Allow assigning a Funcref to autoload variable

[thinca]

In Vim, defining a User function that starts with a lowercase letter is not allowed because it could overwrite a built-in function.
However, defining an autoload function that starts with a lowercase letter is permitted because it does not cause the above problem.

For the same reason, Vim does not allow Funcref to be assigned to a global variable whose name begins with a lowercase letter.
This also applies to the autoload variable; let foo#tr = function('tr') is not allowed and must be let Foo#tr = function('tr').
I see no need for this restriction. let foo#tr = function('tr') should be allowed.

[codecov]

Codecov Report

Merging #11031 (9e95088) into master (be807d5) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #11031      +/-   ##
==========================================
- Coverage   82.47%   82.39%   -0.08%     
==========================================
  Files         152      152              
  Lines      177682   177683       +1     
  Branches    40341    40341              
==========================================
- Hits       146539   146410     -129     
- Misses      18948    19049     +101     
- Partials    12195    12224      +29     

Flag	Coverage Δ
huge-clang-none	82.68% <100.00%> (-0.01%)	⬇️
huge-gcc-none	?
huge-gcc-testgui	52.93% <100.00%> (-0.01%)	⬇️
huge-gcc-unittests	0.29% <0.00%> (ø)
linux	82.39% <100.00%> (-0.08%)	⬇️

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Impacted Files	Coverage Δ
src/evalvars.c	91.30% <100.00%> (+<0.01%)	⬆️
src/main.c	81.18% <0.00%> (-3.53%)	⬇️
src/clipboard.c	71.68% <0.00%> (-1.78%)	⬇️
src/message.c	78.48% <0.00%> (-1.15%)	⬇️
src/popupmenu.c	78.87% <0.00%> (-0.81%)	⬇️
src/beval.c	63.30% <0.00%> (-0.72%)	⬇️
src/if_xcmdsrv.c	76.70% <0.00%> (-0.71%)	⬇️
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src/ex_cmds2.c	81.21% <0.00%> (-0.49%)	⬇️
src/mouse.c	78.74% <0.00%> (-0.32%)	⬇️
... and 16 more

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[brammool]

In Vim, defining a User function that starts with a lowercase letter is not allowed because it could overwrite a built-in function. However, defining an autoload function that starts with a lowercase letter is permitted because it does not cause the above problem. For the same reason, Vim does not allow Funcref to be assigned to a global variable whose name begins with a lowercase letter. This also applies to the autoload variable; `let foo#tr = function('tr')` is not allowed and must be `let Foo#tr = function('tr')`. I see no need for this restriction. `let foo#tr = function('tr')` should be allowed.

Well, not when used with the "name#" prefix. But inside the autoload script it can be used without the prefix, which does cause shadowing a builtin function. Thus when you, like in the test, do: let foo#tr = function('tr') Then in the "autoload/foo.vim" script calling tr() does have the problem. At least in Vim9 script, where the "s:" prefix is not used. Right?

…

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[thinca]

In legacy Vim script, name# prefix is always necessary.

" autoload/name.vim

echo foo  " This is g:foo, not name#foo
echo s:foo  " This is s:foo, not name#foo

function name#func()
  echo foo  " This is l:foo, not name#foo
endfunction

In Vim9 script, as you say, exported variable is an autoload variable and can be access without prefix.
But there is no problem.

vim9script
# autoload/name.vim

# This occurs an error "E704: Funcref variable name must start with a capital: tr"
export var tr = () => 'tr'

vim9script
# autoload/name.vim

# This variable can rewrite by `let name#tr = { -> 'tr' }` from outside of script with this patch.
export var tr = ''

def Foo()
  # But this `tr()` is always built-in function.  Vim9 script is compiled first.
  echo tr('foo', 'o', 'a')
enddef

[brammool]

In legacy Vim script, `name#` prefix is always necessary. ```vim " autoload/name.vim echo foo " This is g:foo, not name#foo echo s:foo " This is s:foo, not name#foo function name#func() echo foo " This is l:foo, not name#foo endfunction ```

OK, and it actually checks if the name of the script starts with a capital, not the variable itself, so that is pointless.

In Vim9 script, as you say, exported variable is an autoload variable and can be access without prefix. But there is no problem. ```vim vim9script # autoload/name.vim # This occurs an error "E704: Funcref variable name must start with a capital: tr" export var tr = () => 'tr' ``` ```vim vim9script # autoload/name.vim # This variable can rewrite by `let name#tr = { -> 'tr' }` from outside of script with this patch. export var tr = '' def Foo() # But this `tr()` is always built-in function. Vim9 script is compiled first. echo tr('foo', 'o', 'a') enddef ```

Hmm, I cannot think of a way to go around this, assigning a variable outside of a Vim9 script can be expected to always fail.

…

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