[PATCH 10/10] fast-export: add --always-show-modify-after-rename

[Elijah Newren <newren@gmail.com>]

fast-export output is traditionally used as an input to a fast-import
program, but it is also useful to help gather statistics about the
history of a repository (particularly when --no-data is also passed).
For example, two of the types of information we may want to collect
could include:
  1) general information about renames that have occurred
  2) what the biggest objects in a repository are and what names
     they appear under.

The first bit of information can be gathered by just passing -M to
fast-export.  The second piece of information can partially be gotten
from running
    git cat-file --batch-check --batch-all-objects
However, that only shows what the biggest objects in the repository are
and their sizes, not what names those objects appear as or what commits
they were introduced in.  We can get that information from fast-export,
but when we only see
    R oldname newname
instead of
    R oldname newname
    M 100644 $SHA1 newname
then it makes the job more difficult.  Add an option which allows us to
force the latter output even when commits have exact renames of files.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 Documentation/git-fast-export.txt | 11 ++++++++++
 builtin/fast-export.c             |  7 +++++-
 t/t9350-fast-export.sh            | 36 +++++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-fast-export.txt b/Documentation/git-fast-export.txt
index 4e40f0b99a..946a5aee1f 100644
--- a/Documentation/git-fast-export.txt
+++ b/Documentation/git-fast-export.txt
@@ -128,6 +128,17 @@ marks the same across runs.
 	for intermediary filters (e.g. for rewriting commit messages
 	which refer to older commits, or for stripping blobs by id).
 
+--always-show-modify-after-rename::
+	When a rename is detected, fast-export normally issues both a
+	'R' (rename) and a 'M' (modify) directive.  However, if the
+	contents of the old and new filename match exactly, it will
+	only issue the rename directive.  Use this flag to have it
+	always issue the modify directive after the rename, which may
+	be useful for tools which are using the fast-export stream as
+	a mechanism for gathering statistics about a repository.  Note
+	that this option only has effect when rename detection is
+	active (see the -M option).
+
 --refspec::
 	Apply the specified refspec to each ref exported. Multiple of them can
 	be specified.
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index cc01dcc90c..db606d1fd0 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -38,6 +38,7 @@ static int use_done_feature;
 static int no_data;
 static int full_tree;
 static int reference_excluded_commits;
+static int always_show_modify_after_rename;
 static int show_original_ids;
 static struct string_list extra_refs = STRING_LIST_INIT_NODUP;
 static struct string_list tag_refs = STRING_LIST_INIT_NODUP;
@@ -407,7 +408,8 @@ static void show_filemodify(struct diff_queue_struct *q,
 				putchar('\n');
 
 				if (oideq(&ospec->oid, &spec->oid) &&
-				    ospec->mode == spec->mode)
+				    ospec->mode == spec->mode &&
+				    !always_show_modify_after_rename)
 					break;
 			}
 			/* fallthrough */
@@ -1099,6 +1101,9 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 			 &reference_excluded_commits, N_("Reference parents which are not in fast-export stream by sha1sum")),
 		OPT_BOOL(0, "show-original-ids", &show_original_ids,
 			    N_("Show original sha1sums of blobs/commits")),
+		OPT_BOOL(0, "always-show-modify-after-rename",
+			    &always_show_modify_after_rename,
+			 N_("Always provide 'M' directive after 'R'")),
 
 		OPT_END()
 	};
diff --git a/t/t9350-fast-export.sh b/t/t9350-fast-export.sh
index 5ad6669910..d0c30672ac 100755
--- a/t/t9350-fast-export.sh
+++ b/t/t9350-fast-export.sh
@@ -638,4 +638,40 @@ test_expect_success 'merge commit gets exported with --import-marks' '
 	)
 '
 
+test_expect_success 'rename detection and --always-show-modify-after-rename' '
+	test_create_repo renames &&
+	(
+		cd renames &&
+		test_seq 0  9  >single_digit &&
+		test_seq 10 98 >double_digit &&
+		git add . &&
+		git commit -m initial &&
+
+		echo 99 >>double_digit &&
+		git mv single_digit single-digit &&
+		git mv double_digit double-digit &&
+		git add double-digit &&
+		git commit -m renames &&
+
+		# First, check normal fast-export -M output
+		git fast-export -M --no-data master >out &&
+
+		grep double-digit out >out2 &&
+		test_line_count = 2 out2 &&
+
+		grep single-digit out >out2 &&
+		test_line_count = 1 out2 &&
+
+		# Now, test with --always-show-modify-after-rename; should
+		# have an extra "M" directive for "single-digit".
+		git fast-export -M --no-data --always-show-modify-after-rename master >out &&
+
+		grep double-digit out >out2 &&
+		test_line_count = 2 out2 &&
+
+		grep single-digit out >out2 &&
+		test_line_count = 2 out2
+	)
+'
+
 test_done
-- 
2.19.1.866.g82735bcbde