tests/testlib/merge-combination-util.sh

interfaces: introduce and use a protocol class for the `mpatch` module

See f2832de2a46c for details when this was done for the `bdiff` module.

Two things worth pointing out-

  1) The `cffi` module "inherits" the `pure` implementation of `patchedsize()`
     because of its wildcard import.
  2) It's odd that the `mpatchError` lives in both `pure` and `cext` modules.

I initially thought to move the exception into the new class, and make the
existing class name an alias to the class in the new location, but the exception
is created in C code by the `cext` module, so that won't work.  I don't think a
protocol class is approriate, because there's nothing special about the class to
distinguish from any other `Exception`.  Fortunately, nobody is catching this
exception in core, so we can kick the can down the road.

# genmerges is the workhorse of the test-merge-combination-*.t tests.

# Given:
# - a `range` function describing the possible values for file a
# - a `isgood` function to filter out uninteresting combination
# - a `createfile` function to actually write the values for file a on the
#   filesystem
#
# it print a series of lines that look like: abcd C: output of -T {files}
# describing the file a at respectively the base, p2, p1, merge
# revision. "C" indicates that hg merge had conflicts.

genmerges () {

  (LC_ALL=C type range | grep -q 'function') || (echo >&2 "missing function: range")
  (LC_ALL=C type isgood | grep -q 'function') || (echo >&2 "missing function: isgood")
  (LC_ALL=C type createfile | grep -q 'function') || (echo >&2 "missing function: createfile")

  for base in `range` -; do
    for r1 in `range $base` -; do
      for r2 in `range $base $r1` -; do
        for m in `range $base $r1 $r2` -; do
          line="$base$r1$r2$m"
          isgood $line || continue
          hg init repo
          cd repo
          make_commit () {
            v=$1; msg=$2; file=$3;
            if [ $v != - ]; then
              createfile $v
            else
              if [ -f a ]
              then rm a
              else touch $file
              fi
            fi
            hg commit -q -Am $msg || exit 123
          }
          echo foo > foo
          make_commit $base base b
          make_commit $r1 r1 c
          hg up -r 0 -q
          make_commit $r2 r2 d
          hg merge -q -r 1 > ../output 2>&1
          if [ $? -ne 0 ]; then rm -f *.orig; hg resolve -m --all -q; fi
          if [ -s ../output ]; then conflicts=" C"; else conflicts="  "; fi
          make_commit $m m e
          if [ $m = $r1 ] && [ $m = $r2 ]
          then expected=
          elif [ $m = $r1 ]
          then if [ $base = $r2 ]
               then expected=
               else expected=a
               fi
          elif [ $m = $r2 ]
          then if [ $base = $r1 ]
               then expected=
               else expected=a
               fi
          else expected=a
          fi
          got=`hg log -r 3 --template '{files}\n' | tr -d 'e '`
          if [ "$got" = "$expected" ]
          then echo "$line$conflicts: agree on \"$got\""
          else echo "$line$conflicts: hg said \"$got\", expected \"$expected\""
          fi
          cd ../
          rm -rf repo
        done
      done
    done
  done
}