From 2ed57ac3675624b9d943d7753f48855e5dbebdbb Mon Sep 17 00:00:00 2001
From: Bram Moolenaar <Bram@vim.org>
Date: Sat, 1 Apr 2023 22:05:38 +0100
Subject: patch 9.0.1436: cannot compare a typed variable with v:none

Problem:    Cannot compare a typed variable with v:none.
Solution:   Allow for "x is v:none" and "x isnot v:none". (issue #12194)
---
 src/testdir/test_vim9_func.vim | 25 +++++++++++++++++++++++++
 src/version.c                  |  2 ++
 src/vim9execute.c              | 10 +++++++++-
 src/vim9instr.c                | 20 ++++++++++++--------
 4 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 0f28ba038f..2965afac8f 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -752,6 +752,31 @@ def Test_call_default_args()
   v9.CheckScriptSuccess(lines)
 enddef
 
+def Test_using_vnone_default()
+  var lines =<< trim END
+      vim9script
+
+      def F(a: string = v:none)
+         if a isnot v:none
+            var b = a
+         endif
+      enddef
+      F()
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # TODO: this should give an error for using a missing argument
+  # lines =<< trim END
+  #    vim9script
+
+  #    def F(a: string = v:none)
+  #       var b = a
+  #    enddef
+  #    F()
+  # END
+  # v9.CheckScriptFailure(lines, 'E99:')
+enddef
+
 def Test_convert_number_to_float()
   var lines =<< trim END
       vim9script
diff --git a/src/version.c b/src/version.c
index 547d6a7b7a..23d4936770 100644
--- a/src/version.c
+++ b/src/version.c
@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1436,
 /**/
     1435,
 /**/
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 18cebdba8c..d558ca0fa2 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -3496,7 +3496,15 @@ exec_instructions(ectx_T *ectx)
 	    case ISN_LOAD:
 		if (GA_GROW_FAILS(&ectx->ec_stack, 1))
 		    goto theend;
-		copy_tv(STACK_TV_VAR(iptr->isn_arg.number), STACK_TV_BOT(0));
+		tv = STACK_TV_VAR(iptr->isn_arg.number);
+		if (tv->v_type == VAR_UNKNOWN)
+		{
+		    // missing argument or default value v:none
+		    STACK_TV_BOT(0)->v_type = VAR_SPECIAL;
+		    STACK_TV_BOT(0)->vval.v_number = VVAL_NONE;
+		}
+		else
+		    copy_tv(tv, STACK_TV_BOT(0));
 		++ectx->ec_stack.ga_len;
 		break;
 
diff --git a/src/vim9instr.c b/src/vim9instr.c
index e2cdc3a78a..52402c14ec 100644
--- a/src/vim9instr.c
+++ b/src/vim9instr.c
@@ -413,7 +413,7 @@ generate_two_op(cctx_T *cctx, char_u *op)
  */
     static isntype_T
 get_compare_isn(
-	exprtype_T exprtype,
+	exprtype_T  exprtype,
 	typval_T    *tv1,
 	typval_T    *tv2,
 	type_T	    *type1,
@@ -485,13 +485,17 @@ get_compare_isn(
 	return ISN_DROP;
     }
     if (isntype == ISN_DROP
-	    || ((exprtype != EXPR_EQUAL && exprtype != EXPR_NEQUAL
-		    && (vartype1 == VAR_BOOL || vartype1 == VAR_SPECIAL
-		       || vartype2 == VAR_BOOL || vartype2 == VAR_SPECIAL)))
-	    || ((exprtype != EXPR_EQUAL && exprtype != EXPR_NEQUAL
-			       && exprtype != EXPR_IS && exprtype != EXPR_ISNOT
-		    && (vartype1 == VAR_BLOB || vartype2 == VAR_BLOB
-			|| vartype1 == VAR_LIST || vartype2 == VAR_LIST))))
+	    || (isntype != ISN_COMPARENULL
+		&& (((exprtype != EXPR_EQUAL
+			&& exprtype != EXPR_NEQUAL
+			&& (vartype1 == VAR_BOOL || vartype1 == VAR_SPECIAL
+			  || vartype2 == VAR_BOOL || vartype2 == VAR_SPECIAL)))
+		    || ((exprtype != EXPR_EQUAL
+			 && exprtype != EXPR_NEQUAL
+			 && exprtype != EXPR_IS
+			 && exprtype != EXPR_ISNOT
+			 && (vartype1 == VAR_BLOB || vartype2 == VAR_BLOB
+			  || vartype1 == VAR_LIST || vartype2 == VAR_LIST))))))
     {
 	semsg(_(e_cannot_compare_str_with_str),
 		vartype_name(vartype1), vartype_name(vartype2));
-- 
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