Ignore new commits for git submodule

Question

Background

Using Git 1.8.1.1 on Linux. The repository looks as follows:

master
  book

The submodule was created as follows:

$ cd /path/to/master
$ git submodule add https://[email protected]/user/repo.git book

The book submodule is clean:

$ cd /path/to/master/book/
$ git status
# On branch master
nothing to commit, working directory clean

Problem

The master, on the other hand, shows there are "new commits" for the book submodule:

$ cd /path/to/master/
$ git status
# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       modified:   book (new commits)
#
no changes added to commit (use "git add" and/or "git commit -a")

Git should ignore the submodule directory completely, so that the master is also clean:

$ cd /path/to/master/
$ git status
# On branch master
nothing to commit, working directory clean

Failed Attempt #1 - dirty

Inside the file master/.gitmodules is the following, as per this answer:

[submodule "book"]
        path = book
        url = https://[email protected]/user/repo.git
        ignore = dirty

Failed Attempt #2 - untracked

Changed master/.gitmodules to the following, as per this answer:

[submodule "book"]
        path = book
        url = https://[email protected]/user/repo.git
        ignore = untracked

Failed Attempt #3 - showUntrackedFiles

Edited master/.git/config to the following, as per this answer:

[status]
   showUntrackedFiles = no

Failed Attempt #4 - ignore

Added the book directory to the master ignore file:

$ cd /path/to/master/
$ echo book > .gitignore

Failed Attempt #5 - clone

Added the book directory to the master as follows:

$ cd /path/to/master/
$ rm -rf book
$ git clone https://[email protected]/user/repo.git book

Question

How can the book submodule be in its own repository directory under the master repository yet have git ignore the book submodule? That is, the following should not display:

#
#       modified:   book (new commits)
#

How to suppress that message when executing git status in the master repository?

An article about git submodule pitfalls suggests this an inappropriate submodule usage?

Answer 1

Just run:

$ git submodule update

This will revert the submodule the to old commit (specified in parent-repo), without updating the parent-repo with the latest version of the submodule.

Answer 2

To include another repository, that needn't be tracked in its super-repo, try this:

$ cd /path/to/master/
$ rm -rf book
$ git clone https://[email protected]/user/repo.git book
$ git add book
$ echo "book" >> .gitignore

Then commit.

As stated in the linked git submodule pitfalls article:

... the only linkage between the parent and the submodule is [the] recorded value of the submodule’s checked-out SHA which is stored in the parent’s commits.

That means that a submodule is not saved by its checked-out branch or tag, but always by a specific commit; that commit (SHA) is saved into the super-repo (the one containing the submodule) like a normal text file (it's marked as such a reference, of course).

When you check out a different commit in the submodule or make a new commit in it, the super-repo will see that its checked out SHA has changed. That's when you get the modified (new commits) line from git status.

To eliminate that, you can either:

• git submodule update, which will reset the submodule to the commit currently saved in the super-repo (for details see the git submodule manpage; or
• git add book && git commit to save the new SHA into the super-repo.

As mentioned in the comments, consider abandoning the book submodule: clone it inside the super-repo, if tracking of its state as part of the super-repo is not necessary.