rust: move pin-init API into its own directory

In preparation of splitting off the pin-init crate from the kernel
crate, move all pin-init API code (including proc-macros) into
`rust/pin-init`.

Moved modules have their import path adjusted via the `#[path = "..."]`
attribute. This allows the files to still be imported in the kernel
crate even though the files are in different directories.

Code that is moved out of files (but the file itself stays where it is)
is imported via the `include!` macro. This also allows the code to be
moved while still being part of the kernel crate.

Note that this commit moves the generics parsing code out of the GPL-2.0
file `rust/macros/helpers.rs` into the Apache-2.0 OR MIT file
`rust/pin_init/internal/src/helpers.rs`. I am the sole author of that
code and it already is available with that license at [1].
The same is true for the entry-points of the proc-macros `pin_data`,
`pinned_drop` and `derive_zeroable` in `rust/macros/lib.rs` that are
moved to `rust/pin_data/internal/src/lib.rs`. Although there are some
smaller patches that fix the doctests.

Link: https://github.com/Rust-for-Linux/pinned-init [1]
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Tested-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250308110339.2997091-3-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 2 insertions, 146 deletions

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index 3e04f8ecfc74..141d8476c197 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -70,152 +70,6 @@ pub(crate) fn expect_end(it: &mut token_stream::IntoIter) {
     }
 }
 
-/// Parsed generics.
-///
-/// See the field documentation for an explanation what each of the fields represents.
-///
-/// # Examples
-///
-/// ```rust,ignore
-/// # let input = todo!();
-/// let (Generics { decl_generics, impl_generics, ty_generics }, rest) = parse_generics(input);
-/// quote! {
-///     struct Foo<$($decl_generics)*> {
-///         // ...
-///     }
-///
-///     impl<$impl_generics> Foo<$ty_generics> {
-///         fn foo() {
-///             // ...
-///         }
-///     }
-/// }
-/// ```
-pub(crate) struct Generics {
-    /// The generics with bounds and default values (e.g. `T: Clone, const N: usize = 0`).
-    ///
-    /// Use this on type definitions e.g. `struct Foo<$decl_generics> ...` (or `union`/`enum`).
-    pub(crate) decl_generics: Vec<TokenTree>,
-    /// The generics with bounds (e.g. `T: Clone, const N: usize`).
-    ///
-    /// Use this on `impl` blocks e.g. `impl<$impl_generics> Trait for ...`.
-    pub(crate) impl_generics: Vec<TokenTree>,
-    /// The generics without bounds and without default values (e.g. `T, N`).
-    ///
-    /// Use this when you use the type that is declared with these generics e.g.
-    /// `Foo<$ty_generics>`.
-    pub(crate) ty_generics: Vec<TokenTree>,
-}
-
-/// Parses the given `TokenStream` into `Generics` and the rest.
-///
-/// The generics are not present in the rest, but a where clause might remain.
-pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
-    // The generics with bounds and default values.
-    let mut decl_generics = vec![];
-    // `impl_generics`, the declared generics with their bounds.
-    let mut impl_generics = vec![];
-    // Only the names of the generics, without any bounds.
-    let mut ty_generics = vec![];
-    // Tokens not related to the generics e.g. the `where` token and definition.
-    let mut rest = vec![];
-    // The current level of `<`.
-    let mut nesting = 0;
-    let mut toks = input.into_iter();
-    // If we are at the beginning of a generic parameter.
-    let mut at_start = true;
-    let mut skip_until_comma = false;
-    while let Some(tt) = toks.next() {
-        if nesting == 1 && matches!(&tt, TokenTree::Punct(p) if p.as_char() == '>') {
-            // Found the end of the generics.
-            break;
-        } else if nesting >= 1 {
-            decl_generics.push(tt.clone());
-        }
-        match tt.clone() {
-            TokenTree::Punct(p) if p.as_char() == '<' => {
-                if nesting >= 1 && !skip_until_comma {
-                    // This is inside of the generics and part of some bound.
-                    impl_generics.push(tt);
-                }
-                nesting += 1;
-            }
-            TokenTree::Punct(p) if p.as_char() == '>' => {
-                // This is a parsing error, so we just end it here.
-                if nesting == 0 {
-                    break;
-                } else {
-                    nesting -= 1;
-                    if nesting >= 1 && !skip_until_comma {
-                        // We are still inside of the generics and part of some bound.
-                        impl_generics.push(tt);
-                    }
-                }
-            }
-            TokenTree::Punct(p) if skip_until_comma && p.as_char() == ',' => {
-                if nesting == 1 {
-                    impl_generics.push(tt.clone());
-                    impl_generics.push(tt);
-                    skip_until_comma = false;
-                }
-            }
-            _ if !skip_until_comma => {
-                match nesting {
-                    // If we haven't entered the generics yet, we still want to keep these tokens.
-                    0 => rest.push(tt),
-                    1 => {
-                        // Here depending on the token, it might be a generic variable name.
-                        match tt.clone() {
-                            TokenTree::Ident(i) if at_start && i.to_string() == "const" => {
-                                let Some(name) = toks.next() else {
-                                    // Parsing error.
-                                    break;
-                                };
-                                impl_generics.push(tt);
-                                impl_generics.push(name.clone());
-                                ty_generics.push(name.clone());
-                                decl_generics.push(name);
-                                at_start = false;
-                            }
-                            TokenTree::Ident(_) if at_start => {
-                                impl_generics.push(tt.clone());
-                                ty_generics.push(tt);
-                                at_start = false;
-                            }
-                            TokenTree::Punct(p) if p.as_char() == ',' => {
-                                impl_generics.push(tt.clone());
-                                ty_generics.push(tt);
-                                at_start = true;
-                            }
-                            // Lifetimes begin with `'`.
-                            TokenTree::Punct(p) if p.as_char() == '\'' && at_start => {
-                                impl_generics.push(tt.clone());
-                                ty_generics.push(tt);
-                            }
-                            // Generics can have default values, we skip these.
-                            TokenTree::Punct(p) if p.as_char() == '=' => {
-                                skip_until_comma = true;
-                            }
-                            _ => impl_generics.push(tt),
-                        }
-                    }
-                    _ => impl_generics.push(tt),
-                }
-            }
-            _ => {}
-        }
-    }
-    rest.extend(toks);
-    (
-        Generics {
-            impl_generics,
-            decl_generics,
-            ty_generics,
-        },
-        rest,
-    )
-}
-
 /// Given a function declaration, finds the name of the function.
 pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
     let mut input = input.into_iter();
@@ -232,3 +86,5 @@ pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
     }
     None
 }
+
+include!("../pin-init/internal/src/helpers.rs");