revision.c: Make --full-history consider more merges

History simplification previously always treated merges as TREESAME
if they were TREESAME to any parent.

While this was consistent with the default behaviour, this could be
extremely unhelpful when searching detailed history, and could not be
overridden. For example, if a merge had ignored a change, as if by "-s
ours", then:

  git log -m -p --full-history -Schange file

would successfully locate "change"'s addition but would not locate the
merge that resolved against it.

Futher, simplify_merges could drop the actual parent that a commit
was TREESAME to, leaving it as a normal commit marked TREESAME that
isn't actually TREESAME to its remaining parent.

Now redefine a commit's TREESAME flag to be true only if a commit is
TREESAME to _all_ of its parents. This doesn't affect either the default
simplify_history behaviour (because partially TREESAME merges are turned
into normal commits), or full-history with parent rewriting (because all
merges are output). But it does affect other modes. The clearest
difference is that --full-history will show more merges - sufficient to
ensure that -m -p --full-history log searches can really explain every
change to the file, including those changes' ultimate fate in merges.

Also modify simplify_merges to recalculate TREESAME after removing
a parent. This is achieved by storing per-parent TREESAME flags on the
initial scan, so the combined flag can be easily recomputed.

This fixes some t6111 failures, but creates a couple of new ones -
we are now showing some merges that don't need to be shown.

Signed-off-by: Kevin Bracey <kevin@bracey.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 55ddf33..d166384 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -409,10 +409,10 @@ parent lines.
 	the example, we get
 +
 -----------------------------------------------------------------------
-	I  A  B  N  D  O
+	I  A  B  N  D  O  P
 -----------------------------------------------------------------------
 +
-`P` and `M` were excluded because they are TREESAME to a parent.  `E`,
+`M` was excluded because it is TREESAME to both parents.  `E`,
 `C` and `B` were all walked, but only `B` was !TREESAME, so the others
 do not appear.
 +
@@ -440,7 +440,7 @@ themselves.  This results in
 Compare to '\--full-history' without rewriting above.  Note that `E`
 was pruned away because it is TREESAME, but the parent list of P was
 rewritten to contain `E`'s parent `I`.  The same happened for `C` and
-`N`.  Note also that `P` was included despite being TREESAME.
+`N`.
 
 In addition to the above settings, you can change whether TREESAME
 affects inclusion: