Hi,

wow! What a long mail! But I probably deserved it, quoting that lengthy 
mail from Junio...

On Fri, 5 Aug 2005, Linus Torvalds wrote:

On Fri, 5 Aug 2005, Johannes Schindelin wrote:

quoted

Tutorial says "cache" aka "index". Though technically, a cache
is the index file _plus_ the related objects in the object database.
git-update-cache.txt even makes the difference between the "index"
and the "directory cache".

I think we should globally rename it to "index".

Totally agree. The index is a central concept. But let's keep in mind -- 
and make future Documentation/ readers do the same -- that the index,
without the referenced objects in the objects database, is only a 
skeleton.

The "directory cache" and later "cache" naming came from when I started
doing the work - before git was even git at all, and had no backing store
what-so-ever, I started out writing "cache.h" and "read-cache.c", and it
was really first a trial at doing a totally SCM-neutral directory cache
front-end.

You don't even see that in the git revision history, because that was 
before git was self-hosting - the project was partly started to also work 
as possibly just a fast front-end to something that wasn't as fast (ie 
think something like a front-end to make "monotone" work better).

So the "directory cache" and "cache" naming comes from that historical 
background: it was really started as a front-end cache, and in fact the 
".git" directory was called ".dircache" initially. You can see some of 
that in the very earliest git releases: by then I had already done the 
backing store, and the thing was already called "git", but the "dircache" 
naming still remains in places.

For example, here's my "backup" target in the initial checkin:

	backup: clean
		cd .. ; tar czvf dircache.tar.gz dir-cache

which shows that not only did I call the resulting tar file "dircache", 
the directory I was developing stuff in was called "dir-cache" as well ;)

The index obviously ended up doing a lot more, and especially with the
different stages it became much more than just a directory cache thing:  
it's integral to how git does the fast part of a merge. So we should call
it "index" and edit out the old "cache" and "director cache" naming
entirely.

I quoted this entirely, for a good reason: Linus, one day you really 
should write a Wikibook about all the "small" projects you started. I 
still remember the words "I'm doing a (free) operating system (just a 
hobby, won't be big...". There's so much to be learnt about good 
engineering. And people do want to add there anecdotes to it.

quoted

  - the directory which corresponds to the top of the hierarchy
    described in the index file; I've seen words like "working
    tree", "working directory", "work tree" used.

The tutorial initially says "working tree", but then "working
directory". Usually, a directory does not include its
subdirectories, though. git-apply-patch-script.txt, git-apply.txt,
git-hash-object.txt, git-read-tree.txt
use "work tree". git-checkout-cache.txt, git-commit-tree.txt,
git-diff-cache.txt, git-ls-tree.txt, git-update-cache.txt contain
"working directory". git-diff-files.txt talks about a "working tree".

I think we should use "working tree" throughout, since "working directory" 
is unix-speak for "pwd" and has a totally different meaning.

I hoped so much.

quoted

  - An index file can be in "merged" or "unmerged" state.  The
    former is when it does not have anything but stage 0 entries,
    the latter otherwise.

I think the "unmerged" case should be mentioned in the "cache entry" 
thing, since it's really a per-entry state, exactly like "dirty/clean".

Then, explaining a "unmerged index" as being an index file with some 
entries being unmerged makes more sense. 

As it is, the above "explains" an index file as being unmerged by talking 
about "stage 0 entries", which in turn haven't been explained at all.

That's right. We probably should copy a bit from git-read-tree.txt, or at 
least reference it in the glossary.

quoted

  - A "tree object" can be recorded as a part of a "commit
    object".  The tree object is said to be "associated with" the
    commit object.

In diffcore.txt, "changeset" is used in place of "commit".

We really should use "commit" throughout. ex-BK users sometimes lip into
"changeset" (which in turn is probably because BK had these per-file
commits too - deltas), but there's no point in the distinction in git. A 
commit is a commit.

That is, if you don't do "git-update-cache <single-file>" (which is not 
possible with some porcelains).

Apart from that: I think that it is quite important to make the 
distinction between a "commit" and a "commit object". Newbies (in that 
case, people working with CVS are newbies to the concepts of git, too) 
tend understand better what you say, if you make that distinction very 
clearly, IMHO.

quoted

  - The following objects are collectively called "tree-ish": a
    tree object, a commit object, a tag object that resolves to
    either a commit or a tree object, and can be given to
    commands that expect to work on a tree object.

We could call this category an "ent".

LOL. You are a total geek.

I take that as a compliment :-)

quoted

  - The files under $GIT_DIR/refs record object names, and are
    called "refs".  What is under refs/heads/ are called "heads",
    refs/tags/ "tags".  Typically, they are either object names
    of commit objects or tag objects that resolve to commit
    objects, but a tag can point at any object.

The tutorial never calls them "refs", but instead "references".

It might be worth saying explicitly that a reference is nothing but the 
same thing as a "object name" aka "sha1". And make it very clear that it 
can point to any object type, although commits tend to be the most common 
thng you want to reference. That then leads naturally into a very specific 
_subcase_ of refs, namely a "head":

Do not forget signed tags! Strictly said, these are references to 
references which are signed.

quoted

  - A "head" is always an object name of a commit, and marks the
    latest commit in one line of development.  A line of
    development is often called a "branch".  We sometimes use the
    word "branch head" to stress the fact that we are talking
    about a single commit that is the latest one in a "branch".

In the tutorial, the latter is used in reverse: it talks about a
"HEAD development branch" and a "HEAD branch".

Actually, I don't think it a good idea to talk about a "HEAD branch" or 
"development branch". I'd prefer "branch".

quoted

I find it a little bit troublesome that $GIT_DIR/branches does not
really refer to a branch, but rather to a (possibly remote) repository.

Yes, I find the $GIT_DIR/branches naming to be confusing too. 

I don't know if we can hide it from the users, or if we should bite the 
apple and rename it to "remotes/", or even better "repositories/".

Jeff has been dragging me into the "local branches are good" camp, and
these days I'm obviously a big believer.

I think that Jeff really deserves the credit for this. Yours truly was 
convinced that one repository should hold one branch only. But I was 
convinced otherwise, too.

quoted

  - The act of finding out the object names recorded in "refs" a
    different repository records, optionally updating a local
    "refs" with their values, and retrieving the objects
    reachable from them is called "fetching".  Fetching immediately
    followed by merging is called "pulling".

In that sense, git-http-pull would be more appropriately named
git-http-fetch, and analogous git-ssh-pull.

Also, git-pull-script.txt says "Pull and merge", contradicting this
definition.

To confuse things even more, cogito calls a fetch "pull" and a pull 
"update".

I really think this should be unified. Pasky?

I personally think "fetch" is unambigious: it's just the act of fetching, 
with no "merge" activity at all. So we should use that.

Agree.

What to call a "fetch+merge" is a bit ambiguous. I obviously prefer
"pull", but cogito disagrees, and you're right, "git-http-pull" and
"git-ssh-pull" both really do just fetches.

Let's rename them before 1.0.

But I think "update" isn't right either: to me, update would be the 
non-merging kind (ie I think "update" implies "refresh" which in turn 
implies a "fetch"-like behaviour).

So I'd vote for making the suggested definition official: "fetch" means
fetching the data, and "pull" means "fetch + merge". 

This should be discussed. Obviously, I come from CVS and understand 
"update" to be what cogito says it is. But then, it is also true that 
CVS's usage of "update" is misleading, because it really does a merge, not 
forcing the user to do a commit before merge (because that is not possible 
in CVS). So basically, I agree: "pull" is unambiguous as far as I am 
concerned.

quoted

  - a "pack" usually consists of two files: a file containing objects
    in a compressed format, and an index to the first file. If the
    pack is uncompressed at once (e.g. when git-clone is called), the
    index is not necessary.

git-pack-objects calls this a "packed archive" first, but then reverts
to "pack". git-show-index.txt and git-verify-pack.txt call the .pack file
"packed GIT archive", and the index "idx file". git-unpack-objects.txt
calls the .pack file "pack archive".

We should just call them packs. An archive can be multiple packs and lots 
of non-packed objects too. 

And they can have pack indices which do not relate at all to the central 
GIT index.

quoted

"type": one of the identifiers "commit","tree","tag" and "blob" describing
the type of an object.

Yes. Some old docs may call this type a "tag", since I was really thinking
in not in the SCM meaning at all, but in the _computer_architecture_
meaning, where people usually call objects with enforced types "tagged".

Ie from a computer architecture standpoint you can have "tagged memory" or
"tagged pointers", and LISP machines are often implemented with the
pointers containing the type ("tag") of the thing they point to (for
example, the low two bits might be the "tag" on the pointer). So I was
talking about "tagged objects" when I just meant that the type of the
object was embedded in the object itself, the way tagged memory
architectures work.

In retrospect, that naming _really_ confused some people, I know I had
trouble explaining git concepts to David Wheeler because I used "tagged
objects" _not_ to mean a SCM style "tag", but to mean "typed objects".

If somebody sees an old reference to "object tags", those should all be 
fixed to say "object types".

Agree.

Ciao,
Dscho