patch 8.2.1747: result of expand() unexpectedly depends on 'completeslash'

Problem:    Result of expand() unexpectedly depends on 'completeslash'.
Solution:   Temporarily reset 'completeslash'. (Yasuhiro Matsumoto,
            closes #7021)

src/evalfunc.c

@@ -2436,6 +2436,12 @@ f_expand(typval_T *argvars, typval_T *rettv)
     expand_T	xpc;
     int		error = FALSE;
     char_u	*result;
+#ifdef BACKSLASH_IN_FILENAME
+    char_u	*p_csl_save = p_csl;
+
+    // avoid using 'completeslash' here
+    p_csl = empty_option;
+#endif
 
     rettv->v_type = VAR_STRING;
     if (argvars[1].v_type != VAR_UNKNOWN
@@ -2488,6 +2494,9 @@ f_expand(typval_T *argvars, typval_T *rettv)
 	else
 	    rettv->vval.v_string = NULL;
     }
+#ifdef BACKSLASH_IN_FILENAME
+    p_csl = p_csl_save;
+#endif
 }
 
 /*

src/testdir/test_ins_complete.vim

@@ -363,12 +363,12 @@ endfunc
 " Test for insert path completion with completeslash option
 func Test_ins_completeslash()
   CheckMSWindows
-  
+
   call mkdir('Xdir')
   let orig_shellslash = &shellslash
   set cpt&
   new
-  
+
   set noshellslash
 
   set completeslash=
@@ -654,4 +654,17 @@ func Test_complete_cmdline()
   close!
 endfunc
 
+func Test_issue_7021()
+  CheckMSWindows
+
+  let orig_shellslash = &shellslash
+  set noshellslash
+
+  set completeslash=slash
+  call assert_false(expand('~') =~ '/')
+
+  let &shellslash = orig_shellslash
+  set completeslash=
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1747,
 /**/
     1746,
 /**/