patch 8.2.1859: Vim9: crash in unpack assignment

Problem:    Vim9: crash in unpack assignment.
Solution:   Make sure an error message is turned into an exception.
            (closes #7159)

src/testdir/test_vim9_assign.vim

@@ -622,6 +622,9 @@ def Test_assignment_failure()
   CheckDefExecFailure(['var x: number',
                        'var y: number',
                        '[x, y] = [1]'], 'E1093:')
+  CheckDefExecFailure(['var x: string',
+                       'var y: string',
+                       '[x, y] = ["x"]'], 'E1093:')
   CheckDefExecFailure(['var x: number',
                        'var y: number',
                        'var z: list<number>',

src/testdir/test_vim9_script.vim

@@ -620,6 +620,7 @@ def Test_throw_vimscript()
 
   lines =<< trim END
     vim9script
+    @r = ''
     def Func()
       throw @r
     enddef
@@ -2818,6 +2819,27 @@ def Test_script_var_scope()
   CheckScriptFailure(lines, 'E121:', 6)
 enddef
 
+def Test_catch_exception_in_callback()
+  var lines =<< trim END
+    vim9script
+    def Callback(...l: any)
+      try
+        var x: string
+        var y: string
+        # this error should be caught with CHECKLEN
+        [x, y] = ['']
+      catch
+        g:caught = 'yes'
+      endtry
+    enddef
+    popup_menu('popup', #{callback: Callback})
+    feedkeys("\r", 'xt')
+  END
+  CheckScriptSuccess(lines)
+
+  unlet g:caught
+enddef
+
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()
   new

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1859,
 /**/
     1858,
 /**/

src/vim9execute.c

@@ -830,6 +830,8 @@ call_def_function(
     int		breakcheck_count = 0;
     int		called_emsg_before = called_emsg;
     int		save_suppress_errthrow = suppress_errthrow;
+    msglist_T	**saved_msg_list = NULL;
+    msglist_T	*private_msg_list = NULL;
 
 // Get pointer to item in the stack.
 #define STACK_TV(idx) (((typval_T *)ectx.ec_stack.ga_data) + idx)
@@ -982,6 +984,11 @@ call_def_function(
     current_sctx = ufunc->uf_script_ctx;
     current_sctx.sc_version = SCRIPT_VERSION_VIM9;
 
+    // Use a specific location for storing error messages to be converted to an
+    // exception.
+    saved_msg_list = msg_list;
+    msg_list = &private_msg_list;
+
     // Do turn errors into exceptions.
     suppress_errthrow = FALSE;
 
@@ -2819,6 +2826,19 @@ failed:
     estack_pop();
     current_sctx = save_current_sctx;
 
+    if (*msg_list != NULL && saved_msg_list != NULL)
+    {
+	msglist_T **plist = saved_msg_list;
+
+	// Append entries from the current msg_list (uncaught exceptions) to
+	// the saved msg_list.
+	while (*plist != NULL)
+	    plist = &(*plist)->next;
+
+	*plist = *msg_list;
+    }
+    msg_list = saved_msg_list;
+
 failed_early:
     // Free all local variables, but not arguments.
     for (idx = 0; idx < ectx.ec_stack.ga_len; ++idx)