Problem with parsing Vimscript boolean variable to if_lua interface (`v:true` becomes `1` instead of `true`, `v:false` becomes 0 instead of `false`)

[brianhuster]

Steps to reproduce

Test 1

1. A Vim >= 8.2 with has('lua') returns 1
2. :let g:t1 = v:false
3. :lua print(vim.g.t1) => returns 0 instead of false

Test 2
4. :lua vim.g.t2 = false
5. :lua print(vim.g.t2) => returns 0 instead of false, even though it was declared as false

Expected behaviour

The line 3 should returns false instead of 0
The line 5 should returns false instead of 0

Given that luaeval successfully convert Lua boolean to Vimscript boolean, I don't understand why vim.eval can't do the same.

Also, this problem doesn't happen in Neovim

Version of Vim

VIM - Vi IMproved 9.1 (2024 Jan 02, compiled Sep 25 2024 10:13:04) Included patches: 1-16, 647, 678, 697

Environment

Kubuntu 24.04.1

Logs and stack traces

No response

[chrisbra]

That seems like an implementation detail (and a seems just like a cosmetic issue). For a long time, Vimscript did not have true boolean types so used 1 and 0 and you can still observe it sometimes. Does it work differently when using Vim9 script?

Given that luaeval successfully convert Lua boolean to Vimscript boolean, I don't understand why vim.eval can't do the same

I think the lua interface predates the creation of boolean vimscript values. However having said that, a PR to fix this would certainly be appreciated.

[brianhuster]

Does it work differently when using Vim9 script?

Yes, if I declare a global variable in Vim9script

vim9script
g:some_bool = v:false

Then I source the Vim file and call the variable in Lua

:so %
:lua print(vim.g.some_bool)`

It still returns 0 instead of false

PR to fix this would certainly be appreciated.

Thank you, I would love to, I will relearn C and research the file if_lua.c next weekend

[chrisbra]

Thank you, I would love to, I will relearn C and research the file if_lua.c next weekend

That is great that you are offering help here. But just as a quick warning: those interface definitions are typically not the easiest to start working with, if you don't have much C experience yet.

[zeertzjq]

I haven't checked if it works, but it may be a simple one-line change:

diff --git a/src/if_lua.c b/src/if_lua.c
index 4d19c3ef5..d01b9f96a 100644
--- a/src/if_lua.c
+++ b/src/if_lua.c
@@ -595,7 +595,7 @@ luaV_pushtypval(lua_State *L, typval_T *tv)
 	case VAR_BOOL:
 	case VAR_SPECIAL:
 	    if (tv->vval.v_number <= VVAL_TRUE)
-		lua_pushinteger(L, (int) tv->vval.v_number);
+		lua_pushboolean(L, (int) tv->vval.v_number);
 	    else
 		lua_pushnil(L);
 	    break;

[chrisbra]

have you tested the patch?

[brianhuster]

Do you mean Vim 9.1.847? Sorry, the problem still persists with if_lua interface, lua print(vim.eval("v:false")) still output 0 instead of false

Btw, the problem doesn't exist in if_python interface, python3 print(vim.eval("v:false")) outputs False instead of 0