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/t4011-diff-symlink.sh

@@ -9,11 +9,24 @@ test_description='Test diff of symlinks.
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/diff-lib.sh
 
+# Print the short OID of a symlink with the given name.
+symlink_oid () {
+	local oid=$(printf "%s" "$1" | git hash-object --stdin) &&
+	git rev-parse --short "$oid"
+}
+
+# Print the short OID of the given file.
+short_oid () {
+	local oid=$(git hash-object "$1") &&
+	git rev-parse --short "$oid"
+}
+
 test_expect_success 'diff new symlink and file' '
-	cat >expected <<-\EOF &&
+	symlink=$(symlink_oid xyzzy) &&
+	cat >expected <<-EOF &&
 	diff --git a/frotz b/frotz
 	new file mode 120000
-	index 0000000..7c465af
+	index 0000000..$symlink
 	--- /dev/null
 	+++ b/frotz
 	@@ -0,0 +1 @@
@@ -21,7 +34,7 @@ test_expect_success 'diff new symlink and file' '
 	\ No newline at end of file
 	diff --git a/nitfol b/nitfol
 	new file mode 100644
-	index 0000000..7c465af
+	index 0000000..$symlink
 	--- /dev/null
 	+++ b/nitfol
 	@@ -0,0 +1 @@
@@ -46,10 +59,10 @@ test_expect_success 'diff unchanged symlink and file'  '
 '
 
 test_expect_success 'diff removed symlink and file' '
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	diff --git a/frotz b/frotz
 	deleted file mode 120000
-	index 7c465af..0000000
+	index $symlink..0000000
 	--- a/frotz
 	+++ /dev/null
 	@@ -1 +0,0 @@
@@ -57,7 +70,7 @@ test_expect_success 'diff removed symlink and file' '
 	\ No newline at end of file
 	diff --git a/nitfol b/nitfol
 	deleted file mode 100644
-	index 7c465af..0000000
+	index $symlink..0000000
 	--- a/nitfol
 	+++ /dev/null
 	@@ -1 +0,0 @@
@@ -90,9 +103,10 @@ test_expect_success 'diff identical, but newly created symlink and file' '
 '
 
 test_expect_success 'diff different symlink and file' '
-	cat >expected <<-\EOF &&
+	new=$(symlink_oid yxyyz) &&
+	cat >expected <<-EOF &&
 	diff --git a/frotz b/frotz
-	index 7c465af..df1db54 120000
+	index $symlink..$new 120000
 	--- a/frotz
 	+++ b/frotz
 	@@ -1 +1 @@
@@ -101,7 +115,7 @@ test_expect_success 'diff different symlink and file' '
 	+yxyyz
 	\ No newline at end of file
 	diff --git a/nitfol b/nitfol
-	index 7c465af..df1db54 100644
+	index $symlink..$new 100644
 	--- a/nitfol
 	+++ b/nitfol
 	@@ -1 +1 @@
@@ -137,14 +151,16 @@ test_expect_success SYMLINKS 'setup symlinks with attributes' '
 '
 
 test_expect_success SYMLINKS 'symlinks do not respect userdiff config by path' '
-	cat >expect <<-\EOF &&
+	file=$(short_oid file.bin) &&
+	link=$(symlink_oid file.bin) &&
+	cat >expect <<-EOF &&
 	diff --git a/file.bin b/file.bin
 	new file mode 100644
-	index 0000000..d95f3ad
+	index 0000000..$file
 	Binary files /dev/null and b/file.bin differ
 	diff --git a/link.bin b/link.bin
 	new file mode 120000
-	index 0000000..dce41ec
+	index 0000000..$link
 	--- /dev/null
 	+++ b/link.bin
 	@@ -0,0 +1 @@