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

["Philippe Blain via GitGitGadget" <gitgitgadget@gmail.com>]

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 shown.

Note that the test must use '--creation-factor=100' to force the second
commit in the range not to be considered a complete rewrite.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
---
    range-diff: show submodule changes irrespective of diff.submodule
    
    This fixes a bug that I reported last summer [1].
    
    [1]
    https://lore.kernel.org/git/e469038c-d78c-cd4b-0214-7094746b9281@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1244%2Fphil-blain%2Frange-diff-submodule-diff-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1244/phil-blain/range-diff-submodule-diff-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1244

 range-diff.c          |  2 +-
 t/t3206-range-diff.sh | 44 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/range-diff.c b/range-diff.c
index b72eb9fdbee..068bf214544 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -44,7 +44,7 @@ static int read_patches(const char *range, struct string_list *list,
 
 	strvec_pushl(&cp.args, "log", "--no-color", "-p", "--no-merges",
 		     "--reverse", "--date-order", "--decorate=no",
-		     "--no-prefix",
+		     "--no-prefix", "--submodule=short",
 		     /*
 		      * Choose indicators that are not used anywhere
 		      * else in diffs, but still look reasonable
diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index e30bc48a290..ac848c42536 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -772,4 +772,48 @@ test_expect_success '--left-only/--right-only' '
 	test_cmp expect actual
 '
 
+test_expect_success 'submodule changes are shown irrespective of diff.submodule' '
+	git init sub-repo &&
+	test_commit -C sub-repo sub-first &&
+	sub_oid1=$(git -C sub-repo rev-parse HEAD) &&
+	test_commit -C sub-repo sub-second &&
+	sub_oid2=$(git -C sub-repo rev-parse HEAD) &&
+	test_commit -C sub-repo sub-third &&
+	sub_oid3=$(git -C sub-repo rev-parse HEAD) &&
+
+	git checkout -b main-sub topic &&
+	git submodule add ./sub-repo sub &&
+	git -C sub checkout --detach sub-first &&
+	git add sub &&
+	git commit -m "add sub" &&
+	sup_oid1=$(git rev-parse --short HEAD) &&
+	git checkout -b topic-sub &&
+	git -C sub checkout sub-second &&
+	git add sub &&
+	git commit -m "change sub" &&
+	sup_oid2=$(git rev-parse --short HEAD) &&
+	git checkout -b modified-sub main-sub &&
+	git -C sub checkout sub-third &&
+	git add sub &&
+	git commit -m "change sub" &&
+	sup_oid3=$(git rev-parse --short HEAD) &&
+
+	test_config diff.submodule log &&
+	git range-diff --creation-factor=100 topic topic-sub modified-sub >actual &&
+	cat >expect <<-EOF &&
+	1:  $sup_oid1 = 1:  $sup_oid1 add sub
+	2:  $sup_oid2 ! 2:  $sup_oid3 change sub
+	    @@ Commit message
+	      ## sub ##
+	     @@
+	     -Subproject commit $sub_oid1
+	    -+Subproject commit $sub_oid2
+	    ++Subproject commit $sub_oid3
+	EOF
+	test_cmp expect actual &&
+	test_config diff.submodule diff &&
+	git range-diff --creation-factor=100 topic topic-sub modified-sub >actual &&
+	test_cmp expect actual
+'
+
 test_done

base-commit: 7a3eb286977746bc09a5de7682df0e5a7085e17c
-- 
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