I think you (and others in the thread) are forgetting that
moving to a particular state by resetting can create a state
that you may want to keep a pointer to, but you do not have any
existing ref.  That's one of the reasons why we do not merely
check if the detached HEAD is not reachable from any of the
existing refs when coming back.  Instead, we check and warn if
the detached HEAD does not exactly match one of the existing
refs.

Imagine "git bisect" did not exist, or was not powerful enough,
and the user was doing it by hand using something other than
"git bisect" to guide him which state to go next, or the user
did not want to use the special "bisect" branch, or some
combination of the above.  You move your detached HEAD around
and finally you are at the commit you are interested in.  You
haven't marked it in some way (perhaps "git tag") yet.  You
haven't made any commit, and the commit is reachable in some
way, but all the work to reach that state will be lost unless
you jot its commit object name down somewhere.

So "until you make commits" is not sufficient, which means that
covering all the way you can make commits isn't, either.



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[ message continues ]

Is that an important distinction?  The way the user got there was by
manually specifying the SHA-1 shash of the commit to git-checkout.  So
if the user could get there once, the user could get there again a
second time.  Just because we don't have a name to that precise commit
inside the git system doesn't necessary mean the user can't get back

My personal belief is that covering all the way you can make commits
is where you want to be putting the check.  If I say something like

git checkout f00b51b8

There's nothing dangerous about that statement.  To argue that this is
dangerous and the git needs to warn me because I might not be able to
get back to it seems silly.  Of _course_ I can get back there; the
same way I got here in the first place --- By simply saying, "git
checkout f00b51b8" again!

And if I tell a user that they should try out a particular version of
the code, issueing a scary message right then there is pointless if
they are only going to be doing a read-only browse of the tree, is
just a Bad Thing.  The best place to warn them really is when they
modify the tree.

Otherwise, we'll be educating users to use the -f flag, or telling
users to "ignore the warning, git's being silly", neither of which is
desirable.

						- Ted
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[ message continues ]

If you mean grep 'git checkout|git reset' perhaps.  After
checking out a specific commit (because the user was told about
the commit out-of-band, say, via e-mail), the user can still

I do not think anybody is arguing that particular checkout is
dangerous.  The warning message is about the fact that your HEAD
is now detached, which might not have been what you intended
(and you will later get a real warning when you do a really
dangerous thing, which is "to come back and lose your point").

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[ message continues ]