t, doc: update tests, reference for "--force-if-includes"

Update test cases for the new option, and document its usage
and update related references.

Update test cases for the new option, and document its usage
and update related references.

 - t/t5533-push-cas.sh:
   Update test cases for "compare-and-swap" when used along with
   "--force-if-includes" helps mitigate overwrites when remote
   refs are updated in the background; allows forced updates when
   changes from remote are integrated locally.

 - Documentation:
   Add reference for the new option, configuration setting
   ("push.useForceIfIncludes") and advise messages.

Signed-off-by: Srinidhi Kaushik <shrinidhi.kaushik@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/advice.txt

@@ -10,9 +10,8 @@ advice.*::
 		that the check is disabled.
 	pushUpdateRejected::
 		Set this variable to 'false' if you want to disable
-		'pushNonFFCurrent',
+		'pushNonFFCurrent', 'pushNonFFMatching', 'pushAlreadyExists',
-		'pushNonFFMatching', 'pushAlreadyExists',
+		'pushFetchFirst', 'pushNeedsForce', and 'pushRefNeedsUpdate'
-		'pushFetchFirst', and 'pushNeedsForce'
 		simultaneously.
 	pushNonFFCurrent::
 		Advice shown when linkgit:git-push[1] fails due to a
@@ -41,6 +40,10 @@ advice.*::
 		we can still suggest that the user push to either
 		refs/heads/* or refs/tags/* based on the type of the
 		source object.
+	pushRefNeedsUpdate::
+		Shown when linkgit:git-push[1] rejects a forced update of
+		a branch when its remote-tracking ref has updates that we
+		do not have locally.
 	statusAheadBehind::
 		Shown when linkgit:git-status[1] computes the ahead/behind
 		counts for a local ref compared to its remote tracking ref,

Documentation/config/push.txt

@@ -114,3 +114,9 @@ push.recurseSubmodules::
 	specifying '--recurse-submodules=check|on-demand|no'.
 	If not set, 'no' is used by default, unless 'submodule.recurse' is
 	set (in which case a 'true' value means 'on-demand').
+
+push.useForceIfIncludes::
+	If set to "true", it is equivalent to specifying
+	`--force-if-includes` as an option to linkgit:git-push[1]
+	in the command line. Adding `--no-force-if-includes` at the
+	time of push overrides this configuration setting.

Documentation/git-push.txt

@@ -13,7 +13,7 @@ SYNOPSIS
 	   [--repo=<repository>] [-f | --force] [-d | --delete] [--prune] [-v | --verbose]
 	   [-u | --set-upstream] [-o <string> | --push-option=<string>]
 	   [--[no-]signed|--signed=(true|false|if-asked)]
-	   [--force-with-lease[=<refname>[:<expect>]]]
+	   [--force-with-lease[=<refname>[:<expect>]] [--force-if-includes]]
 	   [--no-verify] [<repository> [<refspec>...]]
 
 DESCRIPTION
@@ -320,6 +320,14 @@ seen and are willing to overwrite, then rewrite history, and finally
 force push changes to `master` if the remote version is still at
 `base`, regardless of what your local `remotes/origin/master` has been
 updated to in the background.
++
+Alternatively, specifying `--force-if-includes` as an ancillary option
+along with `--force-with-lease[=<refname>]` (i.e., without saying what
+exact commit the ref on the remote side must be pointing at, or which
+refs on the remote side are being protected) at the time of "push" will
+verify if updates from the remote-tracking refs that may have been
+implicitly updated in the background are integrated locally before
+allowing a forced update.
 
 -f::
 --force::
@@ -341,6 +349,22 @@ one branch, use a `+` in front of the refspec to push (e.g `git push
 origin +master` to force a push to the `master` branch). See the
 `<refspec>...` section above for details.
 
+--[no-]force-if-includes::
+	Force an update only if the tip of the remote-tracking ref
+	has been integrated locally.
++
+This option enables a check that verifies if the tip of the
+remote-tracking ref is reachable from one of the "reflog" entries of
+the local branch based in it for a rewrite. The check ensures that any
+updates from the remote have been incorporated locally by rejecting the
+forced update if that is not the case.
++
+If the option is passed without specifying `--force-with-lease`, or
+specified along with `--force-with-lease=<refname>:<expect>`, it is
+a "no-op".
++
+Specifying `--no-force-if-includes` disables this behavior.
+
 --repo=<repository>::
 	This option is equivalent to the <repository> argument. If both
 	are specified, the command-line argument takes precedence.

t/t5533-push-cas.sh

@@ -13,6 +13,46 @@ setup_srcdst_basic () {
 	)
 }
 
+# For tests with "--force-if-includes".
+setup_src_dup_dst () {
+	rm -fr src dup dst &&
+	git init --bare dst &&
+	git clone --no-local dst src &&
+	git clone --no-local dst dup
+	(
+		cd src &&
+		test_commit A &&
+		test_commit B &&
+		test_commit C &&
+		git push origin
+	) &&
+	(
+		cd dup &&
+		git fetch &&
+		git merge origin/master &&
+		git switch -c branch master~2 &&
+		test_commit D &&
+		test_commit E &&
+		git push origin --all
+	) &&
+	(
+		cd src &&
+		git switch master &&
+		git fetch --all &&
+		git branch branch --track origin/branch &&
+		git rebase origin/master
+	) &&
+	(
+		cd dup &&
+		git switch master &&
+		test_commit F &&
+		test_commit G &&
+		git switch branch &&
+		test_commit H &&
+		git push origin --all
+	)
+}
+
 test_expect_success setup '
 	# create template repository
 	test_commit A &&
@@ -256,4 +296,101 @@ test_expect_success 'background updates of REMOTE can be mitigated with a non-up
 	)
 '
 
+test_expect_success 'background updates to remote can be mitigated with "--force-if-includes"' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	git ls-remote dst refs/heads/master >expect.master &&
+	git ls-remote dst refs/heads/branch >expect.branch &&
+	(
+		cd src &&
+		git switch branch &&
+		test_commit I &&
+		git switch master &&
+		test_commit J &&
+		git fetch --all &&
+		test_must_fail git push --force-with-lease --force-if-includes --all
+	) &&
+	git ls-remote dst refs/heads/master >actual.master &&
+	git ls-remote dst refs/heads/branch >actual.branch &&
+	test_cmp expect.master actual.master &&
+	test_cmp expect.branch actual.branch
+'
+
+test_expect_success 'background updates to remote can be mitigated with "push.useForceIfIncludes"' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	git ls-remote dst refs/heads/master >expect.master &&
+	(
+		cd src &&
+		git switch branch &&
+		test_commit I &&
+		git switch master &&
+		test_commit J &&
+		git fetch --all &&
+		git config --local push.useForceIfIncludes true &&
+		test_must_fail git push --force-with-lease=master origin master
+	) &&
+	git ls-remote dst refs/heads/master >actual.master &&
+	test_cmp expect.master actual.master
+'
+
+test_expect_success '"--force-if-includes" should be disabled for --force-with-lease="<refname>:<expect>"' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	git ls-remote dst refs/heads/master >expect.master &&
+	(
+		cd src &&
+		git switch branch &&
+		test_commit I &&
+		git switch master &&
+		test_commit J &&
+		remote_head="$(git rev-parse refs/remotes/origin/master)" &&
+		git fetch --all &&
+		test_must_fail git push --force-if-includes --force-with-lease="master:$remote_head" 2>err &&
+		grep "stale info" err
+	) &&
+	git ls-remote dst refs/heads/master >actual.master &&
+	test_cmp expect.master actual.master
+'
+
+test_expect_success '"--force-if-includes" should allow forced update after a rebase ("pull --rebase")' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	(
+		cd src &&
+		git switch branch &&
+		test_commit I &&
+		git switch master &&
+		test_commit J &&
+		git pull --rebase origin master &&
+		git push --force-if-includes --force-with-lease="master"
+	)
+'
+
+test_expect_success '"--force-if-includes" should allow forced update after a rebase ("pull --rebase", local rebase)' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	(
+		cd src &&
+		git switch branch &&
+		test_commit I &&
+		git switch master &&
+		test_commit J &&
+		git pull --rebase origin master &&
+		git rebase --onto HEAD~4 HEAD~1 &&
+		git push --force-if-includes --force-with-lease="master"
+	)
+'
+
+test_expect_success '"--force-if-includes" should allow deletes' '
+	setup_src_dup_dst &&
+	test_when_finished "rm -fr dst src dup" &&
+	(
+		cd src &&
+		git switch branch &&
+		git pull --rebase origin branch &&
+		git push --force-if-includes --force-with-lease="branch" origin :branch
+	)
+'
+
 test_done