[PATCH v2] range-diff: show submodule changes irrespective of diff.submodule

From: Philippe Blain <levraiphilippeblain@gmail.com>

After generating diffs for each range to be compared using a 'git log' invocation, range-diff.c::read_patches looks for the "diff --git" header in those diffs to recognize the beginning of a new change.

In a project with submodules, and with 'diff.submodule=log' set in the config, this header is missing for the diff of a changed submodule, so any submodule changes are quietly ignored in the range-diff.

When 'diff.submodule=diff' is set in the config, the "diff --git" header is also missing for the submodule itself, but is shown for submodule content changes, which can easily confuse 'git range-diff' and lead to errors such as:

    error: git apply: bad git-diff - inconsistent old filename on line 1
    error: could not parse git header 'diff --git path/to/submodule/and/some/file/within
    '
    error: could not parse log for '@{u}..@{1}'

Force the submodule diff format to its default ("short") when invoking 'git log' to generate the patches for each range, such that submodule changes are always detected.

Add a test, including an invocation with '--creation-factor=100' to force the second commit in the range not to be considered a complete rewrite, in order to verify we do indeed get the "short" format.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
---
    range-diff: show submodule changes irrespective of diff.submodule
    
    Changes since v1:
    
     * added a comparison without '--creation-factor' to the test, as
       suggested by Ævar
     * remove separate 'git add sub' invocations in favor of 'git commit -m
       msg sub', as suggested by Dscho

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1244%2Fphil-blain%2Frange-diff-submodule-diff-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1244/phil-blain/range-diff-submodule-diff-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1244

Range-diff vs v1:

 1:  4ae11694ac6 ! 1:  1982b720a04 range-diff: show submodule changes irrespective of diff.submodule
     @@ Commit message
      
          Force the submodule diff format to its default ("short") when invoking
          'git log' to generate the patches for each range, such that submodule
     -    changes are always shown.
     +    changes are always detected.
      
     -    Note that the test must use '--creation-factor=100' to force the second
     -    commit in the range not to be considered a complete rewrite.
     +    Add a test, including an invocation with '--creation-factor=100' to
     +    force the second commit in the range not to be considered a complete
     +    rewrite, in order to verify we do indeed get the "short" format.
      
          Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
      
     @@ t/t3206-range-diff.sh: test_expect_success '--left-only/--right-only' '
      +	git checkout -b main-sub topic &&
      +	git submodule add ./sub-repo sub &&
      +	git -C sub checkout --detach sub-first &&
     -+	git add sub &&
     -+	git commit -m "add sub" &&
     ++	git commit -m "add sub" sub &&
      +	sup_oid1=$(git rev-parse --short HEAD) &&
      +	git checkout -b topic-sub &&
      +	git -C sub checkout sub-second &&
     -+	git add sub &&
     -+	git commit -m "change sub" &&
     ++	git commit -m "change sub" sub &&
      +	sup_oid2=$(git rev-parse --short HEAD) &&
      +	git checkout -b modified-sub main-sub &&
      +	git -C sub checkout sub-third &&
     -+	git add sub &&
     -+	git commit -m "change sub" &&
     ++	git commit -m "change sub" sub &&
      +	sup_oid3=$(git rev-parse --short HEAD) &&
     ++	sup_oid0=$(test_oid __) &&
      +
      +	test_config diff.submodule log &&
     ++	git range-diff topic topic-sub modified-sub >actual &&
     ++	cat >expect <<-EOF &&
     ++	1:  $sup_oid1 = 1:  $sup_oid1 add sub
     ++	2:  $sup_oid2 < -:  $sup_oid0 change sub
     ++	-:  $sup_oid0 > 2:  $sup_oid3 change sub
     ++	EOF
     ++	test_cmp expect actual &&
     ++	test_config diff.submodule diff &&
     ++	git range-diff topic topic-sub modified-sub >actual &&
      +	git range-diff --creation-factor=100 topic topic-sub modified-sub >actual &&
      +	cat >expect <<-EOF &&
      +	1:  $sup_oid1 = 1:  $sup_oid1 add sub

 range-diff.c          |  2 +-
 t/t3206-range-diff.sh | 51 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)