bindings: rust: expose v2.1 features as flag

v2.1 provided a getter to read the chip name from a request.

This adds v2_1 as feature in order to raise the minimum requested version
to v2.1 for exposing the new API.

This is identical to the concept patch that was posted [1] when this
feature flag mechanism was proposed. Only the commit message was
reworded.

[1] https://lore.kernel.org/all/20231006-b4-bindings-old-version-fix-v1-2-a65f431afb97@linaro.org/

Signed-off-by: Erik Schilling <erik.schilling@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

bindings/rust/libgpiod-sys/Cargo.toml

@@ -18,11 +18,16 @@ exclude = [
     "Makefile.am",
 ]
 
+[features]
+v2_1 = []
+
 [dependencies]
 
 [build-dependencies]
 bindgen = "0.63"
 system-deps = "2.0"
 
-[package.metadata.system-deps]
-libgpiod = "2"
+[package.metadata.system-deps.libgpiod]
+name = "libgpiod"
+version = "2"
+v2_1 = { version = "2.1" }

bindings/rust/libgpiod/Cargo.toml

@@ -19,7 +19,8 @@ exclude = [
 ]
 
 [features]
-vnext = []
+v2_1 = ["libgpiod-sys/v2_1"]
+vnext = ["v2_1"]
 
 [dependencies]
 errno = "0.2.8"

bindings/rust/libgpiod/README.md

@@ -28,6 +28,7 @@ C library will be exposed by default.
 Setting flags allows to increase the base version and export features of newer
 versions:
 
+- `v2_1`: Minimum version of `2.1.x`
 - `vnext`: The upcoming, still unreleased version of the C lib
 
 ## License

bindings/rust/libgpiod/src/line_request.rs

@@ -2,7 +2,7 @@
 // SPDX-FileCopyrightText: 2022 Linaro Ltd.
 // SPDX-FileCopyrightText: 2022 Viresh Kumar <viresh.kumar@linaro.org>
 
-#[cfg(feature = "vnext")]
+#[cfg(feature = "v2_1")]
 use std::ffi::CStr;
 use std::os::unix::prelude::AsRawFd;
 use std::time::Duration;
@@ -32,7 +32,7 @@ impl Request {
     }
 
     /// Get the name of the chip this request was made on.
-    #[cfg(feature = "vnext")]
+    #[cfg(feature = "v2_1")]
     pub fn chip_name(&self) -> Result<&str> {
         // SAFETY: The `gpiod_line_request` is guaranteed to be live as long
         // as `&self`

bindings/rust/libgpiod/tests/line_request.rs

@@ -60,7 +60,7 @@ mod line_request {
         use super::*;
 
         #[test]
-        #[cfg(feature = "vnext")]
+        #[cfg(feature = "v2_1")]
         fn chip_name() {
             const GPIO: Offset = 2;
             let mut config = TestConfig::new(NGPIO).unwrap();