking, in _memimporter) of py2exe.

Even if zipextimporter is enabled, .py/.pyc files are handled by
zipimporter, and it doesn't imply unintentional _demandimport() at
invocation of __import__ via _hgextimport().

#!/bin/sh

# Script to get stable diff output on any platform.
#
# Output of this script is almost equivalent to GNU diff with "-Nru".
#
# Use this script as "hg pdiff" via extdiff extension with preparation
# below in test scripts:
#
#   $ cat >> $HGRCPATH <<EOF
#   > [extdiff]
#   > pdiff = sh "$RUNTESTDIR/pdiff"
#   > EOF

filediff(){
    # USAGE: filediff file1 file2 [header]

    # compare with /dev/null if file doesn't exist (as "-N" option)
    file1="$1"
    if test ! -f "$file1"; then
        file1=/dev/null
    fi
    file2="$2"
    if test ! -f "$file2"; then
        file2=/dev/null
    fi

    if cmp -s "$file1" "$file2" 2> /dev/null; then
        # Return immediately, because comparison isn't needed. This
        # also avoids redundant message of diff like "No differences
        # encountered" (on Solaris)
        return
    fi

    if test -n "$3"; then
        # show header only in recursive case
        echo "$3"
    fi

    # replace "/dev/null" by corresponded filename (as "-N" option)
    diff -u "$file1" "$file2" |
    sed "s@^--- /dev/null\(.*\)\$@--- $1\1@" |
    sed "s@^\+\+\+ /dev/null\(.*\)\$@+++ $2\1@"
}

if test -d "$1" -o -d "$2"; then
    # ensure comparison in dictionary order
    (
    if test -d "$1"; then (cd "$1" && find . -type f); fi
    if test -d "$2"; then (cd "$2" && find . -type f); fi
    ) |
    sed 's@^\./@@g' | sort | uniq |
    while read file; do
        filediff "$1/$file" "$2/$file" "diff -Nru $1/$file $2/$file"
    done
else
    filediff "$1" "$2"
fi