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, 91 insertions, 0 deletions

diff --git a/third_party/git/t/t4068-diff-symmetric.sh b/third_party/git/t/t4068-diff-symmetric.sh
new file mode 100755
index 000000000000..31d17a5af02f
--- /dev/null
+++ b/third_party/git/t/t4068-diff-symmetric.sh
@@ -0,0 +1,91 @@
+#!/bin/sh
+
+test_description='behavior of diff with symmetric-diff setups'
+
+. ./test-lib.sh
+
+# build these situations:
+#  - normal merge with one merge base (br1...b2r);
+#  - criss-cross merge ie 2 merge bases (br1...master);
+#  - disjoint subgraph (orphan branch, br3...master).
+#
+#     B---E   <-- master
+#    / \ /
+#   A   X
+#    \ / \
+#     C---D--G   <-- br1
+#      \    /
+#       ---F   <-- br2
+#
+#  H  <-- br3
+#
+# We put files into a few commits so that we can verify the
+# output as well.
+
+test_expect_success setup '
+	git commit --allow-empty -m A &&
+	echo b >b &&
+	git add b &&
+	git commit -m B &&
+	git checkout -b br1 HEAD^ &&
+	echo c >c &&
+	git add c &&
+	git commit -m C &&
+	git tag commit-C &&
+	git merge -m D master &&
+	git tag commit-D &&
+	git checkout master &&
+	git merge -m E commit-C &&
+	git checkout -b br2 commit-C &&
+	echo f >f &&
+	git add f &&
+	git commit -m F &&
+	git checkout br1 &&
+	git merge -m G br2 &&
+	git checkout --orphan br3 &&
+	git commit -m H
+'
+
+test_expect_success 'diff with one merge base' '
+	git diff commit-D...br1 >tmp &&
+	tail -n 1 tmp >actual &&
+	echo +f >expect &&
+	test_cmp expect actual
+'
+
+# The output (in tmp) can have +b or +c depending
+# on which merge base (commit B or C) is picked.
+# It should have one of those two, which comes out
+# to seven lines.
+test_expect_success 'diff with two merge bases' '
+	git diff br1...master >tmp 2>err &&
+	test_line_count = 7 tmp &&
+	test_line_count = 1 err
+'
+
+test_expect_success 'diff with no merge bases' '
+	test_must_fail git diff br2...br3 >tmp 2>err &&
+	test_i18ngrep "fatal: br2...br3: no merge base" err
+'
+
+test_expect_success 'diff with too many symmetric differences' '
+	test_must_fail git diff br1...master br2...br3 >tmp 2>err &&
+	test_i18ngrep "usage" err
+'
+
+test_expect_success 'diff with symmetric difference and extraneous arg' '
+	test_must_fail git diff master br1...master >tmp 2>err &&
+	test_i18ngrep "usage" err
+'
+
+test_expect_success 'diff with two ranges' '
+	test_must_fail git diff master br1..master br2..br3 >tmp 2>err &&
+	test_i18ngrep "usage" err
+'
+
+test_expect_success 'diff with ranges and extra arg' '
+	test_must_fail git diff master br1..master commit-D >tmp 2>err &&
+	test_i18ngrep "usage" err
+'
+
+test_done