index 1023ac2b59c139cad2d9634a7a88b812d7761102..6d7cf6d51fc5c2511c8ed411ed36aefd93d4ad60 100644 (file)
History Simplification
~~~~~~~~~~~~~~~~~~~~~~
History Simplification
~~~~~~~~~~~~~~~~~~~~~~
-When optional paths are given, 'git rev-list' simplifies commits with
-various strategies, according to the options you have selected.
+Sometimes you are only interested in parts of the history, for example the
+commits modifying a particular <path>. But there are two parts of
+'History Simplification', one part is selecting the commits and the other
+is how to do it, as there are various strategies to simplify the history.
+
+The following options select the commits to be shown:
+
+<paths>::
+
+ Commits modifying the given <paths> are selected.
+
+--simplify-by-decoration::
+
+ Commits that are referred by some branch or tag are selected.
+
+Note that extra commits can be shown to give a meaningful history.
+
+The following options affect the way the simplification is performed:
+
+Default mode::
+
+ Simplifies the history to the simplest history explaining the
+ final state of the tree. Simplest because it prunes some side
+ branches if the end result is the same (i.e. merging branches
+ with the same content)
+
+--full-history::
+
+ As the default mode but does not prune some history.
+
+--dense::
+
+ Only the selected commits are shown, plus some to have a
+ meaningful history.
+
+--sparse::
+
+ All commits in the simplified history are shown.
+
+--simplify-merges::
+
+ Additional option to '--full-history' to remove some needless
+ merges from the resulting history, as there are no selected
+ commits contributing to this merge.
+
+A more detailed explanation follows.
Suppose you specified `foo` as the <paths>. We shall call commits
that modify `foo` !TREESAME, and the rest TREESAME. (In a diff
Suppose you specified `foo` as the <paths>. We shall call commits
that modify `foo` !TREESAME, and the rest TREESAME. (In a diff
one of the parents is TREESAME, we follow only that one, so the other
sides of the merge are never walked.
one of the parents is TREESAME, we follow only that one, so the other
sides of the merge are never walked.
+Finally, there is a fourth simplification mode available:
+
+--simplify-merges::
+
+ First, build a history graph in the same way that
+ '\--full-history' with parent rewriting does (see above).
++
+Then simplify each commit `C` to its replacement `C'` in the final
+history according to the following rules:
++
+--
+* Set `C'` to `C`.
++
+* Replace each parent `P` of `C'` with its simplification `P'`. In
+ the process, drop parents that are ancestors of other parents, and
+ remove duplicates.
++
+* If after this parent rewriting, `C'` is a root or merge commit (has
+ zero or >1 parents), a boundary commit, or !TREESAME, it remains.
+ Otherwise, it is replaced with its only parent.
+--
++
+The effect of this is best shown by way of comparing to
+'\--full-history' with parent rewriting. The example turns into:
++
+-----------------------------------------------------------------------
+ .-A---M---N---O
+ / / /
+ I B D
+ \ / /
+ `---------'
+-----------------------------------------------------------------------
++
+Note the major differences in `N` and `P` over '\--full-history':
++
+--
+* `N`'s parent list had `I` removed, because it is an ancestor of the
+ other parent `M`. Still, `N` remained because it is !TREESAME.
++
+* `P`'s parent list similarly had `I` removed. `P` was then
+ removed completely, because it had one parent and is TREESAME.
+--
+
+The '\--simplify-by-decoration' option allows you to view only the
+big picture of the topology of the history, by omitting commits
+that are not referenced by tags. Commits are marked as !TREESAME
+(in other words, kept after history simplification rules described
+above) if (1) they are referenced by tags, or (2) they change the
+contents of the paths given on the command line. All other
+commits are marked as TREESAME (subject to be simplified away).
ifdef::git-rev-list[]
Bisection Helpers
ifdef::git-rev-list[]
Bisection Helpers