[PATCH] t3424: new rebase testcase documenting a stat-dirty-like failure

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

From: Elijah Newren <newren@gmail.com>

A user discovered a case where they had a stack of 20 simple commits to
rebase, and the rebase would succeed in picking the first commit and
then error out with a pair of "Could not execute the todo command" and
"Your local changes to the following files would be overwritten by
merge" messages.

Their steps actually made use of the -i flag, but I switched it over to
-m to make it simpler to trigger the bug.  With that flag, it bisects
back to commit 68aa495b590d (rebase: implement --merge via the
interactive machinery, 2018-12-11), but that's misleading.  If you
change the -m flag to --keep-empty, then the problem persists and will
bisect back to 356ee4659bb5 (sequencer: try to commit without forking
'git commit', 2017-11-24)

After playing with the testcase for a bit, I discovered that added
--exec "sleep 1" to the command line makes the rebase succeed, making me
suspect there is some kind of discard and reloading of caches that lead
us to believe that something is stat dirty, but I didn't succeed in
digging any further than that.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
    t3424: new rebase testcase documenting a stat-dirty-like failure
    
    A user discovered a case where they had a stack of 20 simple commits to
    rebase, and the rebase would succeed in picking the first commit and
    then error out with a pair of "Could not execute the todo command" and
    "Your local changes to the following files would be overwritten by
    merge" messages.
    
    Their steps actually made use of the -i flag, but I switched it over to
    -m to make it simpler to trigger the bug. With that flag, it bisects
    back to commit 68aa495b590d (rebase: implement --merge via the
    interactive machinery, 2018-12-11), but that's misleading. If you change
    the -m flag to --keep-empty, then the problem persists and will bisect
    back to 356ee4659bb5 (sequencer: try to commit without forking 'git
    commit', 2017-11-24)
    
    After playing with the testcase for a bit, I discovered that added
    --exec "sleep 1" to the command line makes the rebase succeed, making me
    suspect there is some kind of discard and reloading of caches that lead
    us to believe that something is stat dirty, but I didn't succeed in
    digging any further than that.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-712%2Fnewren%2Fdocument-rebase-failure-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-712/newren/document-rebase-failure-v1
Pull-Request: https://github.com/git/git/pull/712

 t/t3424-rebase-across-mode-change.sh | 52 ++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100755 t/t3424-rebase-across-mode-change.sh

diff --git a/t/t3424-rebase-across-mode-change.sh b/t/t3424-rebase-across-mode-change.sh
new file mode 100755
index 00000000000..4d2eb1dd7c6
--- /dev/null
+++ b/t/t3424-rebase-across-mode-change.sh
@@ -0,0 +1,52 @@
+#!/bin/sh
+
+test_description='git rebase across mode change'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	rm -rf ../stupid &&
+	git init ../stupid &&
+	cd ../stupid &&
+	mkdir DS &&
+	>DS/whatever &&
+	git add DS &&
+	git commit -m base &&
+
+	git branch side1 &&
+	git branch side2 &&
+
+	git checkout side1 &&
+	git rm -rf DS &&
+	ln -s unrelated DS &&
+	git add DS &&
+	git commit -m side1 &&
+
+	git checkout side2 &&
+	>unrelated &&
+	git add unrelated &&
+	git commit -m commit1 &&
+
+	echo >>unrelated &&
+	git commit -am commit2
+'
+
+test_expect_success 'rebase changes with the apply backend' '
+	test_when_finished "git rebase --abort || true" &&
+	git checkout -b apply-backend side2 &&
+	git rebase side1
+'
+
+test_expect_failure 'rebase changes with the merge backend' '
+	test_when_finished "git rebase --abort || true" &&
+	git checkout -b merge-backend side2 &&
+	git rebase -m side1
+'
+
+test_expect_success 'rebase changes with the merge backend with a delay' '
+	test_when_finished "git rebase --abort || true" &&
+	git checkout -b merge-delay-backend side2 &&
+	git rebase -m --exec "sleep 1" side1
+'
+
+test_done

base-commit: e68e29171cc2d6968902e0654b5687fbe1ccb903
-- 
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