Documentation: document AUTO_MERGE

Since 5291828df8 (merge-ort: write $GIT_DIR/AUTO_MERGE whenever we hit a
conflict, 2021-03-20), when using the 'ort' merge strategy, the special
ref AUTO_MERGE is written when a merge operation results in conflicts.
This ref points to a tree recording the conflicted state of the working
tree and is very useful during conflict resolution. However, this ref is
not documented.

Add some documentation for AUTO_MERGE in git-diff(1), git-merge(1),
gitrevisions(7) and in the user manual.

In git-diff(1), mention it at the end of the description section, when
we mention that the command also accepts trees instead of commits, and
also add an invocation to the "Various ways to check your working tree"
example.

In git-merge(1), add a step to the list of things that happen "when it
is not obvious how to reconcile the changes", under the "True merge"
section. Also mention AUTO_MERGE in the "How to resolve conflicts"
section, when mentioning 'git diff'.

In gitrevisions(7), add a mention of AUTO_MERGE along with the other
special refs.

In the user manual, add a paragraph describing AUTO_MERGE to the
"Getting conflict-resolution help during a merge" section, and include
an example of a 'git diff AUTO_MERGE' invocation for the example
conflict used in that section. Note that for uniformity we do not use
backticks around AUTO_MERGE here since the rest of the document does not
typeset special refs differently.

Closes: https://github.com/gitgitgadget/git/issues/1471
Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt
index dc9c6a6..aa38513 100644
--- a/Documentation/user-manual.txt
+++ b/Documentation/user-manual.txt
@@ -1343,6 +1343,33 @@ $ git diff -3 file.txt		# diff against stage 3
 $ git diff --theirs file.txt	# same as the above.
 -------------------------------------------------
 
+When using the 'ort' merge strategy (the default), before updating the working
+tree with the result of the merge, Git writes a special ref named AUTO_MERGE
+reflecting the state of the tree it is about to write. Conflicted paths with
+textual conflicts that could not be automatically merged are written to this
+tree with conflict markers, just as in the working tree. AUTO_MERGE can thus be
+used with linkgit:git-diff[1] to show the changes you've made so far to resolve
+conflicts. Using the same example as above, after resolving the conflict we
+get:
+
+-------------------------------------------------
+$ git diff AUTO_MERGE
+diff --git a/file.txt b/file.txt
+index cd10406..8bf5ae7 100644
+--- a/file.txt
++++ b/file.txt
+@@ -1,5 +1 @@
+-<<<<<<< HEAD:file.txt
+-Hello world
+-=======
+-Goodbye
+->>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
++Goodbye world
+-------------------------------------------------
+
+Notice that the diff shows we deleted the conflict markers and both versions of
+the content line, and wrote "Goodbye world" instead.
+
 The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
 for merges: