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

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

third_party/git/t/t3906-stash-submodule.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-test_description='stash apply can handle submodules'
+test_description='stash can handle submodules'
 
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
@@ -8,7 +8,12 @@ test_description='stash apply can handle submodules'
 git_stash () {
 	git status -su >expect &&
 	ls -1pR * >>expect &&
-	git read-tree -u -m "$1" &&
+	may_only_be_test_must_fail "$2" &&
+	$2 git read-tree -u -m "$1" &&
+	if test -n "$2"
+	then
+		return
+	fi &&
 	git stash &&
 	git status -su >actual &&
 	ls -1pR * >>actual &&
@@ -19,6 +24,46 @@ git_stash () {
 KNOWN_FAILURE_STASH_DOES_IGNORE_SUBMODULE_CHANGES=1
 KNOWN_FAILURE_CHERRY_PICK_SEES_EMPTY_COMMIT=1
 KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR=1
-test_submodule_switch "git_stash"
+test_submodule_switch_func "git_stash"
+
+setup_basic () {
+	test_when_finished "rm -rf main sub" &&
+	git init sub &&
+	(
+		cd sub &&
+		test_commit sub_file
+	) &&
+	git init main &&
+	(
+		cd main &&
+		git submodule add ../sub &&
+		test_commit main_file
+	)
+}
+
+test_expect_success 'stash push with submodule.recurse=true preserves dirty submodule worktree' '
+	setup_basic &&
+	(
+		cd main &&
+		git config submodule.recurse true &&
+		echo "x" >main_file.t &&
+		echo "y" >sub/sub_file.t &&
+		git stash push &&
+		test_must_fail git -C sub diff --quiet
+	)
+'
+
+test_expect_success 'stash push and pop with submodule.recurse=true preserves dirty submodule worktree' '
+	setup_basic &&
+	(
+		cd main &&
+		git config submodule.recurse true &&
+		echo "x" >main_file.t &&
+		echo "y" >sub/sub_file.t &&
+		git stash push &&
+		git stash pop &&
+		test_must_fail git -C sub diff --quiet
+	)
+'
 
 test_done