Re: git diff: add option for omitting the contents of deletes

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Jeff King <peff@peff.net> writes:
>
>> I'm not quite sure what lossage you mean. On the recipient's end? They
>> can just "git revert", no?

This is beating on a dead horse, but in my previous life, in a project I
wasn't deeply involved in, a deployment procedure used was to:

 - give git-archive tarball of a major release to the target machine that
   does not have git repository, and extract the tarball;

 - maintain 'maint' branch, and show the tip of 'maint' on a test server,
   but give the client vetoing power on individual changes;

 - hence ending up preparing a format-patch output for selected changes,
   and running git-apply on the target machine to update it.

The -M/-C options would have worked well in this scenario, including the
recovery from "oops--that didn't work, please revert asap" (I don't know
if they actually used -M/-C when preparing the incremental updates,
though).  The -D option does not have the same reversibility.

I am (have been) only reacting to the earlier statement by Michael that -D
is the same as -M/-C and reversibility does not matter.  It does in such a
situation.

Now that the project with that deployment procedure is totally behind me,
I probably shouldn't care too much about such a workflow, but I suspect
there still are people using that sort of workflow, and this would matter
to them.

In any case, a minimum patch to give what Mart wanted to see would
probably look like this.  I'll leave bugfixes, documentation and tests to
the readers ;-).

 diff.c |   12 +++++++++---
 diff.h |    1 +
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/diff.c b/diff.c
index 5422c43..5c66a53 100644
--- a/diff.c
+++ b/diff.c
@@ -1943,7 +1943,11 @@ static void builtin_diff(const char *name_a,
 		}
 	}
 
-	if (!DIFF_OPT_TST(o, TEXT) &&
+	if (o->irreversible_delete && lbl[1][0] == '/') {
+		fprintf(o->file, "%s", header.buf);
+		strbuf_reset(&header);
+		goto free_ab_and_return;
+	} else if (!DIFF_OPT_TST(o, TEXT) &&
 	    ( (!textconv_one && diff_filespec_is_binary(one)) ||
 	      (!textconv_two && diff_filespec_is_binary(two)) )) {
 		if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
@@ -1963,8 +1967,7 @@ static void builtin_diff(const char *name_a,
 			fprintf(o->file, "%sBinary files %s and %s differ\n",
 				line_prefix, lbl[0], lbl[1]);
 		o->found_changes = 1;
-	}
-	else {
+	} else {
 		/* Crazy xdl interfaces.. */
 		const char *diffopts = getenv("GIT_DIFF_OPTS");
 		xpparam_t xpp;
@@ -3160,6 +3163,9 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 			return error("invalid argument to -M: %s", arg+2);
 		options->detect_rename = DIFF_DETECT_RENAME;
 	}
+	else if (!strcmp(arg, "-D") || !strcmp(arg, "--irreversible-delete")) {
+		options->irreversible_delete = 1;
+	}
 	else if (!prefixcmp(arg, "-C") || !prefixcmp(arg, "--find-copies=") ||
 		 !strcmp(arg, "--find-copies")) {
 		if (options->detect_rename == DIFF_DETECT_COPY)
diff --git a/diff.h b/diff.h
index 310bd6b..11d13cf 100644
--- a/diff.h
+++ b/diff.h
@@ -104,6 +104,7 @@ struct diff_options {
 	int interhunkcontext;
 	int break_opt;
 	int detect_rename;
+	int irreversible_delete;
 	int skip_stat_unmatch;
 	int line_termination;
 	int output_format;