linux-kernel - Re: [PATCH 7/7] rust: init: add support for arbitrary paths in init macros

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Date:   Wed, 28 Jun 2023 18:13:59 +0100
From:   Gary Guo <gary@...yguo.net>
To:     Benno Lossin <benno.lossin@...ton.me>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Andreas Hindborg <nmi@...aspace.dk>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Asahi Lina <lina@...hilina.net>
Subject: Re: [PATCH 7/7] rust: init: add support for arbitrary paths in init
 macros

On Wed, 28 Jun 2023 11:26:54 +0000
Benno Lossin <benno.lossin@...ton.me> wrote:

> On 25.06.23 23:01, Gary Guo wrote:
> > On Sat, 24 Jun 2023 09:25:39 +0000
> > Benno Lossin <benno.lossin@...ton.me> wrote:
> >   
> >> Previously only `ident` and generic types were supported in the
> >> `{try_}{pin_}init!` macros. This patch allows arbitrary path fragments,
> >> so for example `Foo::Bar` but also very complex paths such as
> >> `<Foo as Baz>::Bar::<0, i32>`.
> >>
> >> Internally this is accomplished by using `path` fragments. Due to some
> >> peculiar declarative macro limitations, we have to "forget" certain
> >> additional parsing information in the token trees. This is achieved by
> >> the new `retokenize` proc macro. It does not modify the input, but just
> >> strips this information. For example, if a declarative macro takes
> >> `$t:path` as its input, it cannot sensibly propagate this to a macro that
> >> takes `$($p:tt)*` as its input, since the `$t` token will only be
> >> considered one `tt` token for the second macro. If we first pipe the
> >> tokens through `retokenize`, then it parses as expected.  
> > 
> > I think this "retokenize" macro could also be functionally replaced by
> > `paste`. Would you mind to apply my paste patch (referenced in a
> > previous email) and see if it works?  
> 
> I tried your patch and it seems to work. I also executed all of the test
> in the userspace library and they passed.
> The `paste!` code also looks good to me. One thing that I thought was this:
> do we want to accept `paste!( [<= foo bar>])`? Because the `<` token has
> spacing `Joint`, maybe add a check for that? No idea if that would be a problem.
> 

I don't think checking that is necessary, since that wouldn't be
valid Rust anyway?

Best,
Gary