How to make git ignore changes to submodules by default

Solution 1:

Note that even if there were such a config, git 2.0.1 (June 25th, 2014) would still show you a submodule which has been staged.

See commit 1d2f393 by Jens Lehmann (jlehmann)

Currently setting submodule.<name>.ignore and/or diff.ignoreSubmodules to "all" suppresses all output of submodule changes for the diff family, status and commit.

For status and commit this is really confusing, as it even when the user chooses to record a new commit for an ignored submodule by adding it manually this change won't show up under the to-be-committed changes.
To add insult to injury, a later "git commit" will error out with "nothing to commit" when only ignored submodules are staged.

Fix that by making wt_status always print staged submodule changes, no matter what ignore settings are configured.
The only exception is when the user explicitly uses the "--ignore-submodules=all" command line option, in that case the submodule output is still suppressed.
This also makes "git commit" work again when only modifications of ignored submodules are staged, as that command uses the "commitable" member of the wt_status struct to determine if staged changes are present.

See also commit c215d3d for the git commit part.

Solution 2:

So to close this, no, there is not default option for it (sadly).