linux-kernel - Re: [PATCH v2 19/20] rust: syn: enable support in kbuild

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Message-ID: <CAJ-ks9kSFp8CpyNr8zSKh6mniuXiYNrZCc8FC-8Z81GdbnaRog@mail.gmail.com>
Date: Sun, 4 Jan 2026 18:17:01 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	patches@...ts.linux.dev, Jesung Yang <y.j3ms.n@...il.com>
Subject: Re: [PATCH v2 19/20] rust: syn: enable support in kbuild

On Mon, Nov 24, 2025 at 10:25 AM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> With all the new files in place and ready from the new crate, enable
> the support for it in the build system.
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Reviewed-by: Gary Guo <gary@...yguo.net>
> Tested-by: Gary Guo <gary@...yguo.net>
> Tested-by: Jesung Yang <y.j3ms.n@...il.com>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>  Makefile                          |  1 +
>  rust/Makefile                     | 37 ++++++++++++++++++++++++++++---
>  scripts/generate_rust_analyzer.py |  7 ++++++
>  3 files changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 85da055e4f00..96ddbaae7e12 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1835,6 +1835,7 @@ rustfmt:
>                 \( \
>                         -path $(srctree)/rust/proc-macro2 \
>                         -o -path $(srctree)/rust/quote \
> +                       -o -path $(srctree)/rust/syn \
>                 \) -prune -o \
>                 -type f -a -name '*.rs' -a ! -name '*generated*' -print \
>                 | xargs $(RUSTFMT) $(rustfmt_flags)
> diff --git a/rust/Makefile b/rust/Makefile
> index 4f4a00594142..8988ecf32531 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -27,7 +27,7 @@ endif
>
>  obj-$(CONFIG_RUST) += exports.o
>
> -always-$(CONFIG_RUST) += libproc_macro2.rlib libquote.rlib
> +always-$(CONFIG_RUST) += libproc_macro2.rlib libquote.rlib libsyn.rlib
>
>  always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.rs
>  always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c
> @@ -101,6 +101,22 @@ quote-flags := \
>      --extern proc_macro2 \
>      $(call cfgs-to-flags,$(quote-cfgs))
>
> +# `extra-traits`, `fold` and `visit` may be enabled if needed.
> +syn-cfgs := \
> +    feature="clone-impls" \
> +    feature="derive" \
> +    feature="full" \
> +    feature="parsing" \
> +    feature="printing" \
> +    feature="proc-macro" \
> +    feature="visit-mut"
> +
> +syn-flags := \
> +    --cap-lints=allow \
> +    --extern proc_macro2 \
> +    --extern quote \
> +    $(call cfgs-to-flags,$(syn-cfgs))
> +
>  # `rustdoc` did not save the target modifiers, thus workaround for
>  # the time being (https://github.com/rust-lang/rust/issues/144521).
>  rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
> @@ -161,11 +177,16 @@ rustdoc-quote: private skip_flags = $(quote-skip_flags)
>  rustdoc-quote: $(src)/quote/lib.rs rustdoc-clean rustdoc-proc_macro2 FORCE
>         +$(call if_changed,rustdoc)
>
> +rustdoc-syn: private rustdoc_host = yes
> +rustdoc-syn: private rustc_target_flags = $(syn-flags)
> +rustdoc-syn: $(src)/syn/lib.rs rustdoc-clean rustdoc-quote FORCE
> +       +$(call if_changed,rustdoc)
> +
>  rustdoc-macros: private rustdoc_host = yes
>  rustdoc-macros: private rustc_target_flags = --crate-type proc-macro \
>      --extern proc_macro
>  rustdoc-macros: $(src)/macros/lib.rs rustdoc-clean rustdoc-proc_macro2 \
> -    rustdoc-quote FORCE
> +    rustdoc-quote rustdoc-syn FORCE
>         +$(call if_changed,rustdoc)
>
>  # Starting with Rust 1.82.0, skipping `-Wrustdoc::unescaped_backticks` should
> @@ -231,6 +252,10 @@ rusttestlib-quote: private rustc_target_flags = $(quote-flags)
>  rusttestlib-quote: $(src)/quote/lib.rs rusttestlib-proc_macro2 FORCE
>         +$(call if_changed,rustc_test_library)
>
> +rusttestlib-syn: private rustc_target_flags = $(syn-flags)
> +rusttestlib-syn: $(src)/syn/lib.rs rusttestlib-quote FORCE
> +       +$(call if_changed,rustc_test_library)
> +
>  rusttestlib-macros: private rustc_target_flags = --extern proc_macro
>  rusttestlib-macros: private rustc_test_library_proc = yes
>  rusttestlib-macros: $(src)/macros/lib.rs FORCE
> @@ -488,6 +513,11 @@ $(obj)/libquote.rlib: private rustc_target_flags = $(quote-flags)
>  $(obj)/libquote.rlib: $(src)/quote/lib.rs $(obj)/libproc_macro2.rlib FORCE
>         +$(call if_changed_dep,rustc_procmacrolibrary)
>
> +$(obj)/libsyn.rlib: private skip_clippy = 1
> +$(obj)/libsyn.rlib: private rustc_target_flags = $(syn-flags)
> +$(obj)/libsyn.rlib: $(src)/syn/lib.rs $(obj)/libquote.rlib FORCE
> +       +$(call if_changed_dep,rustc_procmacrolibrary)
> +
>  quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>        cmd_rustc_procmacro = \
>         $(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
> @@ -500,7 +530,7 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>
>  # Procedural macros can only be used with the `rustc` that compiled it.
>  $(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/libproc_macro2.rlib \
> -    $(obj)/libquote.rlib FORCE
> +    $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE
>         +$(call if_changed_dep,rustc_procmacro)
>
>  $(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel
> @@ -525,6 +555,7 @@ rust-analyzer:
>                 --cfgs='core=$(core-cfgs)' $(core-edition) \
>                 --cfgs='proc_macro2=$(proc_macro2-cfgs)' \
>                 --cfgs='quote=$(quote-cfgs)' \
> +               --cfgs='syn=$(syn-cfgs)' \
>                 $(realpath $(srctree)) $(realpath $(objtree)) \
>                 $(rustc_sysroot) $(RUST_LIB_SRC) $(if $(KBUILD_EXTMOD),$(srcroot)) \
>                 > rust-project.json
> diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
> index 4faf153ed2ee..5b6f7b8d6918 100755
> --- a/scripts/generate_rust_analyzer.py
> +++ b/scripts/generate_rust_analyzer.py
> @@ -100,6 +100,13 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs, core_edit
>          cfg=crates_cfgs["quote"],
>      )
>
> +    append_crate(
> +        "syn",
> +        srctree / "rust" / "syn" / "lib.rs",
> +        ["proc_macro", "proc_macro2", "quote"],
> +        cfg=crates_cfgs["syn"],
> +    )

I think we need to add "std" here -- without it, navigating to methods
on e.g. Vec items defined in syn doesn't work (it does work with "std"
added).

> +
>      append_crate(
>          "macros",
>          srctree / "rust" / "macros" / "lib.rs",
> --
> 2.52.0
>
>