tests/pdiff

changing-files: rework the way we store changed files in side-data

We need to store new data so this is a good opportunity to rework this fully.

1) We directly store the list of affected file in the side data:

* This avoid having to fetch and parse the `files` list in the revision in
  addition to the sidedata. Making the data more self sufficient.

* This work around situation where that `files` field contains wrong
  information, and open the way to other bug fixing (eg: issue6219)

* The format (fixed initial index, sorted files) allow for fast lookup of
  filename within the structure.

* This unify the storage of affected files and copies sources and destination,
  limiting the number filename stored redundantly.

* This prepare for the fact we should drop the `files` as soon as we do any
  change affecting the revision schema.

* This rely on compression to avoid a significant increase of the changelog.d.
  More testing on this will be done before we freeze the final format.


2) We can store additional data:

* The new "merged" field,

* A future "salvaged" set recording files that might have been deleted but have
  were still present in the final result.

Differential Revision: https://phab.mercurial-scm.org/D9090

#!/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@"

    # in this case, files differ from each other
    return 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

    # TODO: there is no portable way for current while-read based
    # implementation to return 1 at detecting changes.
    #
    # On bash and dash, assignment to variable inside while-block
    # doesn't affect outside, because inside while-block is executed
    # in sub-shell. BTW, it affects outside while-block on ksh (as sh
    # on Solaris).
else
    filediff "$1" "$2"
fi