patch 8.1.0120: buffer 'modified' set even when :sort has no changes

Problem:    Buffer 'modified' set even when :sort has no changes.
Solution:   Only set 'modified' when lines are moved. (Jason Franklin)

src/ex_cmds.c

@@ -398,6 +398,7 @@ ex_sort(exarg_T *eap)
     colnr_T	end_col;
     int		sort_what = 0;
     int		format_found = 0;
+    int		change_occurred = FALSE; // Buffer contents changed.
 
     /* Sorting one line is really quick! */
     if (count <= 1)
@@ -616,12 +617,19 @@ ex_sort(exarg_T *eap)
     lnum = eap->line2;
     for (i = 0; i < count; ++i)
     {
-	s = ml_get(nrs[eap->forceit ? count - i - 1 : i].lnum);
+	linenr_T get_lnum = nrs[eap->forceit ? count - i - 1 : i].lnum;
+
+	// If the original line number of the line being placed is not the same
+	// as "lnum" (accounting for offset), we know that the buffer changed.
+	if (get_lnum + ((linenr_T)count - 1) != lnum)
+	    change_occurred = TRUE;
+
+	s = ml_get(get_lnum);
 	if (!unique || i == 0
 		|| (sort_ic ? STRICMP(s, sortbuf1) : STRCMP(s, sortbuf1)) != 0)
 	{
-	    /* Copy the line into a buffer, it may become invalid in
-	     * ml_append(). And it's needed for "unique". */
+	    // Copy the line into a buffer, it may become invalid in
+	    // ml_append(). And it's needed for "unique".
 	    STRCPY(sortbuf1, s);
 	    if (ml_append(lnum++, sortbuf1, (colnr_T)0, FALSE) == FAIL)
 		break;
@@ -644,7 +652,9 @@ ex_sort(exarg_T *eap)
 	mark_adjust(eap->line2 - deleted, eap->line2, (long)MAXLNUM, -deleted);
     else if (deleted < 0)
 	mark_adjust(eap->line2, MAXLNUM, -deleted, 0L);
-    changed_lines(eap->line1, 0, eap->line2 + 1, -deleted);
+
+    if (change_occurred || deleted != 0)
+	changed_lines(eap->line1, 0, eap->line2 + 1, -deleted);
 
     curwin->w_cursor.lnum = eap->line1;
     beginline(BL_WHITE | BL_FIX);

src/testdir/test_sort.vim

@@ -1,13 +1,13 @@
-" Test sort()
+" Tests for the "sort()" function and for the ":sort" command.
 
-:func Compare1(a, b) abort
+func Compare1(a, b) abort
     call sort(range(3), 'Compare2')
     return a:a - a:b
-:endfunc
+endfunc
 
-:func Compare2(a, b) abort
+func Compare2(a, b) abort
     return a:a - a:b
-:endfunc
+endfunc
 
 func Test_sort_strings()
   " numbers compared as strings
@@ -45,7 +45,7 @@ func Test_sort_default()
   call assert_fails('call sort([3.3, 1, "2"], 3)', "E474")
 endfunc
 
-" Tests for the :sort command
+" Tests for the ":sort" command.
 func Test_sort_cmd()
   let tests = [
 	\ {
@@ -1167,15 +1167,54 @@ func Test_sort_cmd()
 	\	'1.234',
 	\	'123.456'
 	\    ]
-	\ }
+	\ },
+	\ {
+	\    'name' : 'alphabetical, sorted input',
+	\    'cmd' : 'sort',
+	\    'input' : [
+	\	'a',
+	\	'b',
+	\	'c',
+	\    ],
+	\    'expected' : [
+	\	'a',
+	\	'b',
+	\	'c',
+	\    ]
+	\ },
+	\ {
+	\    'name' : 'alphabetical, sorted input, unique at end',
+	\    'cmd' : 'sort u',
+	\    'input' : [
+	\	'aa',
+	\	'bb',
+	\	'cc',
+	\	'cc',
+	\    ],
+	\    'expected' : [
+	\	'aa',
+	\	'bb',
+	\	'cc',
+	\    ]
+	\ },
 	\ ]
 
   for t in tests
     enew!
     call append(0, t.input)
     $delete _
-    exe t.cmd
+    setlocal nomodified
+    execute t.cmd
+
     call assert_equal(t.expected, getline(1, '$'), t.name)
+
+    " Previously, the ":sort" command would set 'modified' even if the buffer
+    " contents did not change.  Here, we check that this problem is fixed.
+    if t.input == t.expected
+      call assert_false(&modified, t.name . ': &mod is not correct')
+    else
+      call assert_true(&modified, t.name . ': &mod is not correct')
+    endif
   endfor
 
   call assert_fails('sort no', 'E474')

src/version.c

@@ -789,6 +789,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    120,
 /**/
     119,
 /**/