vim-patch:8.1.0888: the a: dict is not immutable as documented (#10819)

Problem:    The a: dict is not immutable as documented.
Solution:   Make the a:dict immutable, add a test. (Ozaki Kiichi, Yasuhiro
            Matsumoto, closes vim/vim#3929)
https://github.com/vim/vim/commit/31b816042fca879b11965ddd75287732563ba698

5 files changed, 202 insertions, 10 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 7e0a6c3329..217b7ce1be 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -4183,7 +4183,7 @@ static int ins_compl_get_exp(pos_T *ini)
                 if (tmp_ptr - ptr >= IOSIZE - len) {
                   tmp_ptr = ptr + IOSIZE - len - 1;
                 }
-                STRNCPY(IObuff + len, ptr, tmp_ptr - ptr);
+                STRLCPY(IObuff + len, ptr, IOSIZE - len);
                 len += (int)(tmp_ptr - ptr);
                 flags |= CONT_S_IPOS;
               }
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 6703d15be0..8f6d6cd55e 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -2353,14 +2353,15 @@ static char_u *get_lval(char_u *const name, typval_T *const rettv,
       }
 
       if (lp->ll_di == NULL) {
-        /* Can't add "v:" variable. */
-        if (lp->ll_dict == &vimvardict) {
+        // Can't add "v:" or "a:" variable.
+        if (lp->ll_dict == &vimvardict
+            || &lp->ll_dict->dv_hashtab == get_funccal_args_ht()) {
           EMSG2(_(e_illvar), name);
           tv_clear(&var1);
           return NULL;
         }
 
-        /* Key does not exist in dict: may need to add it. */
+        // Key does not exist in dict: may need to add it.
         if (*p == '[' || *p == '.' || unlet) {
           if (!quiet) {
             emsgf(_(e_dictkey), key);
@@ -20489,8 +20490,8 @@ static void set_var_const(const char *name, const size_t name_len,
     }
     tv_clear(&v->di_tv);
   } else {  // Add a new variable.
-    // Can't add "v:" variable.
-    if (ht == &vimvarht) {
+    // Can't add "v:" or "a:" variable.
+    if (ht == &vimvarht || ht == get_funccal_args_ht()) {
       emsgf(_(e_illvar), name);
       return;
     }
@@ -22622,7 +22623,7 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars,
     name = v->di_key;
     STRCPY(name, "self");
 #endif
-    v->di_flags = DI_FLAGS_RO + DI_FLAGS_FIX;
+    v->di_flags = DI_FLAGS_RO | DI_FLAGS_FIX;
     tv_dict_add(&fc->l_vars, v);
     v->di_tv.v_type = VAR_DICT;
     v->di_tv.v_lock = 0;
@@ -22638,6 +22639,7 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars,
   init_var_dict(&fc->l_avars, &fc->l_avars_var, VAR_SCOPE);
   add_nr_var(&fc->l_avars, (dictitem_T *)&fc->fixvar[fixvar_idx++], "0",
              (varnumber_T)(argcount - fp->uf_args.ga_len));
+  fc->l_avars.dv_lock = VAR_FIXED;
   // Use "name" to avoid a warning from some compiler that checks the
   // destination size.
   v = (dictitem_T *)&fc->fixvar[fixvar_idx++];
diff --git a/src/nvim/testdir/test_let.vim b/src/nvim/testdir/test_let.vim
index 24c6ef5e01..8a6f1bc320 100644
--- a/src/nvim/testdir/test_let.vim
+++ b/src/nvim/testdir/test_let.vim
@@ -25,3 +25,118 @@ func Test_let()
   let s = "\na                     #1\nb                     #2"
   call assert_equal(s, out)
 endfunc
+
+func s:set_arg1(a) abort
+  let a:a = 1
+endfunction
+
+func s:set_arg2(a) abort
+  let a:b = 1
+endfunction
+
+func s:set_arg3(a) abort
+  let b = a:
+  let b['a'] = 1
+endfunction
+
+func s:set_arg4(a) abort
+  let b = a:
+  let b['a'] = 1
+endfunction
+
+func s:set_arg5(a) abort
+  let b = a:
+  let b['a'][0] = 1
+endfunction
+
+func s:set_arg6(a) abort
+  let a:a[0] = 1
+endfunction
+
+func s:set_arg7(a) abort
+  call extend(a:, {'a': 1})
+endfunction
+
+func s:set_arg8(a) abort
+  call extend(a:, {'b': 1})
+endfunction
+
+func s:set_arg9(a) abort
+  let a:['b'] = 1
+endfunction
+
+func s:set_arg10(a) abort
+  let b = a:
+  call extend(b, {'a': 1})
+endfunction
+
+func s:set_arg11(a) abort
+  let b = a:
+  call extend(b, {'b': 1})
+endfunction
+
+func s:set_arg12(a) abort
+  let b = a:
+  let b['b'] = 1
+endfunction
+
+func Test_let_arg_fail()
+  call assert_fails('call s:set_arg1(1)', 'E46:')
+  call assert_fails('call s:set_arg2(1)', 'E461:')
+  call assert_fails('call s:set_arg3(1)', 'E46:')
+  call assert_fails('call s:set_arg4(1)', 'E46:')
+  call assert_fails('call s:set_arg5(1)', 'E46:')
+  call s:set_arg6([0])
+  call assert_fails('call s:set_arg7(1)', 'E742:')
+  call assert_fails('call s:set_arg8(1)', 'E742:')
+  call assert_fails('call s:set_arg9(1)', 'E461:')
+  call assert_fails('call s:set_arg10(1)', 'E742:')
+  call assert_fails('call s:set_arg11(1)', 'E742:')
+  call assert_fails('call s:set_arg12(1)', 'E461:')
+endfunction
+
+func s:set_varg1(...) abort
+  let a:000 = []
+endfunction
+
+func s:set_varg2(...) abort
+  let a:000[0] = 1
+endfunction
+
+func s:set_varg3(...) abort
+  let a:000 += [1]
+endfunction
+
+func s:set_varg4(...) abort
+  call add(a:000, 1)
+endfunction
+
+func s:set_varg5(...) abort
+  let a:000[0][0] = 1
+endfunction
+
+func s:set_varg6(...) abort
+  let b = a:000
+  let b[0] = 1
+endfunction
+
+func s:set_varg7(...) abort
+  let b = a:000
+  call add(b, 1)
+endfunction
+
+func s:set_varg8(...) abort
+  let b = a:000
+  let b[0][0] = 1
+endfunction
+
+func Test_let_varg_fail()
+  call assert_fails('call s:set_varg1(1)', 'E46:')
+  call assert_fails('call s:set_varg2(1)', 'E742:')
+  call assert_fails('call s:set_varg3(1)', 'E46:')
+  call assert_fails('call s:set_varg4(1)', 'E742:')
+  call s:set_varg5([0])
+  call assert_fails('call s:set_varg6(1)', 'E742:')
+  call assert_fails('call s:set_varg7(1)', 'E742:')
+  call s:set_varg8([0])
+endfunction
diff --git a/src/nvim/testdir/test_listdict.vim b/src/nvim/testdir/test_listdict.vim
index 9e060cdff6..bea62cb0ad 100644
--- a/src/nvim/testdir/test_listdict.vim
+++ b/src/nvim/testdir/test_listdict.vim
@@ -500,17 +500,20 @@ endfunc
 
 " No remove() of write-protected scope-level variable
 func! Tfunc(this_is_a_long_parameter_name)
-  call assert_fails("call remove(a:, 'this_is_a_long_parameter_name')", 'E795')
+  call assert_fails("call remove(a:, 'this_is_a_long_parameter_name')", 'E742')
 endfun
 func Test_dict_scope_var_remove()
   call Tfunc('testval')
 endfunc
 
 " No extend() of write-protected scope-level variable
+func Test_dict_scope_var_extend()
+  call assert_fails("call extend(a:, {'this_is_a_long_parameter_name': 1234})", 'E742')
+endfunc
 func! Tfunc(this_is_a_long_parameter_name)
   call assert_fails("call extend(a:, {'this_is_a_long_parameter_name': 1234})", 'E742')
 endfunc
-func Test_dict_scope_var_extend()
+func Test_dict_scope_var_extend_overwrite()
   call Tfunc('testval')
 endfunc
 
@@ -699,3 +702,75 @@ func Test_listdict_extend()
   call assert_fails("call extend([1, 2], 1)", 'E712:')
   call assert_fails("call extend([1, 2], {})", 'E712:')
 endfunc
+
+func s:check_scope_dict(x, fixed)
+  func s:gen_cmd(cmd, x)
+    return substitute(a:cmd, '\<x\ze:', a:x, 'g')
+  endfunc
+
+  let cmd = s:gen_cmd('let x:foo = 1', a:x)
+  if a:fixed
+    call assert_fails(cmd, 'E461')
+  else
+    exe cmd
+    exe s:gen_cmd('call assert_equal(1, x:foo)', a:x)
+  endif
+
+  let cmd = s:gen_cmd('let x:["bar"] = 2', a:x)
+  if a:fixed
+    call assert_fails(cmd, 'E461')
+  else
+    exe cmd
+    exe s:gen_cmd('call assert_equal(2, x:bar)', a:x)
+  endif
+
+  let cmd = s:gen_cmd('call extend(x:, {"baz": 3})', a:x)
+  if a:fixed
+    call assert_fails(cmd, 'E742')
+  else
+    exe cmd
+    exe s:gen_cmd('call assert_equal(3, x:baz)', a:x)
+  endif
+
+  if a:fixed
+    if a:x ==# 'a'
+      call assert_fails('unlet a:x', 'E795')
+      call assert_fails('call remove(a:, "x")', 'E742')
+    elseif a:x ==# 'v'
+      call assert_fails('unlet v:count', 'E795')
+      call assert_fails('call remove(v:, "count")', 'E742')
+    endif
+  else
+    exe s:gen_cmd('unlet x:foo', a:x)
+    exe s:gen_cmd('unlet x:bar', a:x)
+    exe s:gen_cmd('call remove(x:, "baz")', a:x)
+  endif
+
+  delfunc s:gen_cmd
+endfunc
+
+func Test_scope_dict()
+  " Test for g:
+  call s:check_scope_dict('g', v:false)
+
+  " Test for s:
+  call s:check_scope_dict('s', v:false)
+
+  " Test for l:
+  call s:check_scope_dict('l', v:false)
+
+  " Test for a:
+  call s:check_scope_dict('a', v:true)
+
+  " Test for b:
+  call s:check_scope_dict('b', v:false)
+
+  " Test for w:
+  call s:check_scope_dict('w', v:false)
+
+  " Test for t:
+  call s:check_scope_dict('t', v:false)
+
+  " Test for v:
+  call s:check_scope_dict('v', v:true)
+endfunc
diff --git a/test/functional/legacy/055_list_and_dict_types_spec.lua b/test/functional/legacy/055_list_and_dict_types_spec.lua
index dcbd8b7dff..91ba8bb106 100644
--- a/test/functional/legacy/055_list_and_dict_types_spec.lua
+++ b/test/functional/legacy/055_list_and_dict_types_spec.lua
@@ -666,7 +666,7 @@ describe('list and dictionary types', function()
       Vim(put):E741: 
       {'a': 99, 'b': 100}
       No remove() of write-protected scope-level variable:
-      Vim(put):E795: 
+      Vim(put):E742: 
       No extend() of write-protected scope-level variable:
       Vim(put):E742: 
       No :unlet of variable in locked scope: