Put bindgen behind a seperate feature (georust#191)

This commit changes proj-sys to not depend on bindgen by default as that
introduces a quite heavy build time dependency (libclang) which might
not be there on all systems. Instead bundled bindings for the proj
version build by the `bundled_proj` feature are provided.

CHANGES.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 - Update to proj-sys 0.24.0 (libproj 9.4.0)
+- Provide bundled bindings by default and move support for build time generated bindings behind the `buildtime_bindgen` feature of proj-sys
 - Bump MSRV to 1.65
 
 ## 0.27.2

DEVELOPMENT.md

@@ -0,0 +1,10 @@
+# Development related notices
+
+
+Bindings were generated with the following command:
+
+```sh
+bindgen --distrust-clang-mangling --blocklist-type max_align_t wrapper.h -- -I  PROJSRC/proj-9.4.0/src
+```
+
+If you update the above command line you also need to update the arguments for the buildtime_bindgen feature in `build.rs`

proj-sys/Cargo.toml

@@ -16,7 +16,7 @@ libsqlite3-sys = "0.28"
 link-cplusplus = "1.0"
 
 [build-dependencies]
-bindgen = "0.69.0"
+bindgen = { version = "0.69", optional = true }
 pkg-config = "0.3.25"
 cmake = "0.1.50"
 flate2 = "1.0.24"
@@ -29,6 +29,7 @@ bundled_proj = []
 pkg_config = []
 network = ["tiff"]
 tiff = []
+buildtime_bindgen = ["dep:bindgen"]
 
 [package.metadata.docs.rs]
 features = [ "nobuild" ] # This feature will be enabled during the docs.rs build

proj-sys/build.rs

@@ -46,9 +46,22 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         })?
     };
 
+    #[cfg(feature = "buildtime_bindgen")]
+    generate_bindings(include_path)?;
+    #[cfg(not(feature = "buildtime_bindgen"))]
+    let _ = include_path;
+
+    Ok(())
+}
+
+#[cfg(feature = "buildtime_bindgen")]
+fn generate_bindings(include_path: std::path::PathBuf) -> Result<(), Box<dyn std::error::Error>> {
     // The bindgen::Builder is the main entry point
     // to bindgen, and lets you build up options for
     // the resulting bindings.
+    // If you update the configuration here you also
+    // need to update the corresponding bindgen command in
+    // `DEVELOPMENT.md`
     let bindings = bindgen::Builder::default()
         .clang_arg(format!("-I{}", include_path.to_string_lossy()))
         .trust_clang_mangling(false)