[PATCH 2 of 6] merge: introduce a ``mergemarkersscope`` config option
pierre-yves.david at ens-lyon.org
pierre-yves.david at ens-lyon.org
Tue Jun 10 15:50:26 CDT 2014
# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1402311202 25200
# Mon Jun 09 03:53:22 2014 -0700
# Node ID a0d2858a720b665e594372fc3953fcdb20d1ce52
# Parent 2fb39405980681c1bdbc97d898285bc2012ef586
merge: introduce a ``mergemarkersscope`` config option
This option control the amount of information included in markers. It currently
have two possible values ``minimalist`` and ``plain``. "minimalist" matches the
current behavior where conflict markers try to be reduced to strictly different
lines. ``plain`` exposes whole conflicting chunks (see detailed explanation
below). The default behavior remains unchanged for now. A third value, "base"
is expected to be added in a later changeset. It will include the content from
"base" file.
Detailled explanation
=====================
The ``simplemerge`` code use in ``internal:merge`` has a feature called
"minimization". It reprocess conflicting chunks to find common changes
inside them and excludes such common sections from the marker.
This approach seems a significant win at first glance but produces very
confusing results in some other cases.
Simple example
--------------
A simple example is enough to show the benefit of this feature. In this merge,
both sides change all numbers from letters to digits, but one side is also
changing some values.
$ cat << EOF > base
> Small Mathematical Series.
> One
> Two
> Three
> Four
> Five
> Hop we are done.
> EOF
$ cat << EOF > local
> Small Mathematical Series.
> 1
> 2
> 3
> 4
> 5
> Hop we are done.
> EOF
$ cat << EOF > other
> Small Mathematical Series.
> 1
> 2
> 3
> 6
> 8
> Hop we are done.
> EOF
In the minimalists case, the markers focus on the disagreement between the two
sides.
$ $TESTDIR/../contrib/simplemerge --print local base other
Small Mathematical Series.
1
2
3
<<<<<<< local
4
5
=======
6
8
>>>>>>> other
Hop we are done.
warning: conflicts during merge.
[1]
In the non minimalist case, the whole chunk is included in the conflict marker.
Making it harder spot actual differences.
$ $TESTDIR/../contrib/simplemerge --print --no-minimal local base other
Small Mathematical Series.
<<<<<<< local
1
2
3
4
5
=======
1
2
3
6
8
>>>>>>> other
Hop we are done.
warning: conflicts during merge.
[1]
Practical Advantages of minimalisation: merge of grafted change
---------------------------------------------------------------
This feature can be very useful when a change have been grafted in another
branch and then some change have been made to the grafted code.
$ cat << EOF > base
> # empty file
> EOF
$ cat << EOF > local
> def somefunction(one, two):
> some = one
> stuff = two
> are(happening)
> here()
> EOF
$ cat << EOF > other
> def somefunction(one, two):
> some = one
> change = two
> are(happening)
> here()
> EOF
The minimalist case recognises the grafted content as similar and highlight the
actual change.
$ $TESTDIR/../contrib/simplemerge --print local base other
def somefunction(one, two):
some = one
<<<<<<< local
stuff = two
=======
change = two
>>>>>>> other
are(happening)
here()
warning: conflicts during merge.
[1]
Again, the non-minimalist case produces a larger conflict. Making it harder to
spot the actual conflict.
$ $TESTDIR/../contrib/simplemerge --print --no-minimal local base other
<<<<<<< local
def somefunction(one, two):
some = one
stuff = two
are(happening)
here()
=======
def somefunction(one, two):
some = one
change = two
are(happening)
here()
>>>>>>> other
warning: conflicts during merge.
[1]
Practical disadvantage: multiple functions on each side
---------------------------------------------------------------
So, if this "minimalist" help so much, why introduce a setting to disable it?
The issue is that this minimisation will grab any common lines for breaking
chunks. This may result in partial context when solving a merge. The most
simple example is a merge where both side added some (different) functions
separated by blank lines. The "minimalist" approach will recognise the blank
line as "common" and over slice the chunks, turning a simple conflict case into
multiple pairs of conflicting functions.
$ cat << EOF > base
> # empty file
> EOF
$ cat << EOF > local
> def function1():
> bla()
> bla()
> bla()
>
> def function2():
> ble()
> ble()
> ble()
> EOF
$ cat << EOF > other
> def function3():
> bli()
> bli()
> bli()
>
> def function4():
> blo()
> blo()
> blo()
> EOF
The minimal case presents each function as a separated context.
$ $TESTDIR/../contrib/simplemerge --print local base other
<<<<<<< local
def function1():
bla()
bla()
bla()
=======
def function3():
bli()
bli()
bli()
>>>>>>> other
<<<<<<< local
def function2():
ble()
ble()
ble()
=======
def function4():
blo()
blo()
blo()
>>>>>>> other
warning: conflicts during merge.
[1]
The non-minimalist approach produces a simpler version with more context in
each block. Solving such conflicts is usually as simple as dropping the 3 lines
dedicated to markers.
$ $TESTDIR/../contrib/simplemerge --prin --no-minimal local base other
<<<<<<< local
def function1():
bla()
bla()
bla()
def function2():
ble()
ble()
ble()
=======
def function3():
bli()
bli()
bli()
def function4():
blo()
blo()
blo()
>>>>>>> other
warning: conflicts during merge.
[1]
Practical disaster: programing language have a lot of common line
=================================================================
If only blank lines between function where the only frequent content of a code
file. But programming language tend to repeat them self much more often. In that
case, the minimalist approach turns a simple conflict into a massive mess.
Consider this example where two unrelated functions are added on each side.
Those function shares common programming constructs by chance.
$ cat << EOF > base
> # empty file
> EOF
$ cat << EOF > local
> def longfunction():
> if bla:
> foo
> else:
> bar
> try:
> ret = some stuff
> except Exception:
> ret = None
> if ret is not None:
> return ret
> return 0
>
> def shortfunction(foo):
> goo()
> ret = foo + 5
> return ret
> EOF
$ cat << EOF > other
> def otherlongfunction():
> for x in xxx:
> if coin:
> break
> tutu
> else:
> bar()
> baz()
> ret = week()
> try:
> groumpf = tutu
> fool()
> except Exception:
> zoo()
> pool()
> if cond:
> return ret
>
> # some big block
> ret ** 6
> koin()
> return ret
> EOF
The minimalist approach will hash the whole conflict into small chunks that
does not match any meaningful semantic and are impossible to solve.
$ $TESTDIR/../contrib/simplemerge --print local base other
<<<<<<< local
def longfunction():
if bla:
foo
=======
def otherlongfunction():
for x in xxx:
if coin:
break
tutu
>>>>>>> other
else:
<<<<<<< local
bar
=======
bar()
baz()
ret = week()
>>>>>>> other
try:
<<<<<<< local
ret = some stuff
=======
groumpf = tutu
fool()
>>>>>>> other
except Exception:
<<<<<<< local
ret = None
if ret is not None:
=======
zoo()
pool()
if cond:
>>>>>>> other
return ret
<<<<<<< local
return 0
=======
>>>>>>> other
<<<<<<< local
def shortfunction(foo):
goo()
ret = foo + 5
=======
# some big block
ret ** 6
koin()
>>>>>>> other
return ret
warning: conflicts during merge.
[1]
The non minimalist approach will properly produce a single set of conflict
markers. Highlighting that the two chunk are unrelated. Such conflict from
unrelated content added at the same place is usually solved by dropping the
marker an keeping both content. Something impossible with minimised markers.
$ $TESTDIR/../contrib/simplemerge --prin --no-minimal local base other
<<<<<<< local
def longfunction():
if bla:
foo
else:
bar
try:
ret = some stuff
except Exception:
ret = None
if ret is not None:
return ret
return 0
def shortfunction(foo):
goo()
ret = foo + 5
return ret
=======
def otherlongfunction():
for x in xxx:
if coin:
break
tutu
else:
bar()
baz()
ret = week()
try:
groumpf = tutu
fool()
except Exception:
zoo()
pool()
if cond:
return ret
# some big block
ret ** 6
koin()
return ret
>>>>>>> other
warning: conflicts during merge.
[1]
diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -188,11 +188,13 @@ def _premerge(repo, toolconf, files, lab
raise error.ConfigError(_("%s.premerge not valid "
"('%s' is neither boolean nor %s)") %
(tool, premerge, _valid))
if premerge:
- r = simplemerge.simplemerge(ui, a, b, c, quiet=True, label=labels)
+ scope = ui.config('ui', 'mergemarkersscope', 'minimal')
+ r = simplemerge.simplemerge(ui, a, b, c, quiet=True, label=labels,
+ no_minimal=(scope == 'plain'))
if not r:
ui.debug(" premerge successful\n")
return 0
if premerge != 'keep':
util.copyfile(back, a) # restore from backup and try again
@@ -215,11 +217,13 @@ def _imerge(repo, mynode, orig, fcd, fco
if r:
a, b, c, back = files
ui = repo.ui
- r = simplemerge.simplemerge(ui, a, b, c, label=labels)
+ scope = ui.config('ui', 'mergemarkersscope', 'minimal')
+ r = simplemerge.simplemerge(ui, a, b, c, label=labels,
+ no_minimal=(scope == 'plain'))
return True, r
return False, 0
@internaltool('dump', True)
def _idump(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -1226,10 +1226,15 @@ User interface controls.
marker during merge conflicts. See :hg:`help templates` for the template
format.
Defaults to showing the hash, tags, branches, bookmarks, author, and
the first line of the commit description.
+``mergemarkersscope``
+ Set the amount of information included in the markers. The default
+ ``minimal`` reduce the size of conflicting chunk as much as possible.
+ ``plain`` can be used to include the whole content of the conflicting chunk.
+
``portablefilenames``
Check for portable filenames. Can be ``warn``, ``ignore`` or ``abort``.
Default is ``warn``.
If set to ``warn`` (or ``true``), a warning message is printed on POSIX
platforms, if a file with a non-portable filename is added (e.g. a file
diff --git a/tests/test-conflict.t b/tests/test-conflict.t
--- a/tests/test-conflict.t
+++ b/tests/test-conflict.t
@@ -114,5 +114,62 @@ Verify basic conflict markers
=======
4
5
>>>>>>> other
Hop we are done.
+
+Test minimalist config settings
+
+("plain" setting)
+
+ $ hg up -q --clean .
+ $ printf "\n[ui]\nmergemarkersscope=plain\n" >> .hg/hgrc
+
+ $ hg merge 1
+ merging a
+ warning: conflicts during merge.
+ merging a incomplete! (edit conflicts, then use 'hg resolve --mark')
+ 0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+ use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+ [1]
+ $ cat a
+ Small Mathematical Series.
+ <<<<<<< local
+ 1
+ 2
+ 3
+ 6
+ 8
+ =======
+ 1
+ 2
+ 3
+ 4
+ 5
+ >>>>>>> other
+ Hop we are done.
+
+("minimal" setting)
+
+ $ hg up -q --clean .
+ $ printf "\n[ui]\nmergemarkersscope=minimal\n" >> .hg/hgrc
+
+ $ hg merge 1
+ merging a
+ warning: conflicts during merge.
+ merging a incomplete! (edit conflicts, then use 'hg resolve --mark')
+ 0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+ use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+ [1]
+ $ cat a
+ Small Mathematical Series.
+ 1
+ 2
+ 3
+ <<<<<<< local
+ 6
+ 8
+ =======
+ 4
+ 5
+ >>>>>>> other
+ Hop we are done.
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