Merge branch 'ml/submodule-add-existing'

* ml/submodule-add-existing:
  git-submodule - Allow adding a submodule in-place

Documentation/git-submodule.txt

@@ -18,8 +18,9 @@ COMMANDS
 --------
 add::
 	Add the given repository as a submodule at the given path
-	to the changeset to be committed next.  In particular, the
-	repository is cloned at the specified path, added to the
+	to the changeset to be committed next.  If path is a valid
+	repository within the project, it is added as is. Otherwise,
+	repository is cloned at the specified path. path is added to the
 	changeset and registered in .gitmodules.   If no path is
 	specified, the path is deduced from the repository specification.
 	If the repository url begins with ./ or ../, it is stored as

git-submodule.sh

@@ -153,36 +153,46 @@ cmd_add()
 		usage
 	fi
 
-	case "$repo" in
-	./*|../*)
-		# dereference source url relative to parent's url
-		realrepo="$(resolve_relative_url $repo)" ;;
-	*)
-		# Turn the source into an absolute path if
-		# it is local
-		if base=$(get_repo_base "$repo"); then
-			repo="$base"
-		fi
-		realrepo=$repo
-		;;
-	esac
-
 	# Guess path from repo if not specified or strip trailing slashes
 	if test -z "$path"; then
 		path=$(echo "$repo" | sed -e 's|/*$||' -e 's|:*/*\.git$||' -e 's|.*[/:]||g')
 	else
 		path=$(echo "$path" | sed -e 's|/*$||')
 	fi
 
-	test -e "$path" &&
-	die "'$path' already exists"
-
 	git ls-files --error-unmatch "$path" > /dev/null 2>&1 &&
 	die "'$path' already exists in the index"
 
-	module_clone "$path" "$realrepo" || exit
-	(unset GIT_DIR; cd "$path" && git checkout -q ${branch:+-b "$branch" "origin/$branch"}) ||
-	die "Unable to checkout submodule '$path'"
+	# perhaps the path exists and is already a git repo, else clone it
+	if test -e "$path"
+	then
+		if test -d "$path/.git" &&
+		test "$(unset GIT_DIR; cd $path; git rev-parse --git-dir)" = ".git"
+		then
+			echo "Adding existing repo at '$path' to the index"
+		else
+			die "'$path' already exists and is not a valid git repo"
+		fi
+	else
+		case "$repo" in
+		./*|../*)
+			# dereference source url relative to parent's url
+			realrepo="$(resolve_relative_url $repo)" ;;
+		*)
+			# Turn the source into an absolute path if
+			# it is local
+			if base=$(get_repo_base "$repo"); then
+				repo="$base"
+			fi
+			realrepo=$repo
+			;;
+		esac
+
+		module_clone "$path" "$realrepo" || exit
+		(unset GIT_DIR; cd "$path" && git checkout -q ${branch:+-b "$branch" "origin/$branch"}) ||
+		die "Unable to checkout submodule '$path'"
+	fi
+
 	git add "$path" ||
 	die "Failed to add submodule '$path'"