comparison mercurial/simplemerge.py @ 28072:c3e9269d9602

merge: minimize conflicts when common base is not shown (issue4447)

Previously, two changes that were nearly, but not quite, identical would result
in large merge conflict regions that looked very similar, and were thus very
confusing to users, and lead people used to other source control systems to
claim that "mercurial's merge algorithms suck". In the relatively common case
of a new file being introduced in two branches with very slight modifications,
the old behavior would show the entire file as a conflict, and it would be very
difficult for a user to determine what was going on.

In the past, mercurial attempted to solve this with a "very smart" algorithm
that would find all common lines, but this has significant problems as
described in 2ea6d906cf9b.

Instead, we use a "very dumb" algorithm introduced in the previous patch that
simply matches lines at the periphery of conflict regions. This minimizes most
conflict regions well, though there may still be some degenerate edge cases,
like small modification to the beginning and end of a large file.

28071:261324dd5f5b

                    name_base=None,
                    start_marker='<<<<<<<',
                    mid_marker='=======',
                    end_marker='>>>>>>>',
                    base_marker=None,
                    localorother=None):
        """Return merge in cvs-like form.
        """
        self.conflicts = False
        newline = '\n'
        if len(self.a) > 0:

        if name_b and end_marker:
            end_marker = end_marker + ' ' + name_b
        if name_base and base_marker:
            base_marker = base_marker + ' ' + name_base
        merge_regions = self.merge_regions()
        for t in merge_regions:
            what = t[0]
            if what == 'unchanged':
                for i in range(t[1], t[2]):
                    yield self.base[i]

        out = opener(os.path.basename(local), "w", atomictemp=True)
    else:
        out = sys.stdout

    m3 = Merge3Text(basetext, localtext, othertext)
    extrakwargs = {"localorother": opts.get("localorother", None)}
    if mode == 'union':
        extrakwargs['start_marker'] = None
        extrakwargs['mid_marker'] = None
        extrakwargs['end_marker'] = None
    elif name_base is not None:
        extrakwargs['base_marker'] = '|||||||'
        extrakwargs['name_base'] = name_base
    for line in m3.merge_lines(name_a=name_a, name_b=name_b, **extrakwargs):
        out.write(line)

    if not opts.get('print'):
        out.close()

28072:c3e9269d9602

                    name_base=None,
                    start_marker='<<<<<<<',
                    mid_marker='=======',
                    end_marker='>>>>>>>',
                    base_marker=None,
                    localorother=None,
                    minimize=False):
        """Return merge in cvs-like form.
        """
        self.conflicts = False
        newline = '\n'
        if len(self.a) > 0:

        if name_b and end_marker:
            end_marker = end_marker + ' ' + name_b
        if name_base and base_marker:
            base_marker = base_marker + ' ' + name_base
        merge_regions = self.merge_regions()
        if minimize:
            merge_regions = self.minimize(merge_regions)
        for t in merge_regions:
            what = t[0]
            if what == 'unchanged':
                for i in range(t[1], t[2]):
                    yield self.base[i]

        out = opener(os.path.basename(local), "w", atomictemp=True)
    else:
        out = sys.stdout

    m3 = Merge3Text(basetext, localtext, othertext)
    extrakwargs = {
            "localorother": opts.get("localorother", None),
            'minimize': True,
        }
    if mode == 'union':
        extrakwargs['start_marker'] = None
        extrakwargs['mid_marker'] = None
        extrakwargs['end_marker'] = None
    elif name_base is not None:
        extrakwargs['base_marker'] = '|||||||'
        extrakwargs['name_base'] = name_base
        extrakwargs['minimize'] = False
    for line in m3.merge_lines(name_a=name_a, name_b=name_b, **extrakwargs):
        out.write(line)

    if not opts.get('print'):
        out.close()