MDEV-5612 - my_rename() deletes files when it shouldn't

Ported fix for MySQL BUG#51861.

mysql-test/suite/csv/csv.result

@@ -5485,3 +5485,11 @@ SELECT * FROM t1;
 ERROR HY000: Table 't1' is marked as crashed and should be repaired
 DROP TABLE t1;
 End of 5.1 tests
+#
+# MDEV-5612 - my_rename() deletes files when it shouldn't
+#
+CREATE TABLE t1(a INT NOT NULL) ENGINE=CSV;
+RENAME TABLE t1 TO t2;
+SELECT * FROM t2;
+a
+DROP TABLE t2;

mysql-test/suite/csv/csv.test

@@ -1917,3 +1917,12 @@ SELECT * FROM t1;
 
 DROP TABLE t1;
 --echo End of 5.1 tests
+
+--echo #
+--echo # MDEV-5612 - my_rename() deletes files when it shouldn't
+--echo #
+CREATE TABLE t1(a INT NOT NULL) ENGINE=CSV;
+move_file $MYSQLD_DATADIR/test/t1.CSV $MYSQLD_DATADIR/test/t2.CSV;
+RENAME TABLE t1 TO t2;
+SELECT * FROM t2;
+DROP TABLE t2;

mysys/my_rename.c

@@ -27,19 +27,18 @@ int my_rename(const char *from, const char *to, myf MyFlags)
   DBUG_ENTER("my_rename");
   DBUG_PRINT("my",("from %s to %s MyFlags %lu", from, to, MyFlags));
 
-#if defined(HAVE_RENAME)
 #if defined(__WIN__)
-  /*
-    On windows we can't rename over an existing file:
-    Remove any conflicting files:
-  */
-  (void) my_delete(to, MYF(0));
-#endif
+  if (!MoveFileEx(from, to, MOVEFILE_COPY_ALLOWED |
+                            MOVEFILE_REPLACE_EXISTING))
+  {
+    my_osmaperr(GetLastError());
+#elif defined(HAVE_RENAME)
   if (rename(from,to))
+  {
 #else
   if (link(from, to) || unlink(from))
-#endif
   {
+#endif
     my_errno=errno;
     error = -1;
     if (MyFlags & (MY_FAE+MY_WME))