t: teach test_cmp_rev to accept ! for not-equals

In the case where we are using test_cmp_rev() to report not-equals, we
write `! test_cmp_rev`. However, since test_cmp_rev() contains

	r1=$(git rev-parse --verify "$1") &&
	r2=$(git rev-parse --verify "$2") &&

`! test_cmp_rev` will succeed if any of the rev-parses fail. This
behavior is not desired. We want the rev-parses to _always_ be
successful.

Rewrite test_cmp_rev() to optionally accept "!" as the first argument to
do a not-equals comparison. Rewrite `! test_cmp_rev` to `test_cmp_rev !`
in all tests to take advantage of this new functionality.

Also, rewrite the rev-parse logic to end with a `|| return 1` instead of
&&-chaining into the rev-comparison logic. This makes it obvious to
future readers that we explicitly intend on returning early if either of
the rev-parses fail.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2400-worktree-add.sh

@@ -438,7 +438,7 @@ test_expect_success 'git worktree add does not match remote' '
 		cd foo &&
 		test_must_fail git config "branch.foo.remote" &&
 		test_must_fail git config "branch.foo.merge" &&
-		! test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+		test_cmp_rev ! refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
 
@@ -483,7 +483,7 @@ test_expect_success 'git worktree --no-guess-remote option overrides config' '
 		cd foo &&
 		test_must_fail git config "branch.foo.remote" &&
 		test_must_fail git config "branch.foo.merge" &&
-		! test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+		test_cmp_rev ! refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
 

t/t3400-rebase.sh

@@ -64,7 +64,7 @@ test_expect_success 'rebase sets ORIG_HEAD to pre-rebase state' '
 	pre="$(git rev-parse --verify HEAD)" &&
 	git rebase master &&
 	test_cmp_rev "$pre" ORIG_HEAD &&
-	! test_cmp_rev "$pre" HEAD
+	test_cmp_rev ! "$pre" HEAD
 '
 
 test_expect_success 'rebase, with <onto> and <upstream> specified as :/quuxery' '

t/t3421-rebase-topology-linear.sh

@@ -61,7 +61,7 @@ test_run_rebase () {
 	test_expect_$result "rebase $* -f rewrites even if upstream is an ancestor" "
 		reset_rebase &&
 		git rebase $* -f b e &&
-		! test_cmp_rev e HEAD &&
+		test_cmp_rev ! e HEAD &&
 		test_cmp_rev b HEAD~2 &&
 		test_linear_range 'd e' b..
 	"
@@ -78,7 +78,7 @@ test_run_rebase () {
 	test_expect_$result "rebase $* -f rewrites even if remote upstream is an ancestor" "
 		reset_rebase &&
 		git rebase $* -f branch-b branch-e &&
-		! test_cmp_rev branch-e origin/branch-e &&
+		test_cmp_rev ! branch-e origin/branch-e &&
 		test_cmp_rev branch-b HEAD~2 &&
 		test_linear_range 'd e' branch-b..
 	"
@@ -368,7 +368,7 @@ test_run_rebase () {
 	test_expect_$result "rebase $* -f --root on linear history causes re-write" "
 		reset_rebase &&
 		git rebase $* -f --root c &&
-		! test_cmp_rev a HEAD~2 &&
+		test_cmp_rev ! a HEAD~2 &&
 		test_linear_range 'a b c' HEAD
 	"
 }

t/t3430-rebase-merges.sh

@@ -346,7 +346,7 @@ test_expect_success 'A root commit can be a cousin, treat it that way' '
 	git merge --allow-unrelated-histories khnum &&
 	test_tick &&
 	git rebase -f -r HEAD^ &&
-	! test_cmp_rev HEAD^2 khnum &&
+	test_cmp_rev ! HEAD^2 khnum &&
 	test_cmp_graph HEAD^.. <<-\EOF &&
 	*   Merge branch '\''khnum'\'' into asherah
 	|\

t/t3432-rebase-fast-forward.sh

@@ -64,7 +64,7 @@ test_rebase_same_head_ () {
 			test_cmp_rev \$oldhead \$newhead
 		elif test $cmp = diff
 		then
-			! test_cmp_rev \$oldhead \$newhead
+			test_cmp_rev ! \$oldhead \$newhead
 		fi
 	"
 }

t/t3501-revert-cherry-pick.sh

@@ -106,7 +106,7 @@ test_expect_success 'cherry-pick on unborn branch' '
 	rm -rf * &&
 	git cherry-pick initial &&
 	git diff --quiet initial &&
-	! test_cmp_rev initial HEAD
+	test_cmp_rev ! initial HEAD
 '
 
 test_expect_success 'cherry-pick "-" to pick from previous branch' '

t/t3508-cherry-pick-many-commits.sh

@@ -5,7 +5,7 @@ test_description='test cherry-picking many commits'
 . ./test-lib.sh
 
 check_head_differs_from() {
-	! test_cmp_rev HEAD "$1"
+	test_cmp_rev ! HEAD "$1"
 }
 
 check_head_equals() {

t/test-lib-functions.sh

@@ -1012,19 +1012,30 @@ test_must_be_empty () {
 	fi
 }
 
-# Tests that its two parameters refer to the same revision
+# Tests that its two parameters refer to the same revision, or if '!' is
+# provided first, that its other two parameters refer to different
+# revisions.
 test_cmp_rev () {
+	local op='=' wrong_result=different
+
+	if test $# -ge 1 && test "x$1" = 'x!'
+	then
+	    op='!='
+	    wrong_result='the same'
+	    shift
+	fi
 	if test $# != 2
 	then
 		error "bug in the test script: test_cmp_rev requires two revisions, but got $#"
 	else
 		local r1 r2
 		r1=$(git rev-parse --verify "$1") &&
-		r2=$(git rev-parse --verify "$2") &&
-		if test "$r1" != "$r2"
+		r2=$(git rev-parse --verify "$2") || return 1
+
+		if ! test "$r1" "$op" "$r2"
 		then
 			cat >&4 <<-EOF
-			error: two revisions point to different objects:
+			error: two revisions point to $wrong_result objects:
 			  '$1': $r1
 			  '$2': $r2
 			EOF