[RFC PATCH 0/9] Use a structure for object IDs.

This is a preliminary RFC patch series to move all the relevant uses of unsigned char [20] to struct object_id. It should not be applied to any branch yet.

The goal of this series to improve type-checking in the codebase and to make it easier to move to a different hash function if the project decides to do that. This series does not convert all of the codebase, but only parts. I'm looking for feedback to see if there is consensus that this is the right direction before investing a large amount of time.

Certain parts of the code have to be converted before others to keep the patch sizes small, maintainable, and bisectable, so functions and structures that are used across the codebase (e.g. hashcmp and struct object) will be converted later. Conversion has been done in a roughly alphabetical order by name of file.

The constants for raw and hex sizes of SHA-1 values are maintained. These constants are used where the quantity is the size of an SHA-1 value, and sizeof(struct object_id) is used wherever memory is to be allocated. This is done to permit the struct to turn into a union later if multiple hashes are supported. I left the names at GIT_OID_RAWSZ and GIT_OID_HEXSZ because that's what libgit2 uses and what Junio seemed to prefer, but they can be changed later if there's a desire to do that.

I called the structure member "oid" because it was easily grepable and distinct from the rest of the codebase. It, too, can be changed if we decide on a better name. I specifically did not choose "sha1" since it looks weird to have "sha1->sha1" and I didn't want to rename lots of variables.

Comments?

brian m. carlson (9):
  Define a structure for object IDs.
  bisect.c: convert to use struct object_id
  archive.c: convert to use struct object_id
  zip: use GIT_OID_HEXSZ for trailers
  branch.c: convert to use struct object_id
  bulk-checkin.c: convert to use struct object_id
  bundle.c: convert leaf functions to struct object_id
  cache-tree: convert struct cache_tree to use object_id
  diff: convert struct combine_diff_path to object_id

 archive-zip.c          |  4 ++--
 archive.c              | 16 +++++++--------
 archive.h              |  1 +
 bisect.c               | 30 ++++++++++++++--------------
 branch.c               | 16 +++++++--------
 builtin/commit.c       |  2 +-
 builtin/fsck.c         |  4 ++--
 bulk-checkin.c         | 12 +++++------
 bundle.c               | 38 +++++++++++++++++------------------
 cache-tree.c           | 30 ++++++++++++++--------------
 cache-tree.h           |  3 ++-
 combine-diff.c         | 54 +++++++++++++++++++++++++-------------------------
 diff-lib.c             | 10 +++++-----
 diff.h                 |  5 +++--
 merge-recursive.c      |  2 +-
 object.h               | 13 +++++++++++-
 reachable.c            |  2 +-
 sequencer.c            |  2 +-
 test-dump-cache-tree.c |  4 ++--
 19 files changed, 131 insertions(+), 117 deletions(-)