Fix parsing of braced expressions followed by a method

[jjvn84]

This is an attempt at solving issue #3945 when parsing attributes.
I added code that checks if there is a TokenTree::Group followed by a dot. If it finds it, it parses the whole attribute as an expression. It stops if it finds a comma, signaling the end of the attribute.
I added the example in the original issue to the "complex_kitchen_sink" test, and everything passed.

[ealmloff]

Thanks for working on this! Unfortunately, I think the issue is slightly broader than just method calls. If we find anything except a comma after a braced expression we should try to parse it as a normal expression. The check you added fixes this expression width: {"100%"}.to_string(),, but this expression still fails width: {|| "100%"}(),

[jjvn84]

@ealmloff These new changes should fix the issue. Could you please check again if there is another case I'm missing?
And thank you for the review.

[ealmloff]

I found a few more cases that are broken. This test fails on the PR, but passes on the main branch:

#[test]
fn invalid_braced_expression() {
    let item = quote::quote! {
        // Partial expressions in braces rsx should be allowed and output as-is
        // for autocomplete
        {invalid.}
        div {}
        {invalid.}
        // Comments should be ignored
        div {}
        {invalid.}
        "hello world"
        {invalid.}
        if true {}
    };

    let cb: CallBody = syn::parse2(item).unwrap();
    println!("{}", cb.to_token_stream());
}

These all pass now which is great!

#[test]
fn expressions_after_braced() {
    let item = quote::quote! {
        div {
            width: {100} - 50,
            width: {"100%"}.to_string(),
            width: {|| "100%"}(),
        }
    };

    let cb: CallBody = syn::parse2(item).unwrap();
    println!("{}", cb.to_token_stream());
}

I think these two cases should cover everything?

1. Braced expression followed by a symbol other than a brace (-, *, (, etc) should be parsed as a syn::Expr
2. Braced expression followed by a term which is either another braced expression, a raw ident or a literal should be parsed as a partial expression

[jjvn84]

This new change fixes the missing cases. Please let me know if there are more test cases I should include.

[ealmloff]

Looks great, thanks for fixing this! Confirmed autocomplete still works with the base raw brace expressions