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/lib-rebase.sh

@@ -44,10 +44,10 @@ set_fake_editor () {
 	rm -f "$1"
 	echo 'rebase -i script before editing:'
 	cat "$1".tmp
-	action=pick
+	action=\&
 	for line in $FAKE_LINES; do
 		case $line in
-		pick|p|squash|s|fixup|f|edit|e|reword|r|drop|d)
+		pick|p|squash|s|fixup|f|edit|e|reword|r|drop|d|label|l|reset|r|merge|m)
 			action="$line";;
 		exec_*|x_*|break|b)
 			echo "$line" | sed 's/_/ /g' >> "$1";;
@@ -58,11 +58,12 @@ set_fake_editor () {
 		bad)
 			action="badcmd";;
 		fakesha)
+			test \& != "$action" || action=pick
 			echo "$action XXXXXXX False commit" >> "$1"
 			action=pick;;
 		*)
-			sed -n "${line}s/^pick/$action/p" < "$1".tmp >> "$1"
-			action=pick;;
+			sed -n "${line}s/^[a-z][a-z]*/$action/p" < "$1".tmp >> "$1"
+			action=\&;;
 		esac
 	done
 	echo 'rebase -i script after editing:'
@@ -118,3 +119,31 @@ make_empty () {
 	git commit --allow-empty -m "$1" &&
 	git tag "$1"
 }
+
+# Call this (inside test_expect_success) at the end of a test file to
+# check that no tests have changed editor related environment
+# variables or config settings
+test_editor_unchanged () {
+	# We're only interested in exported variables hence 'sh -c'
+	sh -c 'cat >actual <<-EOF
+	EDITOR=$EDITOR
+	FAKE_COMMIT_AMEND=$FAKE_COMMIT_AMEND
+	FAKE_COMMIT_MESSAGE=$FAKE_COMMIT_MESSAGE
+	FAKE_LINES=$FAKE_LINES
+	GIT_EDITOR=$GIT_EDITOR
+	GIT_SEQUENCE_EDITOR=$GIT_SEQUENCE_EDITOR
+	core.editor=$(git config core.editor)
+	sequence.editor=$(git config sequence.editor)
+	EOF'
+	cat >expect <<-\EOF
+	EDITOR=:
+	FAKE_COMMIT_AMEND=
+	FAKE_COMMIT_MESSAGE=
+	FAKE_LINES=
+	GIT_EDITOR=
+	GIT_SEQUENCE_EDITOR=
+	core.editor=
+	sequence.editor=
+	EOF
+	test_cmp expect actual
+}