rust: pin-init: add syn dependency and remove proc-macro[2] and quote workarounds

`syn` makes parsing Rust from proc-macros a lot simpler. `pin-init` has
not used `syn` up until now, because the we did not support it. That
changed in commit 54e3eae ("Merge patch series "`syn` support""),
so we can finally utilize the added ergonomics of parsing proc-macro
input with `syn`.

Previously we only had the `proc-macro` library available, whereas the
user-space version also used `proc-macro2` and `quote`. Now both are
available, so remove the workarounds.

Due to these changes, clippy emits warnings about unnecessary
`.to_string()` as `proc-macro2` provides an additional `PartialEq` impl
on `Ident`, so the warnings are fixed.

[ Adjusted wording from upstream version and added build system changes
  for the kernel - Benno ]

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

rust/Makefile

@@ -212,9 +212,10 @@ rustdoc-ffi: $(src)/ffi.rs rustdoc-core FORCE
 
 rustdoc-pin_init_internal: private rustdoc_host = yes
 rustdoc-pin_init_internal: private rustc_target_flags = --cfg kernel \
-    --extern proc_macro --crate-type proc-macro
+    --extern proc_macro --extern proc_macro2 --extern quote --extern syn \
+    --crate-type proc-macro
 rustdoc-pin_init_internal: $(src)/pin-init/internal/src/lib.rs \
-    rustdoc-clean FORCE
+    rustdoc-clean rustdoc-proc_macro2 rustdoc-quote rustdoc-syn FORCE
 	+$(call if_changed,rustdoc)
 
 rustdoc-pin_init: private rustdoc_host = yes
@@ -273,9 +274,10 @@ rusttestlib-macros: $(src)/macros/lib.rs \
 	+$(call if_changed,rustc_test_library)
 
 rusttestlib-pin_init_internal: private rustc_target_flags = --cfg kernel \
-    --extern proc_macro
+    --extern proc_macro --extern proc_macro2 --extern quote --extern syn
 rusttestlib-pin_init_internal: private rustc_test_library_proc = yes
-rusttestlib-pin_init_internal: $(src)/pin-init/internal/src/lib.rs FORCE
+rusttestlib-pin_init_internal: $(src)/pin-init/internal/src/lib.rs \
+    rusttestlib-proc_macro2 rusttestlib-quote rusttestlib-syn FORCE
 	+$(call if_changed,rustc_test_library)
 
 rusttestlib-pin_init: private rustc_target_flags = --extern pin_init_internal \
@@ -547,8 +549,10 @@ $(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/libproc_macro2.rlib \
     $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE
 	+$(call if_changed_dep,rustc_procmacro)
 
-$(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel
-$(obj)/$(libpin_init_internal_name): $(src)/pin-init/internal/src/lib.rs FORCE
+$(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel \
+    --extern proc_macro2 --extern quote --extern syn
+$(obj)/$(libpin_init_internal_name): $(src)/pin-init/internal/src/lib.rs \
+    $(obj)/libproc_macro2.rlib $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE
 	+$(call if_changed_dep,rustc_procmacro)
 
 quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L $@

rust/pin-init/internal/src/helpers.rs

@@ -1,9 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-#[cfg(not(kernel))]
-use proc_macro2 as proc_macro;
-
-use proc_macro::{TokenStream, TokenTree};
+use proc_macro2::{TokenStream, TokenTree};
 
 /// Parsed generics.
 ///
@@ -101,7 +98,7 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
                     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" => {
+                            TokenTree::Ident(i) if at_start && i == "const" => {
                                 let Some(name) = toks.next() else {
                                     // Parsing error.
                                     break;

rust/pin-init/internal/src/lib.rs

@@ -7,27 +7,11 @@
 //! `pin-init` proc macros.
 
 #![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
-// Allow `.into()` to convert
-// - `proc_macro2::TokenStream` into `proc_macro::TokenStream` in the user-space version.
-// - `proc_macro::TokenStream` into `proc_macro::TokenStream` in the kernel version.
-//   Clippy warns on this conversion, but it's required by the user-space version.
-//
-// Remove once we have `proc_macro2` in the kernel.
-#![allow(clippy::useless_conversion)]
 // Documentation is done in the pin-init crate instead.
 #![allow(missing_docs)]
 
 use proc_macro::TokenStream;
 
-#[cfg(kernel)]
-#[path = "../../../macros/quote.rs"]
-#[macro_use]
-#[cfg_attr(not(kernel), rustfmt::skip)]
-mod quote;
-#[cfg(not(kernel))]
-#[macro_use]
-extern crate quote;
-
 mod helpers;
 mod pin_data;
 mod pinned_drop;

rust/pin-init/internal/src/pin_data.rs

@@ -1,10 +1,8 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-#[cfg(not(kernel))]
-use proc_macro2 as proc_macro;
-
 use crate::helpers::{parse_generics, Generics};
-use proc_macro::{Group, Punct, Spacing, TokenStream, TokenTree};
+use proc_macro2::{Group, Punct, Spacing, TokenStream, TokenTree};
+use quote::quote;
 
 pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
     // This proc-macro only does some pre-parsing and then delegates the actual parsing to
@@ -28,7 +26,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
     // The name of the struct with ty_generics.
     let struct_name = rest
         .iter()
-        .skip_while(|tt| !matches!(tt, TokenTree::Ident(i) if i.to_string() == "struct"))
+        .skip_while(|tt| !matches!(tt, TokenTree::Ident(i) if i == "struct"))
         .nth(1)
         .and_then(|tt| match tt {
             TokenTree::Ident(_) => {
@@ -65,7 +63,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
         .into_iter()
         .flat_map(|tt| {
             // We ignore top level `struct` tokens, since they would emit a compile error.
-            if matches!(&tt, TokenTree::Ident(i) if i.to_string() == "struct") {
+            if matches!(&tt, TokenTree::Ident(i) if i == "struct") {
                 vec![tt]
             } else {
                 replace_self_and_deny_type_defs(&struct_name, tt, &mut errs)
@@ -98,11 +96,7 @@ fn replace_self_and_deny_type_defs(
 ) -> Vec<TokenTree> {
     match tt {
         TokenTree::Ident(ref i)
-            if i.to_string() == "enum"
-                || i.to_string() == "trait"
-                || i.to_string() == "struct"
-                || i.to_string() == "union"
-                || i.to_string() == "impl" =>
+            if i == "enum" || i == "trait" || i == "struct" || i == "union" || i == "impl" =>
         {
             errs.extend(
                 format!(
@@ -119,7 +113,7 @@ fn replace_self_and_deny_type_defs(
             );
             vec![tt]
         }
-        TokenTree::Ident(i) if i.to_string() == "Self" => struct_name.clone(),
+        TokenTree::Ident(i) if i == "Self" => struct_name.clone(),
         TokenTree::Literal(_) | TokenTree::Punct(_) | TokenTree::Ident(_) => vec![tt],
         TokenTree::Group(g) => vec![TokenTree::Group(Group::new(
             g.delimiter(),

rust/pin-init/internal/src/pinned_drop.rs

@@ -1,15 +1,13 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-#[cfg(not(kernel))]
-use proc_macro2 as proc_macro;
-
-use proc_macro::{TokenStream, TokenTree};
+use proc_macro2::{TokenStream, TokenTree};
+use quote::quote;
 
 pub(crate) fn pinned_drop(_args: TokenStream, input: TokenStream) -> TokenStream {
     let mut toks = input.into_iter().collect::<Vec<_>>();
     assert!(!toks.is_empty());
     // Ensure that we have an `impl` item.
-    assert!(matches!(&toks[0], TokenTree::Ident(i) if i.to_string() == "impl"));
+    assert!(matches!(&toks[0], TokenTree::Ident(i) if i == "impl"));
     // Ensure that we are implementing `PinnedDrop`.
     let mut nesting: usize = 0;
     let mut pinned_drop_idx = None;
@@ -27,7 +25,7 @@ pub(crate) fn pinned_drop(_args: TokenStream, input: TokenStream) -> TokenStream
         if i >= 1 && nesting == 0 {
             // Found the end of the generics, this should be `PinnedDrop`.
             assert!(
-                matches!(tt, TokenTree::Ident(i) if i.to_string() == "PinnedDrop"),
+                matches!(tt, TokenTree::Ident(i) if i == "PinnedDrop"),
                 "expected 'PinnedDrop', found: '{tt:?}'"
             );
             pinned_drop_idx = Some(i);

rust/pin-init/internal/src/zeroable.rs

@@ -1,10 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 
-#[cfg(not(kernel))]
-use proc_macro2 as proc_macro;
-
 use crate::helpers::{parse_generics, Generics};
-use proc_macro::{TokenStream, TokenTree};
+use proc_macro2::{TokenStream, TokenTree};
+use quote::quote;
 
 pub(crate) fn parse_zeroable_derive_input(
     input: TokenStream,

scripts/generate_rust_analyzer.py

@@ -123,7 +123,7 @@ def append_sysroot_crate(
     append_crate(
         "pin_init_internal",
         srctree / "rust" / "pin-init" / "internal" / "src" / "lib.rs",
-        [],
+        ["std", "proc_macro", "proc_macro2", "quote", "syn"],
         cfg=["kernel"],
         is_proc_macro=True,
     )