Merge branch 'jc/diff-irreversible-delete'

* jc/diff-irreversible-delete:
  git diff -D: omit the preimage of deletes

Documentation/diff-options.txt

@@ -263,6 +263,19 @@ endif::git-log[]
 	projects, so use it with caution.  Giving more than one
 	`-C` option has the same effect.
 
+-D::
+--irreversible-delete::
+	Omit the preimage for deletes, i.e. print only the header but not
+	the diff between the preimage and `/dev/null`. The resulting patch
+	is not meant to be applied with `patch` nor `git apply`; this is
+	solely for people who want to just concentrate on reviewing the
+	text after the change. In addition, the output obviously lack
+	enough information to apply such a patch in reverse, even manually,
+	hence the name of the option.
++
+When used together with `-B`, omit also the preimage in the deletion part
+of a delete/create pair.
+
 -l<num>::
 	The `-M` and `-C` options require O(n^2) processing time where n
 	is the number of potential rename/copy targets.  This

diff.c

@@ -581,11 +581,14 @@ static void emit_rewrite_diff(const char *name_a,
 		line_prefix, metainfo, a_name.buf, name_a_tab, reset,
 		line_prefix, metainfo, b_name.buf, name_b_tab, reset,
 		line_prefix, fraginfo);
-	print_line_count(o->file, lc_a);
+	if (!o->irreversible_delete)
+		print_line_count(o->file, lc_a);
+	else
+		fprintf(o->file, "?,?");
 	fprintf(o->file, " +");
 	print_line_count(o->file, lc_b);
 	fprintf(o->file, " @@%s\n", reset);
-	if (lc_a)
+	if (lc_a && !o->irreversible_delete)
 		emit_rewrite_lines(&ecbdata, '-', data_one, size_one);
 	if (lc_b)
 		emit_rewrite_lines(&ecbdata, '+', data_two, size_two);
@@ -1981,7 +1984,11 @@ 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)
@@ -2001,8 +2008,7 @@ 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;
@@ -3200,6 +3206,9 @@ 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.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;

t/t4022-diff-rewrite.sh

@@ -11,7 +11,9 @@ test_expect_success setup '
 	tr \
 	  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" \
 	  "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM" \
-	  <"$TEST_DIRECTORY"/../COPYING >test
+	  <"$TEST_DIRECTORY"/../COPYING >test &&
+	echo "to be deleted" >test2 &&
+	git add test2
 
 '
 
@@ -25,5 +27,44 @@ test_expect_success 'detect rewrite' '
 
 '
 
+cat >expect <<EOF
+diff --git a/test2 b/test2
+deleted file mode 100644
+index 4202011..0000000
+--- a/test2
++++ /dev/null
+@@ -1 +0,0 @@
+-to be deleted
+EOF
+test_expect_success 'show deletion diff without -D' '
+
+	rm test2 &&
+	git diff -- test2 >actual &&
+	test_cmp expect actual
+'
+
+cat >expect <<EOF
+diff --git a/test2 b/test2
+deleted file mode 100644
+index 4202011..0000000
+EOF
+test_expect_success 'suppress deletion diff with -D' '
+
+	git diff -D -- test2 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'show deletion diff with -B' '
+
+	git diff -B -- test >actual &&
+	grep "Linus Torvalds" actual
+'
+
+test_expect_success 'suppress deletion diff with -B -D' '
+
+	git diff -B -D -- test >actual &&
+	grep -v "Linus Torvalds" actual
+'
+
 test_done