Merge branch 'wk/submodule-on-branch'

Make sure 'submodule update' modes that do not detach HEADs can
be used more pleasantly by checking out a concrete branch when
cloning them to prime the well.

* wk/submodule-on-branch:
  Documentation: describe 'submodule update --remote' use case
  submodule: explicit local branch creation in module_clone
  submodule: document module_clone arguments in comments
  submodule: make 'checkout' update_module mode more explicit

Documentation/git-submodule.txt

@@ -15,8 +15,8 @@ SYNOPSIS
 'git submodule' [--quiet] init [--] [<path>...]
 'git submodule' [--quiet] deinit [-f|--force] [--] <path>...
 'git submodule' [--quiet] update [--init] [--remote] [-N|--no-fetch]
-	      [-f|--force] [--rebase] [--reference <repository>] [--depth <depth>]
-	      [--merge] [--recursive] [--] [<path>...]
+	      [-f|--force] [--rebase|--merge|--checkout] [--reference <repository>]
+	      [--depth <depth>] [--recursive] [--] [<path>...]
 'git submodule' [--quiet] summary [--cached|--files] [(-n|--summary-limit) <n>]
 	      [commit] [--] [<path>...]
 'git submodule' [--quiet] foreach [--recursive] <command>
@@ -155,13 +155,31 @@ it contains local modifications.
 
 update::
 	Update the registered submodules, i.e. clone missing submodules and
-	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.$name.update` is set to
-	`rebase`, `merge` or `none`. `none` can be overridden by specifying
-	`--checkout`. Setting the key `submodule.$name.update` to `!command`
-	will cause `command` to be run. `command` can be any arbitrary shell
-	command that takes a single argument, namely the sha1 to update to.
+	checkout the commit specified in the index of the containing
+	repository.  The update mode defaults to `checkout`, but can be
+	configured with the `submodule.<name>.update` setting or the
+	`--rebase`, `--merge`, or `--checkout` options.
++
+For updates that clone missing submodules, checkout-mode updates will
+create submodules with detached HEADs; all other modes will create
+submodules with a local branch named after `submodule.<path>.branch`.
++
+For updates that do not clone missing submodules, the submodule's HEAD
+is only touched when the remote reference does not match the
+submodule's HEAD (for none-mode updates, the submodule is never
+touched).  The remote reference is usually the gitlinked commit from
+the superproject's tree, but with `--remote` it is the upstream
+subproject's `submodule.<name>.branch`.  This remote reference is
+integrated with the submodule's HEAD using the specified update mode.
+For checkout-mode updates, that will result in a detached HEAD.  For
+rebase- and merge-mode updates, the commit referenced by the
+submodule's HEAD may change, but the symbolic reference will remain
+unchanged (i.e. checked-out branches will still be checked-out
+branches, and detached HEADs will still be detached HEADs).  If none
+of the builtin modes fit your needs, set `submodule.<name>.update` to
+`!command` to configure a custom integration command.  `command` can
+be any arbitrary shell command that takes a single argument, namely
+the sha1 to update to.
 +
 If the submodule is not yet initialized, and you just want to use the
 setting as stored in .gitmodules, you can automatically initialize the
@@ -281,6 +299,16 @@ In order to ensure a current tracking branch state, `update --remote`
 fetches the submodule's remote repository before calculating the
 SHA-1.  If you don't want to fetch, you should use `submodule update
 --remote --no-fetch`.
++
+Use this option to integrate changes from the upstream subproject with
+your submodule's current HEAD.  Alternatively, you can run `git pull`
+from the submodule, which is equivalent except for the remote branch
+name: `update --remote` uses the default upstream repository and
+`submodule.<name>.branch`, while `git pull` uses the submodule's
+`branch.<name>.merge`.  Prefer `submodule.<name>.branch` if you want
+to distribute the default upstream branch with the superproject and
+`branch.<name>.merge` if you want a more native feel while working in
+the submodule itself.
 
 -N::
 --no-fetch::

Documentation/gitmodules.txt

@@ -55,6 +55,10 @@ submodule.<name>.branch::
 	A remote branch name for tracking updates in the upstream submodule.
 	If the option is not specified, it defaults to 'master'.  See the
 	`--remote` documentation in linkgit:git-submodule[1] for details.
++
+This branch name is also used for the local branch created by
+non-checkout cloning updates.  See the `update` documentation in
+linkgit:git-submodule[1] for details.
 
 submodule.<name>.fetchRecurseSubmodules::
 	This option can be used to control recursive fetching of this

git-submodule.sh

@@ -241,6 +241,15 @@ module_name()
 #
 # Clone a submodule
 #
+# $1 = submodule path
+# $2 = submodule name
+# $3 = URL to clone
+# $4 = reference repository to reuse (empty for independent)
+# $5 = depth argument for shallow clones (empty for deep)
+# $6 = (remote-tracking) starting point for the local branch (empty for HEAD)
+# $7 = local branch to create (empty for a detached HEAD, unless $6 is
+#      also empty, in which case the local branch is left unchanged)
+#
 # Prior to calling, cmd_update checks that a possibly existing
 # path is not a git repository.
 # Likewise, cmd_add checks that path does not exist at all,
@@ -253,6 +262,8 @@ module_clone()
 	url=$3
 	reference="$4"
 	depth="$5"
+	start_point="$6"
+	local_branch="$7"
 	quiet=
 	if test -n "$GIT_QUIET"
 	then
@@ -306,7 +317,16 @@ module_clone()
 	echo "gitdir: $rel/$a" >"$sm_path/.git"
 
 	rel=$(echo $a | sed -e 's|[^/][^/]*|..|g')
-	(clear_local_git_env; cd "$sm_path" && GIT_WORK_TREE=. git config core.worktree "$rel/$b")
+	(
+		clear_local_git_env
+		cd "$sm_path" &&
+		GIT_WORK_TREE=. git config core.worktree "$rel/$b" &&
+		# ash fails to wordsplit ${local_branch:+-B "$local_branch"...}
+		case "$local_branch" in
+		'') git checkout -f -q ${start_point:+"$start_point"} ;;
+		?*) git checkout -f -q -B "$local_branch" ${start_point:+"$start_point"} ;;
+		esac
+	) || die "$(eval_gettext "Unable to setup cloned submodule '\$sm_path'")"
 }
 
 isnumber()
@@ -469,16 +489,15 @@ Use -f if you really want to add it." >&2
 				echo "$(eval_gettext "Reactivating local git directory for submodule '\$sm_name'.")"
 			fi
 		fi
-		module_clone "$sm_path" "$sm_name" "$realrepo" "$reference" "$depth" || exit
-		(
-			clear_local_git_env
-			cd "$sm_path" &&
-			# ash fails to wordsplit ${branch:+-b "$branch"...}
-			case "$branch" in
-			'') git checkout -f -q ;;
-			?*) git checkout -f -q -B "$branch" "origin/$branch" ;;
-			esac
-		) || die "$(eval_gettext "Unable to checkout submodule '\$sm_path'")"
+		if test -n "$branch"
+		then
+			start_point="origin/$branch"
+			local_branch="$branch"
+		else
+			start_point=""
+			local_branch=""
+		fi
+		module_clone "$sm_path" "$sm_name" "$realrepo" "$reference" "$depth" "$start_point" "$local_branch" || exit
 	fi
 	git config submodule."$sm_name".url "$realrepo"
 
@@ -799,32 +818,35 @@ cmd_update()
 		fi
 		name=$(module_name "$sm_path") || exit
 		url=$(git config submodule."$name".url)
-		branch=$(get_submodule_config "$name" branch master)
+		config_branch=$(get_submodule_config "$name" branch)
+		branch="${config_branch:-master}"
+		local_branch="$branch"
 		if ! test -z "$update"
 		then
 			update_module=$update
 		else
 			update_module=$(git config submodule."$name".update)
-			case "$update_module" in
-			'')
-				;; # Unset update mode
-			checkout | rebase | merge | none)
-				;; # Known update modes
-			!*)
-				;; # Custom update command
-			*)
-				die "$(eval_gettext "Invalid update mode '$update_module' for submodule '$name'")"
-				;;
-			esac
+			if test -z "$update_module"
+			then
+				update_module="checkout"
+			fi
 		fi
 
 		displaypath=$(relative_path "$prefix$sm_path")
 
-		if test "$update_module" = "none"
-		then
+		case "$update_module" in
+		none)
 			echo "Skipping submodule '$displaypath'"
 			continue
-		fi
+			;;
+		checkout)
+			local_branch=""
+			;;
+		rebase | merge | !*)
+			;;
+		*)
+			die "$(eval_gettext "Invalid update mode '$update_module' for submodule '$name'")"
+		esac
 
 		if test -z "$url"
 		then
@@ -838,7 +860,8 @@ Maybe you want to use 'update --init'?")"
 
 		if ! test -d "$sm_path"/.git -o -f "$sm_path"/.git
 		then
-			module_clone "$sm_path" "$name" "$url" "$reference" "$depth" || exit
+			start_point="origin/${branch}"
+			module_clone "$sm_path" "$name" "$url" "$reference" "$depth" "$start_point" "$local_branch" || exit
 			cloned_modules="$cloned_modules;$name"
 			subsha1=
 		else
@@ -884,11 +907,16 @@ Maybe you want to use 'update --init'?")"
 			case ";$cloned_modules;" in
 			*";$name;"*)
 				# then there is no local change to integrate
-				update_module= ;;
+				update_module='!git reset --hard -q'
 			esac
 
 			must_die_on_failure=
 			case "$update_module" in
+			checkout)
+				command="git checkout $subforce -q"
+				die_msg="$(eval_gettext "Unable to checkout '\$sha1' in submodule path '\$displaypath'")"
+				say_msg="$(eval_gettext "Submodule path '\$displaypath': checked out '\$sha1'")"
+				;;
 			rebase)
 				command="git rebase"
 				die_msg="$(eval_gettext "Unable to rebase '\$sha1' in submodule path '\$displaypath'")"
@@ -908,10 +936,7 @@ Maybe you want to use 'update --init'?")"
 				must_die_on_failure=yes
 				;;
 			*)
-				command="git checkout $subforce -q"
-				die_msg="$(eval_gettext "Unable to checkout '\$sha1' in submodule path '\$displaypath'")"
-				say_msg="$(eval_gettext "Submodule path '\$displaypath': checked out '\$sha1'")"
-				;;
+				die "$(eval_gettext "Invalid update mode '$update_module' for submodule '$name'")"
 			esac
 
 			if (clear_local_git_env; cd "$sm_path" && $command "$sha1")

t/t7406-submodule-update.sh

@@ -63,6 +63,9 @@ test_expect_success 'setup a submodule tree' '
 	 git submodule add ../none none &&
 	 test_tick &&
 	 git commit -m "none"
+	) &&
+	(cd super &&
+	 git tag initial-setup
 	)
 '
 
@@ -703,7 +706,7 @@ test_expect_success 'submodule update places git-dir in superprojects git-dir re
 	git clone super_update_r super_update_r2 &&
 	(cd super_update_r2 &&
 	 git submodule update --init --recursive >actual &&
-	 test_i18ngrep "Submodule path .submodule/subsubmodule.: checked out" actual &&
+	 test_i18ngrep "Submodule path .submodule/subsubmodule.: .git reset --hard -q" actual &&
 	 (cd submodule/subsubmodule &&
 	  git log > ../../expected
 	 ) &&
@@ -775,4 +778,37 @@ test_expect_success 'submodule update --recursive drops module name before recur
 	)
 '
 
+test_expect_success 'submodule update --checkout clones detached HEAD' '
+	git clone super super4 &&
+	echo "detached HEAD" >expected &&
+	(cd super4 &&
+	 git reset --hard initial-setup &&
+	 git submodule init submodule &&
+	 git submodule update >> /tmp/log 2>&1 &&
+	 (cd submodule &&
+	  git symbolic-ref HEAD > ../../actual ||
+	  echo "detached HEAD" > ../../actual
+	 )
+	) &&
+	test_cmp actual expected &&
+	rm -rf super4
+'
+
+test_expect_success 'submodule update --merge clones attached HEAD' '
+	git clone super super4 &&
+	echo "refs/heads/master" >expected &&
+	(cd super4 &&
+	 git reset --hard initial-setup &&
+	 git submodule init submodule &&
+	 git config submodule.submodule.update merge &&
+	 git submodule update --merge &&
+	 (cd submodule &&
+	  git symbolic-ref HEAD > ../../actual ||
+	  echo "detached HEAD" > ../../actual
+	 )
+	) &&
+	test_cmp actual expected &&
+	rm -rf super4
+'
+
 test_done