How can we make progress here? I've kind of lost track of what the latest proposal and status is... :-)

I am happy with this change:
https://phabricator.services.mozilla.com/D15521
except:

• add the support of "git add -p "
• and improve the hg hook

I will try to finish it this week

For git add -p something like the following should work:

git stash --keep-index && $(git rev-parse --show-toplevel)/mach clang-format && git add -u && git stash pop

Or something of that sort.

I think the only case it wouldn't handle is the case where there's nothing to save (both the commit and the staging area is empty), which you could do with git commit --allow-empty, because in that case the stash will actually not save anything and the pop will pop whatever was on the stack beforehand. You can detect that easily before-hand though.

Not sure if there's a better way to do it.

Ah! A much faster way could be:

git diff --staged | clang-format-diff.py -p 1 | git apply -p 0 --cached

(You may want to apply the patch both with and without --cached, so that it gets reflected both in the index and the working tree)

Thanks for the suggestion
clang-format-diff.py isn't perfect but this is better than nothing

And also, on the hg hook, the issue is that it isn't trivial to retrieve the list of touched files in the commit hook.

pretxncommit would be perfect as it provides the node id (which is necessary to retrieve the list of files) except that it has no info about the files being added.

For example, using pretxnopen and pretxnclose don't provide the node id.
Sheeshan suggested that I use $HG_NODE but it doesn't exist where I am.

I could use the hg python interface to retrieve these data but it seems pretty overkill.

Sheehan told me the following:

so you would use pretxncommit as the hook phase, add node=None to your function signature, and then do the steps a mentioned
above to get the list of changed files

I took a different approach for hg:
https://phabricator.services.mozilla.com/D18883

and maybe move the git hook in bash to make it easier

Depends on D23789

Here is that I used to test the work:

git checkout dom/presentation/
git reset dom/presentation/AvailabilityCollection.cpp
sed -i -e "s|;$| ;|g" dom/presentation/AvailabilityCollection.cpp

echo "int foo( ){}" >> dom/presentation/AvailabilityCollection.cpp
# No action as no file added to git
git commit -m "foo - should not do anything"

# Should have the execution
git add dom/presentation/
git commit -m "foo - should commit the file with the change"
git show

sed -i -e "s|#include |#include    |g" dom/presentation/AvailabilityCollection.cpp
echo "int foo( ){}" >> dom/presentation/AvailabilityCollection.cpp
git diff dom/presentation/
git add -p dom/presentation/
git commit -m "foo - will commit everything when it should not"
git show

sed -i -e "s|#include |#include    |g" dom/presentation/AvailabilityCollection.cpp
echo "int bar( ){}" >> dom/presentation/AvailabilityCollection.cpp
# Nothing should happen (just renaming)
git commit --amend
# update the title + reformat it
git commit --amend -m "updated" dom/presentation/AvailabilityCollection.cpp

I would like to land that first, and then work on "git add -p" support

https://hg.mozilla.org/mozilla-central/rev/cc1347e7b69b

git diff --staged | clang-format-diff.py -p 1 | git apply -p 0 --cached

To explain why I am not using this:

• because clang-format-diff.py doesn't always have the whole context, clang-format-diff.py can provide different results (we had an issue with that)
• "mach clang-format" has more features (third party ignore, parallel execution, etc)