vim-patch:8.2.3788: lambda for option that is a function may be freed

Problem:    Lambda for option that is a function may be garbage collected.
Solution:   Set a reference in the funcref. (Yegappan Lakshmanan,
            closes vim/vim#9330)

https://github.com/vim/vim/commit/6ae8fae8696623b527c7fb22567f6a3705b2f0dd

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

10 files changed, 978 insertions, 764 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index daae6416dc..7c6f81df40 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -30,6 +30,7 @@
 #include "nvim/ex_session.h"
 #include "nvim/getchar.h"
 #include "nvim/highlight_group.h"
+#include "nvim/insexpand.h"
 #include "nvim/locale.h"
 #include "nvim/lua/executor.h"
 #include "nvim/mark.h"
@@ -49,6 +50,7 @@
 #include "nvim/search.h"
 #include "nvim/sign.h"
 #include "nvim/syntax.h"
+#include "nvim/tag.h"
 #include "nvim/ui.h"
 #include "nvim/ui_compositor.h"
 #include "nvim/undo.h"
@@ -4168,10 +4170,23 @@ bool garbage_collect(bool testing)
     ABORTING(set_ref_dict)(buf->additional_data, copyID);
 
     // buffer callback functions
-    set_ref_in_callback(&buf->b_prompt_callback, copyID, NULL, NULL);
-    set_ref_in_callback(&buf->b_prompt_interrupt, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_prompt_callback, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_prompt_interrupt, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_cfu_cb, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_ofu_cb, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_tsrfu_cb, copyID, NULL, NULL);
+    ABORTING(set_ref_in_callback)(&buf->b_tfu_cb, copyID, NULL, NULL);
   }
 
+  // 'completefunc', 'omnifunc' and 'thesaurusfunc' callbacks
+  ABORTING(set_ref_in_insexpand_funcs)(copyID);
+
+  // 'operatorfunc' callback
+  ABORTING(set_ref_in_opfunc)(copyID);
+
+  // 'tagfunc' callback
+  ABORTING(set_ref_in_tagfunc)(copyID);
+
   FOR_ALL_TAB_WINDOWS(tp, wp) {
     // window-local variables
     ABORTING(set_ref_in_item)(&wp->w_winvar.di_tv, copyID, NULL, NULL);
@@ -5910,8 +5925,8 @@ bool callback_call(Callback *const callback, const int argcount_in, typval_T *co
   return call_func(name, -1, rettv, argcount_in, argvars_in, &funcexe);
 }
 
-static bool set_ref_in_callback(Callback *callback, int copyID, ht_stack_T **ht_stack,
-                                list_stack_T **list_stack)
+bool set_ref_in_callback(Callback *callback, int copyID, ht_stack_T **ht_stack,
+                         list_stack_T **list_stack)
 {
   typval_T tv;
   switch (callback->type) {
diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index 7d4e77b263..78d820c2a7 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -2299,6 +2299,17 @@ int set_thesaurusfunc_option(void)
   return retval;
 }
 
+/// Mark the global 'completefunc' 'omnifunc' and 'thesaurusfunc' callbacks with
+/// "copyID" so that they are not garbage collected.
+bool set_ref_in_insexpand_funcs(int copyID)
+{
+  bool abort = set_ref_in_callback(&cfu_cb, copyID, NULL, NULL);
+  abort = abort || set_ref_in_callback(&ofu_cb, copyID, NULL, NULL);
+  abort = abort || set_ref_in_callback(&tsrfu_cb, copyID, NULL, NULL);
+
+  return abort;
+}
+
 /// Get the user-defined completion function name for completion "type"
 static char_u *get_complete_funcname(int type)
 {
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index 2d53918ded..65fc42bc08 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -5606,6 +5606,13 @@ void free_operatorfunc_option(void)
 }
 #endif
 
+/// Mark the global 'operatorfunc' callback with "copyID" so that it is not
+/// garbage collected.
+bool set_ref_in_opfunc(int copyID)
+{
+  return set_ref_in_callback(&opfunc_cb, copyID, NULL, NULL);
+}
+
 /// Handle the "g@" operator: call 'operatorfunc'.
 static void op_function(const oparg_T *oap)
   FUNC_ATTR_NONNULL_ALL
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index 5d101ee415..7ecb4e4956 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -6686,7 +6686,8 @@ int set_errorlist(win_T *wp, list_T *list, int action, char *title, dict_T *what
   return retval;
 }
 
-/// Mark the context as in use for all the lists in a quickfix stack.
+/// Mark the quickfix context and callback function as in use for all the lists
+/// in a quickfix stack.
 static bool mark_quickfix_ctx(qf_info_T *qi, int copyID)
 {
   bool abort = false;
@@ -6695,8 +6696,11 @@ static bool mark_quickfix_ctx(qf_info_T *qi, int copyID)
     typval_T *ctx = qi->qf_lists[i].qf_ctx;
     if (ctx != NULL && ctx->v_type != VAR_NUMBER
         && ctx->v_type != VAR_STRING && ctx->v_type != VAR_FLOAT) {
-      abort = set_ref_in_item(ctx, copyID, NULL, NULL);
+      abort = abort || set_ref_in_item(ctx, copyID, NULL, NULL);
     }
+
+    Callback *cb = &qi->qf_lists[i].qf_qftf_cb;
+    abort = abort || set_ref_in_callback(cb, copyID, NULL, NULL);
   }
 
   return abort;
@@ -6711,6 +6715,11 @@ bool set_ref_in_quickfix(int copyID)
     return abort;
   }
 
+  abort = set_ref_in_callback(&qftf_cb, copyID, NULL, NULL);
+  if (abort) {
+    return abort;
+  }
+
   FOR_ALL_TAB_WINDOWS(tp, win) {
     if (win->w_llist != NULL) {
       abort = mark_quickfix_ctx(win->w_llist, copyID);
diff --git a/src/nvim/tag.c b/src/nvim/tag.c
index d57bbead63..9ea0b71dc1 100644
--- a/src/nvim/tag.c
+++ b/src/nvim/tag.c
@@ -149,6 +149,13 @@ void free_tagfunc_option(void)
 }
 #endif
 
+/// Mark the global 'tagfunc' callback with "copyID" so that it is not garbage
+/// collected.
+bool set_ref_in_tagfunc(int copyID)
+{
+  return set_ref_in_callback(&tfu_cb, copyID, NULL, NULL);
+}
+
 /// Copy the global 'tagfunc' callback function to the buffer-local 'tagfunc'
 /// callback for 'buf'.
 void set_buflocal_tfu_callback(buf_T *buf)
diff --git a/src/nvim/testdir/test_ins_complete.vim b/src/nvim/testdir/test_ins_complete.vim
index eaac66dae0..db2bb2e2a0 100644
--- a/src/nvim/testdir/test_ins_complete.vim
+++ b/src/nvim/testdir/test_ins_complete.vim
@@ -1,5 +1,8 @@
+" Test for insert completion
+
 source screendump.vim
 source check.vim
+source vim9.vim
 
 " Test for insert expansion
 func Test_ins_complete()
@@ -1292,154 +1295,179 @@ func Test_completefunc_callback()
     return a:findstart ? 0 : []
   endfunc
 
-  " Test for using a function()
-  set completefunc=function('MycompleteFunc1',[10])
-  new | only
-  call setline(1, 'one')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MycompleteFunc1_args)
-  bw!
+  let lines =<< trim END
+    #" Test for using a function()
+    set completefunc=function('g:MycompleteFunc1',\ [10])
+    new | only
+    call setline(1, 'one')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MycompleteFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'completefunc'
-  let Fn = function('MycompleteFunc1', [11])
-  let &completefunc = Fn
-  new | only
-  call setline(1, 'two')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MycompleteFunc1_args)
-  bw!
+    #" Using a funcref variable to set 'completefunc'
+    VAR Fn = function('g:MycompleteFunc1', [11])
+    LET &completefunc = Fn
+    new | only
+    call setline(1, 'two')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MycompleteFunc1_args)
+    bw!
 
-  " Using string(funcref_variable) to set 'completefunc'
-  let Fn = function('MycompleteFunc1', [12])
-  let &completefunc = string(Fn)
-  new | only
-  call setline(1, 'two')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MycompleteFunc1_args)
-  bw!
+    #" Using string(funcref_variable) to set 'completefunc'
+    LET Fn = function('g:MycompleteFunc1', [12])
+    LET &completefunc = string(Fn)
+    new | only
+    call setline(1, 'two')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MycompleteFunc1_args)
+    bw!
 
-  " Test for using a funcref()
-  set completefunc=funcref('MycompleteFunc1',\ [13])
-  new | only
-  call setline(1, 'three')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MycompleteFunc1_args)
-  bw!
+    #" Test for using a funcref()
+    set completefunc=funcref('g:MycompleteFunc1',\ [13])
+    new | only
+    call setline(1, 'three')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MycompleteFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'completefunc'
-  let Fn = funcref('MycompleteFunc1', [14])
-  let &completefunc = Fn
-  new | only
-  call setline(1, 'four')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MycompleteFunc1_args)
-  bw!
+    #" Using a funcref variable to set 'completefunc'
+    LET Fn = funcref('g:MycompleteFunc1', [14])
+    LET &completefunc = Fn
+    new | only
+    call setline(1, 'four')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MycompleteFunc1_args)
+    bw!
 
-  " Using a string(funcref_variable) to set 'completefunc'
-  let Fn = funcref('MycompleteFunc1', [15])
-  let &completefunc = string(Fn)
-  new | only
-  call setline(1, 'four')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MycompleteFunc1_args)
-  bw!
+    #" Using a string(funcref_variable) to set 'completefunc'
+    LET Fn = funcref('g:MycompleteFunc1', [15])
+    LET &completefunc = string(Fn)
+    new | only
+    call setline(1, 'four')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MycompleteFunc1_args)
+    bw!
 
-  " Test for using a lambda function
-  set completefunc={a,\ b\ ->\ MycompleteFunc1(16,\ a,\ b)}
-  new | only
-  call setline(1, 'five')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MycompleteFunc1_args)
-  bw!
+    #" Test for using a lambda function with set
+    VAR optval = "LSTART a, b LMIDDLE MycompleteFunc1(16, a, b) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set completefunc=" .. optval
+    new | only
+    call setline(1, 'five')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MycompleteFunc1_args)
+    bw!
 
-  " Set 'completefunc' to a lambda expression
-  let &completefunc = {a, b -> MycompleteFunc1(17, a, b)}
-  new | only
-  call setline(1, 'six')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MycompleteFunc1_args)
-  bw!
+    #" Set 'completefunc' to a lambda expression
+    LET &completefunc = LSTART a, b LMIDDLE MycompleteFunc1(17, a, b) LEND
+    new | only
+    call setline(1, 'six')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MycompleteFunc1_args)
+    bw!
 
-  " Set 'completefunc' to string(lambda_expression)
-  let &completefunc = '{a, b -> MycompleteFunc1(18, a, b)}'
-  new | only
-  call setline(1, 'six')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MycompleteFunc1_args)
-  bw!
+    #" Set 'completefunc' to string(lambda_expression)
+    LET &completefunc = 'LSTART a, b LMIDDLE MycompleteFunc1(18, a, b) LEND'
+    new | only
+    call setline(1, 'six')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MycompleteFunc1_args)
+    bw!
 
-  " Set 'completefunc' to a variable with a lambda expression
-  let Lambda = {a, b -> MycompleteFunc1(19, a, b)}
-  let &completefunc = Lambda
-  new | only
-  call setline(1, 'seven')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MycompleteFunc1_args)
-  bw!
+    #" Set 'completefunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a, b LMIDDLE MycompleteFunc1(19, a, b) LEND
+    LET &completefunc = Lambda
+    new | only
+    call setline(1, 'seven')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MycompleteFunc1_args)
+    bw!
 
-  " Set 'completefunc' to a string(variable with a lambda expression)
-  let Lambda = {a, b -> MycompleteFunc1(20, a, b)}
-  let &completefunc = string(Lambda)
-  new | only
-  call setline(1, 'seven')
-  let g:MycompleteFunc1_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MycompleteFunc1_args)
-  bw!
+    #" Set 'completefunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a, b LMIDDLE MycompleteFunc1(20, a, b) LEND
+    LET &completefunc = string(Lambda)
+    new | only
+    call setline(1, 'seven')
+    LET g:MycompleteFunc1_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MycompleteFunc1_args)
+    bw!
 
-  " Test for using a lambda function with incorrect return value
-  let Lambda = {s -> strlen(s)}
-  let &completefunc = Lambda
-  new | only
-  call setline(1, 'eight')
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  bw!
+    #" Test for using a lambda function with incorrect return value
+    LET Lambda = LSTART a, b LMIDDLE strlen(a) LEND
+    LET &completefunc = Lambda
+    new | only
+    call setline(1, 'eight')
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    bw!
 
-  " Test for clearing the 'completefunc' option
-  set completefunc=''
-  set completefunc&
+    #" Test for clearing the 'completefunc' option
+    set completefunc=''
+    set completefunc&
+    call assert_fails("set completefunc=function('abc')", "E700:")
+    call assert_fails("set completefunc=funcref('abc')", "E700:")
+
+    #" set 'completefunc' to a non-existing function
+    func MycompleteFunc2(findstart, base)
+      call add(g:MycompleteFunc2_args, [a:findstart, a:base])
+      return a:findstart ? 0 : []
+    endfunc
+    set completefunc=MycompleteFunc2
+    call setline(1, 'five')
+    call assert_fails("set completefunc=function('NonExistingFunc')", 'E700:')
+    call assert_fails("LET &completefunc = function('NonExistingFunc')", 'E700:')
+    LET g:MycompleteFunc2_args = []
+    call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    call assert_equal([[1, ''], [0, 'five']], g:MycompleteFunc2_args)
+    bw!
+  END
+  call CheckLegacyAndVim9Success(lines)
 
-  call assert_fails("set completefunc=function('abc')", "E700:")
-  call assert_fails("set completefunc=funcref('abc')", "E700:")
   let &completefunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
 
   " Using Vim9 lambda expression in legacy context should fail
-  " set completefunc=(a,\ b)\ =>\ g:MycompleteFunc1(21,\ a,\ b)
+  " set completefunc=(a,\ b)\ =>\ MycompleteFunc1(21,\ a,\ b)
   new | only
   let g:MycompleteFunc1_args = []
   " call assert_fails('call feedkeys("A\<C-X>\<C-U>\<Esc>", "x")', 'E117:')
   call assert_equal([], g:MycompleteFunc1_args)
 
-  " set 'completefunc' to a non-existing function
-  func MycompleteFunc2(findstart, base)
-    call add(g:MycompleteFunc2_args, [a:findstart, a:base])
-    return a:findstart ? 0 : []
+  " set 'completefunc' to a partial with dict. This used to cause a crash.
+  func SetCompleteFunc()
+    let params = {'complete': function('g:DictCompleteFunc')}
+    let &completefunc = params.complete
   endfunc
-  set completefunc=MycompleteFunc2
-  call setline(1, 'five')
-  call assert_fails("set completefunc=function('NonExistingFunc')", 'E700:')
-  call assert_fails("let &completefunc = function('NonExistingFunc')", 'E700:')
-  let g:MycompleteFunc2_args = []
-  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-  call assert_equal([[1, ''], [0, 'five']], g:MycompleteFunc2_args)
-  bw!
+  func g:DictCompleteFunc(_) dict
+  endfunc
+  call SetCompleteFunc()
+  new
+  call SetCompleteFunc()
+  bw
+  call test_garbagecollect_now()
+  new
+  set completefunc=
+  wincmd w
+  set completefunc=
+  %bw!
+  delfunc g:DictCompleteFunc
+  delfunc SetCompleteFunc
 
   " Vim9 tests
   let lines =<< trim END
     vim9script
 
-    # Test for using function()
+    # Test for using a def function with completefunc
     def Vim9CompleteFunc(val: number, findstart: number, base: string): any
       add(g:Vim9completeFuncArgs, [val, findstart, base])
       return findstart ? 0 : []
@@ -1451,44 +1479,6 @@ func Test_completefunc_callback()
     feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
     assert_equal([[60, 1, ''], [60, 0, 'one']], g:Vim9completeFuncArgs)
     bw!
-
-    # Test for using a lambda
-    &completefunc = (a, b) => Vim9CompleteFunc(61, a, b)
-    new | only
-    setline(1, 'two')
-    g:Vim9completeFuncArgs = []
-    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-    assert_equal([[61, 1, ''], [61, 0, 'two']], g:Vim9completeFuncArgs)
-    bw!
-
-    # Test for using a string(lambda)
-    &completefunc = '(a, b) => Vim9CompleteFunc(62, a, b)'
-    new | only
-    setline(1, 'two')
-    g:Vim9completeFuncArgs = []
-    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-    assert_equal([[62, 1, ''], [62, 0, 'two']], g:Vim9completeFuncArgs)
-    bw!
-
-    # Test for using a variable with a lambda expression
-    var Fn: func = (a, b) => Vim9CompleteFunc(63, a, b)
-    &completefunc = Fn
-    new | only
-    setline(1, 'three')
-    g:Vim9completeFuncArgs = []
-    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-    assert_equal([[63, 1, ''], [63, 0, 'three']], g:Vim9completeFuncArgs)
-    bw!
-
-    # Test for using a string(variable with a lambda expression)
-    Fn = (a, b) => Vim9CompleteFunc(64, a, b)
-    &completefunc = string(Fn)
-    new | only
-    setline(1, 'three')
-    g:Vim9completeFuncArgs = []
-    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
-    assert_equal([[64, 1, ''], [64, 0, 'three']], g:Vim9completeFuncArgs)
-    bw!
   END
   " call CheckScriptSuccess(lines)
 
@@ -1506,154 +1496,179 @@ func Test_omnifunc_callback()
     return a:findstart ? 0 : []
   endfunc
 
-  " Test for using a function()
-  set omnifunc=function('MyomniFunc1',[10])
-  new | only
-  call setline(1, 'one')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MyomniFunc1_args)
-  bw!
+  let lines =<< trim END
+    #" Test for using a function()
+    set omnifunc=function('g:MyomniFunc1',\ [10])
+    new | only
+    call setline(1, 'one')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MyomniFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'omnifunc'
-  let Fn = function('MyomniFunc1', [11])
-  let &omnifunc = Fn
-  new | only
-  call setline(1, 'two')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MyomniFunc1_args)
-  bw!
+    #" Using a funcref variable to set 'omnifunc'
+    VAR Fn = function('g:MyomniFunc1', [11])
+    LET &omnifunc = Fn
+    new | only
+    call setline(1, 'two')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MyomniFunc1_args)
+    bw!
 
-  " Using a string(funcref_variable) to set 'omnifunc'
-  let Fn = function('MyomniFunc1', [12])
-  let &omnifunc = string(Fn)
-  new | only
-  call setline(1, 'two')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MyomniFunc1_args)
-  bw!
+    #" Using a string(funcref_variable) to set 'omnifunc'
+    LET Fn = function('g:MyomniFunc1', [12])
+    LET &omnifunc = string(Fn)
+    new | only
+    call setline(1, 'two')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MyomniFunc1_args)
+    bw!
 
-  " Test for using a funcref()
-  set omnifunc=funcref('MyomniFunc1',\ [13])
-  new | only
-  call setline(1, 'three')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MyomniFunc1_args)
-  bw!
+    #" Test for using a funcref()
+    set omnifunc=funcref('g:MyomniFunc1',\ [13])
+    new | only
+    call setline(1, 'three')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MyomniFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'omnifunc'
-  let Fn = funcref('MyomniFunc1', [14])
-  let &omnifunc = Fn
-  new | only
-  call setline(1, 'four')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MyomniFunc1_args)
-  bw!
+    #" Use let to set 'omnifunc' to a funcref
+    LET Fn = funcref('g:MyomniFunc1', [14])
+    LET &omnifunc = Fn
+    new | only
+    call setline(1, 'four')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MyomniFunc1_args)
+    bw!
 
-  " Using a string(funcref_variable) to set 'omnifunc'
-  let Fn = funcref('MyomniFunc1', [15])
-  let &omnifunc = string(Fn)
-  new | only
-  call setline(1, 'four')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MyomniFunc1_args)
-  bw!
+    #" Using a string(funcref) to set 'omnifunc'
+    LET Fn = funcref("g:MyomniFunc1", [15])
+    LET &omnifunc = string(Fn)
+    new | only
+    call setline(1, 'four')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MyomniFunc1_args)
+    bw!
 
-  " Test for using a lambda function
-  set omnifunc={a,\ b\ ->\ MyomniFunc1(16,\ a,\ b)}
-  new | only
-  call setline(1, 'five')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MyomniFunc1_args)
-  bw!
+    #" Test for using a lambda function with set
+    VAR optval = "LSTART a, b LMIDDLE MyomniFunc1(16, a, b) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set omnifunc=" .. optval
+    new | only
+    call setline(1, 'five')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MyomniFunc1_args)
+    bw!
 
-  " Set 'omnifunc' to a lambda expression
-  let &omnifunc = {a, b -> MyomniFunc1(17, a, b)}
-  new | only
-  call setline(1, 'six')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MyomniFunc1_args)
-  bw!
+    #" Set 'omnifunc' to a lambda expression
+    LET &omnifunc = LSTART a, b LMIDDLE MyomniFunc1(17, a, b) LEND
+    new | only
+    call setline(1, 'six')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MyomniFunc1_args)
+    bw!
 
-  " Set 'omnifunc' to a string(lambda_expression)
-  let &omnifunc = '{a, b -> MyomniFunc1(18, a, b)}'
-  new | only
-  call setline(1, 'six')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MyomniFunc1_args)
-  bw!
+    #" Set 'omnifunc' to a string(lambda_expression)
+    LET &omnifunc = 'LSTART a, b LMIDDLE MyomniFunc1(18, a, b) LEND'
+    new | only
+    call setline(1, 'six')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MyomniFunc1_args)
+    bw!
 
-  " Set 'omnifunc' to a variable with a lambda expression
-  let Lambda = {a, b -> MyomniFunc1(19, a, b)}
-  let &omnifunc = Lambda
-  new | only
-  call setline(1, 'seven')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MyomniFunc1_args)
-  bw!
+    #" Set 'omnifunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a, b LMIDDLE MyomniFunc1(19, a, b) LEND
+    LET &omnifunc = Lambda
+    new | only
+    call setline(1, 'seven')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MyomniFunc1_args)
+    bw!
 
-  " Set 'omnifunc' to a string(variable with a lambda expression)
-  let Lambda = {a, b -> MyomniFunc1(20, a, b)}
-  let &omnifunc = string(Lambda)
-  new | only
-  call setline(1, 'seven')
-  let g:MyomniFunc1_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MyomniFunc1_args)
-  bw!
+    #" Set 'omnifunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a, b LMIDDLE MyomniFunc1(20, a, b) LEND
+    LET &omnifunc = string(Lambda)
+    new | only
+    call setline(1, 'seven')
+    LET g:MyomniFunc1_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MyomniFunc1_args)
+    bw!
 
-  " Test for using a lambda function with incorrect return value
-  let Lambda = {s -> strlen(s)}
-  let &omnifunc = Lambda
-  new | only
-  call setline(1, 'eight')
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  bw!
+    #" Test for using a lambda function with incorrect return value
+    LET Lambda = LSTART a, b LMIDDLE strlen(a) LEND
+    LET &omnifunc = Lambda
+    new | only
+    call setline(1, 'eight')
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    bw!
 
-  " Test for clearing the 'omnifunc' option
-  set omnifunc=''
-  set omnifunc&
+    #" Test for clearing the 'omnifunc' option
+    set omnifunc=''
+    set omnifunc&
+    call assert_fails("set omnifunc=function('abc')", "E700:")
+    call assert_fails("set omnifunc=funcref('abc')", "E700:")
+
+    #" set 'omnifunc' to a non-existing function
+    func MyomniFunc2(findstart, base)
+      call add(g:MyomniFunc2_args, [a:findstart, a:base])
+      return a:findstart ? 0 : []
+    endfunc
+    set omnifunc=MyomniFunc2
+    call setline(1, 'nine')
+    call assert_fails("set omnifunc=function('NonExistingFunc')", 'E700:')
+    call assert_fails("LET &omnifunc = function('NonExistingFunc')", 'E700:')
+    LET g:MyomniFunc2_args = []
+    call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    call assert_equal([[1, ''], [0, 'nine']], g:MyomniFunc2_args)
+    bw!
+  END
+  call CheckLegacyAndVim9Success(lines)
 
-  call assert_fails("set omnifunc=function('abc')", "E700:")
-  call assert_fails("set omnifunc=funcref('abc')", "E700:")
   let &omnifunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
 
   " Using Vim9 lambda expression in legacy context should fail
-  " set omnifunc=(a,\ b)\ =>\ g:MyomniFunc1(21,\ a,\ b)
+  " set omnifunc=(a,\ b)\ =>\ MyomniFunc1(21,\ a,\ b)
   new | only
   let g:MyomniFunc1_args = []
   " call assert_fails('call feedkeys("A\<C-X>\<C-O>\<Esc>", "x")', 'E117:')
   call assert_equal([], g:MyomniFunc1_args)
 
-  " set 'omnifunc' to a non-existing function
-  func MyomniFunc2(findstart, base)
-    call add(g:MyomniFunc2_args, [a:findstart, a:base])
-    return a:findstart ? 0 : []
+  " set 'omnifunc' to a partial with dict. This used to cause a crash.
+  func SetOmniFunc()
+    let params = {'omni': function('g:DictOmniFunc')}
+    let &omnifunc = params.omni
   endfunc
-  set omnifunc=MyomniFunc2
-  call setline(1, 'nine')
-  call assert_fails("set omnifunc=function('NonExistingFunc')", 'E700:')
-  call assert_fails("let &omnifunc = function('NonExistingFunc')", 'E700:')
-  let g:MyomniFunc2_args = []
-  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-  call assert_equal([[1, ''], [0, 'nine']], g:MyomniFunc2_args)
-  bw!
+  func g:DictOmniFunc(_) dict
+  endfunc
+  call SetOmniFunc()
+  new
+  call SetOmniFunc()
+  bw
+  call test_garbagecollect_now()
+  new
+  set omnifunc=
+  wincmd w
+  set omnifunc=
+  %bw!
+  delfunc g:DictOmniFunc
+  delfunc SetOmniFunc
 
   " Vim9 tests
   let lines =<< trim END
     vim9script
 
-    # Test for using function()
+    # Test for using a def function with omnifunc
     def Vim9omniFunc(val: number, findstart: number, base: string): any
       add(g:Vim9omniFunc_Args, [val, findstart, base])
       return findstart ? 0 : []
@@ -1665,44 +1680,6 @@ func Test_omnifunc_callback()
     feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
     assert_equal([[60, 1, ''], [60, 0, 'one']], g:Vim9omniFunc_Args)
     bw!
-
-    # Test for using a lambda
-    &omnifunc = (a, b) => Vim9omniFunc(61, a, b)
-    new | only
-    setline(1, 'two')
-    g:Vim9omniFunc_Args = []
-    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-    assert_equal([[61, 1, ''], [61, 0, 'two']], g:Vim9omniFunc_Args)
-    bw!
-
-    # Test for using a string(lambda)
-    &omnifunc = '(a, b) => Vim9omniFunc(62, a, b)'
-    new | only
-    setline(1, 'two')
-    g:Vim9omniFunc_Args = []
-    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-    assert_equal([[62, 1, ''], [62, 0, 'two']], g:Vim9omniFunc_Args)
-    bw!
-
-    # Test for using a variable with a lambda expression
-    var Fn: func = (a, b) => Vim9omniFunc(63, a, b)
-    &omnifunc = Fn
-    new | only
-    setline(1, 'three')
-    g:Vim9omniFunc_Args = []
-    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-    assert_equal([[63, 1, ''], [63, 0, 'three']], g:Vim9omniFunc_Args)
-    bw!
-
-    # Test for using a string(variable with a lambda expression)
-    Fn = (a, b) => Vim9omniFunc(64, a, b)
-    &omnifunc = string(Fn)
-    new | only
-    setline(1, 'three')
-    g:Vim9omniFunc_Args = []
-    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
-    assert_equal([[64, 1, ''], [64, 0, 'three']], g:Vim9omniFunc_Args)
-    bw!
   END
   " call CheckScriptSuccess(lines)
 
@@ -1720,178 +1697,215 @@ func Test_thesaurusfunc_callback()
     return a:findstart ? 0 : []
   endfunc
 
-  " Test for using a function()
-  set thesaurusfunc=function('MytsrFunc1',[10])
-  new | only
-  call setline(1, 'one')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MytsrFunc1_args)
-  bw!
+  let lines =<< trim END
+    #" Test for using a function()
+    set thesaurusfunc=function('g:MytsrFunc1',\ [10])
+    new | only
+    call setline(1, 'one')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[10, 1, ''], [10, 0, 'one']], g:MytsrFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'thesaurusfunc'
-  let Fn = function('MytsrFunc1', [11])
-  let &thesaurusfunc = Fn
-  new | only
-  call setline(1, 'two')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MytsrFunc1_args)
-  bw!
+    #" Using a funcref variable to set 'thesaurusfunc'
+    VAR Fn = function('g:MytsrFunc1', [11])
+    LET &thesaurusfunc = Fn
+    new | only
+    call setline(1, 'two')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[11, 1, ''], [11, 0, 'two']], g:MytsrFunc1_args)
+    bw!
 
-  " Using a string(funcref_variable) to set 'thesaurusfunc'
-  let Fn = function('MytsrFunc1', [12])
-  let &thesaurusfunc = string(Fn)
-  new | only
-  call setline(1, 'two')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MytsrFunc1_args)
-  bw!
+    #" Using a string(funcref_variable) to set 'thesaurusfunc'
+    LET Fn = function('g:MytsrFunc1', [12])
+    LET &thesaurusfunc = string(Fn)
+    new | only
+    call setline(1, 'two')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[12, 1, ''], [12, 0, 'two']], g:MytsrFunc1_args)
+    bw!
 
-  " Test for using a funcref()
-  set thesaurusfunc=funcref('MytsrFunc1',[13])
-  new | only
-  call setline(1, 'three')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MytsrFunc1_args)
-  bw!
+    #" Test for using a funcref()
+    set thesaurusfunc=funcref('g:MytsrFunc1',\ [13])
+    new | only
+    call setline(1, 'three')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[13, 1, ''], [13, 0, 'three']], g:MytsrFunc1_args)
+    bw!
 
-  " Using a funcref variable to set 'thesaurusfunc'
-  let Fn = funcref('MytsrFunc1', [14])
-  let &thesaurusfunc = Fn
-  new | only
-  call setline(1, 'four')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MytsrFunc1_args)
-  bw!
+    #" Using a funcref variable to set 'thesaurusfunc'
+    LET Fn = funcref('g:MytsrFunc1', [14])
+    LET &thesaurusfunc = Fn
+    new | only
+    call setline(1, 'four')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[14, 1, ''], [14, 0, 'four']], g:MytsrFunc1_args)
+    bw!
 
-  " Using a string(funcref_variable) to set 'thesaurusfunc'
-  let Fn = funcref('MytsrFunc1', [15])
-  let &thesaurusfunc = string(Fn)
-  new | only
-  call setline(1, 'four')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MytsrFunc1_args)
-  bw!
+    #" Using a string(funcref_variable) to set 'thesaurusfunc'
+    LET Fn = funcref('g:MytsrFunc1', [15])
+    LET &thesaurusfunc = string(Fn)
+    new | only
+    call setline(1, 'four')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[15, 1, ''], [15, 0, 'four']], g:MytsrFunc1_args)
+    bw!
 
-  " Test for using a lambda function
-  set thesaurusfunc={a,\ b\ ->\ MytsrFunc1(16,\ a,\ b)}
-  new | only
-  call setline(1, 'five')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MytsrFunc1_args)
-  bw!
+    #" Test for using a lambda function
+    VAR optval = "LSTART a, b LMIDDLE MytsrFunc1(16, a, b) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set thesaurusfunc=" .. optval
+    new | only
+    call setline(1, 'five')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[16, 1, ''], [16, 0, 'five']], g:MytsrFunc1_args)
+    bw!
 
-  " Set 'thesaurusfunc' to a lambda expression
-  let &thesaurusfunc = {a, b -> MytsrFunc1(17, a, b)}
-  new | only
-  call setline(1, 'six')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MytsrFunc1_args)
-  bw!
+    #" Test for using a lambda function with set
+    LET &thesaurusfunc = LSTART a, b LMIDDLE MytsrFunc1(17, a, b) LEND
+    new | only
+    call setline(1, 'six')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[17, 1, ''], [17, 0, 'six']], g:MytsrFunc1_args)
+    bw!
 
-  " Set 'thesaurusfunc' to a string(lambda expression)
-  let &thesaurusfunc = '{a, b -> MytsrFunc1(18, a, b)}'
-  new | only
-  call setline(1, 'six')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MytsrFunc1_args)
-  bw!
+    #" Set 'thesaurusfunc' to a string(lambda expression)
+    LET &thesaurusfunc = 'LSTART a, b LMIDDLE MytsrFunc1(18, a, b) LEND'
+    new | only
+    call setline(1, 'six')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[18, 1, ''], [18, 0, 'six']], g:MytsrFunc1_args)
+    bw!
 
-  " Set 'thesaurusfunc' to a variable with a lambda expression
-  let Lambda = {a, b -> MytsrFunc1(19, a, b)}
-  let &thesaurusfunc = Lambda
-  new | only
-  call setline(1, 'seven')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MytsrFunc1_args)
-  bw!
+    #" Set 'thesaurusfunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a, b LMIDDLE MytsrFunc1(19, a, b) LEND
+    LET &thesaurusfunc = Lambda
+    new | only
+    call setline(1, 'seven')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[19, 1, ''], [19, 0, 'seven']], g:MytsrFunc1_args)
+    bw!
 
-  " Set 'thesaurusfunc' to a string(variable with a lambda expression)
-  let Lambda = {a, b -> MytsrFunc1(20, a, b)}
-  let &thesaurusfunc = string(Lambda)
-  new | only
-  call setline(1, 'seven')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MytsrFunc1_args)
-  bw!
+    #" Set 'thesaurusfunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a, b LMIDDLE MytsrFunc1(20, a, b) LEND
+    LET &thesaurusfunc = string(Lambda)
+    new | only
+    call setline(1, 'seven')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[20, 1, ''], [20, 0, 'seven']], g:MytsrFunc1_args)
+    bw!
 
-  " Test for using a lambda function with incorrect return value
-  let Lambda = {s -> strlen(s)}
-  let &thesaurusfunc = Lambda
-  new | only
-  call setline(1, 'eight')
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  bw!
+    #" Test for using a lambda function with incorrect return value
+    LET Lambda = LSTART a, b LMIDDLE strlen(a) LEND
+    LET &thesaurusfunc = Lambda
+    new | only
+    call setline(1, 'eight')
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    bw!
 
-  " Test for clearing the 'thesaurusfunc' option
-  set thesaurusfunc=''
-  set thesaurusfunc&
+    #" Test for clearing the 'thesaurusfunc' option
+    set thesaurusfunc=''
+    set thesaurusfunc&
+    call assert_fails("set thesaurusfunc=function('abc')", "E700:")
+    call assert_fails("set thesaurusfunc=funcref('abc')", "E700:")
+
+    #" set 'thesaurusfunc' to a non-existing function
+    func MytsrFunc2(findstart, base)
+      call add(g:MytsrFunc2_args, [a:findstart, a:base])
+      return a:findstart ? 0 : ['sunday']
+    endfunc
+    set thesaurusfunc=MytsrFunc2
+    call setline(1, 'ten')
+    call assert_fails("set thesaurusfunc=function('NonExistingFunc')", 'E700:')
+    call assert_fails("LET &thesaurusfunc = function('NonExistingFunc')", 'E700:')
+    LET g:MytsrFunc2_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    call assert_equal([[1, ''], [0, 'ten']], g:MytsrFunc2_args)
+    bw!
+
+    #" Use a buffer-local value and a global value
+    set thesaurusfunc&
+    setlocal thesaurusfunc=function('g:MytsrFunc1',\ [22])
+    call setline(1, 'sun')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
+    call assert_equal('sun', getline(1))
+    call assert_equal([[22, 1, ''], [22, 0, 'sun']], g:MytsrFunc1_args)
+    new
+    call setline(1, 'sun')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
+    call assert_equal('sun', getline(1))
+    call assert_equal([], g:MytsrFunc1_args)
+    set thesaurusfunc=function('g:MytsrFunc1',\ [23])
+    wincmd w
+    call setline(1, 'sun')
+    LET g:MytsrFunc1_args = []
+    call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
+    call assert_equal('sun', getline(1))
+    call assert_equal([[22, 1, ''], [22, 0, 'sun']], g:MytsrFunc1_args)
+    :%bw!
+  END
+  call CheckLegacyAndVim9Success(lines)
 
-  call assert_fails("set thesaurusfunc=function('abc')", "E700:")
-  call assert_fails("set thesaurusfunc=funcref('abc')", "E700:")
   let &thesaurusfunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
 
   " Using Vim9 lambda expression in legacy context should fail
-  " set thesaurusfunc=(a,\ b)\ =>\ g:MytsrFunc1(21,\ a,\ b)
+  " set thesaurusfunc=(a,\ b)\ =>\ MytsrFunc1(21,\ a,\ b)
   new | only
   let g:MytsrFunc1_args = []
   " call assert_fails('call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")', 'E117:')
   call assert_equal([], g:MytsrFunc1_args)
   bw!
 
-  " Use a buffer-local value and a global value
-  set thesaurusfunc&
-  setlocal thesaurusfunc=function('MytsrFunc1',[22])
-  call setline(1, 'sun')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
-  call assert_equal('sun', getline(1))
-  call assert_equal([[22, 1, ''], [22, 0, 'sun']], g:MytsrFunc1_args)
+  " set 'thesaurusfunc' to a partial with dict. This used to cause a crash.
+  func SetTsrFunc()
+    let params = {'thesaurus': function('g:DictTsrFunc')}
+    let &thesaurusfunc = params.thesaurus
+  endfunc
+  func g:DictTsrFunc(_) dict
+  endfunc
+  call SetTsrFunc()
   new
-  call setline(1, 'sun')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
-  call assert_equal('sun', getline(1))
-  call assert_equal([], g:MytsrFunc1_args)
-  set thesaurusfunc=function('MytsrFunc1',[23])
+  call SetTsrFunc()
+  bw
+  call test_garbagecollect_now()
+  new
+  set thesaurusfunc=
   wincmd w
-  call setline(1, 'sun')
-  let g:MytsrFunc1_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", "x")
-  call assert_equal('sun', getline(1))
-  call assert_equal([[22, 1, ''], [22, 0, 'sun']], g:MytsrFunc1_args)
   %bw!
+  delfunc SetTsrFunc
 
-  " set 'thesaurusfunc' to a non-existing function
-  func MytsrFunc2(findstart, base)
-    call add(g:MytsrFunc2_args, [a:findstart, a:base])
-    return a:findstart ? 0 : ['sunday']
+  " set buffer-local 'thesaurusfunc' to a partial with dict. This used to
+  " cause a crash.
+  func SetLocalTsrFunc()
+    let params = {'thesaurus': function('g:DictTsrFunc')}
+    let &l:thesaurusfunc = params.thesaurus
   endfunc
-  set thesaurusfunc=MytsrFunc2
-  call setline(1, 'ten')
-  call assert_fails("set thesaurusfunc=function('NonExistingFunc')", 'E700:')
-  call assert_fails("let &thesaurusfunc = function('NonExistingFunc')", 'E700:')
-  let g:MytsrFunc2_args = []
-  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-  call assert_equal([[1, ''], [0, 'ten']], g:MytsrFunc2_args)
+  call SetLocalTsrFunc()
+  call test_garbagecollect_now()
+  call SetLocalTsrFunc()
+  set thesaurusfunc=
   bw!
+  delfunc g:DictTsrFunc
+  delfunc SetLocalTsrFunc
 
   " Vim9 tests
   let lines =<< trim END
     vim9script
 
-    # Test for using function()
+    # Test for using a def function with thesaurusfunc
     def Vim9tsrFunc(val: number, findstart: number, base: string): any
       add(g:Vim9tsrFunc_Args, [val, findstart, base])
       return findstart ? 0 : []
@@ -1903,44 +1917,6 @@ func Test_thesaurusfunc_callback()
     feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
     assert_equal([[60, 1, ''], [60, 0, 'one']], g:Vim9tsrFunc_Args)
     bw!
-
-    # Test for using a lambda
-    &thesaurusfunc = (a, b) => Vim9tsrFunc(61, a, b)
-    new | only
-    setline(1, 'two')
-    g:Vim9tsrFunc_Args = []
-    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-    assert_equal([[61, 1, ''], [61, 0, 'two']], g:Vim9tsrFunc_Args)
-    bw!
-
-    # Test for using a string(lambda)
-    &thesaurusfunc = '(a, b) => Vim9tsrFunc(62, a, b)'
-    new | only
-    setline(1, 'two')
-    g:Vim9tsrFunc_Args = []
-    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-    assert_equal([[62, 1, ''], [62, 0, 'two']], g:Vim9tsrFunc_Args)
-    bw!
-
-    # Test for using a variable with a lambda expression
-    var Fn: func = (a, b) => Vim9tsrFunc(63, a, b)
-    &thesaurusfunc = Fn
-    new | only
-    setline(1, 'three')
-    g:Vim9tsrFunc_Args = []
-    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-    assert_equal([[63, 1, ''], [63, 0, 'three']], g:Vim9tsrFunc_Args)
-    bw!
-
-    # Test for using a string(variable with a lambda expression)
-    Fn = (a, b) => Vim9tsrFunc(64, a, b)
-    &thesaurusfunc = string(Fn)
-    new | only
-    setline(1, 'three')
-    g:Vim9tsrFunc_Args = []
-    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
-    assert_equal([[64, 1, ''], [64, 0, 'three']], g:Vim9tsrFunc_Args)
-    bw!
   END
   " call CheckScriptSuccess(lines)
 
diff --git a/src/nvim/testdir/test_normal.vim b/src/nvim/testdir/test_normal.vim
index b9cc858cdb..b3e0be8f77 100644
--- a/src/nvim/testdir/test_normal.vim
+++ b/src/nvim/testdir/test_normal.vim
@@ -3,6 +3,7 @@
 source shared.vim
 source check.vim
 source view_util.vim
+source vim9.vim
 source screendump.vim
 
 func Setup_NewWindow()
@@ -463,110 +464,122 @@ func Test_opfunc_callback()
     let g:OpFuncArgs = [a:val, a:type]
   endfunc
 
-  " Test for using a function()
-  set opfunc=function('MyopFunc',\ [11])
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([11, 'char'], g:OpFuncArgs)
-
-  " Using a funcref variable to set 'operatorfunc'
-  let Fn = function('MyopFunc', [12])
-  let &opfunc = Fn
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([12, 'char'], g:OpFuncArgs)
-
-  " Using a string(funcref_variable) to set 'operatorfunc'
-  let Fn = function('MyopFunc', [13])
-  let &operatorfunc = string(Fn)
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([13, 'char'], g:OpFuncArgs)
-
-  " Test for using a funcref()
-  set operatorfunc=funcref('MyopFunc',\ [14])
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([14, 'char'], g:OpFuncArgs)
-
-  " Using a funcref variable to set 'operatorfunc'
-  let Fn = funcref('MyopFunc', [15])
-  let &opfunc = Fn
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([15, 'char'], g:OpFuncArgs)
-
-  " Using a string(funcref_variable) to set 'operatorfunc'
-  let Fn = funcref('MyopFunc', [16])
-  let &opfunc = string(Fn)
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([16, 'char'], g:OpFuncArgs)
+  let lines =<< trim END
+    #" Test for using a function()
+    set opfunc=function('g:MyopFunc',\ [10])
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([10, 'char'], g:OpFuncArgs)
 
-  " Test for using a lambda function using set
-  set opfunc={a\ ->\ MyopFunc(17,\ a)}
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([17, 'char'], g:OpFuncArgs)
+    #" Using a funcref variable to set 'operatorfunc'
+    VAR Fn = function('g:MyopFunc', [11])
+    LET &opfunc = Fn
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([11, 'char'], g:OpFuncArgs)
 
-  " Test for using a lambda function using let
-  let &opfunc = {a -> MyopFunc(18, a)}
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([18, 'char'], g:OpFuncArgs)
+    #" Using a string(funcref_variable) to set 'operatorfunc'
+    LET Fn = function('g:MyopFunc', [12])
+    LET &operatorfunc = string(Fn)
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([12, 'char'], g:OpFuncArgs)
 
-  " Set 'operatorfunc' to a string(lambda expression)
-  let &opfunc = '{a -> MyopFunc(19, a)}'
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([19, 'char'], g:OpFuncArgs)
+    #" Test for using a funcref()
+    set operatorfunc=funcref('g:MyopFunc',\ [13])
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([13, 'char'], g:OpFuncArgs)
 
-  " Set 'operatorfunc' to a variable with a lambda expression
-  let Lambda = {a -> MyopFunc(20, a)}
-  let &opfunc = Lambda
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([20, 'char'], g:OpFuncArgs)
+    #" Using a funcref variable to set 'operatorfunc'
+    LET Fn = funcref('g:MyopFunc', [14])
+    LET &opfunc = Fn
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([14, 'char'], g:OpFuncArgs)
 
-  " Set 'operatorfunc' to a string(variable with a lambda expression)
-  let Lambda = {a -> MyopFunc(21, a)}
-  let &opfunc = string(Lambda)
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([21, 'char'], g:OpFuncArgs)
+    #" Using a string(funcref_variable) to set 'operatorfunc'
+    LET Fn = funcref('g:MyopFunc', [15])
+    LET &opfunc = string(Fn)
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([15, 'char'], g:OpFuncArgs)
 
-  " Try to use 'operatorfunc' after the function is deleted
-  func TmpOpFunc(type)
-    let g:OpFuncArgs = [22, a:type]
-  endfunc
-  let &opfunc = function('TmpOpFunc')
-  delfunc TmpOpFunc
-  call test_garbagecollect_now()
-  let g:OpFuncArgs = []
-  call assert_fails('normal! g@l', 'E117:')
-  call assert_equal([], g:OpFuncArgs)
+    #" Test for using a lambda function using set
+    VAR optval = "LSTART a LMIDDLE MyopFunc(16, a) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set opfunc=" .. optval
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([16, 'char'], g:OpFuncArgs)
 
-  " Try to use a function with two arguments for 'operatorfunc'
-  func! MyopFunc2(x, y)
-    let g:OpFuncArgs = [a:x, a:y]
-  endfunc
-  set opfunc=MyopFunc2
-  let g:OpFuncArgs = []
-  call assert_fails('normal! g@l', 'E119:')
-  call assert_equal([], g:OpFuncArgs)
+    #" Test for using a lambda function using LET
+    LET &opfunc = LSTART a LMIDDLE MyopFunc(17, a) LEND
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([17, 'char'], g:OpFuncArgs)
 
-  " Try to use a lambda function with two arguments for 'operatorfunc'
-  let &opfunc = {a, b -> MyopFunc(23, b)}
-  let g:OpFuncArgs = []
-  call assert_fails('normal! g@l', 'E119:')
-  call assert_equal([], g:OpFuncArgs)
+    #" Set 'operatorfunc' to a string(lambda expression)
+    LET &opfunc = 'LSTART a LMIDDLE MyopFunc(18, a) LEND'
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([18, 'char'], g:OpFuncArgs)
 
-  " Test for clearing the 'operatorfunc' option
-  set opfunc=''
-  set opfunc&
+    #" Set 'operatorfunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a LMIDDLE MyopFunc(19, a) LEND
+    LET &opfunc = Lambda
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([19, 'char'], g:OpFuncArgs)
 
-  call assert_fails("set opfunc=function('abc')", "E700:")
-  call assert_fails("set opfunc=funcref('abc')", "E700:")
+    #" Set 'operatorfunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a LMIDDLE MyopFunc(20, a) LEND
+    LET &opfunc = string(Lambda)
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([20, 'char'], g:OpFuncArgs)
+
+    #" Try to use 'operatorfunc' after the function is deleted
+    func g:TmpOpFunc(type)
+      LET g:OpFuncArgs = [21, a:type]
+    endfunc
+    LET &opfunc = function('g:TmpOpFunc')
+    delfunc g:TmpOpFunc
+    call test_garbagecollect_now()
+    LET g:OpFuncArgs = []
+    call assert_fails('normal! g@l', 'E117:')
+    call assert_equal([], g:OpFuncArgs)
+
+    #" Try to use a function with two arguments for 'operatorfunc'
+    func MyopFunc2(x, y)
+      LET g:OpFuncArgs = [a:x, a:y]
+    endfunc
+    set opfunc=MyopFunc2
+    LET g:OpFuncArgs = []
+    call assert_fails('normal! g@l', 'E119:')
+    call assert_equal([], g:OpFuncArgs)
+
+    #" Try to use a lambda function with two arguments for 'operatorfunc'
+    LET &opfunc = LSTART a, b LMIDDLE MyopFunc(22, b) LEND
+    LET g:OpFuncArgs = []
+    call assert_fails('normal! g@l', 'E119:')
+    call assert_equal([], g:OpFuncArgs)
+
+    #" Test for clearing the 'operatorfunc' option
+    set opfunc=''
+    set opfunc&
+    call assert_fails("set opfunc=function('abc')", "E700:")
+    call assert_fails("set opfunc=funcref('abc')", "E700:")
+
+    #" set 'operatorfunc' to a non-existing function
+    LET &opfunc = function('g:MyopFunc', [23])
+    call assert_fails("set opfunc=function('NonExistingFunc')", 'E700:')
+    call assert_fails("LET &opfunc = function('NonExistingFunc')", 'E700:')
+    LET g:OpFuncArgs = []
+    normal! g@l
+    call assert_equal([23, 'char'], g:OpFuncArgs)
+  END
+  call CheckTransLegacySuccess(lines)
 
   " Using Vim9 lambda expression in legacy context should fail
   " set opfunc=(a)\ =>\ MyopFunc(24,\ a)
@@ -574,19 +587,24 @@ func Test_opfunc_callback()
   " call assert_fails('normal! g@l', 'E117:')
   call assert_equal([], g:OpFuncArgs)
 
-  " set 'operatorfunc' to a non-existing function
-  let &opfunc = function('MyopFunc', [25])
-  call assert_fails("set opfunc=function('NonExistingFunc')", 'E700:')
-  call assert_fails("let &opfunc = function('NonExistingFunc')", 'E700:')
-  let g:OpFuncArgs = []
-  normal! g@l
-  call assert_equal([25, 'char'], g:OpFuncArgs)
+  " set 'operatorfunc' to a partial with dict. This used to cause a crash.
+  func SetOpFunc()
+    let operator = {'execute': function('OperatorExecute')}
+    let &opfunc = operator.execute
+  endfunc
+  func OperatorExecute(_) dict
+  endfunc
+  call SetOpFunc()
+  call test_garbagecollect_now()
+  set operatorfunc=
+  delfunc SetOpFunc
+  delfunc OperatorExecute
 
   " Vim9 tests
   let lines =<< trim END
     vim9script
 
-    # Test for using function()
+    # Test for using a def function with opfunc
     def g:Vim9opFunc(val: number, type: string): void
       g:OpFuncArgs = [val, type]
     enddef
@@ -594,33 +612,6 @@ func Test_opfunc_callback()
     g:OpFuncArgs = []
     normal! g@l
     assert_equal([60, 'char'], g:OpFuncArgs)
-
-    # Test for using a lambda
-    &opfunc = (a) => Vim9opFunc(61, a)
-    g:OpFuncArgs = []
-    normal! g@l
-    assert_equal([61, 'char'], g:OpFuncArgs)
-
-    # Test for using a string(lambda)
-    &opfunc = '(a) => Vim9opFunc(62, a)'
-    g:OpFuncArgs = []
-    normal! g@l
-    assert_equal([62, 'char'], g:OpFuncArgs)
-
-    # Test for using a variable with a lambda expression
-    var Fn: func = (a) => Vim9opFunc(63, a)
-    &opfunc = Fn
-    g:OpFuncArgs = []
-    normal! g@l
-    assert_equal([63, 'char'], g:OpFuncArgs)
-
-    # Test for using a string(variable with a lambda expression)
-    Fn = (a) => Vim9opFunc(64, a)
-    &opfunc = string(Fn)
-    g:OpFuncArgs = []
-    normal! g@l
-    assert_equal([64, 'char'], g:OpFuncArgs)
-    bw!
   END
   " call CheckScriptSuccess(lines)
 
diff --git a/src/nvim/testdir/test_quickfix.vim b/src/nvim/testdir/test_quickfix.vim
index 9d9fc5e77b..a18d6fd6ab 100644
--- a/src/nvim/testdir/test_quickfix.vim
+++ b/src/nvim/testdir/test_quickfix.vim
@@ -1,6 +1,7 @@
 " Test for the quickfix feature.
 
 source check.vim
+source vim9.vim
 CheckFeature quickfix
 
 source screendump.vim
@@ -5690,6 +5691,131 @@ func Test_qftextfunc()
   call Xtest_qftextfunc('l')
 endfunc
 
+func Test_qftextfunc_callback()
+  let lines =<< trim END
+    set efm=%f:%l:%c:%m
+
+    #" Test for using a function()
+    set qftf=function('g:Tqfexpr')
+    cexpr "F1:1:1:L1"
+    copen
+    call assert_equal('F1-L1C1-L1', getline(1))
+    cclose
+
+    #" Using a funcref variable to set 'quickfixtextfunc'
+    VAR Fn = function('g:Tqfexpr')
+    LET &qftf = Fn
+    cexpr "F2:2:2:L2"
+    copen
+    call assert_equal('F2-L2C2-L2', getline(1))
+    cclose
+
+    #" Using string(funcref_variable) to set 'quickfixtextfunc'
+    LET Fn = function('g:Tqfexpr')
+    LET &qftf = string(Fn)
+    cexpr "F3:3:3:L3"
+    copen
+    call assert_equal('F3-L3C3-L3', getline(1))
+    cclose
+
+    #" Test for using a funcref()
+    set qftf=funcref('g:Tqfexpr')
+    cexpr "F4:4:4:L4"
+    copen
+    call assert_equal('F4-L4C4-L4', getline(1))
+    cclose
+
+    #" Using a funcref variable to set 'quickfixtextfunc'
+    LET Fn = funcref('g:Tqfexpr')
+    LET &qftf = Fn
+    cexpr "F5:5:5:L5"
+    copen
+    call assert_equal('F5-L5C5-L5', getline(1))
+    cclose
+
+    #" Using a string(funcref_variable) to set 'quickfixtextfunc'
+    LET Fn = funcref('g:Tqfexpr')
+    LET &qftf = string(Fn)
+    cexpr "F5:5:5:L5"
+    copen
+    call assert_equal('F5-L5C5-L5', getline(1))
+    cclose
+
+    #" Test for using a lambda function with set
+    VAR optval = "LSTART a LMIDDLE Tqfexpr(a) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set qftf=" .. optval
+    cexpr "F6:6:6:L6"
+    copen
+    call assert_equal('F6-L6C6-L6', getline(1))
+    cclose
+
+    #" Set 'quickfixtextfunc' to a lambda expression
+    LET &qftf = LSTART a LMIDDLE Tqfexpr(a) LEND
+    cexpr "F7:7:7:L7"
+    copen
+    call assert_equal('F7-L7C7-L7', getline(1))
+    cclose
+
+    #" Set 'quickfixtextfunc' to string(lambda_expression)
+    LET &qftf = "LSTART a LMIDDLE Tqfexpr(a) LEND"
+    cexpr "F8:8:8:L8"
+    copen
+    call assert_equal('F8-L8C8-L8', getline(1))
+    cclose
+
+    #" Set 'quickfixtextfunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a LMIDDLE Tqfexpr(a) LEND
+    LET &qftf = Lambda
+    cexpr "F9:9:9:L9"
+    copen
+    call assert_equal('F9-L9C9-L9', getline(1))
+    cclose
+
+    #" Set 'quickfixtextfunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a LMIDDLE Tqfexpr(a) LEND
+    LET &qftf = string(Lambda)
+    cexpr "F9:9:9:L9"
+    copen
+    call assert_equal('F9-L9C9-L9', getline(1))
+    cclose
+  END
+  call CheckLegacyAndVim9Success(lines)
+
+  " set 'quickfixtextfunc' to a partial with dict. This used to cause a crash.
+  func SetQftfFunc()
+    let params = {'qftf': function('g:DictQftfFunc')}
+    let &quickfixtextfunc = params.qftf
+  endfunc
+  func g:DictQftfFunc(_) dict
+  endfunc
+  call SetQftfFunc()
+  new
+  call SetQftfFunc()
+  bw
+  call test_garbagecollect_now()
+  new
+  set qftf=
+  wincmd w
+  set qftf=
+  :%bw!
+
+  " set per-quickfix list 'quickfixtextfunc' to a partial with dict. This used
+  " to cause a crash.
+  let &qftf = ''
+  func SetLocalQftfFunc()
+    let params = {'qftf': function('g:DictQftfFunc')}
+    call setqflist([], 'a', {'quickfixtextfunc' : params.qftf})
+  endfunc
+  call SetLocalQftfFunc()
+  call test_garbagecollect_now()
+  call setqflist([], 'a', {'quickfixtextfunc' : ''})
+  delfunc g:DictQftfFunc
+  delfunc SetQftfFunc
+  delfunc SetLocalQftfFunc
+  set efm&
+endfunc
+
 " Test for updating a location list for some other window and check that
 " 'qftextfunc' uses the correct location list.
 func Test_qftextfunc_other_loclist()
diff --git a/src/nvim/testdir/test_tagfunc.vim b/src/nvim/testdir/test_tagfunc.vim
index 79b1110b43..827159e3c8 100644
--- a/src/nvim/testdir/test_tagfunc.vim
+++ b/src/nvim/testdir/test_tagfunc.vim
@@ -1,5 +1,7 @@
 " Test 'tagfunc'
 
+source vim9.vim
+
 func TagFunc(pat, flag, info)
   let g:tagfunc_args = [a:pat, a:flag, a:info]
   let tags = []
@@ -130,55 +132,121 @@ func Test_tagfunc_callback()
     return v:null
   endfunc
 
-  " Test for using a function()
-  set tagfunc=function('MytagFunc1',[10])
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a11', 'E433:')
-  call assert_equal([10, 'a11', '', {}], g:MytagFunc1_args)
+  let lines =<< trim END
+    #" Test for using a function()
+    set tagfunc=function('g:MytagFunc1',\ [10])
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a11', 'E433:')
+    call assert_equal([10, 'a11', '', {}], g:MytagFunc1_args)
 
-  " Using a funcref variable to set 'tagfunc'
-  let Fn = function('MytagFunc1', [11])
-  let &tagfunc = Fn
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a12', 'E433:')
-  call assert_equal([11, 'a12', '', {}], g:MytagFunc1_args)
+    #" Using a funcref variable to set 'tagfunc'
+    VAR Fn = function('g:MytagFunc1', [11])
+    LET &tagfunc = Fn
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a12', 'E433:')
+    call assert_equal([11, 'a12', '', {}], g:MytagFunc1_args)
 
-  " Using a string(funcref_variable) to set 'tagfunc'
-  let Fn = function('MytagFunc1', [12])
-  let &tagfunc = string(Fn)
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a12', 'E433:')
-  call assert_equal([12, 'a12', '', {}], g:MytagFunc1_args)
+    #" Using a string(funcref_variable) to set 'tagfunc'
+    LET Fn = function('g:MytagFunc1', [12])
+    LET &tagfunc = string(Fn)
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a12', 'E433:')
+    call assert_equal([12, 'a12', '', {}], g:MytagFunc1_args)
 
-  " Test for using a funcref()
-  func MytagFunc2(pat, flags, info)
-    let g:MytagFunc2_args = [a:pat, a:flags, a:info]
-    return v:null
-  endfunc
-  set tagfunc=funcref('MytagFunc1',[13])
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a13', 'E433:')
-  call assert_equal([13, 'a13', '', {}], g:MytagFunc1_args)
+    #" Test for using a funcref()
+    set tagfunc=funcref('g:MytagFunc1',\ [13])
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a13', 'E433:')
+    call assert_equal([13, 'a13', '', {}], g:MytagFunc1_args)
 
-  " Using a funcref variable to set 'tagfunc'
-  let Fn = funcref('MytagFunc1', [14])
-  let &tagfunc = Fn
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a14', 'E433:')
-  call assert_equal([14, 'a14', '', {}], g:MytagFunc1_args)
+    #" Using a funcref variable to set 'tagfunc'
+    LET Fn = funcref('g:MytagFunc1', [14])
+    LET &tagfunc = Fn
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a14', 'E433:')
+    call assert_equal([14, 'a14', '', {}], g:MytagFunc1_args)
+
+    #" Using a string(funcref_variable) to set 'tagfunc'
+    LET Fn = funcref('g:MytagFunc1', [15])
+    LET &tagfunc = string(Fn)
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a14', 'E433:')
+    call assert_equal([15, 'a14', '', {}], g:MytagFunc1_args)
+
+    #" Test for using a lambda function
+    VAR optval = "LSTART a, b, c LMIDDLE MytagFunc1(16, a, b, c) LEND"
+    LET optval = substitute(optval, ' ', '\\ ', 'g')
+    exe "set tagfunc=" .. optval
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a17', 'E433:')
+    call assert_equal([16, 'a17', '', {}], g:MytagFunc1_args)
+
+    #" Set 'tagfunc' to a lambda expression
+    LET &tagfunc = LSTART a, b, c LMIDDLE MytagFunc1(17, a, b, c) LEND
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a18', 'E433:')
+    call assert_equal([17, 'a18', '', {}], g:MytagFunc1_args)
 
-  " Using a string(funcref_variable) to set 'tagfunc'
-  let Fn = funcref('MytagFunc1', [15])
-  let &tagfunc = string(Fn)
+    #" Set 'tagfunc' to a string(lambda expression)
+    LET &tagfunc = 'LSTART a, b, c LMIDDLE MytagFunc1(18, a, b, c) LEND'
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails('tag a18', 'E433:')
+    call assert_equal([18, 'a18', '', {}], g:MytagFunc1_args)
+
+    #" Set 'tagfunc' to a variable with a lambda expression
+    VAR Lambda = LSTART a, b, c LMIDDLE MytagFunc1(19, a, b, c) LEND
+    LET &tagfunc = Lambda
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails("tag a19", "E433:")
+    call assert_equal([19, 'a19', '', {}], g:MytagFunc1_args)
+
+    #" Set 'tagfunc' to a string(variable with a lambda expression)
+    LET Lambda = LSTART a, b, c LMIDDLE MytagFunc1(20, a, b, c) LEND
+    LET &tagfunc = string(Lambda)
+    new | only
+    LET g:MytagFunc1_args = []
+    call assert_fails("tag a19", "E433:")
+    call assert_equal([20, 'a19', '', {}], g:MytagFunc1_args)
+
+    #" Test for using a lambda function with incorrect return value
+    LET Lambda = LSTART a, b, c LMIDDLE strlen(a) LEND
+    LET &tagfunc = string(Lambda)
+    new | only
+    call assert_fails("tag a20", "E987:")
+
+    #" Test for clearing the 'tagfunc' option
+    set tagfunc=''
+    set tagfunc&
+    call assert_fails("set tagfunc=function('abc')", "E700:")
+    call assert_fails("set tagfunc=funcref('abc')", "E700:")
+
+    #" set 'tagfunc' to a non-existing function
+    LET &tagfunc = function('g:MytagFunc1', [21])
+    call assert_fails("set tagfunc=function('NonExistingFunc')", 'E700:')
+    call assert_fails("LET &tagfunc = function('NonExistingFunc')", 'E700:')
+    call assert_fails("tag axb123", 'E426:')
+  END
+  call CheckLegacyAndVim9Success(lines)
+
+  let &tagfunc = "{a -> 'abc'}"
+  call assert_fails("echo taglist('a')", "E987:")
+
+  " Using Vim9 lambda expression in legacy context should fail
+  " set tagfunc=(a,\ b,\ c)\ =>\ g:MytagFunc1(21,\ a,\ b,\ c)
   new | only
   let g:MytagFunc1_args = []
-  call assert_fails('tag a14', 'E433:')
-  call assert_equal([15, 'a14', '', {}], g:MytagFunc1_args)
+  " call assert_fails("tag a17", "E117:")
+  call assert_equal([], g:MytagFunc1_args)
 
   " Test for using a script local function
   set tagfunc=<SID>ScriptLocalTagFunc
@@ -203,70 +271,25 @@ func Test_tagfunc_callback()
   call assert_fails('tag a16', 'E433:')
   call assert_equal(['a16', '', {}], g:ScriptLocalFuncArgs)
 
-  " Test for using a lambda function
-  set tagfunc={a,\ b,\ c\ ->\ MytagFunc1(16,\ a,\ b,\ c)}
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a17', 'E433:')
-  call assert_equal([16, 'a17', '', {}], g:MytagFunc1_args)
-
-  " Set 'tagfunc' to a lambda expression
-  let &tagfunc = {a, b, c -> MytagFunc1(17, a, b, c)}
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a18', 'E433:')
-  call assert_equal([17, 'a18', '', {}], g:MytagFunc1_args)
-
-  " Set 'tagfunc' to a string(lambda expression)
-  let &tagfunc = '{a, b, c -> MytagFunc1(18, a, b, c)}'
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails('tag a18', 'E433:')
-  call assert_equal([18, 'a18', '', {}], g:MytagFunc1_args)
-
-  " Set 'tagfunc' to a variable with a lambda expression
-  let Lambda = {a, b, c -> MytagFunc1(19, a, b, c)}
-  let &tagfunc = Lambda
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails("tag a19", "E433:")
-  call assert_equal([19, 'a19', '', {}], g:MytagFunc1_args)
-
-  " Set 'tagfunc' to a string(variable with a lambda expression)
-  let Lambda = {a, b, c -> MytagFunc1(20, a, b, c)}
-  let &tagfunc = string(Lambda)
-  new | only
-  let g:MytagFunc1_args = []
-  call assert_fails("tag a19", "E433:")
-  call assert_equal([20, 'a19', '', {}], g:MytagFunc1_args)
-
-  " Test for using a lambda function with incorrect return value
-  let Lambda = {s -> strlen(s)}
-  let &tagfunc = string(Lambda)
-  new | only
-  call assert_fails("tag a20", "E987:")
-
-  " Test for clearing the 'tagfunc' option
-  set tagfunc=''
-  set tagfunc&
-
-  call assert_fails("set tagfunc=function('abc')", "E700:")
-  call assert_fails("set tagfunc=funcref('abc')", "E700:")
-  let &tagfunc = "{a -> 'abc'}"
-  call assert_fails("echo taglist('a')", "E987:")
-
-  " Using Vim9 lambda expression in legacy context should fail
-  " set tagfunc=(a,\ b,\ c)\ =>\ g:MytagFunc1(21,\ a,\ b,\ c)
-  new | only
-  let g:MytagFunc1_args = []
-  " call assert_fails("tag a17", "E117:")
-  call assert_equal([], g:MytagFunc1_args)
-
-  " set 'tagfunc' to a non-existing function
-  call assert_fails("set tagfunc=function('NonExistingFunc')", 'E700:')
-  call assert_fails("let &tagfunc = function('NonExistingFunc')", 'E700:')
-  call assert_fails("tag axb123", 'E426:')
-  bw!
+  " set 'tagfunc' to a partial with dict. This used to cause a crash.
+  func SetTagFunc()
+    let params = {'tagfn': function('g:DictTagFunc')}
+    let &tagfunc = params.tagfn
+  endfunc
+  func g:DictTagFunc(_) dict
+  endfunc
+  call SetTagFunc()
+  new
+  call SetTagFunc()
+  bw
+  call test_garbagecollect_now()
+  new
+  set tagfunc=
+  wincmd w
+  set tagfunc=
+  :%bw!
+  delfunc g:DictTagFunc
+  delfunc SetTagFunc
 
   " Vim9 tests
   let lines =<< trim END
@@ -282,42 +305,11 @@ func Test_tagfunc_callback()
     g:Vim9tagFuncArgs = []
     assert_fails('tag a10', 'E433:')
     assert_equal([60, 'a10', '', {}], g:Vim9tagFuncArgs)
-
-    # Test for using a lambda
-    &tagfunc = (a, b, c) => MytagFunc1(61, a, b, c)
-    new | only
-    g:MytagFunc1_args = []
-    assert_fails('tag a20', 'E433:')
-    assert_equal([61, 'a20', '', {}], g:MytagFunc1_args)
-
-    # Test for using a string(lambda)
-    &tagfunc = '(a, b, c) => MytagFunc1(62, a, b, c)'
-    new | only
-    g:MytagFunc1_args = []
-    assert_fails('tag a20', 'E433:')
-    assert_equal([62, 'a20', '', {}], g:MytagFunc1_args)
-
-    # Test for using a variable with a lambda expression
-    var Fn: func = (a, b, c) => MytagFunc1(63, a, b, c)
-    &tagfunc = Fn
-    new | only
-    g:MytagFunc1_args = []
-    assert_fails('tag a30', 'E433:')
-    assert_equal([63, 'a30', '', {}], g:MytagFunc1_args)
-
-    # Test for using a variable with a lambda expression
-    Fn = (a, b, c) => MytagFunc1(64, a, b, c)
-    &tagfunc = string(Fn)
-    new | only
-    g:MytagFunc1_args = []
-    assert_fails('tag a30', 'E433:')
-    assert_equal([64, 'a30', '', {}], g:MytagFunc1_args)
   END
   " call CheckScriptSuccess(lines)
 
   " cleanup
   delfunc MytagFunc1
-  delfunc MytagFunc2
   set tagfunc&
   %bw!
 endfunc
diff --git a/src/nvim/testdir/vim9.vim b/src/nvim/testdir/vim9.vim
new file mode 100644
index 0000000000..db74ce3b11
--- /dev/null
+++ b/src/nvim/testdir/vim9.vim
@@ -0,0 +1,80 @@
+
+" Use a different file name for each run.
+let s:sequence = 1
+
+" Check that "lines" inside a legacy function has no error.
+func CheckLegacySuccess(lines)
+  let cwd = getcwd()
+  let fname = 'XlegacySuccess' .. s:sequence
+  let s:sequence += 1
+  call writefile(['func Func()'] + a:lines + ['endfunc'], fname)
+  try
+    exe 'so ' .. fname
+    call Func()
+  finally
+    delfunc! Func
+    call chdir(cwd)
+    call delete(fname)
+  endtry
+endfunc
+
+" Check that "lines" inside a legacy function results in the expected error
+func CheckLegacyFailure(lines, error)
+  let cwd = getcwd()
+  let fname = 'XlegacyFails' .. s:sequence
+  let s:sequence += 1
+  call writefile(['func Func()'] + a:lines + ['endfunc', 'call Func()'], fname)
+  try
+    call assert_fails('so ' .. fname, a:error)
+  finally
+    delfunc! Func
+    call chdir(cwd)
+    call delete(fname)
+  endtry
+endfunc
+
+" Execute "lines" in a legacy function, translated as in
+" CheckLegacyAndVim9Success()
+func CheckTransLegacySuccess(lines)
+  let legacylines = a:lines->deepcopy()->map({_, v ->
+                              \ v->substitute('\<VAR\>', 'let', 'g')
+                              \  ->substitute('\<LET\>', 'let', 'g')
+                              \  ->substitute('\<LSTART\>', '{', 'g')
+                              \  ->substitute('\<LMIDDLE\>', '->', 'g')
+                              \  ->substitute('\<LEND\>', '}', 'g')
+                              \  ->substitute('\<TRUE\>', '1', 'g')
+                              \  ->substitute('\<FALSE\>', '0', 'g')
+                              \  ->substitute('#"', ' "', 'g')
+                              \ })
+  call CheckLegacySuccess(legacylines)
+endfunc
+
+" Execute "lines" in a legacy function
+" Use 'VAR' for a declaration.
+" Use 'LET' for an assignment
+" Use ' #"' for a comment
+" Use LSTART arg LMIDDLE expr LEND for lambda
+" Use 'TRUE' for 1
+" Use 'FALSE' for 0
+func CheckLegacyAndVim9Success(lines)
+  call CheckTransLegacySuccess(a:lines)
+endfunc
+
+" Execute "lines" in a legacy function
+" Use 'VAR' for a declaration.
+" Use 'LET' for an assignment
+" Use ' #"' for a comment
+func CheckLegacyAndVim9Failure(lines, error)
+  if type(a:error) == type('string')
+    let legacyError = error
+  else
+    let legacyError = error[0]
+  endif
+
+  let legacylines = a:lines->deepcopy()->map({_, v ->
+                              \ v->substitute('\<VAR\>', 'let', 'g')
+                              \  ->substitute('\<LET\>', 'let', 'g')
+                              \  ->substitute('#"', ' "', 'g')
+                              \ })
+  call CheckLegacyFailure(legacylines, legacyError)
+endfunc