linux-kernel - Re: [PATCH 18/18] rust: syn: enable support in kbuild

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Message-ID: <62b806eb-2e89-4e92-8b94-b932199778d3@nvidia.com>
Date: Mon, 10 Nov 2025 11:43:06 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>
Cc: 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
Subject: Re: [PATCH 18/18] rust: syn: enable support in kbuild

On 11/10/25 1:50 AM, Miguel Ojeda wrote:
> With all the new files in place and ready from the new crate, enable
> the support for it in the build system.
> 
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>  Makefile                          |  1 +
>  rust/Makefile                     | 39 +++++++++++++++++++++++++++----
>  scripts/generate_rust_analyzer.py |  7 ++++++
>  3 files changed, 43 insertions(+), 4 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index f1b38b7fed1e..5364b3ad3600 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1833,6 +1833,7 @@ rustfmt:
>  		\( \
>  			-path $(srctree)/rust/proc-macro2 \
>  			-o -path $(srctree)/rust/quote \
> +			-o -path $(srctree)/rust/syn \

At this point, a "vendored" subdirectory for these three items is
starting to sound even better, from a self-documenting point of
view, yes?

thanks,
-- 
John Hubbard

>  		\) -prune -o \
>  		-type f -a -name '*.rs' -a ! -name '*generated*' -print \
>  		| xargs $(RUSTFMT) $(rustfmt_flags)
> diff --git a/rust/Makefile b/rust/Makefile
> index 801a8cbf3bdd..984aec608c27 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -27,7 +27,7 @@ endif
>  
>  obj-$(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)
> @@ -164,11 +180,16 @@ 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
> @@ -240,6 +261,10 @@ 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
> @@ -497,19 +522,24 @@ $(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_hostlibrary)
>  
> +$(obj)/libsyn.rlib: private skip_clippy = 1
> +$(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_hostlibrary)
> +
>  quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>        cmd_rustc_procmacro = \
>  	$(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
>  		-Clinker-flavor=gcc -Clinker=$(HOSTCC) \
>  		-Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \
>  		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
> -		--crate-type proc-macro \
> +		--crate-type proc-macro -L$(objtree)/$(obj) \
>  		--crate-name $(patsubst lib%.$(libmacros_extension),%,$(notdir $@)) \
>  		@$(objtree)/include/generated/rustc_cfg $<
>  
>  # 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
> @@ -534,6 +564,7 @@ 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"],
> +    )
> +
>      append_crate(
>          "macros",
>          srctree / "rust" / "macros" / "lib.rs",