[RFC PATCH 3/4] range-diff: add section header instead of diff header

[Thomas Gummerer <t.gummerer@gmail.com>]

Currently range-diff keeps the diff header of the inner diff
intact (apart from stripping lines starting with index).  This diff
header is somewhat useful, especially when files get different
names in different ranges.

However there is no real need to keep the whole diff header for that.
The main reason we currently do that is probably because it is easy to
do.

Introduce a new range diff hunk header, that's enclosed by "##",
similar to how line numbers in diff hunks are enclosed by "@@", and
give human readable information of what exactly happened to the file,
including the file name.

At this point, this is only a marginal improvement in readability of
the range-diff output.  More interestingly however, this allows us to
add these range diff hunk headers to the outer diffs hunk headers
using a custom userdiff pattern, which should help making the
range-diff more readable.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---
 range-diff.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/range-diff.c b/range-diff.c
index f365141ade..aa466060ef 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -33,6 +33,7 @@ static int read_patches(const char *range, struct string_list *list)
 	struct child_process cp = CHILD_PROCESS_INIT;
 	FILE *in;
 	struct strbuf buf = STRBUF_INIT, line = STRBUF_INIT;
+	struct strbuf filename_a = STRBUF_INIT;
 	struct patch_util *util = NULL;
 	int in_header = 1;
 
@@ -90,8 +91,37 @@ static int read_patches(const char *range, struct string_list *list)
 			strbuf_addch(&buf, '\n');
 			if (!util->diff_offset)
 				util->diff_offset = buf.len;
-			strbuf_addch(&buf, ' ');
-			strbuf_addbuf(&buf, &line);
+		} else if (starts_with(line.buf, "--- ")) {
+			if (!strcmp(line.buf, "--- /dev/null"))
+				strbuf_remove(&line, 0, 4);
+			else
+				strbuf_remove(&line, 0, 6);
+			strbuf_rtrim(&line);
+			strbuf_reset(&filename_a);
+			strbuf_addbuf(&filename_a, &line);
+		} else if (starts_with(line.buf, "+++ ")) {
+			strbuf_addstr(&buf, " ## ");
+			if (!strcmp(line.buf, "--- /dev/null"))
+				strbuf_remove(&line, 0, 4);
+			else
+				strbuf_remove(&line, 0, 6);
+			strbuf_rtrim(&line);
+			if (!strcmp(filename_a.buf, "/dev/null")) {
+				strbuf_addstr(&buf, "new file ");
+				strbuf_addbuf(&buf, &line);
+			} else if (!strcmp(line.buf, "/dev/null")) {
+				strbuf_addstr(&buf, "removed file ");
+				strbuf_addbuf(&buf, &line);
+			} else if (strbuf_cmp(&filename_a, &line)) {
+				strbuf_addstr(&buf, "renamed file ");
+				strbuf_addbuf(&buf, &filename_a);
+				strbuf_addstr(&buf, " -> ");
+				strbuf_addbuf(&buf, &line);
+			} else {
+				strbuf_addstr(&buf, "modified file ");
+				strbuf_addbuf(&buf, &line);
+			}
+			strbuf_addstr(&buf, " ##\n");
 		} else if (in_header) {
 			if (starts_with(line.buf, "Author: ")) {
 				strbuf_addbuf(&buf, &line);
-- 
2.21.0.593.g511ec345e1