[PATCH net-next v7 3/5] rust: add second `bindgen` pass for enum exhaustiveness checking

[FUJITA Tomonori <fujita.tomonori@gmail.com>]

From: Miguel Ojeda <ojeda@kernel.org>

This patch makes sure that the C's enum is sync with Rust sides. If
the enum is out of sync, compiling fails with an error like the
following.

Note that this is a temporary solution. It will be replaced with
bindgen when it supports generating the enum conversion code.

    error[E0005]: refutable pattern in function argument
         --> rust/bindings/bindings_enum_check.rs:29:6
          |
    29    |       (phy_state::PHY_DOWN
          |  ______^
    30    | |     | phy_state::PHY_READY
    31    | |     | phy_state::PHY_HALTED
    32    | |     | phy_state::PHY_ERROR
    ...     |
    35    | |     | phy_state::PHY_NOLINK
    36    | |     | phy_state::PHY_CABLETEST): phy_state,
          | |______________________________^ pattern `phy_state::PHY_NEW` not covered
          |
    note: `phy_state` defined here
         --> rust/bindings/bindings_generated_enum_check.rs:60739:10
          |
    60739 | pub enum phy_state {
          |          ^^^^^^^^^
    ...
    60745 |     PHY_NEW = 5,
          |     ------- not covered
          = note: the matched value is of type `phy_state`

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
 rust/.gitignore                      |  1 +
 rust/Makefile                        | 14 +++++++++++
 rust/bindings/bindings_enum_check.rs | 36 ++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 rust/bindings/bindings_enum_check.rs

diff --git a/rust/.gitignore b/rust/.gitignore
index d3829ffab80b..1a76ad0d6603 100644
--- a/rust/.gitignore
+++ b/rust/.gitignore
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 bindings_generated.rs
+bindings_generated_enum_check.rs
 bindings_helpers_generated.rs
 doctests_kernel_generated.rs
 doctests_kernel_generated_kunit.c
diff --git a/rust/Makefile b/rust/Makefile
index 87958e864be0..a622111c8c50 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -15,6 +15,7 @@ always-$(CONFIG_RUST) += libmacros.so
 no-clean-files += libmacros.so
 
 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
+always-$(CONFIG_RUST) += bindings/bindings_generated_enum_check.rs
 obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
     exports_kernel_generated.h
@@ -341,6 +342,19 @@ $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_helper.h \
     $(src)/bindgen_parameters FORCE
 	$(call if_changed_dep,bindgen)
 
+$(obj)/bindings/bindings_generated_enum_check.rs: private bindgen_target_flags = \
+    $(shell grep -v '^#\|^$$' $(srctree)/$(src)/bindgen_parameters) \
+    --default-enum-style rust
+$(obj)/bindings/bindings_generated_enum_check.rs: private bindgen_target_extra = ; \
+    OBJTREE=$(abspath $(objtree)) $(RUSTC_OR_CLIPPY) $(rust_flags) $(rustc_target_flags) \
+        --crate-type rlib -L$(objtree)/$(obj) \
+        --emit=dep-info=$(obj)/bindings/.bindings_enum_check.rs.d \
+        --emit=metadata=$(obj)/bindings/libbindings_enum_check.rmeta \
+        --crate-name enum_check $(srctree)/$(src)/bindings/bindings_enum_check.rs
+$(obj)/bindings/bindings_generated_enum_check.rs: $(src)/bindings/bindings_helper.h \
+    $(src)/bindings/bindings_enum_check.rs $(src)/bindgen_parameters FORCE
+	$(call if_changed_dep,bindgen)
+
 $(obj)/uapi/uapi_generated.rs: private bindgen_target_flags = \
     $(shell grep -v '^#\|^$$' $(srctree)/$(src)/bindgen_parameters)
 $(obj)/uapi/uapi_generated.rs: $(src)/uapi/uapi_helper.h \
diff --git a/rust/bindings/bindings_enum_check.rs b/rust/bindings/bindings_enum_check.rs
new file mode 100644
index 000000000000..eef7e9ca3c54
--- /dev/null
+++ b/rust/bindings/bindings_enum_check.rs
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Bindings' enum exhaustiveness check.
+//!
+//! Eventually, this should be replaced by a safe version of `--rustified-enum`, see
+//! https://github.com/rust-lang/rust-bindgen/issues/2646.
+
+#![no_std]
+#![allow(
+    clippy::all,
+    dead_code,
+    missing_docs,
+    non_camel_case_types,
+    non_upper_case_globals,
+    non_snake_case,
+    improper_ctypes,
+    unreachable_pub,
+    unsafe_op_in_unsafe_fn
+)]
+
+include!(concat!(
+    env!("OBJTREE"),
+    "/rust/bindings/bindings_generated_enum_check.rs"
+));
+
+fn check_phy_state(
+    (phy_state::PHY_DOWN
+    | phy_state::PHY_READY
+    | phy_state::PHY_HALTED
+    | phy_state::PHY_ERROR
+    | phy_state::PHY_UP
+    | phy_state::PHY_RUNNING
+    | phy_state::PHY_NOLINK
+    | phy_state::PHY_CABLETEST): phy_state,
+) {
+}
-- 
2.34.1