Fix Dynamic Linking (#44)

* Only do the cc build if `system-dylib` feature is disabled.

* dynamic linking: Generate bindings using system headers

* dylib: Link against libwebp

`pkg_config` automaticially links against libwebp when we probe it.
libwebp is already probed if `generate-bindings` (in `include_paths`),
but we need to manually probe if `generate-bindings` is disabled.

Author: abezukor

build.rs

@@ -1,13 +1,65 @@
+#[cfg(not(feature = "system-dylib"))]
 use std::env;
 use std::path::PathBuf;
 
-fn main() {
-    #[cfg(feature = "system-dylib")]
-    system_dylib();
+#[cfg(feature = "system-dylib")]
+const PACKAGE_CONFIG_NAME: &str = "libwebp";
 
+fn main() {
     #[cfg(feature = "generate-bindings")]
     generate_bindings();
 
+    #[cfg(all(not(feature = "generate-bindings"), feature = "system-dylib"))]
+    pkg_config::Config::new()
+        .probe(PACKAGE_CONFIG_NAME)
+        .unwrap();
+
+    #[cfg(not(feature = "system-dylib"))]
+    do_build();
+}
+
+#[cfg(feature = "generate-bindings")]
+fn generate_bindings() {
+    println!("cargo:rerun-if-changed=wrap.h");
+    let bindings = bindgen::Builder::default()
+        .header("wrap.h")
+        .default_enum_style(bindgen::EnumVariation::Rust {
+            non_exhaustive: false,
+        })
+        .trust_clang_mangling(false)
+        .clang_args(
+            include_paths()
+                .into_iter()
+                .map(|include_path| format!("-I{}", include_path.to_str().unwrap())),
+        )
+        .impl_debug(true)
+        .allowlist_function("[wW][eE][bB].*")
+        .allowlist_var("[wW][eE][bB].*")
+        .allowlist_type("[wW][eE][bB].*")
+        .use_core()
+        .generate()
+        .expect("Unable to generate bindings");
+
+    bindings
+        .write_to_file("src/ffi.rs")
+        .expect("Couldn't write bindings to ffi.rs");
+}
+
+#[cfg(all(feature = "system-dylib", feature = "generate-bindings"))]
+fn include_paths() -> Vec<PathBuf> {
+    let system_libwebp = pkg_config::Config::new()
+        .probe(PACKAGE_CONFIG_NAME)
+        .unwrap();
+    system_libwebp.include_paths
+}
+
+#[cfg(all(not(feature = "system-dylib"), feature = "generate-bindings"))]
+fn include_paths() -> Vec<PathBuf> {
+    vec![PathBuf::from("vendor/src")]
+}
+
+#[cfg(not(feature = "system-dylib"))]
+fn do_build() {
     let manifest_dir =
         PathBuf::from(env::var_os("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR"));
     let vendor = manifest_dir.join("vendor");
@@ -36,38 +88,7 @@ fn main() {
     cc.compile("webpsys");
 }
 
-#[cfg(feature = "system-dylib")]
-fn system_dylib() {
-    let lib_name = "libwebp";
-    let find_system_lib = pkg_config::Config::new().probe(lib_name).is_ok();
-
-    if find_system_lib {
-        println!("cargo:rustc-link-lib={lib_name}");
-        return;
-    }
-}
-
-#[cfg(feature = "generate-bindings")]
-fn generate_bindings() {
-    let bindings = bindgen::Builder::default()
-        .header("wrap.h")
-        .default_enum_style(bindgen::EnumVariation::Rust {
-            non_exhaustive: false,
-        })
-        .trust_clang_mangling(false)
-        .impl_debug(true)
-        .allowlist_function("[wW][eE][bB].*")
-        .allowlist_var("[wW][eE][bB].*")
-        .allowlist_type("[wW][eE][bB].*")
-        .use_core()
-        .generate()
-        .expect("Unable to generate bindings");
-
-    bindings
-        .write_to_file("src/ffi.rs")
-        .expect("Couldn't write bindings to ffi.rs");
-}
-
+#[cfg(not(feature = "system-dylib"))]
 fn setup_build(build: &mut cc::Build, include_dir: &PathBuf) {
     build.include(include_dir);
     build.define("NDEBUG", Some("1"));

wrap.h

@@ -1,5 +1,5 @@
-#include "vendor/src/webp/types.h"
-#include "vendor/src/webp/encode.h"
-#include "vendor/src/webp/decode.h"
-#include "vendor/src/webp/mux.h"
-#include "vendor/src/webp/demux.h"
+#include "webp/types.h"
+#include "webp/encode.h"
+#include "webp/decode.h"
+#include "webp/mux.h"
+#include "webp/demux.h"