patch 8.1.0278: 'incsearch' highlighting does not accept reverse range

Problem:    'incsearch' highlighting does not accept reverse range.
Solution:   Swap the range when needed. (issue #3321)

src/ex_getln.c

@@ -320,8 +320,17 @@ do_incsearch_highlighting(int firstc, incsearch_state_T *is_state,
 			parse_cmd_address(&ea, &dummy);
 			if (ea.addr_count > 0)
 			{
-			    search_first_line = ea.line1;
+			    // Allow for reverse match.
-			    search_last_line = ea.line2;
+			    if (ea.line2 < ea.line1)
+			    {
+				search_first_line = ea.line2;
+				search_last_line = ea.line1;
+			    }
+			    else
+			    {
+				search_first_line = ea.line1;
+				search_last_line = ea.line2;
+			    }
 			}
 			else if (*cmd == 's')
 			{

src/testdir/dumps/Test_incsearch_substitute_04.dump

@@ -0,0 +1,9 @@
+|f+0&#ffffff0|o@1| |1| @64
+|f+1&&|o@1| +0&&|2| @64
+|f+0&#ffff4012|o@1| +0&#ffffff0|3| @64
+|f+0&#ffff4012|o@1| +0&#ffffff0|4| @64
+|f+0&#ffff4012|o@1| +0&#ffffff0|5| @64
+|f|o@1| |6| @64
+|f|o@1| |7| @64
+|f|o@1| |8| @64
+|:|5|,|2|s|/|f|o@1> @60

src/testdir/test_search.vim

@@ -862,6 +862,12 @@ func Test_incsearch_substitute_dump()
   call term_sendkeys(buf, "\<BS>")
   sleep 100m
   call VerifyScreenDump(buf, 'Test_incsearch_substitute_03', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  " Reverse range is accepted
+  call term_sendkeys(buf, ':5,2s/foo')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_substitute_04', {})
 
   call term_sendkeys(buf, "\<Esc>")
   call StopVimInTerminal(buf)

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    278,
 /**/
     277,
 /**/