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/t8002-blame.sh

@@ -6,6 +6,10 @@ test_description='git blame'
 PROG='git blame -c'
 . "$TEST_DIRECTORY"/annotate-tests.sh
 
+test_expect_success 'setup' '
+	hexsz=$(test_oid hexsz)
+'
+
 test_expect_success 'blame untracked file in empty repo' '
 	>untracked &&
 	test_must_fail git blame untracked
@@ -105,21 +109,32 @@ test_expect_success 'blame --abbrev=<n> works' '
 '
 
 test_expect_success 'blame -l aligns regular and boundary commits' '
-	check_abbrev 40 -l HEAD &&
-	check_abbrev 39 -l ^HEAD
+	check_abbrev $hexsz         -l HEAD &&
+	check_abbrev $((hexsz - 1)) -l ^HEAD
 '
 
-test_expect_success 'blame --abbrev=40 behaves like -l' '
-	check_abbrev 40 --abbrev=40 HEAD &&
-	check_abbrev 39 --abbrev=40 ^HEAD
+test_expect_success 'blame --abbrev with full length behaves like -l' '
+	check_abbrev $hexsz         --abbrev=$hexsz HEAD &&
+	check_abbrev $((hexsz - 1)) --abbrev=$hexsz ^HEAD
 '
 
-test_expect_success '--no-abbrev works like --abbrev=40' '
-	check_abbrev 40 --no-abbrev
+test_expect_success '--no-abbrev works like --abbrev with full length' '
+	check_abbrev $hexsz --no-abbrev
 '
 
 test_expect_success '--exclude-promisor-objects does not BUG-crash' '
 	test_must_fail git blame --exclude-promisor-objects one
 '
 
+test_expect_success 'blame with uncommitted edits in partial clone does not crash' '
+	git init server &&
+	echo foo >server/file.txt &&
+	git -C server add file.txt &&
+	git -C server commit -m file &&
+
+	git clone --filter=blob:none "file://$(pwd)/server" client &&
+	echo bar >>client/file.txt &&
+	git -C client blame file.txt
+'
+
 test_done