patch 9.0.0861: solution for "!!sort" in closed fold is not optimal

Problem:    Solution for "!!sort" in closed fold is not optimal.
Solution:   Use a different range instead of the subtle difference in handling
            a range with an offset. (issue #11487)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 02bca38..d5037a4 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -4308,9 +4308,6 @@
     lnum = MAXLNUM;
     do
     {
-#ifdef FEAT_FOLDING
-	int base_char = *cmd;
-#endif
 	switch (*cmd)
 	{
 	    case '.':			    // '.' - Cursor position
@@ -4631,16 +4628,10 @@
 	    else
 	    {
 #ifdef FEAT_FOLDING
-		// Relative line addressing: need to adjust for closed folds
-		// after the first address.
-		// Subtle difference: "number,+number" and "number,-number"
-		// adjusts to end of closed fold before adding/subtracting,
-		// while "number,.+number" adjusts to end of closed fold after
-		// adding to make "!!" expanded into ".,.+N" work correctly.
-		int adjust_for_folding = addr_type == ADDR_LINES
-						      && (i == '-' || i == '+')
-						      && address_count >= 2;
-		if (adjust_for_folding && (i == '-' || base_char != '.'))
+		// Relative line addressing: need to adjust for lines in a
+		// closed fold after the first address.
+		if (addr_type == ADDR_LINES && (i == '-' || i == '+')
+							 && address_count >= 2)
 		    (void)hasFolding(lnum, NULL, &lnum);
 #endif
 		if (i == '-')
@@ -4653,12 +4644,6 @@
 			goto error;
 		    }
 		    lnum += n;
-#ifdef FEAT_FOLDING
-		    // ".+number" rounds up to the end of a closed fold after
-		    // adding, so that ":!!sort" sorts one closed fold.
-		    if (adjust_for_folding && base_char == '.')
-			(void)hasFolding(lnum, NULL, &lnum);
-#endif
 		}
 	    }
 	}
diff --git a/src/ops.c b/src/ops.c
index 4515453..ed8a5d8 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -3333,14 +3333,32 @@
 	    stuffcharReadbuff('.');
 	else
 	    stuffnumReadbuff((long)oap->start.lnum);
-	if (oap->end.lnum != oap->start.lnum)
+
+#ifdef FEAT_FOLDING
+	// When using !! on a closed fold the range ".!" works best to operate
+	// on, it will be made the whole closed fold later.
+	linenr_T endOfStartFold = oap->start.lnum;
+	(void)hasFolding(oap->start.lnum, NULL, &endOfStartFold);
+#endif
+	if (oap->end.lnum != oap->start.lnum
+#ifdef FEAT_FOLDING
+		&& oap->end.lnum != endOfStartFold
+#endif
+	   )
 	{
+	    // Make it a range with the end line.
 	    stuffcharReadbuff(',');
 	    if (oap->end.lnum == curwin->w_cursor.lnum)
 		stuffcharReadbuff('.');
 	    else if (oap->end.lnum == curbuf->b_ml.ml_line_count)
 		stuffcharReadbuff('$');
-	    else if (oap->start.lnum == curwin->w_cursor.lnum)
+	    else if (oap->start.lnum == curwin->w_cursor.lnum
+#ifdef FEAT_FOLDING
+		    // do not use ".+number" for a closed fold, it would count
+		    // folded lines twice
+		    && !hasFolding(oap->end.lnum, NULL, NULL)
+#endif
+		    )
 	    {
 		stuffReadbuff((char_u *)".+");
 		stuffnumReadbuff((long)oap->line_count - 1);
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index a147721..2f4aade 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -72,6 +72,54 @@
   quit!
 endfunc
 
+func Test_address_offsets()
+  " check the help for :range-closed-fold
+  enew
+  call setline(1, [
+        \ '1 one',
+        \ '2 two',
+        \ '3 three',
+        \ '4 four FOLDED',
+        \ '5 five FOLDED',
+        \ '6 six',
+        \ '7 seven',
+        \ '8 eight',
+        \])
+  set foldmethod=manual
+  normal 4Gvjzf
+  3,4+2yank
+  call assert_equal([
+        \ '3 three',
+        \ '4 four FOLDED',
+        \ '5 five FOLDED',
+        \ '6 six',
+        \ '7 seven',
+        \ ], getreg(0,1,1))
+
+  enew!
+  call setline(1, [
+        \ '1 one',
+        \ '2 two',
+        \ '3 three FOLDED',
+        \ '4 four FOLDED',
+        \ '5 five FOLDED',
+        \ '6 six FOLDED',
+        \ '7 seven',
+        \ '8 eight',
+        \])
+  normal 3Gv3jzf
+  2,4-1yank
+  call assert_equal([
+        \ '2 two',
+        \ '3 three FOLDED',
+        \ '4 four FOLDED',
+        \ '5 five FOLDED',
+        \ '6 six FOLDED',
+        \ ], getreg(0,1,1))
+
+  bwipe!
+endfunc
+
 func Test_indent_fold()
     new
     call setline(1, ['', 'a', '    b', '    c'])
diff --git a/src/version.c b/src/version.c
index 0e991a3..dd69273 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    861,
+/**/
     860,
 /**/
     859,