The 'git worktree' command used to be just another mode in 'git
checkout', namely 'git checkout --to'.  When the tests for the latter
were retrofitted for the former, the test name was adjusted, but the
test number was kept, even though the test is testing a different
command now.  t/README states: "Second digit tells the particular
command we are testing.", so 'git worktree' should have a separate
number just for itself.

Move the worktree tests to t24* to adhere to that guideline. We're
going to make use of the free'd up numbers in a subsequent commit.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Factor out the 'unlink_entry()' function from unpack-trees.c to
entry.c.  It will be used in other places as well in subsequent
steps.

As it's no longer a static function, also move the documentation to
the header file to make it more discoverable.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

'checkout_entry()' currently only supports creating new entries in the
working tree, but not deleting them.  Add the ability to remove
entries at the same time if the entry is marked with the CE_WT_REMOVE
flag.

Currently this doesn't have any effect, as the CE_WT_REMOVE flag is
only used in unpack-tree, however we will make use of this in a
subsequent step in the series.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

When marking cache entries for removal, and later removing them all at
once using 'remove_marked_cache_entries()', cache entries currently
have to be invalidated manually in the cache tree and in the untracked
cache.

Add an invalidate flag to the function.  With the flag set, the
function will take care of invalidating the path in the cache tree and
in the untracked cache.

Note that the current callsites already do the invalidation properly
in other places, so we're just passing 0 from there to keep the status
quo.

This will be useful in a subsequent commit.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

The key point for the if statement is that read_tree_some did not
update the entry, because either it doesn't exist in tree-ish or
doesn't match the pathspec.  Clarify that.

Suggested-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Factor out the code that marks a cache entry as matched for checkout
into a separate function.  We are going to introduce a new mode in
'git checkout' in a subsequent commit, that is going to have a
slightly different logic.  This would make this code unnecessarily
complex.

Moving that complexity into separate functions will make the code in
the subsequent step easier to follow.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Currently 'git checkout' is defined as an overlay operation, which
means that if in 'git checkout <tree-ish> -- [<pathspec>]' we have an
entry in the index that matches <pathspec>, but that doesn't exist in
<tree-ish>, that entry will not be removed from the index or the
working tree.

Introduce a new --{,no-}overlay option, which allows using 'git
checkout' in non-overlay mode, thus removing files from the working
tree if they do not exist in <tree-ish> but match <pathspec>.

Note that 'git checkout -p <tree-ish> -- [<pathspec>]' already works
this way, so no changes are needed for the patch mode.  We disallow
'git checkout --overlay -p' to avoid confusing users who would expect
to be able to force overlay mode in 'git checkout -p' this way.

Untracked files are not affected by this change, so 'git checkout
--no-overlay HEAD -- untracked' will not remove untracked from the
working tree.  This is so e.g. 'git checkout --no-overlay HEAD -- dir/'
doesn't delete all untracked files in dir/, but rather just resets the
state of files that are known to git.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

In the previous patch we introduced a new no-overlay mode for git
checkout.  Some users (such as the author of this commit) may want to
have this mode turned on by default as it matches their mental model
more closely.  Make that possible by introducing a new config option
to that extend.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This reverts 1495ff7 ("checkout: introduce checkout.overlayMode
config", 2019-01-08) and thus removes the checkout.overlayMode config
option.

The option was originally introduced to give users the option to make
the new no-overlay behaviour the default.  However users may be using
'git checkout' in scripts, even though it is porcelain.  Users setting
the option to false may actually end up accidentally breaking scripts.

With the introduction of a new subcommand that will make the behaviour
the default, the config option will not be needed anymore anyway.
Revert the commit and remove the config option, so we don't risk
breaking scripts.

Suggested-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>