We peek objects from submodule's object store by linking it to the
list of alternate object databases, but the code to do so forgot to
correctly initialize the list.

* jk/initialization-fix-to-add-submodule-odb:
  add_submodule_odb: initialize alt_odb list earlier

The add_submodule_odb function tries to add a submodule's
object store as an "alternate". It needs the existing list
to be initialized (from the objects/info/alternates file)
for two reasons:

  1. We look for duplicates with the existing alternate
     stores, but obviously this doesn't work if we haven't
     loaded any yet.

  2. We link our new entry into the list by prepending it to
     alt_odb_list. But we do _not_ modify alt_odb_tail.
     This variable starts as NULL, and is a signal to the
     alt_odb code that the list has not yet been
     initialized.

     We then call read_info_alternates on the submodule (to
     recursively load its alternates), which will try to
     append to that tail, assuming it has been initialized.
     This causes us to segfault if it is NULL.

This rarely comes up in practice, because we will have
initialized the alt_odb any time we do an object lookup. So
you can trigger this only when:

  - you try to access a submodule (e.g., a diff with
    diff.submodule=log)

  - the access happens before any other object has been
    accessed (e.g., because the diff is between the working
    tree and the index)

  - the submodule contains an alternates file (so we try to
    add an entry to the NULL alt_odb_tail)

To fix this, we just need to call prepare_alt_odb at the
start of the function (and if we have already initialized,
it is a noop).

Note that we can remove the prepare_alt_odb call from the
end. It is guaranteed to be a noop, since we will have
called it earlier.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Functions which directly operate submodule's object database do not
handle the case when the submodule is linked worktree (which are
introduced in c7b3a3d2fe). Instead of fixing the path calculation use
already existing strbuf_git_path_submodule() function without changing
overall behaviour. Then it will be possible to modify only that function
whenever we need to change real location of submodule's repository
content.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Recent reimplementation of "git am" changed the format of state
files kept in $GIT_DIR/rebase-apply/ without meaning to do so,
primarily because write_file() API was cumbersome to use and it was
easy to mistakenly make text files with incomplete lines.  Update
write_file() interface to make it harder to misuse.

* jc/am-state-fix:
  write_file(): drop caller-supplied LF from calls to create a one-liner file
  write_file_v(): do not leave incomplete line at the end
  write_file(): drop "fatal" parameter
  builtin/am: make sure state files are text
  builtin/am: introduce write_state_*() helper functions

The gitmodules API accessed from the C code learned to cache stuff
lazily.

* hv/submodule-config:
  submodule: allow erroneous values for the fetchRecurseSubmodules option
  submodule: use new config API for worktree configurations
  submodule: extract functions for config set and lookup
  submodule: implement a config API for lookup of .gitmodules values

All of the callsites covered by this change call write_file() or
write_file_gently() to create a one-liner file.  Drop the caller
supplied LF and let these callees to append it as necessary.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

All callers except three passed 1 for the "fatal" parameter to ask
this function to die upon error, but to a casual reader of the code,
it was not all obvious what that 1 meant.  Instead, split the
function into two based on a common write_file_v() that takes the
flag, introduce write_file_gently() as a new way to attempt creating
a file without dying on error, and make three callers to call it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

We should not die when reading the submodule config cache since the
user might not be able to get out of that situation when the
configuration is part of the history.

We should handle this condition later when the value is about to be
used.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

We remove the extracted functions and directly parse into and read out
of the cache. This allows us to have one unified way of accessing
submodule configuration values specific to single submodules. Regardless
whether we need to access a configuration from history or from the
worktree.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This is one step towards using the new configuration API. We just
extract these functions to make replacing the actual code easier.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>