sha1_name.c: get_describe_name() by definition groks only commits

Teach get_describe_name() to pass the disambiguation hint down the
callchain to get_short_sha1().

Also add tests to show various syntactic elements that we could take
advantage of the object type information to help disambiguration of
abbreviated object names.  Many of them are marked as broken, and
some of them will be fixed in later patches in this series.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_name.c: get_sha1_1() takes lookup flags

This is to pass the disambiguation hints from the caller down the
callchain.  Nothing is changed in this step, as everybody just
passes 0 in the flag.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_name.c: many short names can only be committish

We know that the token "$name" that appear in "$name^{commit}",
"$name^4", "$name~4" etc. can only name a committish (either a
commit or a tag that peels to a commit).  Teach get_short_sha1() to
take advantage of that knowledge when disambiguating an abbreviated
SHA-1 given as an object name.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_name.c: teach lookup context to get_sha1_with_context()

The function takes user input string and returns the object name
(binary SHA-1) with mode bits and path when the object was looked
up in a tree.

Additionally give hints to help disambiguation of abbreviated object
names when the caller knows what it is looking for.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_name.c: introduce get_sha1_committish()

Many callers know that the user meant to name a committish by
syntactical positions where the object name appears.  Calling this
function allows the machinery to disambiguate shorter-than-unique
abbreviated object names between committish and others.

Note that this does NOT error out when the named object is not a
committish. It is merely to give a hint to the disambiguation
machinery.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
revision.c: allow handle_revision_arg() to take other flags

The existing "cant_be_filename" that tells the function that the
caller knows the arg is not a path (hence it does not have to be
checked for absense of the file whose name matches it) is made into
a bit in the flag word.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
revision.c: the "log" family, except for "show", takes committish

Add a field to setup_revision_opt structure and allow these callers
to tell the setup_revisions command parsing machinery that short SHA1
it encounters are meant to name committish.

This step does not go all the way to connect the setup_revisions()
to sha1_name.c yet.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_name.c: add support for disambiguating other types

This teaches the revision parser that in "$name:$path" (used for a
blob object name), "$name" must be a tree-ish.

There are many more places where we know what types of objects are
called for.  This patch adds support for "commit", "treeish", "tree",
and "blob", which could be used in the following contexts:

 - "git apply --build-fake-ancestor" reads the "index" lines from
   the patch; they must name blob objects (not even "blob-ish");

 - "git commit-tree" reads a tree object name (not "tree-ish"), and
   zero or more commit object names (not "committish");

 - "git reset $rev" wants a committish; "git reset $rev -- $path"
   wants a treeish.

They will come in later patches in the series.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
apply: --build-fake-ancestor expects blobs

The "index" line read from the patch to reconstruct a partial
preimage tree records the object names of blob objects.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
commit-tree: the command wants a tree and commits

Signed-off-by: Junio C Hamano <gitster@pobox.com>
reset: the command takes committish

This is not strictly correct, in that resetting selected index
entries from corresponding paths out of a given tree without moving
HEAD is a valid operation, and in such case a tree-ish would suffice.

But the existing code already requires a committish in the codepath,
so let's be consistent with it for now.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
rev-parse: A and B in "rev-parse A..B" refer to committish

Signed-off-by: Junio C Hamano <gitster@pobox.com>
rev-parse --disambiguate=<prefix>

The new option allows you to feed an ambiguous prefix and enumerate
all the objects that share it as a prefix of their object names.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'mm/push-default-switch-warning' into jch

Hopefully we can have a solidly tested series early in 1.7.12 or
1.7.13 at the latest.

# By Matthieu Moy
* mm/push-default-switch-warning:
  push: start warning upcoming default change for push.default
Merge branch 'jn/perl-makemaker-leading-paths' into jch

Minor build tweak.  People who do not use ExtUtils::MakeMaker may
want to test this before it hits the 'master' branch.

# By Johannes Sixt (1) and Jonathan Nieder (1)
* jn/perl-makemaker-leading-paths:
  perl/Makefile: Fix a missing double-quote
  perl/Makefile: move "mkdir -p" to module installation loop for maintainability
Merge branch 'mm/config-xdg' into jch

Teach git to read various information from $XDG_CONFIG_HOME/git/ to allow
the user to avoid cluttering $HOME.

# By Huynh Khoi Nguyen Nguyen
* mm/config-xdg:
  config: write to $XDG_CONFIG_HOME/git/config file when appropriate
  Let core.attributesfile default to $XDG_CONFIG_HOME/git/attributes
  Let core.excludesfile default to $XDG_CONFIG_HOME/git/ignore
  config: read (but not write) from $XDG_CONFIG_HOME/git/config file
Merge branch 'mm/credential-plumbing' into jch

Expose the credential API to scripted Porcelain writers.

# By Matthieu Moy (2) and Javier Roucher Iglesias (1)
* mm/credential-plumbing:
  git-remote-mediawiki: add credential support
  git credential fill: output the whole 'struct credential'
  add 'git credential' plumbing command
Merge branch 'rj/platform-pread-may-be-thread-unsafe' into jch

On Cygwin, the platform pread(3) is not thread safe, just like our
own compat/ emulation, and cannot be used in the index-pack program.

* rj/platform-pread-may-be-thread-unsafe:
  index-pack: Disable threading on cygwin
Merge branch 'vr/use-our-perl-in-tests' into jch

Some implementations of Perl terminates "lines" with CRLF even when
the script is operating on just a sequence of bytes.  Make sure to
use "$PERL_PATH", the version of Perl the user told Git to use, in
our tests to avoid unnecessary breakages in tests.

# By Junio C Hamano (3) and Vincent van Ravesteijn (1)
* vr/use-our-perl-in-tests:
  t/README: add a bit more Don'ts
  tests: enclose $PERL_PATH in double quotes
  t/test-lib.sh: export PERL_PATH for use in scripts
  t: Replace 'perl' by $PERL_PATH
Merge branch 'cw/no-detaching-an-unborn' into jch

"git checkout --detach", when you are still on an unborn branch,
should be forbidden, but it wasn't.

# By Chris Webb
* cw/no-detaching-an-unborn:
  git-checkout: disallow --detach on unborn branch