Describe the bug

In Vim9 script, we cannot put an inline comment after the opening parenthesis in a function header.

To Reproduce

Run this shell command:

vim -Nu NONE -S <(cat <<'EOF'
    vim9
    def Func(      # this is the function name
        n: number, # this is a number
        s: string  # this is a string
        )
        echo [n, s]
    enddef
    Func(123, 'string')
EOF
)

E125 is raised:

E125: Illegal argument: # this is the function name

Expected behavior

No error is raised.

Environment

• Vim version: 8.2 Included patches: 1-2293
• OS: Ubuntu 16.04.7 LTS
• Terminal: xterm(363)

Additional context

The same code doesn't raise any error when we remove the inline comment after the opening parenthesis.

vim9
def Func(
    n: number, # this is a number
    s: string  # this is a string
    )
    echo [n, s]
enddef
Func(123, 'string')

[123, 'string']

Vim is perfectly able to skip over an inline comment after the opening parenthesis in a function call:

vim9

def Func(n: number, s: string)
    echo [n, s]
enddef

Func(        # some comment
    123,     # some comment
    'string' # some comment
    )

[123, 'string']

All of this is inconsistent.

We can put an inline comment after:

• ( in a function call
• an argument in a function call
• an argument in a function header

But we cannot put an inline comment after ( in a function header.

It would be useful, for example, for a folding marker:

def Func( #{{{1

Otherwise, if we want to fold a function with a long header, and we want to split the latter on multiple lines, we need to do either this:

def ComplexHeaderWithLotsOfArguments(arg1: number, #{{{1
    arg2: string,
    arg3: bool,
    ...

Or this:

ComplexHeaderWithLotsOfArguments #{{{1
def ComplexHeaderWithLotsOfArguments(
    arg1: number,
    arg2: string,
    arg3: bool,
    ...

It's subjective, but I find the first snippet ugly because asymmetric (only the first argument is joined with the function name line), and the second snippet forces us to repeat the function name.

For a real example, see here.