add update 'none' flag to disable update of submodule by default

This is useful to mark a submodule as unneeded by default. When this
option is set and the user wants to work with such a submodule he
needs to configure 'submodule.<name>.update=checkout' or pass the
--checkout option. Then the submodule can be handled like a normal
submodule.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: hvoigt

Documentation/git-submodule.txt

@@ -120,6 +120,8 @@ too (and can also report changes to a submodule's work tree).
 init::
 	Initialize the submodules, i.e. register each submodule name
 	and url found in .gitmodules into .git/config.
+	It will also copy the value of `submodule.$name.update` into
+	.git/config.
 	The key used in .git/config is `submodule.$name.url`.
 	This command does not alter existing information in .git/config.
 	You can then customize the submodule clone URLs in .git/config
@@ -133,14 +135,18 @@ update::
 	checkout the commit specified in the index of the containing repository.
 	This will make the submodules HEAD be detached unless `--rebase` or
 	`--merge` is specified or the key `submodule.$name.update` is set to
-	`rebase` or `merge`.
+	`rebase`, `merge` or `none`.
 +
 If the submodule is not yet initialized, and you just want to use the
 setting as stored in .gitmodules, you can automatically initialize the
 submodule with the `--init` option.
 +
 If `--recursive` is specified, this command will recurse into the
 registered submodules, and update any nested submodules within.
++
+If the configuration key `submodule.$name.update` is set to `none` the
+submodule with name `$name` will not be updated by default. This can be
+overriden by adding `--checkout` to the command.
 
 summary::
 	Show commit summary between the given commit (defaults to HEAD) and

git-submodule.sh

@@ -429,6 +429,9 @@ cmd_update()
 		--recursive)
 			recursive=1
 			;;
+		--checkout)
+			update="checkout"
+			;;
 		--)
 			shift
 			break
@@ -468,6 +471,12 @@ cmd_update()
 			update_module=$(git config submodule."$name".update)
 		fi
 
+		if test "$update_module" = "none"
+		then
+			echo "Skipping submodule '$path'"
+			continue
+		fi
+
 		if test -z "$url"
 		then
 			# Only mention uninitialized submodules when its

t/t7406-submodule-update.sh

@@ -30,6 +30,7 @@ test_expect_success 'setup a submodule tree' '
 	git clone super submodule &&
 	git clone super rebasing &&
 	git clone super merging &&
+	git clone super none &&
 	(cd super &&
 	 git submodule add ../submodule submodule &&
 	 test_tick &&
@@ -58,6 +59,11 @@ test_expect_success 'setup a submodule tree' '
 	 test_tick &&
 	 git commit -m "rebasing"
 	)
+	(cd super &&
+	 git submodule add ../none none &&
+	 test_tick &&
+	 git commit -m "none"
+	)
 '
 
 test_expect_success 'submodule update detaching the HEAD ' '
@@ -298,6 +304,62 @@ test_expect_success 'submodule update ignores update=rebase config for new submo
 	)
 '
 
+test_expect_success 'submodule init picks up update=none' '
+	(cd super &&
+	 git config -f .gitmodules submodule.none.update none &&
+	 git submodule init none &&
+	 test "none" = "$(git config submodule.none.update)"
+	)
+'
+
+test_expect_success 'submodule update - update=none in .git/config' '
+	(cd super &&
+	 git config submodule.submodule.update none &&
+	 (cd submodule &&
+	  git checkout master &&
+	  compare_head
+	 ) &&
+	 git diff --raw | grep "	submodule" &&
+	 git submodule update &&
+	 git diff --raw | grep "	submodule" &&
+	 (cd submodule &&
+	  compare_head
+	 ) &&
+	 git config --unset submodule.submodule.update &&
+	 git submodule update submodule
+	)
+'
+
+test_expect_success 'submodule update - update=none in .git/config but --checkout given' '
+	(cd super &&
+	 git config submodule.submodule.update none &&
+	 (cd submodule &&
+	  git checkout master &&
+	  compare_head
+	 ) &&
+	 git diff --raw | grep "	submodule" &&
+	 git submodule update --checkout &&
+	 test_must_fail git diff --raw \| grep "	submodule" &&
+	 (cd submodule &&
+	  test_must_fail compare_head
+	 ) &&
+	 git config --unset submodule.submodule.update
+	)
+'
+
+test_expect_success 'submodule update --init skips submodule with update=none' '
+	(cd super &&
+	 git add .gitmodules &&
+	 git commit -m ".gitmodules"
+	) &&
+	git clone super cloned &&
+	(cd cloned &&
+	 git submodule update --init &&
+	 test -e submodule/.git &&
+	 test_must_fail test -e none/.git
+	)
+'
+
 test_expect_success 'submodule update continues after checkout error' '
 	(cd super &&
 	 git reset --hard HEAD &&