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, 195 insertions, 0 deletions

diff --git a/third_party/git/t/t6436-merge-overwrite.sh b/third_party/git/t/t6436-merge-overwrite.sh
new file mode 100755
index 0000000000..dd8ab7ede1
--- /dev/null
+++ b/third_party/git/t/t6436-merge-overwrite.sh
@@ -0,0 +1,195 @@
+#!/bin/sh
+
+test_description='git-merge
+
+Do not overwrite changes.'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit c0 c0.c &&
+	test_commit c1 c1.c &&
+	test_commit c1a c1.c "c1 a" &&
+	git reset --hard c0 &&
+	test_commit c2 c2.c &&
+	git reset --hard c0 &&
+	mkdir sub &&
+	echo "sub/f" > sub/f &&
+	mkdir sub2 &&
+	echo "sub2/f" > sub2/f &&
+	git add sub/f sub2/f &&
+	git commit -m sub &&
+	git tag sub &&
+	echo "VERY IMPORTANT CHANGES" > important
+'
+
+test_expect_success 'will not overwrite untracked file' '
+	git reset --hard c1 &&
+	cp important c2.c &&
+	test_must_fail git merge c2 &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important c2.c
+'
+
+test_expect_success 'will overwrite tracked file' '
+	git reset --hard c1 &&
+	cp important c2.c &&
+	git add c2.c &&
+	git commit -m important &&
+	git checkout c2
+'
+
+test_expect_success 'will not overwrite new file' '
+	git reset --hard c1 &&
+	cp important c2.c &&
+	git add c2.c &&
+	test_must_fail git merge c2 &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important c2.c
+'
+
+test_expect_success 'will not overwrite staged changes' '
+	git reset --hard c1 &&
+	cp important c2.c &&
+	git add c2.c &&
+	rm c2.c &&
+	test_must_fail git merge c2 &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	git checkout c2.c &&
+	test_cmp important c2.c
+'
+
+test_expect_success 'will not overwrite removed file' '
+	git reset --hard c1 &&
+	git rm c1.c &&
+	git commit -m "rm c1.c" &&
+	cp important c1.c &&
+	test_must_fail git merge c1a &&
+	test_cmp important c1.c
+'
+
+test_expect_success 'will not overwrite re-added file' '
+	git reset --hard c1 &&
+	git rm c1.c &&
+	git commit -m "rm c1.c" &&
+	cp important c1.c &&
+	git add c1.c &&
+	test_must_fail git merge c1a &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important c1.c
+'
+
+test_expect_success 'will not overwrite removed file with staged changes' '
+	git reset --hard c1 &&
+	git rm c1.c &&
+	git commit -m "rm c1.c" &&
+	cp important c1.c &&
+	git add c1.c &&
+	rm c1.c &&
+	test_must_fail git merge c1a &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	git checkout c1.c &&
+	test_cmp important c1.c
+'
+
+test_expect_success 'will not overwrite unstaged changes in renamed file' '
+	git reset --hard c1 &&
+	git mv c1.c other.c &&
+	git commit -m rename &&
+	cp important other.c &&
+	test_must_fail git merge c1a >out &&
+	test_i18ngrep "Refusing to lose dirty file at other.c" out &&
+	test_path_is_file other.c~HEAD &&
+	test $(git hash-object other.c~HEAD) = $(git rev-parse c1a:c1.c) &&
+	test_cmp important other.c
+'
+
+test_expect_success 'will not overwrite untracked subtree' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	mkdir -p sub/f &&
+	cp important sub/f/important &&
+	test_must_fail git merge sub &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important sub/f/important
+'
+
+cat >expect <<\EOF
+error: The following untracked working tree files would be overwritten by merge:
+	sub
+	sub2
+Please move or remove them before you merge.
+Aborting
+EOF
+
+test_expect_success 'will not overwrite untracked file in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	cp important sub &&
+	cp important sub2 &&
+	test_must_fail git merge sub 2>out &&
+	test_i18ncmp out expect &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important sub &&
+	test_cmp important sub2 &&
+	rm -f sub sub2
+'
+
+test_expect_success SYMLINKS 'will not overwrite untracked symlink in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	mkdir sub2 &&
+	ln -s sub2 sub &&
+	test_must_fail git merge sub &&
+	test_path_is_missing .git/MERGE_HEAD
+'
+
+test_expect_success 'will not be confused by symlink in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	test_ln_s_add sub2 sub &&
+	git commit -m ln &&
+	git checkout sub
+'
+
+cat >expect <<\EOF
+error: Untracked working tree file 'c0.c' would be overwritten by merge.
+fatal: read-tree failed
+EOF
+
+test_expect_success 'will not overwrite untracked file on unborn branch' '
+	git reset --hard c0 &&
+	git rm -fr . &&
+	git checkout --orphan new &&
+	cp important c0.c &&
+	test_must_fail git merge c0 2>out &&
+	test_i18ncmp out expect
+'
+
+test_expect_success 'will not overwrite untracked file on unborn branch .git/MERGE_HEAD sanity etc.' '
+	test_when_finished "rm c0.c" &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important c0.c
+'
+
+test_expect_success 'failed merge leaves unborn branch in the womb' '
+	test_must_fail git rev-parse --verify HEAD
+'
+
+test_expect_success 'set up unborn branch and content' '
+	git symbolic-ref HEAD refs/heads/unborn &&
+	rm -f .git/index &&
+	echo foo > tracked-file &&
+	git add tracked-file &&
+	echo bar > untracked-file
+'
+
+test_expect_success 'will not clobber WT/index when merging into unborn' '
+	git merge master &&
+	grep foo tracked-file &&
+	git show :tracked-file >expect &&
+	grep foo expect &&
+	grep bar untracked-file
+'
+
+test_done