mergetools: add a test for premerge --keep It works! No surprise.

test-merge-tools: introduce a "revision 4" that merges with conflict We need conflicts to test the premerge=keep configuration.

merge: add an internal:merge3 tool This variant gives access to a feature already present in ``internal:merge``: displaying merge base content. In the basic merge (calling ``hg merge``) case, including more context to the merge markers is an interesting addition. But this extra information is the only viable option in case conflict from grafting (, rebase, etc…). When grafting ``source`` on ``destination``, the parent of ``source`` is used as the ``base``. When all three changesets add content in the same location, the marker for ``source`` will contains both ``base`` and ``source`` content. Without the content of base exposed, there is no way for the user to discriminate content coming from ``base`` and content commit from ``source``. Practical example (all addition are in the same place): * ``destination`` adds ``Dest-Content`` * ``base`` adds ``Base-Content`` * ``source`` adds ``Src-Content`` Grafting ``source`` on ``destination`` will produce the following conflict: <<<<<<< destination Dest-Content ======= Base-Content Src-Content >>>>>>> source This that case there is no way to distinct ``base`` from ``source``. As a result content from ``base`` are likely to slip in the resolution result. However, adding the base make the situation very clear: <<<<<<< destination Dest-Content ||||||| base Base-Content ======= base Base-Content Src-Content >>>>>>> source Once the base is added, the addition from the grafted changeset is made clear. User can compare the content from ``base`` and ``source`` to make an enlightened decision during merge resolution.

internal:merge: update documentation Highlight the fact there are two regions in the markers and what their contents are. This prepares for the arrival of merge3.

filemerge: allow the formatting of three labels instead of two When a third label is provided (to included the base content) it is properly processed as the two others. Nothing changes if only two labels are provided.

filemerge: drop extra white space There should be no white space around the brace.

simplemerge: support three labels when merging If a third label is provided it will be used for the "base" content: <<<<<<< local content from local ||||||| base former common ======= other conflicting >>>>>>> other

simplemerge: burn "minimal" feature to the ground Matt Mackall said: The goal of simplemerge should have always been to be a drop-in replacement for RCS merge. Please nuke this minimization thing entirely. This whole things is now dead.

merge: use no-minimal for premerge too ecc1387138ba disabled minimal for `internal:merge` but forgot to also disabled it for premerge. This is now done. This gives me an occasion to shamelessly includes my explanation of why this minimisation feature must disappear: [this is why it's pointless to reject patches with misspellings in the description - mpm] 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]

merge: refactor labels selection code The code is simplified to prepare the future introduction of a third labels for the merge base.