[vim/vim] Vim script can overwrite builtin function (#8302)

[mattn]

let g:.foo = 1 let 1 to global variable foo. And this way can overwrite builtin functions.

Describe the bug

let g:.foo = 1 let 1 to global variable foo. And this way can overwrite builtin functions.

To Reproduce

let g:.trim = {x-> ' '..x..' '}
echo '['..trim(' foo ')..']'

This get [ foo ].

Expected behavior

[foo]

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[mattn]

This is also wrong.

let g:['trim'] = {x-> ' '..x..' '}
echo '['..trim(' foo ')..']'

—

[mattn]

This should fix the issue.

diff --git a/src/userfunc.c b/src/userfunc.c
index f5d906302..e463d73cd 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -1436,6 +1436,12 @@ deref_func_name(
 
     cc = name[*lenp];
     name[*lenp] = NUL;
+
+    if (builtin_function(name, -1)) {
+	name[*lenp] = cc;
+	return name;
+    }
+
     v = find_var(name, &ht, no_autoload);
     name[*lenp] = cc;
     if (v != NULL)

[Bram Moolenaar]

Besides that check, it should not even be possible to add that variable in g: or s:

[Bram Moolenaar]

Closed #8302 via 3d9c4ee.

[Bram Moolenaar]

Actually, we cannot use builtin_function(), because in lambda's using a lower case name is possible.

[mattn]

@brammool Thank you. But still wrong.

call extend(g:, #{foo: { -> 'foo' }})

[mattn]

@brammool another degrade with this fix.

let s:trim = {x-> ' '..x..' '}

This makes error E704.

[mattn]

I prefer checking for the referencing to the symbol, Not checking for letting variables.

[Bram Moolenaar]

> @brammool another degrade with this fix.
>
> ```
> let s:trim = {x-> ' '..x..' '}
> ```
> This makes error E704.

That looks correct, it should use "s:Trim".

Did this work OK before? Then we might have to check this only in Vim9
script, where script-local variables can be used without s: prefix.

Actually, I cannot reproduce the error in legacy script. And I do get
the error in Vim 9 script, looks OK to me. Did you have some context to
trigger the error?

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[mattn]

:let s:.foo = { -> 'foo' }
:echo s:foo()

Vim(let):E704: Funcref variable name must start with a capital: foo

[mattn]

:let g:s = s:
function! CallS(name)
  return s:[a:name]()
endfunction
:let g:s.foo = { -> 'foo' }
:echo CallS('foo')

[K.Takata]

:help E704 says:

<							*E704* *E705* *E707*
A Funcref variable must start with a capital, "s:", "w:", "t:" or "b:".  You
can use "g:" but the following name must still start with a capital.  You
cannot have both a Funcref variable and a function with the same name.

so, I think "s:" should be able to be followed by a lower letter.

And, I think that "s:" in this part should be changed to "l:"
3d9c4ee#diff-3452ba3ede8c12266b78c613c3171f5a19f42244731749b3bc60072cdf45be46R2687-R2688
as follows:

  call assert_fails('let l:["trim"] = {x -> " " .. x}', 'E704:')
  call assert_fails('let l:.trim = {x -> " " .. x}', 'E704:')

[Bram Moolenaar]

> ```

> :let s:.foo = { -> 'foo' }
> :echo s:foo()
> ```
> >Vim(let):E704: Funcref variable name must start with a capital: foo

Looks like I missed the dot.

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[Bram Moolenaar]

> `:help E704` says:
> ```
> < *E704* *E705* *E707*
> A Funcref variable must start with a capital, "s:", "w:", "t:" or "b:". You
> can use "g:" but the following name must still start with a capital. You
> cannot have both a Funcref variable and a function with the same name.
> ```
> so, I think "s:" should be able to be followed by a lower letter.

In legacy script, yes. But in Vim9 script a script-local variable can
be accessed without s:, so there we won't allow it.

But in Vim9 script assigning to s:.trim won't work, it tries to parse
".trim" as a type. Same for s:['trim'].

> And, I think that "s:" in this part should be changed to "l:"

> https://github.com/vim/vim/commit/3d9c4eefe656ee8bf58c0496a48bd56bac180056#diff-3452ba3ede8c12266b78c613c3171f5a19f42244731749b3bc60072cdf45be46R2687-R2688
> as follows:
> ```vim

> call assert_fails('let l:["trim"] = {x -> " " .. x}', 'E704:')
> call assert_fails('let l:.trim = {x -> " " .. x}', 'E704:')

> ```

Except that this doesn't fail yet.

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[Bram Moolenaar]

> ```

> :let g:s = s:
> function! CallS(name)
> return s:[a:name]()
> endfunction
> :let g:s.foo = { -> 'foo' }
> :echo CallS('foo')

> ```

After the recent changes this also works correctly. For legacy script
this is allowed, s:foo can be a function. For Vim9 script it gives the
E704 error.

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