From f5bfc48c0596aead6dd30438930d2cb621b18a35 Mon Sep 17 00:00:00 2001
From: Hirohito Higashi <h.east.727@gmail.com>
Date: Thu, 1 May 2025 08:56:39 +0200
Subject: [PATCH] patch 9.1.1356: Vim9: crash when unletting variable

Problem:  Vim9: crash when unletting variable
Solution: fix crash, allow to use :unlet
          (Hirohito Higashi)

closes: #17226

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/proto/vim9compile.pro        |  1 -
 src/testdir/test_vim9_assign.vim | 19 +++++++++++++------
 src/version.c                    |  2 ++
 src/vim9cmds.c                   |  2 +-
 src/vim9compile.c                | 11 +----------
 5 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/src/proto/vim9compile.pro b/src/proto/vim9compile.pro
index 080a2ffaaf..6d91bc86a0 100644
--- a/src/proto/vim9compile.pro
+++ b/src/proto/vim9compile.pro
@@ -2,7 +2,6 @@
 int lookup_local(char_u *name, size_t len, lvar_T *lvar, cctx_T *cctx);
 int arg_exists(char_u *name, size_t len, int *idxp, type_T **type, int *gen_load_outer, cctx_T *cctx);
 void update_script_var_block_id(char_u *name, int block_id);
-int script_is_vim9(void);
 int script_var_exists(char_u *name, size_t len, cctx_T *cctx, cstack_T *cstack);
 int cctx_class_method_idx(cctx_T *cctx, char_u *name, size_t len, class_T **cl_ret);
 int cctx_class_member_idx(cctx_T *cctx, char_u *name, size_t len, class_T **cl_ret);
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 960dd7116f..3b0838430c 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -2499,12 +2499,11 @@ def Test_unlet()
   assert_false(exists('g:somevar'))
   unlet! g:somevar
 
-  # also works for script-local variable in legacy Vim script
-  s:somevar = 'legacy'
+  # script-local variable cannot be removed in Vim9 script
+  s:somevar = 'local'
   assert_true(exists('s:somevar'))
-  unlet s:somevar
-  assert_false(exists('s:somevar'))
-  unlet! s:somevar
+  v9.CheckDefExecFailure(['unlet s:somevar'], 'E1081:', 1)
+  v9.CheckDefExecFailure(['unlet! s:somevar'], 'E1081:', 1)
 
   if 0
     unlet g:does_not_exist
@@ -2677,13 +2676,21 @@ def Test_unlet()
    'enddef',
    'defcompile',
    ], 'E1081:')
-  v9.CheckScriptFailure([
+  v9.CheckScriptSuccess([
    'vim9script',
    'var svar = 123',
    'func Func()',
    '  unlet s:svar',
    'endfunc',
    'Func()',
+   ])
+  v9.CheckScriptFailure([
+   'vim9script',
+   'var svar = 123',
+   'def Func()',
+   '  vim9cmd unlet s:svar',
+   'enddef',
+   'defcompile',
    ], 'E1081:')
   v9.CheckScriptFailure([
    'vim9script',
diff --git a/src/version.c b/src/version.c
index 0c731a88dd..d82060838a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1356,
 /**/
     1355,
 /**/
diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 6295090110..d4ffb93313 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -99,7 +99,7 @@ check_vim9_unlet(char_u *name)
     if (name[1] != ':' || vim_strchr((char_u *)"gwtb", *name) == NULL)
     {
 	// "unlet s:var" is allowed in legacy script.
-	if (*name == 's' && !script_is_vim9())
+	if (*name == 's' && !in_vim9script())
 	    return OK;
 	semsg(_(e_cannot_unlet_str), name);
 	return FAIL;
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 0a4c3facb6..b3cf86c98d 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -287,15 +287,6 @@ update_script_var_block_id(char_u *name, int block_id)
     sav->sav_block_id = block_id;
 }
 
-/*
- * Return TRUE if the script context is Vim9 script.
- */
-    int
-script_is_vim9(void)
-{
-    return SCRIPT_ITEM(current_sctx.sc_sid)->sn_version == SCRIPT_VERSION_VIM9;
-}
-
 /*
  * Lookup a variable (without s: prefix) in the current script.
  * "cctx" is NULL at the script level, "cstack" is NULL in a function.
@@ -306,7 +297,7 @@ script_var_exists(char_u *name, size_t len, cctx_T *cctx, cstack_T *cstack)
 {
     if (current_sctx.sc_sid <= 0)
 	return FAIL;
-    if (script_is_vim9())
+    if (current_script_is_vim9())
     {
 	// Check script variables that were visible where the function was
 	// defined.