Subject: [PATCH 2/2] diff --no-index: support reading from pipes

From: Dennis Kaarsemaker <[email-masked]>
Date: Fri, 11 Nov 2016 21:19:58 +0100

diff <(command1) <(command2) provides useful output, let's make it
possible for git to do the same.

Signed-off-by: Dennis Kaarsemaker <[email-masked]>
---
 diff-no-index.c |  8 ++++++++
 diff.c          | 13 +++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/diff-no-index.c b/diff-no-index.c
index 15811c2..487dbf5 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -83,6 +83,14 @@ static struct diff_filespec *noindex_filespec(const char *name, int mode)
 		name = "/dev/null";
 	s = alloc_filespec(name);
 	fill_filespec(s, null_sha1, 0, mode);
+	/*
+	 * In --no-index mode, we support reading from pipes. canon_mode, called by
+	 * fill_filespec, gets confused by this and thinks we now have subprojects.
+	 * Detect this and tell the rest of the diff machinery to treat pipes as
+	 * normal files.
+	 */
+	if (S_ISGITLINK(s->mode))
+		s->mode = S_IFREG | ce_permissions(mode);
 	if (name == file_from_standard_input)
 		populate_from_stdin(s);
 	return s;
diff --git a/diff.c b/diff.c
index 1eaf604..c599efb 100644
--- a/diff.c
+++ b/diff.c
@@ -2839,9 +2839,18 @@ int diff_populate_filespec(struct diff_filespec *s, unsigned int flags)
 		fd = open(s->path, O_RDONLY);
 		if (fd < 0)
 			goto err_empty;
-		s->data = xmmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
+		if (!S_ISREG(st.st_mode)) {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_read(&sb, fd, 0);
+			s->size = sb.len;
+			s->data = strbuf_detach(&sb, NULL);
+			s->should_free = 1;
+		}
+		else {
+			s->data = xmmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
+			s->should_munmap = 1;
+		}
 		close(fd);
-		s->should_munmap = 1;
 
 		/*
 		 * Convert from working tree format to canonical git format
-- 
2.10.1-449-gab0f84c