[PATCH v2] merge-ort: fix bug with renormalization and rename/delete conflicts

["Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Elijah Newren <newren@gmail.com>

Ever since commit a492d5331c ("merge-ort: ensure we consult df_conflict
and path_conflicts", 2021-06-30), when renormalization is active AND a
file is involved in a rename/delete conflict BUT the file is unmodified
(either before or after renormalization), merge-ort was running into an
assertion failure.  Prior to that commit (or if assertions were compiled
out), merge-ort would mis-merge instead, ignoring the rename/delete
conflict and just deleting the file.

Remove the assertions, fix the code appropriately, leave some good
comments in the code, and add a testcase for this situation.

Reported-by: Ralf Thielow <ralf.thielow@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
---
    merge-ort: fix bug with renormalization and rename/delete conflicts
    
    Original report:
    https://lore.kernel.org/git/CAN0XMOK8iHZnbtYw7CPAQGJcmuVSDxQoFNFEwiaa41V89F1rzA@mail.gmail.com/
    
    Built in v2.34.1, but rebases onto and/or merges cleanly with newer
    versions.
    
    Changes since v1:
    
     * Added Stolee's Reviewed-by

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1174%2Fnewren%2Fmerge-ort-rename-delete-renormalization-bug-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1174/newren/merge-ort-rename-delete-renormalization-bug-v2
Pull-Request: https://github.com/git/git/pull/1174

Range-diff vs v1:

 1:  5841f3d901d ! 1:  72876b9c106 merge-ort: fix bug with renormalization and rename/delete conflicts
     @@ Commit message
          comments in the code, and add a testcase for this situation.
      
          Reported-by: Ralf Thielow <ralf.thielow@gmail.com>
     +    Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
       ## merge-ort.c ##


 merge-ort.c                | 19 ++++++++++++++++---
 t/t6418-merge-text-auto.sh | 26 ++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/merge-ort.c b/merge-ort.c
index 0342f104836..c3197970219 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -3841,9 +3841,22 @@ static void process_entry(struct merge_options *opt,
 		if (opt->renormalize &&
 		    blob_unchanged(opt, &ci->stages[0], &ci->stages[side],
 				   path)) {
-			ci->merged.is_null = 1;
-			ci->merged.clean = 1;
-			assert(!ci->df_conflict && !ci->path_conflict);
+			if (!ci->path_conflict) {
+				/*
+				 * Blob unchanged after renormalization, so
+				 * there's no modify/delete conflict after all;
+				 * we can just remove the file.
+				 */
+				ci->merged.is_null = 1;
+				ci->merged.clean = 1;
+				 /*
+				  * file goes away => even if there was a
+				  * directory/file conflict there isn't one now.
+				  */
+				ci->df_conflict = 0;
+			} else {
+				/* rename/delete, so conflict remains */
+			}
 		} else if (ci->path_conflict &&
 			   oideq(&ci->stages[0].oid, &ci->stages[side].oid)) {
 			/*
diff --git a/t/t6418-merge-text-auto.sh b/t/t6418-merge-text-auto.sh
index 1e0296dd172..41288a60ceb 100755
--- a/t/t6418-merge-text-auto.sh
+++ b/t/t6418-merge-text-auto.sh
@@ -204,4 +204,30 @@ test_expect_success 'Test delete/normalize conflict' '
 	test_path_is_missing file
 '
 
+test_expect_success 'rename/delete vs. renormalization' '
+	git init subrepo &&
+	(
+		cd subrepo &&
+		echo foo >oldfile &&
+		git add oldfile &&
+		git commit -m original &&
+
+		git branch rename &&
+		git branch nuke &&
+
+		git checkout rename &&
+		git mv oldfile newfile &&
+		git commit -m renamed &&
+
+		git checkout nuke &&
+		git rm oldfile &&
+		git commit -m deleted &&
+
+		git checkout rename^0 &&
+		test_must_fail git -c merge.renormalize=true merge nuke >out &&
+
+		grep "rename/delete" out
+	)
+'
+
 test_done

base-commit: e9d7761bb94f20acc98824275e317fa82436c25d
-- 
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