[PATCH v3 0/3] Fix difftool problem with intent-to-add files

This problem was reported in https://github.com/git-for-windows/git/issues/2677, but the problem actually lies with git diff --raw, and it seems that the bug has been with us ever since --intent-to-add was introduced.

Changes since v2:

 * Now we also drop the no-longer-used definition of hash_t in t2203.

Changes since v1:

 * Rebased onto sk/diff-files-show-i-t-a-as-new.
 * Verified that sk/diff-files-show-i-t-a-as-new does not completely resolve
   the issue (the --raw output still claims the empty blob as the
   post-image, although the difftool symptom "went away").
 * Amended the central patch of this PR to include a fix for the regression
   test that was introduced in sk/diff-files-show-i-t-a-as-new: it expected
   the raw diff to contain the hash of the empty tree object (which is
   incorrect no matter how you turn it: any hash in any raw diff should
   refer to blob objects).
 * Reordered the patches so that the central patch comes first (otherwise,
   the "empty tree" fix would cause a test failure in t2203).

Johannes Schindelin (3):
  diff-files --raw: handle intent-to-add files correctly
  diff-files: fix incorrect usage of an empty tree
  difftool -d: ensure that intent-to-add files are handled correctly

 diff-lib.c             | 16 +++++++++++++++-
 t/t2203-add-intent.sh  |  5 ++---
 t/t4000-diff-format.sh | 10 ++++++++++
 t/t7800-difftool.sh    |  8 ++++++++
 4 files changed, 35 insertions(+), 4 deletions(-)

base-commit: feea6946a5b746ff4ebf8ccdf959e303203a6011
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-654%2Fdscho%2Fdifftool-ita-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-654/dscho/difftool-ita-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/654

Range-diff vs v2:

 1:  640e225550 ! 1:  8c27c78831 diff-files --raw: handle intent-to-add files correctly
     @@ diff-lib.c: int run_diff_files(struct rev_info *revs, unsigned int option)
      
       ## t/t2203-add-intent.sh ##
      @@ t/t2203-add-intent.sh: test_expect_success 'i-t-a files shown as new for "diff", "diff-files"; not-new
     + 
     + 	hash_e=$(git hash-object empty) &&
     + 	hash_n=$(git hash-object not-empty) &&
     +-	hash_t=$(git hash-object -t tree /dev/null) &&
     + 
     + 	cat >expect.diff_p <<-EOF &&
     + 	diff --git a/empty b/empty
     +@@ t/t2203-add-intent.sh: test_expect_success 'i-t-a files shown as new for "diff", "diff-files"; not-new
       	 create mode 100644 not-empty
       	EOF
       	cat >expect.diff_a <<-EOF &&
 2:  b9633315a2 = 2:  a9e06427ec diff-files: fix incorrect usage of an empty tree
 3:  d2e9f704c9 = 3:  f51cbedd3f difftool -d: ensure that intent-to-add files are handled correctly