merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 74 insertions, 88 deletions

diff --git a/third_party/git/t/t3427-rebase-subtree.sh b/third_party/git/t/t3427-rebase-subtree.sh
index d8640522a086..2a7d958ea753 100755
--- a/third_party/git/t/t3427-rebase-subtree.sh
+++ b/third_party/git/t/t3427-rebase-subtree.sh
@@ -11,113 +11,99 @@ commit_message() {
 	git log --pretty=format:%s -1 "$1"
 }
 
+# There are a few bugs in the rebase with regards to the subtree strategy, and
+# this test script tries to document them.  First, the following commit history
+# is generated (the onelines are shown, time flows from left to right):
+#
+# topic_1 - topic_2 - topic_3
+#                             \
+# README ---------------------- Add subproject master - topic_4 - files_subtree/topic_5
+#
+# Where the merge moves the files master[123].t into the subdirectory
+# files_subtree/ and topic_4 as well as files_subtree/topic_5 add files to that
+# directory directly.
+#
+# Then, in subsequent test cases, `git filter-branch` is used to distill just
+# the commits that touch files_subtree/. To give it a final pre-rebase touch,
+# an empty commit is added on top. The pre-rebase commit history looks like
+# this:
+#
+# Add subproject master - topic_4 - files_subtree/topic_5 - Empty commit
+#
+# where the root commit adds three files: topic_1.t, topic_2.t and topic_3.t.
+#
+# This commit history is then rebased onto `topic_3` with the
+# `-Xsubtree=files_subtree` option in three different ways:
+#
+# 1. using `--preserve-merges`
+# 2. using `--preserve-merges` and --keep-empty
+# 3. without specifying a rebase backend
+
 test_expect_success 'setup' '
 	test_commit README &&
-	mkdir files &&
-	(
-		cd files &&
-		git init &&
-		test_commit master1 &&
-		test_commit master2 &&
-		test_commit master3
-	) &&
-	git fetch files master &&
-	git branch files-master FETCH_HEAD &&
-	git read-tree --prefix=files_subtree files-master &&
-	git checkout -- files_subtree &&
-	tree=$(git write-tree) &&
-	head=$(git rev-parse HEAD) &&
-	rev=$(git rev-parse --verify files-master^0) &&
-	commit=$(git commit-tree -p $head -p $rev -m "Add subproject master" $tree) &&
-	git update-ref HEAD $commit &&
-	(
-		cd files_subtree &&
-		test_commit master4
-	) &&
-	test_commit files_subtree/master5
-'
 
-# FAILURE: Does not preserve master4.
-test_expect_failure REBASE_P \
-	'Rebase -Xsubtree --preserve-merges --onto commit 4' '
-	reset_rebase &&
-	git checkout -b rebase-preserve-merges-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --preserve-merges --onto files-master master &&
-	verbose test "$(commit_message HEAD~)" = "files_subtree/master4"
-'
+	git init files &&
+	test_commit -C files topic_1 &&
+	test_commit -C files topic_2 &&
+	test_commit -C files topic_3 &&
 
-# FAILURE: Does not preserve master5.
-test_expect_failure REBASE_P \
-	'Rebase -Xsubtree --preserve-merges --onto commit 5' '
-	reset_rebase &&
-	git checkout -b rebase-preserve-merges-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --preserve-merges --onto files-master master &&
-	verbose test "$(commit_message HEAD)" = "files_subtree/master5"
-'
+	: perform subtree merge into files_subtree/ &&
+	git fetch files refs/heads/master:refs/heads/files-master &&
+	git merge -s ours --no-commit --allow-unrelated-histories \
+		files-master &&
+	git read-tree --prefix=files_subtree -u files-master &&
+	git commit -m "Add subproject master" &&
 
-# FAILURE: Does not preserve master4.
-test_expect_failure REBASE_P \
-	'Rebase -Xsubtree --keep-empty --preserve-merges --onto commit 4' '
-	reset_rebase &&
-	git checkout -b rebase-keep-empty-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
-	verbose test "$(commit_message HEAD~2)" = "files_subtree/master4"
+	: add two extra commits to rebase &&
+	test_commit -C files_subtree topic_4 &&
+	test_commit files_subtree/topic_5 &&
+
+	git checkout -b to-rebase &&
+	git fast-export --no-data HEAD -- files_subtree/ |
+		sed -e "s%\([0-9a-f]\{40\} \)files_subtree/%\1%" |
+		git fast-import --force --quiet &&
+	git reset --hard &&
+	git commit -m "Empty commit" --allow-empty
 '
 
-# FAILURE: Does not preserve master5.
-test_expect_failure REBASE_P \
-	'Rebase -Xsubtree --keep-empty --preserve-merges --onto commit 5' '
+# FAILURE: Does not preserve topic_4.
+test_expect_failure REBASE_P 'Rebase -Xsubtree --preserve-merges --onto commit' '
 	reset_rebase &&
-	git checkout -b rebase-keep-empty-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
-	verbose test "$(commit_message HEAD~)" = "files_subtree/master5"
+	git checkout -b rebase-preserve-merges to-rebase &&
+	git rebase -Xsubtree=files_subtree --preserve-merges --onto files-master master &&
+	verbose test "$(commit_message HEAD~)" = "topic_4" &&
+	verbose test "$(commit_message HEAD)" = "files_subtree/topic_5"
 '
 
-# FAILURE: Does not preserve Empty.
-test_expect_failure REBASE_P \
-	'Rebase -Xsubtree --keep-empty --preserve-merges --onto empty commit' '
+# FAILURE: Does not preserve topic_4.
+test_expect_failure REBASE_P 'Rebase -Xsubtree --keep-empty --preserve-merges --onto commit' '
 	reset_rebase &&
-	git checkout -b rebase-keep-empty-empty master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-keep-empty to-rebase &&
 	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
+	verbose test "$(commit_message HEAD~2)" = "topic_4" &&
+	verbose test "$(commit_message HEAD~)" = "files_subtree/topic_5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-# FAILURE: fatal: Could not parse object
-test_expect_failure 'Rebase -Xsubtree --onto commit 4' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --onto commit' '
 	reset_rebase &&
-	git checkout -b rebase-onto-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --onto files-master master &&
-	verbose test "$(commit_message HEAD~2)" = "files_subtree/master4"
+	git checkout -b rebase-onto to-rebase &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --onto files-master master &&
+	: first pick results in no changes &&
+	git rebase --skip &&
+	verbose test "$(commit_message HEAD~2)" = "topic_4" &&
+	verbose test "$(commit_message HEAD~)" = "files_subtree/topic_5" &&
+	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-# FAILURE: fatal: Could not parse object
-test_expect_failure 'Rebase -Xsubtree --onto commit 5' '
-	reset_rebase &&
-	git checkout -b rebase-onto-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --onto files-master master &&
-	verbose test "$(commit_message HEAD~)" = "files_subtree/master5"
-'
-# FAILURE: fatal: Could not parse object
-test_expect_failure 'Rebase -Xsubtree --onto empty commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --rebase-merges --onto commit' '
 	reset_rebase &&
-	git checkout -b rebase-onto-empty master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
-	git rebase -Xsubtree=files_subtree --onto files-master master &&
+	git checkout -b rebase-merges-onto to-rebase &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --rebase-merges --onto files-master --root &&
+	: first pick results in no changes &&
+	git rebase --skip &&
+	verbose test "$(commit_message HEAD~2)" = "topic_4" &&
+	verbose test "$(commit_message HEAD~)" = "files_subtree/topic_5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '