/brz/remove-bazaar

# Copyright (C) 2005, 2006 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

import os

from cStringIO import StringIO

import errno

import subprocess

from tempfile import TemporaryFile

from bzrlib.diff import internal_diff, external_diff, show_diff_trees

from bzrlib.errors import BinaryFile, NoDiff

import bzrlib.osutils as osutils

import bzrlib.patiencediff

from bzrlib.tests import (Feature, TestCase, TestCaseWithTransport,

                          TestCaseInTempDir, TestSkipped)

class _UnicodeFilename(Feature):

    """Does the filesystem support Unicode filenames?"""

    def _probe(self):

        try:

            os.stat(u'\u03b1')

        except UnicodeEncodeError:

            return False

        except (IOError, OSError):

            # The filesystem allows the Unicode filename but the file doesn't

            # exist.

            return True

        else:

            # The filesystem allows the Unicode filename and the file exists,

            # for some reason.

            return True

UnicodeFilename = _UnicodeFilename()

class TestUnicodeFilename(TestCase):

    def test_probe_passes(self):

        """UnicodeFilename._probe passes."""

        # We can't test much more than that because the behaviour depends

        # on the platform.

        UnicodeFilename._probe()

def udiff_lines(old, new, allow_binary=False):

    output = StringIO()

    internal_diff('old', old, 'new', new, output, allow_binary)

    output.seek(0, 0)

    return output.readlines()

def external_udiff_lines(old, new, use_stringio=False):

    if use_stringio:

        # StringIO has no fileno, so it tests a different codepath

        output = StringIO()

    else:

        output = TemporaryFile()

    try:

        external_diff('old', old, 'new', new, output, diff_opts=['-u'])

    except NoDiff:

        raise TestSkipped('external "diff" not present to test')

    output.seek(0, 0)

    lines = output.readlines()

    output.close()

    return lines

class TestDiff(TestCase):

    def test_add_nl(self):

        """diff generates a valid diff for patches that add a newline"""

        lines = udiff_lines(['boo'], ['boo\n'])

        self.check_patch(lines)

        self.assertEquals(lines[4], '\\ No newline at end of file\n')

            ## "expected no-nl, got %r" % lines[4]

    def test_add_nl_2(self):

        """diff generates a valid diff for patches that change last line and

        add a newline.

        """

        lines = udiff_lines(['boo'], ['goo\n'])

        self.check_patch(lines)

        self.assertEquals(lines[4], '\\ No newline at end of file\n')

            ## "expected no-nl, got %r" % lines[4]

    def test_remove_nl(self):

        """diff generates a valid diff for patches that change last line and

        add a newline.

        """

        lines = udiff_lines(['boo\n'], ['boo'])

        self.check_patch(lines)

        self.assertEquals(lines[5], '\\ No newline at end of file\n')

            ## "expected no-nl, got %r" % lines[5]

    def check_patch(self, lines):

        self.assert_(len(lines) > 1)

            ## "Not enough lines for a file header for patch:\n%s" % "".join(lines)

        self.assert_(lines[0].startswith ('---'))

            ## 'No orig line for patch:\n%s' % "".join(lines)

        self.assert_(lines[1].startswith ('+++'))

            ## 'No mod line for patch:\n%s' % "".join(lines)

        self.assert_(len(lines) > 2)

            ## "No hunks for patch:\n%s" % "".join(lines)

        self.assert_(lines[2].startswith('@@'))

            ## "No hunk header for patch:\n%s" % "".join(lines)

        self.assert_('@@' in lines[2][2:])

            ## "Unterminated hunk header for patch:\n%s" % "".join(lines)

    def test_binary_lines(self):

        self.assertRaises(BinaryFile, udiff_lines, [1023 * 'a' + '\x00'], [])

        self.assertRaises(BinaryFile, udiff_lines, [], [1023 * 'a' + '\x00'])

        udiff_lines([1023 * 'a' + '\x00'], [], allow_binary=True)

        udiff_lines([], [1023 * 'a' + '\x00'], allow_binary=True)

    def test_external_diff(self):

        lines = external_udiff_lines(['boo\n'], ['goo\n'])

        self.check_patch(lines)

        self.assertEqual('\n', lines[-1])

    def test_external_diff_no_fileno(self):

        # Make sure that we can handle not having a fileno, even

        # if the diff is large

        lines = external_udiff_lines(['boo\n']*10000,

                                     ['goo\n']*10000,

                                     use_stringio=True)

        self.check_patch(lines)

    def test_external_diff_binary_lang_c(self):

        old_env = {}

        for lang in ('LANG', 'LC_ALL', 'LANGUAGE'):

            old_env[lang] = osutils.set_or_unset_env(lang, 'C')

        try:

            lines = external_udiff_lines(['\x00foobar\n'], ['foo\x00bar\n'])

            # Older versions of diffutils say "Binary files", newer

            # versions just say "Files".

            self.assertContainsRe(lines[0],

                                  '(Binary f|F)iles old and new differ\n')

            self.assertEquals(lines[1:], ['\n'])

        finally:

            for lang, old_val in old_env.iteritems():

                osutils.set_or_unset_env(lang, old_val)

    def test_no_external_diff(self):

        """Check that NoDiff is raised when diff is not available"""

        # Use os.environ['PATH'] to make sure no 'diff' command is available

        orig_path = os.environ['PATH']

        try:

            os.environ['PATH'] = ''

            self.assertRaises(NoDiff, external_diff,

                              'old', ['boo\n'], 'new', ['goo\n'],

                              StringIO(), diff_opts=['-u'])

        finally:

            os.environ['PATH'] = orig_path

    def test_internal_diff_default(self):

        # Default internal diff encoding is utf8

        output = StringIO()

        internal_diff(u'old_\xb5', ['old_text\n'],

                    u'new_\xe5', ['new_text\n'], output)

        lines = output.getvalue().splitlines(True)

        self.check_patch(lines)

        self.assertEquals(['--- old_\xc2\xb5\n',

                           '+++ new_\xc3\xa5\n',

                           '@@ -1,1 +1,1 @@\n',

                           '-old_text\n',

                           '+new_text\n',

                           '\n',

                          ]

                          , lines)

    def test_internal_diff_utf8(self):

        output = StringIO()

        internal_diff(u'old_\xb5', ['old_text\n'],

                    u'new_\xe5', ['new_text\n'], output,

                    path_encoding='utf8')

        lines = output.getvalue().splitlines(True)

        self.check_patch(lines)

        self.assertEquals(['--- old_\xc2\xb5\n',

                           '+++ new_\xc3\xa5\n',

                           '@@ -1,1 +1,1 @@\n',

                           '-old_text\n',

                           '+new_text\n',

                           '\n',

                          ]

                          , lines)

    def test_internal_diff_iso_8859_1(self):

        output = StringIO()

        internal_diff(u'old_\xb5', ['old_text\n'],

                    u'new_\xe5', ['new_text\n'], output,

                    path_encoding='iso-8859-1')

        lines = output.getvalue().splitlines(True)

        self.check_patch(lines)

        self.assertEquals(['--- old_\xb5\n',

                           '+++ new_\xe5\n',

                           '@@ -1,1 +1,1 @@\n',

                           '-old_text\n',

                           '+new_text\n',

                           '\n',

                          ]

                          , lines)

    def test_internal_diff_returns_bytes(self):

        import StringIO

        output = StringIO.StringIO()

        internal_diff(u'old_\xb5', ['old_text\n'],

                    u'new_\xe5', ['new_text\n'], output)

        self.failUnless(isinstance(output.getvalue(), str),

            'internal_diff should return bytestrings')

class TestDiffFiles(TestCaseInTempDir):

    def test_external_diff_binary(self):

        """The output when using external diff should use diff's i18n error"""

        # Make sure external_diff doesn't fail in the current LANG

        lines = external_udiff_lines(['\x00foobar\n'], ['foo\x00bar\n'])

        cmd = ['diff', '-u', '--binary', 'old', 'new']

        open('old', 'wb').write('\x00foobar\n')

        open('new', 'wb').write('foo\x00bar\n')

        pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE,

                                     stdin=subprocess.PIPE)

        out, err = pipe.communicate()

        # Diff returns '2' on Binary files.

        self.assertEqual(2, pipe.returncode)

        # We should output whatever diff tells us, plus a trailing newline

        self.assertEqual(out.splitlines(True) + ['\n'], lines)

class TestShowDiffTreesHelper(TestCaseWithTransport):

    """Has a helper for running show_diff_trees"""

    def get_diff(self, tree1, tree2, specific_files=None, working_tree=None):

        output = StringIO()

        if working_tree is not None:

            extra_trees = (working_tree,)

        else:

            extra_trees = ()

        show_diff_trees(tree1, tree2, output, specific_files=specific_files,

                        extra_trees=extra_trees, old_label='old/',

                        new_label='new/')

        return output.getvalue()

class TestDiffDates(TestShowDiffTreesHelper):

    def setUp(self):

        super(TestDiffDates, self).setUp()

        self.wt = self.make_branch_and_tree('.')

        self.b = self.wt.branch

        self.build_tree_contents([

            ('file1', 'file1 contents at rev 1\n'),

            ('file2', 'file2 contents at rev 1\n')

            ])

        self.wt.add(['file1', 'file2'])

        self.wt.commit(

            message='Revision 1',

            timestamp=1143849600, # 2006-04-01 00:00:00 UTC

            timezone=0,

            rev_id='rev-1')

        self.build_tree_contents([('file1', 'file1 contents at rev 2\n')])

        self.wt.commit(

            message='Revision 2',

            timestamp=1143936000, # 2006-04-02 00:00:00 UTC

            timezone=28800,

            rev_id='rev-2')

        self.build_tree_contents([('file2', 'file2 contents at rev 3\n')])

        self.wt.commit(

            message='Revision 3',

            timestamp=1144022400, # 2006-04-03 00:00:00 UTC

            timezone=-3600,

            rev_id='rev-3')

        self.wt.remove(['file2'])

        self.wt.commit(

            message='Revision 4',

            timestamp=1144108800, # 2006-04-04 00:00:00 UTC

            timezone=0,

            rev_id='rev-4')

        self.build_tree_contents([

            ('file1', 'file1 contents in working tree\n')

            ])

        # set the date stamps for files in the working tree to known values

        os.utime('file1', (1144195200, 1144195200)) # 2006-04-05 00:00:00 UTC

    def test_diff_rev_tree_working_tree(self):

        output = self.get_diff(self.wt.basis_tree(), self.wt)

        # note that the date for old/file1 is from rev 2 rather than from

        # the basis revision (rev 4)

        self.assertEqualDiff(output, '''\

=== modified file 'file1'

--- old/file1\t2006-04-02 00:00:00 +0000

+++ new/file1\t2006-04-05 00:00:00 +0000

@@ -1,1 +1,1 @@

-file1 contents at rev 2

+file1 contents in working tree

''')

    def test_diff_rev_tree_rev_tree(self):

        tree1 = self.b.repository.revision_tree('rev-2')

        tree2 = self.b.repository.revision_tree('rev-3')

        output = self.get_diff(tree1, tree2)

        self.assertEqualDiff(output, '''\

=== modified file 'file2'

--- old/file2\t2006-04-01 00:00:00 +0000

+++ new/file2\t2006-04-03 00:00:00 +0000

@@ -1,1 +1,1 @@

-file2 contents at rev 1

+file2 contents at rev 3

''')

    def test_diff_add_files(self):

        tree1 = self.b.repository.revision_tree(None)

        tree2 = self.b.repository.revision_tree('rev-1')

        output = self.get_diff(tree1, tree2)

        # the files have the epoch time stamp for the tree in which

        # they don't exist.

        self.assertEqualDiff(output, '''\

=== added file 'file1'

--- old/file1\t1970-01-01 00:00:00 +0000

+++ new/file1\t2006-04-01 00:00:00 +0000

@@ -0,0 +1,1 @@

+file1 contents at rev 1

=== added file 'file2'

--- old/file2\t1970-01-01 00:00:00 +0000

+++ new/file2\t2006-04-01 00:00:00 +0000

@@ -0,0 +1,1 @@

+file2 contents at rev 1

''')

    def test_diff_remove_files(self):

        tree1 = self.b.repository.revision_tree('rev-3')

        tree2 = self.b.repository.revision_tree('rev-4')

        output = self.get_diff(tree1, tree2)

        # the file has the epoch time stamp for the tree in which

        # it doesn't exist.

        self.assertEqualDiff(output, '''\

=== removed file 'file2'

--- old/file2\t2006-04-03 00:00:00 +0000

+++ new/file2\t1970-01-01 00:00:00 +0000

@@ -1,1 +0,0 @@

-file2 contents at rev 3

''')

    def test_show_diff_specified(self):

        """A working tree filename can be used to identify a file"""

        self.wt.rename_one('file1', 'file1b')

        old_tree = self.b.repository.revision_tree('rev-1')

        new_tree = self.b.repository.revision_tree('rev-4')

        out = self.get_diff(old_tree, new_tree, specific_files=['file1b'], 

                            working_tree=self.wt)

        self.assertContainsRe(out, 'file1\t')

    def test_recursive_diff(self):

        """Children of directories are matched"""

        os.mkdir('dir1')

        os.mkdir('dir2')

        self.wt.add(['dir1', 'dir2'])

        self.wt.rename_one('file1', 'dir1/file1')

        old_tree = self.b.repository.revision_tree('rev-1')

        new_tree = self.b.repository.revision_tree('rev-4')

        out = self.get_diff(old_tree, new_tree, specific_files=['dir1'], 

                            working_tree=self.wt)

        self.assertContainsRe(out, 'file1\t')

        out = self.get_diff(old_tree, new_tree, specific_files=['dir2'], 

                            working_tree=self.wt)

        self.assertNotContainsRe(out, 'file1\t')

class TestShowDiffTrees(TestShowDiffTreesHelper):

    """Direct tests for show_diff_trees"""

    def test_modified_file(self):

        """Test when a file is modified."""

        tree = self.make_branch_and_tree('tree')

        self.build_tree_contents([('tree/file', 'contents\n')])

        tree.add(['file'], ['file-id'])

        tree.commit('one', rev_id='rev-1')

        self.build_tree_contents([('tree/file', 'new contents\n')])

        diff = self.get_diff(tree.basis_tree(), tree)

        self.assertContainsRe(diff, "=== modified file 'file'\n")

        self.assertContainsRe(diff, '--- old/file\t')

        self.assertContainsRe(diff, '\\+\\+\\+ new/file\t')

        self.assertContainsRe(diff, '-contents\n'

                                    '\\+new contents\n')

    def test_modified_file_in_renamed_dir(self):

        """Test when a file is modified in a renamed directory."""

        tree = self.make_branch_and_tree('tree')

        self.build_tree(['tree/dir/'])

        self.build_tree_contents([('tree/dir/file', 'contents\n')])

        tree.add(['dir', 'dir/file'], ['dir-id', 'file-id'])

        tree.commit('one', rev_id='rev-1')

        tree.rename_one('dir', 'other')

        self.build_tree_contents([('tree/other/file', 'new contents\n')])

        diff = self.get_diff(tree.basis_tree(), tree)

        self.assertContainsRe(diff, "=== renamed directory 'dir' => 'other'\n")

        self.assertContainsRe(diff, "=== modified file 'other/file'\n")

        # XXX: This is technically incorrect, because it used to be at another

        # location. What to do?

        self.assertContainsRe(diff, '--- old/dir/file\t')

        self.assertContainsRe(diff, '\\+\\+\\+ new/other/file\t')

        self.assertContainsRe(diff, '-contents\n'

                                    '\\+new contents\n')

    def test_renamed_directory(self):

        """Test when only a directory is only renamed."""

        tree = self.make_branch_and_tree('tree')

        self.build_tree(['tree/dir/'])

        self.build_tree_contents([('tree/dir/file', 'contents\n')])

        tree.add(['dir', 'dir/file'], ['dir-id', 'file-id'])

        tree.commit('one', rev_id='rev-1')

        tree.rename_one('dir', 'newdir')

        diff = self.get_diff(tree.basis_tree(), tree)

        # Renaming a directory should be a single "you renamed this dir" even

        # when there are files inside.

        self.assertEqual("=== renamed directory 'dir' => 'newdir'\n", diff)

    def test_renamed_file(self):

        """Test when a file is only renamed."""

        tree = self.make_branch_and_tree('tree')

        self.build_tree_contents([('tree/file', 'contents\n')])

        tree.add(['file'], ['file-id'])

        tree.commit('one', rev_id='rev-1')

        tree.rename_one('file', 'newname')

        diff = self.get_diff(tree.basis_tree(), tree)

        self.assertContainsRe(diff, "=== renamed file 'file' => 'newname'\n")

        # We shouldn't have a --- or +++ line, because there is no content

        # change

        self.assertNotContainsRe(diff, '---')

    def test_renamed_and_modified_file(self):

        """Test when a file is only renamed."""

        tree = self.make_branch_and_tree('tree')

        self.build_tree_contents([('tree/file', 'contents\n')])

        tree.add(['file'], ['file-id'])

        tree.commit('one', rev_id='rev-1')

        tree.rename_one('file', 'newname')

        self.build_tree_contents([('tree/newname', 'new contents\n')])

        diff = self.get_diff(tree.basis_tree(), tree)

        self.assertContainsRe(diff, "=== renamed file 'file' => 'newname'\n")

        self.assertContainsRe(diff, '--- old/file\t')

        self.assertContainsRe(diff, '\\+\\+\\+ new/newname\t')

        self.assertContainsRe(diff, '-contents\n'

                                    '\\+new contents\n')

    def test_binary_unicode_filenames(self):

        """Test that contents of files are *not* encoded in UTF-8 when there

        is a binary file in the diff.

        """

        # See https://bugs.launchpad.net/bugs/110092.

        self.requireFeature(UnicodeFilename)

        # This bug isn't triggered with cStringIO.

        from StringIO import StringIO

        tree = self.make_branch_and_tree('tree')

        alpha, omega = u'\u03b1', u'\u03c9'

        alpha_utf8, omega_utf8 = alpha.encode('utf8'), omega.encode('utf8')

        self.build_tree_contents(

            [('tree/' + alpha, chr(0)),

             ('tree/' + omega,

              ('The %s and the %s\n' % (alpha_utf8, omega_utf8)))])

        tree.add([alpha], ['file-id'])

        tree.add([omega], ['file-id-2'])

        diff_content = StringIO()

        show_diff_trees(tree.basis_tree(), tree, diff_content)

        diff = diff_content.getvalue()

        self.assertContainsRe(diff, r"=== added file '%s'" % alpha_utf8)

        self.assertContainsRe(

            diff, "Binary files a/%s.*and b/%s.* differ\n" % (alpha_utf8, alpha_utf8))

        self.assertContainsRe(diff, r"=== added file '%s'" % omega_utf8)

        self.assertContainsRe(diff, r"--- a/%s" % (omega_utf8,))

        self.assertContainsRe(diff, r"\+\+\+ b/%s" % (omega_utf8,))

    def test_unicode_filename(self):

        """Test when the filename are unicode."""

        self.requireFeature(UnicodeFilename)

        alpha, omega = u'\u03b1', u'\u03c9'

        autf8, outf8 = alpha.encode('utf8'), omega.encode('utf8')

        tree = self.make_branch_and_tree('tree')

        self.build_tree_contents([('tree/ren_'+alpha, 'contents\n')])

        tree.add(['ren_'+alpha], ['file-id-2'])

        self.build_tree_contents([('tree/del_'+alpha, 'contents\n')])

        tree.add(['del_'+alpha], ['file-id-3'])

        self.build_tree_contents([('tree/mod_'+alpha, 'contents\n')])

        tree.add(['mod_'+alpha], ['file-id-4'])

        tree.commit('one', rev_id='rev-1')

        tree.rename_one('ren_'+alpha, 'ren_'+omega)

        tree.remove('del_'+alpha)

        self.build_tree_contents([('tree/add_'+alpha, 'contents\n')])

        tree.add(['add_'+alpha], ['file-id'])

        self.build_tree_contents([('tree/mod_'+alpha, 'contents_mod\n')])

        diff = self.get_diff(tree.basis_tree(), tree)

        self.assertContainsRe(diff,

                "=== renamed file 'ren_%s' => 'ren_%s'\n"%(autf8, outf8))

        self.assertContainsRe(diff, "=== added file 'add_%s'"%autf8)

        self.assertContainsRe(diff, "=== modified file 'mod_%s'"%autf8)

        self.assertContainsRe(diff, "=== removed file 'del_%s'"%autf8)

class TestPatienceDiffLib(TestCase):

    def test_unique_lcs(self):

        unique_lcs = bzrlib.patiencediff.unique_lcs

        self.assertEquals(unique_lcs('', ''), [])

        self.assertEquals(unique_lcs('a', 'a'), [(0,0)])

        self.assertEquals(unique_lcs('a', 'b'), [])

        self.assertEquals(unique_lcs('ab', 'ab'), [(0,0), (1,1)])

        self.assertEquals(unique_lcs('abcde', 'cdeab'), [(2,0), (3,1), (4,2)])

        self.assertEquals(unique_lcs('cdeab', 'abcde'), [(0,2), (1,3), (2,4)])

        self.assertEquals(unique_lcs('abXde', 'abYde'), [(0,0), (1,1), 

                                                         (3,3), (4,4)])

        self.assertEquals(unique_lcs('acbac', 'abc'), [(2,1)])

    def test_recurse_matches(self):

        def test_one(a, b, matches):

            test_matches = []

            bzrlib.patiencediff.recurse_matches(a, b, 0, 0, len(a), len(b),

                test_matches, 10)

            self.assertEquals(test_matches, matches)

        test_one(['a', '', 'b', '', 'c'], ['a', 'a', 'b', 'c', 'c'],

                 [(0, 0), (2, 2), (4, 4)])

        test_one(['a', 'c', 'b', 'a', 'c'], ['a', 'b', 'c'],

                 [(0, 0), (2, 1), (4, 2)])

        # recurse_matches doesn't match non-unique 

        # lines surrounded by bogus text.

        # The update has been done in patiencediff.SequenceMatcher instead

        # This is what it could be

        #test_one('aBccDe', 'abccde', [(0,0), (2,2), (3,3), (5,5)])

        # This is what it currently gives:

        test_one('aBccDe', 'abccde', [(0,0), (5,5)])

    def test_matching_blocks(self):

        def chk_blocks(a, b, expected_blocks):

            # difflib always adds a signature of the total

            # length, with no matching entries at the end

            s = bzrlib.patiencediff.PatienceSequenceMatcher(None, a, b)

            blocks = s.get_matching_blocks()

            self.assertEquals((len(a), len(b), 0), blocks[-1])

            self.assertEquals(expected_blocks, blocks[:-1])

        # Some basic matching tests

        chk_blocks('', '', [])

        chk_blocks([], [], [])

        chk_blocks('abcd', 'abcd', [(0, 0, 4)])

        chk_blocks('abcd', 'abce', [(0, 0, 3)])

        chk_blocks('eabc', 'abce', [(1, 0, 3)])

        chk_blocks('eabce', 'abce', [(1, 0, 4)])

        chk_blocks('abcde', 'abXde', [(0, 0, 2), (3, 3, 2)])

        chk_blocks('abcde', 'abXYZde', [(0, 0, 2), (3, 5, 2)])

        chk_blocks('abde', 'abXYZde', [(0, 0, 2), (2, 5, 2)])

        # This may check too much, but it checks to see that 

        # a copied block stays attached to the previous section,

        # not the later one.

        # difflib would tend to grab the trailing longest match

        # which would make the diff not look right

        chk_blocks('abcdefghijklmnop', 'abcdefxydefghijklmnop',

                   [(0, 0, 6), (6, 11, 10)])

        # make sure it supports passing in lists

        chk_blocks(

                   ['hello there\n',

                    'world\n',

                    'how are you today?\n'],

                   ['hello there\n',

                    'how are you today?\n'],

                [(0, 0, 1), (2, 1, 1)])

        # non unique lines surrounded by non-matching lines

        # won't be found

        chk_blocks('aBccDe', 'abccde', [(0,0,1), (5,5,1)])

        # But they only need to be locally unique

        chk_blocks('aBcDec', 'abcdec', [(0,0,1), (2,2,1), (4,4,2)])

        # non unique blocks won't be matched

        chk_blocks('aBcdEcdFg', 'abcdecdfg', [(0,0,1), (8,8,1)])

        # but locally unique ones will

        chk_blocks('aBcdEeXcdFg', 'abcdecdfg', [(0,0,1), (2,2,2),

                                              (5,4,1), (7,5,2), (10,8,1)])