[PATCH v2 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 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  |  4 ++--
 t/t4000-diff-format.sh | 10 ++++++++++
 t/t7800-difftool.sh    |  8 ++++++++
 4 files changed, 35 insertions(+), 3 deletions(-)

base-commit: feea6946a5b746ff4ebf8ccdf959e303203a6011
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-654%2Fdscho%2Fdifftool-ita-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-654/dscho/difftool-ita-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/654

Range-diff vs v1:

 2:  6d423928512 ! 1:  640e2255508 diff-files --raw: handle intent-to-add files correctly
     @@ Commit message
      
          This fixes https://github.com/git-for-windows/git/issues/2677
      
     +    This patch _also_ fixes the expectations set by the regression test
     +    introduced in feea6946a5b (diff-files: treat "i-t-a" files as
     +    "not-in-index", 2020-06-20).
     +
          Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
      
       ## diff-lib.c ##
      @@ diff-lib.c: int run_diff_files(struct rev_info *revs, unsigned int option)
     - 					       the_hash_algo->empty_blob, 0,
     + 					       !is_null_oid(&ce->oid),
       					       ce->name, 0);
       				continue;
      +			} else if (ce_intent_to_add(ce) &&
     @@ diff-lib.c: int run_diff_files(struct rev_info *revs, unsigned int option)
      +				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
      +					       &oid, ret >= 0, ce->name, 0);
      +				continue;
     - 			}
     + 			} else if (revs->diffopt.ita_invisible_in_index &&
     + 				   ce_intent_to_add(ce)) {
     + 				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
     +
     + ## 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
     + 	 create mode 100644 not-empty
     + 	EOF
     + 	cat >expect.diff_a <<-EOF &&
     +-	:000000 100644 0000000 $(git rev-parse --short $hash_t) A$(printf "\t")empty
     +-	:000000 100644 0000000 $(git rev-parse --short $hash_t) A$(printf "\t")not-empty
     ++	:000000 100644 0000000 $(git rev-parse --short $hash_e) A$(printf "\t")empty
     ++	:000000 100644 0000000 $(git rev-parse --short $hash_n) A$(printf "\t")not-empty
     + 	EOF
       
     - 			changed = match_stat_with_submodule(&revs->diffopt, ce, &st,
     + 	git add -N empty not-empty &&
      
       ## t/t4000-diff-format.sh ##
      @@ t/t4000-diff-format.sh: test_expect_success 'git diff-files --patch --no-patch does not show the patch'
 1:  9c96c43f3d7 ! 2:  b9633315a2f diff-files: fix incorrect usage of an empty tree
     @@ Commit message
      
          In c26022ea8f5 (diff: convert diff_addremove to struct object_id,
          2017-05-30), the OID to use for intent-to-add files was inadvertently
     -    changed from the empty blob to the empty tree. Let's revert that.
     +    changed from the empty blob to the empty tree.
     +
     +    Let's revert that.
     +
     +    To be able to do that, we just taught the regression test introduced in
     +    feea6946a5b (diff-files: treat "i-t-a" files as "not-in-index",
     +    2020-06-20) to _not_ expect the raw diff to contain the hash of the
     +    empty tree (we also had to fix the code to actually produce the expected
     +    output, but for the sake of this here patch, that's beside the point).
      
          Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
      
 3:  a1c889e2cd1 = 3:  d2e9f704c9e difftool -d: ensure that intent-to-add files are handled correctly