Subject: [PATCH v2 13/13] git-merge-tree.txt: add a section on potentional usage mistakes

From: "Elijah Newren via GitGitGadget" <[email-masked]>
Date: Sat, 29 Jan 2022 18:07:13 +0000

From: Elijah Newren <[email-masked]>

Signed-off-by: Elijah Newren <[email-masked]>
---
 Documentation/git-merge-tree.txt | 46 ++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/Documentation/git-merge-tree.txt b/Documentation/git-merge-tree.txt
index d35710c81d5..b97ddc58a7a 100644
--- a/Documentation/git-merge-tree.txt
+++ b/Documentation/git-merge-tree.txt
@@ -133,6 +133,52 @@ that they'd have access to if using `git merge`:
   * any messages that would have been printed to stdout (the <Informational
     messages>)
 
+MISTAKES TO AVOID
+-----------------
+
+Do NOT look through the resulting toplevel tree to try to find which
+files conflict; parse the <Conflicted file info> section instead.  Not
+only would parsing an entire tree be horrendously slow in large
+repositories, there are numerous types of conflicts not representable by
+conflict markers (modify/delete, mode conflict, binary file changed on
+both sides, file/directory conflicts, various rename conflict
+permutations, etc.)
+
+Do NOT interpret an empty <Conflicted file info> list as a clean merge;
+check the exit status.  A merge can have conflicts without having
+individual files conflict (there are a few types of directory rename
+conflicts that fall into this category, and others might also be added
+in the future).
+
+Do NOT attempt to guess or make the user guess the conflict types from
+the <Conflicted file info> list.  The information there is insufficient
+to do so.  For example: Rename/rename(1to2) conflicts (both sides
+renamed the same file differently) will result in three different file
+having higher order stages (but each only has one higher order stage),
+with no way (short of the <Informational messages> section) to determine
+which three files are related.  File/directory conflicts also result in
+a file with exactly one higher order stage.
+Possibly-involved-in-directory-rename conflicts (when
+"merge.directoryRenames" is unset or set to "conflicts") also result in
+a file with exactly one higher order stage.  In all cases, the
+<Informational messages> section has the necessary info, though it is
+not designed to be machine parseable.
+
+Do NOT assume all filenames listed in the <Informational messages>
+section had conflicts.  Messages can be included for files that have no
+conflicts, such as "Auto-merging <file>".
+
+AVOID taking the OIDS from the <Conflicted file info> and re-merging
+them to present the conflicts to the user.  This will lose information.
+Instead, look up the version of the file found within the <OID of
+toplevel tree> and show that instead.  In particular, the latter will
+have conflict markers annotated with the original branch/commit being
+merged and, if renames were involved, the original filename.  While you
+could include the original branch/commit in the conflict marker
+annotations when re-merging, the original filename is not available from
+the <Conflicted file info> and thus you would be losing information that
+might help the user resolve the conflict.
+
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 ---
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