Automatically use CMake for Windows builds

This PR changes the `rdkafka-sys/build.rs` script to automatically choose CMake
if the target platform is Windows. The `cmake-build` cargo feature no longer
has an effect on Windows. It can still be used to select the CMake build for
other targets. The official rdkafka build system remains the default for other
targets.

This solves a number of problems:
 - Projects using `rdkafka`/`rdkafka-sys` no longer have to conditionally
	enable `cmake-build` when they reference the crates just to have something that
	compiles across platforms.
 - JetBrains RustRover + rust-analyzer fail to initialize on Windows because the
	`rdkafka-sys/build.rs` script fails. In RustRover, even if you otherwise enable
	the `cmake-build` feature, there is an early "disovery" execution of the project
	that uses default features and fails miserably.
 - People evaluating the crate have a better experience if they happen to run
	Windows

.github/workflows/ci.yml

@@ -29,8 +29,9 @@ jobs:
         include:
           - os: macos-11.0
           - os: windows-2019
-            features: cmake-build,libz-static,curl-static
-            rdkafka-sys-features: cmake-build,libz-static,curl-static
+            # The Windows build should automatically use CMake
+            features: libz-static,curl-static
+            rdkafka-sys-features: libz-static,curl-static
           - os: ubuntu-20.04
             features: tracing
           - os: ubuntu-20.04

changelog.md

@@ -7,6 +7,7 @@ See also the [rdkafka-sys changelog](rdkafka-sys/changelog.md).
 * Update MSRV to 1.70
 * Remove testign for old Kafka versions (before 3.0). Add tests for 3.7.
 * Fix test dependency on docker compose.
+* Automatically use CMake for Windows targets
 
 ## 0.36.2 (2024-01-16)
 

rdkafka-sys/Cargo.toml

@@ -26,6 +26,12 @@ sasl2-sys = { version = "0.1.6", optional = true }
 pkg-config = "0.3.9"
 cmake = { version = "0.1.0", optional = true }
 
+# Windows only supports the CMake build. As we can't conditionally
+# make cmake-build a default feature only on some platforms, we instead
+# have to make the cmake dependency required.
+[target.'cfg(target_os = "windows")'.build-dependencies]
+cmake = { version = "0.1.0", optional = false }
+
 [lib]
 name = "rdkafka_sys"
 path = "src/lib.rs"

rdkafka-sys/README.md

@@ -1,94 +1,95 @@
-# rdkafka-sys
-
-Low level bindings to [librdkafka](https://github.com/edenhill/librdkafka),
-a C library for the [Apache Kafka] protocol with producer, consumer, and
-admin clients.
-
-For a safe wrapper, see the [rdkafka] crate.
-
-## Version
-
-The rdkafka-sys version number is in the format `X.Y.Z+RX.RY.RZ`, where
-`X.Y.Z` is the version of this crate and follows SemVer conventions, while
-`RX.RY.RZ` is the version of the bundled librdkafka.
-
-Note that versions before v2.0.0+1.4.2 did not follow this convention, and
-instead directly correspond to the bundled librdkafka version.
-
-## Build
-
-### Known issues
-
-* When any of librdkafka's optional dependencies are enabled, like libz or
-  OpenSSL, if you have multiple versions of that library installed upon your
-  system, librdkafka's build system may disagree with Cargo about which
-  version of the library to use! **This can result in subtly broken
-  builds,** if librdkafka compiles against the headers for one version but
-  Cargo links against a different version.  For complete confidence when
-  building release binaries, use an environment like a Docker container or a
-  chroot jail where you can guarantee that only one version of each
-  dependency is present. The current design of Cargo unfortunately makes
-  this nearly impossible to fix.
-
-* Windows is only supported when using the CMake build system via the
-  `cmake-build` Cargo feature.
-
-### Features
-
-By default a submodule with the librdkafka sources will be used to compile
-and statically link the library.
-
-The **`dynamic-linking`** feature can be used to link rdkafka to a locally
-installed version of librdkafka: if the feature is enabled, the build script
-will use `pkg-config` to check the version of the library installed in the
-system, and it will configure the compiler to dynamically link against it.
-The system version of librdkafka must exactly match the version of
-librdkafka bundled with this crate.
-
-The **`cmake-build`** feature builds librdkafka with its [CMake] build
-system, rather than its default [mklove]-based build system. This feature
-requires that CMake is installed on the build machine.
-
-The following features directly correspond to librdkafka features (i.e.,
-flags you would pass to `configure` if you were compiling manually).
-
-  * The **`ssl`** feature enables SSL support. By default, the system's
-    OpenSSL library is dynamically linked, but static linking of the version
-    bundled with the [openssl-sys] crate can be requested with the
-    `ssl-vendored` feature.
-  * The **`gssapi`** feature enables SASL GSSAPI support with Cyrus
-    libsasl2. By default the system's libsasl2 is dynamically linked, but
-    static linking of the version bundled with the [sasl2-sys] crate can be
-    requested with the `gssapi-vendored` feature.
-  * The **`libz`** feature enables support for zlib compression. This
-    feature is enabled by default. By default, the system's libz is
-    dynamically linked, but static linking of the version bundled with the
-    [libz-sys] crate can be requested with the `libz-static` feature.
-  * The **`curl`** feature enables the HTTP client via curl. By default, the
-    system's curl is dynamically linked, but static linking of the version
-    bundled with the [curl-sys] create can be requested with the
-    `curl-static` feature.
-  * The **`zstd`** feature enables support for ZSTD compression. By default,
-    this builds and statically links the version bundled with the [zstd-sys]
-    crate, but dynamic linking of the system's version can be requested with
-    the `zstd-pkg-config` feature.
-  * The **`external-lz4`** feature statically links against the copy of
-    liblz4 bundled with the [lz4-sys] crate. By default, librdkafka
-    statically links against its own bundled version of liblz4. Due to
-    limitations with lz4-sys, it is not yet possible to dynamically link
-    against the system's version of liblz4.
-
-All features are disabled by default unless noted otherwise above. The build
-process is defined in [`build.rs`].
-
-[`build.rs`]: https://github.com/fede1024/rust-rdkafka/tree/master/rdkafka-sys/build.rs
-[Apache Kafka]: https://kafka.apache.org
-[CMake]: https://cmake.org
-[libz-sys]: https://crates.io/crates/libz-sys
-[curl-sys]: https://crates.io/crates/curl-sys
-[lz4-sys]: https://crates.io/crates/lz4-sys
-[mklove]: https://github.com/edenhill/mklove
-[openssl-sys]: https://crates.io/crates/openssl-sys
-[rdkafka]: https://docs.rs/rdkafka
-[sasl2-sys]: https://docs.rs/sasl2-sys
-[zstd-sys]: https://crates.io/crates/zstd-sys
+# rdkafka-sys
+
+Low level bindings to [librdkafka](https://github.com/edenhill/librdkafka),
+a C library for the [Apache Kafka] protocol with producer, consumer, and
+admin clients.
+
+For a safe wrapper, see the [rdkafka] crate.
+
+## Version
+
+The rdkafka-sys version number is in the format `X.Y.Z+RX.RY.RZ`, where
+`X.Y.Z` is the version of this crate and follows SemVer conventions, while
+`RX.RY.RZ` is the version of the bundled librdkafka.
+
+Note that versions before v2.0.0+1.4.2 did not follow this convention, and
+instead directly correspond to the bundled librdkafka version.
+
+## Build
+
+### Known issues
+
+* When any of librdkafka's optional dependencies are enabled, like libz or
+  OpenSSL, if you have multiple versions of that library installed upon your
+  system, librdkafka's build system may disagree with Cargo about which
+  version of the library to use! **This can result in subtly broken
+  builds,** if librdkafka compiles against the headers for one version but
+  Cargo links against a different version.  For complete confidence when
+  building release binaries, use an environment like a Docker container or a
+  chroot jail where you can guarantee that only one version of each
+  dependency is present. The current design of Cargo unfortunately makes
+  this nearly impossible to fix.
+
+* Windows builds always use the CMake build system, regardless of whether
+  the `cmake-build` Cargo feature is enabled or not. This is because Windows
+  is only supported with CMake as the build system.
+
+### Features
+
+By default a submodule with the librdkafka sources will be used to compile
+and statically link the library.
+
+The **`dynamic-linking`** feature can be used to link rdkafka to a locally
+installed version of librdkafka: if the feature is enabled, the build script
+will use `pkg-config` to check the version of the library installed in the
+system, and it will configure the compiler to dynamically link against it.
+The system version of librdkafka must exactly match the version of
+librdkafka bundled with this crate.
+
+The **`cmake-build`** feature builds librdkafka with its [CMake] build
+system, rather than its default [mklove]-based build system. This feature
+requires that CMake is installed on the build machine.
+
+The following features directly correspond to librdkafka features (i.e.,
+flags you would pass to `configure` if you were compiling manually).
+
+  * The **`ssl`** feature enables SSL support. By default, the system's
+    OpenSSL library is dynamically linked, but static linking of the version
+    bundled with the [openssl-sys] crate can be requested with the
+    `ssl-vendored` feature.
+  * The **`gssapi`** feature enables SASL GSSAPI support with Cyrus
+    libsasl2. By default the system's libsasl2 is dynamically linked, but
+    static linking of the version bundled with the [sasl2-sys] crate can be
+    requested with the `gssapi-vendored` feature.
+  * The **`libz`** feature enables support for zlib compression. This
+    feature is enabled by default. By default, the system's libz is
+    dynamically linked, but static linking of the version bundled with the
+    [libz-sys] crate can be requested with the `libz-static` feature.
+  * The **`curl`** feature enables the HTTP client via curl. By default, the
+    system's curl is dynamically linked, but static linking of the version
+    bundled with the [curl-sys] create can be requested with the
+    `curl-static` feature.
+  * The **`zstd`** feature enables support for ZSTD compression. By default,
+    this builds and statically links the version bundled with the [zstd-sys]
+    crate, but dynamic linking of the system's version can be requested with
+    the `zstd-pkg-config` feature.
+  * The **`external-lz4`** feature statically links against the copy of
+    liblz4 bundled with the [lz4-sys] crate. By default, librdkafka
+    statically links against its own bundled version of liblz4. Due to
+    limitations with lz4-sys, it is not yet possible to dynamically link
+    against the system's version of liblz4.
+
+All features are disabled by default unless noted otherwise above. The build
+process is defined in [`build.rs`].
+
+[`build.rs`]: https://github.com/fede1024/rust-rdkafka/tree/master/rdkafka-sys/build.rs
+[Apache Kafka]: https://kafka.apache.org
+[CMake]: https://cmake.org
+[libz-sys]: https://crates.io/crates/libz-sys
+[curl-sys]: https://crates.io/crates/curl-sys
+[lz4-sys]: https://crates.io/crates/lz4-sys
+[mklove]: https://github.com/edenhill/mklove
+[openssl-sys]: https://crates.io/crates/openssl-sys
+[rdkafka]: https://docs.rs/rdkafka
+[sasl2-sys]: https://docs.rs/sasl2-sys
+[zstd-sys]: https://crates.io/crates/zstd-sys

rdkafka-sys/build.rs

@@ -1,8 +1,6 @@
 use std::borrow::Borrow;
 use std::env;
 use std::ffi::OsStr;
-#[cfg(feature = "cmake-build")]
-use std::fs;
 use std::path::{Path, PathBuf};
 use std::process::{self, Command};
 
@@ -88,7 +86,7 @@ fn main() {
     }
 }
 
-#[cfg(not(feature = "cmake-build"))]
+#[cfg(all(not(feature = "cmake-build"), not(target_os = "windows")))]
 fn build_librdkafka() {
     let mut configure_flags: Vec<String> = Vec::new();
 
@@ -200,8 +198,9 @@ fn build_librdkafka() {
     println!("cargo:root={}", out_dir);
 }
 
-#[cfg(feature = "cmake-build")]
+#[cfg(any(feature = "cmake-build", target_os = "windows"))]
 fn build_librdkafka() {
+    use std::fs;
     let mut config = cmake::Config::new("librdkafka");
     let mut cmake_library_paths = vec![];
 

rdkafka-sys/src/lib.rs

@@ -28,8 +28,9 @@
 //!   dependency is present. The current design of Cargo unfortunately makes
 //!   this nearly impossible to fix.
 //!
-//! * Windows is only supported when using the CMake build system via the
-//!   `cmake-build` Cargo feature.
+//! * Windows builds always use the CMake build system, regardless of whether
+//!   the `cmake-build` Cargo feature is enabled or not. This is because Windows
+//!   is only supported with CMake as the build system.
 //!
 //! ### Features
 //!

src/lib.rs

@@ -152,13 +152,14 @@
 //! * GNU `make`
 //! * `pthreads`
 //! * `zlib`: optional, but included by default (feature: `libz`)
-//! * `cmake`: optional, *not* included by default (feature: `cmake-build`)
+//! * `cmake`: optional¹, *not* included by default (feature: `cmake-build`)
 //! * `libssl-dev`: optional, *not* included by default (feature: `ssl`)
 //! * `libsasl2-dev`: optional, *not* included by default (feature: `gssapi`)
 //! * `libzstd-dev`: optional, *not* included by default (feature: `zstd-pkg-config`)
 //!
 //! Note that using the CMake build system, via the `cmake-build` feature, is
-//! encouraged if you can take the dependency on CMake.
+//! encouraged if you can take the dependency on CMake. ¹Windows is only supported
+//! via CMake, where it is the default build system.
 //!
 //! By default a submodule with the librdkafka sources pinned to a specific
 //! commit will be used to compile and statically link the library. The