range-diff: add filename to inner diff

In a range-diff it's not always clear which file a certain funcname of
the inner diff belongs to, because the diff header (or section header
as added in a previous commit) is not always visible in the
range-diff.

Add the filename to the inner diffs header, so it's always visible to
users.

This also allows us to add the filename + the funcname to the outer
diffs hunk headers using a custom userdiff pattern, which will be done
in the next commit.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

range-diff.c

@@ -46,7 +46,7 @@ static int read_patches(const char *range, struct string_list *list)
 	struct strbuf buf = STRBUF_INIT, contents = STRBUF_INIT;
 	struct patch_util *util = NULL;
 	int in_header = 1;
-	char *line;
+	char *line, *current_filename = NULL;
 	int offset, len;
 	size_t size;
 
@@ -125,6 +125,12 @@ static int read_patches(const char *range, struct string_list *list)
 			else
 				strbuf_addstr(&buf, patch.new_name);
 
+			free(current_filename);
+			if (patch.is_delete > 0)
+				current_filename = xstrdup(patch.old_name);
+			else
+				current_filename = xstrdup(patch.new_name);
+
 			if (patch.new_mode && patch.old_mode &&
 			    patch.old_mode != patch.new_mode)
 				strbuf_addf(&buf, " (mode change %06o => %06o)",
@@ -145,7 +151,11 @@ static int read_patches(const char *range, struct string_list *list)
 			continue;
 		} else if (skip_prefix(line, "@@ ", &p)) {
 			p = strstr(p, "@@");
-			strbuf_addstr(&buf, p ? p : "@@");
+			strbuf_addstr(&buf, "@@");
+			if (current_filename && p[2])
+				strbuf_addf(&buf, " %s:", current_filename);
+			if (p)
+				strbuf_addstr(&buf, p + 2);
 		} else if (!line[0])
 			/*
 			 * A completely blank (not ' \n', which is context)
@@ -177,6 +187,7 @@ static int read_patches(const char *range, struct string_list *list)
 	if (util)
 		string_list_append(list, buf.buf)->util = util;
 	strbuf_release(&buf);
+	free(current_filename);
 
 	if (finish_command(&cp))
 		return -1;

t/t3206-range-diff.sh

@@ -110,7 +110,7 @@ test_expect_success 'changed commit' '
 	      14
 	4:  a63e992 ! 4:  d966c5c s/12/B/
 	    @@
-	     @@ A
+	     @@ file: A
 	      9
 	      10
 	    - B
@@ -169,7 +169,7 @@ test_expect_success 'changed commit with sm config' '
 	      14
 	4:  a63e992 ! 4:  d966c5c s/12/B/
 	    @@
-	     @@ A
+	     @@ file: A
 	      9
 	      10
 	    - B
@@ -203,20 +203,24 @@ test_expect_success 'renamed file' '
 	    Z    s/11/B/
 	    Z
 	    - ## file ##
+	    -@@ file: A
 	    + ## renamed-file ##
-	    Z@@ A
+	    +@@ renamed-file: A
 	    Z 8
 	    Z 9
+	    Z 10
 	4:  a63e992 ! 4:  1e6226b s/12/B/
 	    @@
 	    Z
 	    Z    s/12/B/
 	    Z
 	    - ## file ##
+	    -@@ file: A
 	    + ## renamed-file ##
-	    Z@@ A
+	    +@@ renamed-file: A
 	    Z 9
 	    Z 10
+	    Z B
 	EOF
 	test_cmp expected actual
 '
@@ -248,7 +252,7 @@ test_expect_success 'file added and later removed' '
 	    +    s/11/B/ + remove file
 	    Z
 	    Z ## file ##
-	    Z@@ A
+	    Z@@ file: A
 	    @@
 	    Z 12
 	    Z 13
@@ -310,7 +314,7 @@ test_expect_success 'dual-coloring' '
 	:      14<RESET>
 	:<RED>4:  d966c5c <RESET><YELLOW>!<RESET><GREEN> 4:  8add5f1<RESET><YELLOW> s/12/B/<RESET>
 	:    <REVERSE><CYAN>@@<RESET>
-	:    <CYAN> @@ A<RESET>
+	:    <CYAN> @@ file: A<RESET>
 	:      9<RESET>
 	:      10<RESET>
 	:    <REVERSE><RED>-<RESET><FAINT> BB<RESET>