Merge branch 'en/merge-strategy-docs' into maint

Documentation updates.

* en/merge-strategy-docs:
  Update error message and code comment
  merge-strategies.txt: add coverage of the `ort` merge strategy
  git-rebase.txt: correct out-of-date and misleading text about renames
  merge-strategies.txt: fix simple capitalization error
  merge-strategies.txt: avoid giving special preference to patience algorithm
  merge-strategies.txt: do not imply using copy detection is desired
  merge-strategies.txt: update wording for the resolve strategy
  Documentation: edit awkward references to `git merge-recursive`
  directory-rename-detection.txt: small updates due to merge-ort optimizations
  git-rebase.txt: correct antiquated claims about --rebase-merges

4 files changed, 53 insertions, 40 deletions

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 55af6fd24e..73d49ec8d9 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -340,9 +340,7 @@ See also INCOMPATIBLE OPTIONS below.
 
 -m::
 --merge::
-	Use merging strategies to rebase.  When the recursive (default) merge
-	strategy is used, this allows rebase to be aware of renames on the
-	upstream side.  This is the default.
+	Using merging strategies to rebase (default).
 +
 Note that a rebase merge works by replaying each commit from the working
 branch on top of the <upstream> branch.  Because of this, when a merge
@@ -354,9 +352,8 @@ See also INCOMPATIBLE OPTIONS below.
 
 -s <strategy>::
 --strategy=<strategy>::
-	Use the given merge strategy.
-	If there is no `-s` option 'git merge-recursive' is used
-	instead.  This implies --merge.
+	Use the given merge strategy, instead of the default
+	`recursive`.  This implies `--merge`.
 +
 Because 'git rebase' replays each commit from the working branch
 on top of the <upstream> branch using the given strategy, using
@@ -530,7 +527,7 @@ The `--rebase-merges` mode is similar in spirit to the deprecated
 where commits can be reordered, inserted and dropped at will.
 +
 It is currently only possible to recreate the merge commits using the
-`recursive` merge strategy; Different merge strategies can be used only via
+`recursive` merge strategy; different merge strategies can be used only via
 explicit `exec git merge -s <strategy> [...]` commands.
 +
 See also REBASING MERGES and INCOMPATIBLE OPTIONS below.
@@ -1219,12 +1216,16 @@ successful merge so that the user can edit the message.
 If a `merge` command fails for any reason other than merge conflicts (i.e.
 when the merge operation did not even start), it is rescheduled immediately.
 
-At this time, the `merge` command will *always* use the `recursive`
-merge strategy for regular merges, and `octopus` for octopus merges,
-with no way to choose a different one. To work around
-this, an `exec` command can be used to call `git merge` explicitly,
-using the fact that the labels are worktree-local refs (the ref
-`refs/rewritten/onto` would correspond to the label `onto`, for example).
+By default, the `merge` command will use the `recursive` merge
+strategy for regular merges, and `octopus` for octopus merges.  One
+can specify a default strategy for all merges using the `--strategy`
+argument when invoking rebase, or can override specific merges in the
+interactive list of commands by using an `exec` command to call `git
+merge` explicitly with a `--strategy` argument.  Note that when
+calling `git merge` explicitly like this, you can make use of the fact
+that the labels are worktree-local refs (the ref `refs/rewritten/onto`
+would correspond to the label `onto`, for example) in order to refer
+to the branches you want to merge.
 
 Note: the first command (`label onto`) labels the revision onto which
 the commits are rebased; The name `onto` is just a convention, as a nod
diff --git a/Documentation/merge-options.txt b/Documentation/merge-options.txt
index 52565014c1..f66e650064 100644
--- a/Documentation/merge-options.txt
+++ b/Documentation/merge-options.txt
@@ -112,8 +112,8 @@ With --squash, --commit is not allowed, and will fail.
 	Use the given merge strategy; can be supplied more than
 	once to specify them in the order they should be tried.
 	If there is no `-s` option, a built-in list of strategies
-	is used instead ('git merge-recursive' when merging a single
-	head, 'git merge-octopus' otherwise).
+	is used instead (`recursive` when merging a single head,
+	`octopus` otherwise).
 
 -X <option>::
 --strategy-option=<option>::
diff --git a/Documentation/merge-strategies.txt b/Documentation/merge-strategies.txt
index 2912de706b..210f0f850b 100644
--- a/Documentation/merge-strategies.txt
+++ b/Documentation/merge-strategies.txt
@@ -6,13 +6,6 @@ backend 'merge strategies' to be chosen with `-s` option.  Some strategies
 can also take their own options, which can be passed by giving `-X<option>`
 arguments to `git merge` and/or `git pull`.
 
-resolve::
-	This can only resolve two heads (i.e. the current branch
-	and another branch you pulled from) using a 3-way merge
-	algorithm.  It tries to carefully detect criss-cross
-	merge ambiguities and is considered generally safe and
-	fast.
-
 recursive::
 	This can only resolve two heads using a 3-way merge
 	algorithm.  When there is more than one common
@@ -23,9 +16,9 @@ recursive::
 	causing mismerges by tests done on actual merge commits
 	taken from Linux 2.6 kernel development history.
 	Additionally this can detect and handle merges involving
-	renames, but currently cannot make use of detected
-	copies.  This is the default merge strategy when pulling
-	or merging one branch.
+	renames.  It does not make use of detected copies.  This
+	is the default merge strategy when pulling or merging one
+	branch.
 +
 The 'recursive' strategy can take the following options:
 
@@ -44,17 +37,14 @@ theirs;;
 	no 'theirs' merge strategy to confuse this merge option with.
 
 patience;;
-	With this option, 'merge-recursive' spends a little extra time
-	to avoid mismerges that sometimes occur due to unimportant
-	matching lines (e.g., braces from distinct functions).  Use
-	this when the branches to be merged have diverged wildly.
-	See also linkgit:git-diff[1] `--patience`.
+	Deprecated synonym for `diff-algorithm=patience`.
 
 diff-algorithm=[patience|minimal|histogram|myers];;
-	Tells 'merge-recursive' to use a different diff algorithm, which
-	can help avoid mismerges that occur due to unimportant matching
-	lines (such as braces from distinct functions).  See also
-	linkgit:git-diff[1] `--diff-algorithm`.
+	Use a different diff algorithm while merging, which can help
+	avoid mismerges that occur due to unimportant matching lines
+	(such as braces from distinct functions).  See also
+	linkgit:git-diff[1] `--diff-algorithm`.  Defaults to the
+	`diff.algorithm` config setting.
 
 ignore-space-change;;
 ignore-all-space;;
@@ -105,6 +95,26 @@ subtree[=<path>];;
 	is prefixed (or stripped from the beginning) to make the shape of
 	two trees to match.
 
+ort::
+	This is meant as a drop-in replacement for the `recursive`
+	algorithm (as reflected in its acronym -- "Ostensibly
+	Recursive's Twin"), and will likely replace it in the future.
+	It fixes corner cases that the `recursive` strategy handles
+	suboptimally, and is significantly faster in large
+	repositories -- especially when many renames are involved.
++
+The `ort` strategy takes all the same options as `recursive`.
+However, it ignores three of those options: `no-renames`,
+`patience` and `diff-algorithm`.  It always runs with rename
+detection (it handles it much faster than `recursive` does), and
+it specifically uses `diff-algorithm=histogram`.
+
+resolve::
+	This can only resolve two heads (i.e. the current branch
+	and another branch you pulled from) using a 3-way merge
+	algorithm.  It tries to carefully detect criss-cross
+	merge ambiguities.  It does not handle renames.
+
 octopus::
 	This resolves cases with more than two heads, but refuses to do
 	a complex merge that needs manual resolution.  It is
diff --git a/Documentation/technical/directory-rename-detection.txt b/Documentation/technical/directory-rename-detection.txt
index 49b83ef3cc..029ee2cedc 100644
--- a/Documentation/technical/directory-rename-detection.txt
+++ b/Documentation/technical/directory-rename-detection.txt
@@ -2,9 +2,9 @@ Directory rename detection
 ==========================
 
 Rename detection logic in diffcore-rename that checks for renames of
-individual files is aggregated and analyzed in merge-recursive for cases
-where combinations of renames indicate that a full directory has been
-renamed.
+individual files is also aggregated there and then analyzed in either
+merge-ort or merge-recursive for cases where combinations of renames
+indicate that a full directory has been renamed.
 
 Scope of abilities
 ------------------
@@ -88,9 +88,11 @@ directory rename detection support in:
     Folks have requested in the past that `git diff` detect directory
     renames and somehow simplify its output.  It is not clear whether this
     would be desirable or how the output should be simplified, so this was
-    simply not implemented.  Further, to implement this, directory rename
-    detection logic would need to move from merge-recursive to
-    diffcore-rename.
+    simply not implemented.  Also, while diffcore-rename has most of the
+    logic for detecting directory renames, some of the logic is still found
+    within merge-ort and merge-recursive.  Fully supporting directory
+    rename detection in diffs would require copying or moving the remaining
+    bits of logic to the diff machinery.
 
   * am