builtin/diff-pairs: allow explicit diff queue flush

The diffs queued from git-diff-pairs(1) stdin are not flushed EOF is
reached. To enable greater flexibility, allow control over when the diff
queue is flushed by writing a single nul byte on stdin between input
file pairs. Diff output between flushes is separated by a single line
terminator.

Signed-off-by: Justin Tobler <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jltobler

Documentation/git-diff-pairs.adoc

@@ -32,6 +32,10 @@ compute diffs progressively over the course of multiple invocations of
 Each blob pair is fed to the diff machinery individually queued and the output
 is flushed on stdin EOF.
 
+To explicitly flush the diff queue, a single nul byte can be written to stdin
+between filepairs. Diff output between flushes is separated by a single line
+terminator.
+
 OPTIONS
 -------
 

builtin/diff-pairs.c

@@ -99,6 +99,17 @@ int cmd_diff_pairs(int argc, const char **argv, const char *prefix,
 			break;
 
 		p = meta.buf;
+		if (!*p) {
+			flush_diff_queue(&revs.diffopt);
+			/*
+			 * When the diff queue is explicitly flushed, append an
+			 * additional terminator to separate batches of diffs.
+			 */
+			fprintf(revs.diffopt.file, "%c",
+				revs.diffopt.line_termination);
+			continue;
+		}
+
 		if (*p != ':')
 			die("invalid raw diff input");
 		p++;

t/t4070-diff-pairs.sh

@@ -77,4 +77,26 @@ test_expect_success 'split input across multiple diff-pairs' '
 	test_cmp expect actual
 '
 
+test_expect_success 'diff-pairs explicit queue flush' '
+	git diff-tree -r -M -C -C -z base new >input &&
+	printf "\0" >>input &&
+	git diff-tree -r -M -C -C -z base new >>input &&
+
+	git diff-tree -r -M -C -C base new >expect &&
+	printf "\n" >>expect &&
+	git diff-tree -r -M -C -C base new >>expect &&
+
+	git diff-pairs <input >actual &&
+	test_cmp expect actual
+'
+j
+test_expect_success 'diff-pairs explicit queue flush null terminated' '
+	git diff-tree -r -M -C -C -z base new >expect &&
+	printf "\0" >>expect &&
+	git diff-tree -r -M -C -C -z base new >>expect &&
+
+	git diff-pairs -z <expect >actual &&
+	test_cmp expect actual
+'
+
 test_done