patch 9.0.0858: "!!sort" in a closed fold sorts too many lines

Problem:    "!!sort" in a closed fold sorts too many lines.
Solution:   Round to end of fold after adding the line count. (closes #11487)

src/ex_docmd.c

@@ -4308,6 +4308,8 @@ get_address(
     lnum = MAXLNUM;
     do
     {
+	int base_char = *cmd;
+
 	switch (*cmd)
 	{
 	    case '.':			    // '.' - Cursor position
@@ -4602,10 +4604,11 @@ get_address(
 		i = '+';		// "number" is same as "+number"
 	    else
 		i = *cmd++;
-	    if (!VIM_ISDIGIT(*cmd))	// '+' is '+1', but '+0' is not '+1'
+	    if (!VIM_ISDIGIT(*cmd))	// '+' is '+1'
 		n = 1;
 	    else
 	    {
+		// "number", "+number" or "-number"
 		n = getdigits(&cmd);
 		if (n == MAXLNUM)
 		{
@@ -4627,10 +4630,16 @@ get_address(
 	    else
 	    {
 #ifdef FEAT_FOLDING
-		// Relative line addressing, need to adjust for folded lines
+		// Relative line addressing: need to adjust for closed folds
-		// now, but only do it after the first address.
+		// after the first address.
-		if (addr_type == ADDR_LINES && (i == '-' || i == '+')
+		// Subtle difference: "number,+number" and "number,-number"
-							 && address_count >= 2)
+		// 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 != '.'))
 		    (void)hasFolding(lnum, NULL, &lnum);
 #endif
 		if (i == '-')
@@ -4643,6 +4652,12 @@ get_address(
 			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
 		}
 	    }
 	}

src/testdir/test_fold.vim

@@ -1570,4 +1570,40 @@ func Test_indent_append_blank_small_fold_close()
   bw!
 endfunc
 
+func Test_sort_closed_fold()
+  CheckExecutable sort
+
+  call setline(1, [
+        \ 'Section 1',
+        \ '   how',
+        \ '   now',
+        \ '   brown',
+        \ '   cow',
+        \ 'Section 2',
+        \ '   how',
+        \ '   now',
+        \ '   brown',
+        \ '   cow',
+        \])
+  setlocal foldmethod=indent sw=3
+  normal 2G
+
+  " The "!!" expands to ".,.+3" and must only sort four lines
+  call feedkeys("!!sort\<CR>", 'xt')
+  call assert_equal([
+        \ 'Section 1',
+        \ '   brown',
+        \ '   cow',
+        \ '   how',
+        \ '   now',
+        \ 'Section 2',
+        \ '   how',
+        \ '   now',
+        \ '   brown',
+        \ '   cow',
+        \ ], getline(1, 10))
+
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    858,
 /**/
     857,
 /**/