Allow static and dynamic linking

Currently bindgen always uses clang-sys with the "runtime" feature -
that is, load libclang at runtime with dlopen (or similar)
at runtime.  This PR keeps this default, but also
- adds "static" to statically link libclang
- without either "runtime" or "static", link with the shared library

Many distributions don't ship with a static libclang, but linking with the dynamic
library will use normal ld.so mechanisms to define where the .so file should be found.
(Ditto for the Mac and Windows equivalents.)

Author: jsgf

Cargo.toml

@@ -49,7 +49,7 @@ cexpr = "0.3.3"
 cfg-if = "0.1.0"
 # This kinda sucks: https://github.com/rust-lang/cargo/issues/1982
 clap = { version = "2", optional = true }
-clang-sys = { version = "0.28.0", features = ["runtime", "clang_6_0"] }
+clang-sys = { version = "0.28.0", features = ["clang_6_0"] }
 lazy_static = "1"
 peeking_take_while = "0.1.2"
 quote = { version = "1", default-features = false }
@@ -70,9 +70,10 @@ optional = true
 version = "0.4"
 
 [features]
-default = ["logging", "clap"]
+default = ["logging", "clap", "runtime"]
 logging = ["env_logger", "log"]
-static = []
+static = ["clang-sys/static"]
+runtime = ["clang-sys/runtime"]
 
 # These features only exist for CI testing -- don't use them if you're not hacking
 # on bindgen!

src/lib.rs

@@ -95,7 +95,6 @@ use std::io::{self, Write};
 use std::{env, iter};
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
-use std::sync::Arc;
 
 // Some convenient typedefs for a fast hash map and hash set.
 type HashMap<K, V> = ::fxhash::FxHashMap<K, V>;
@@ -1697,6 +1696,7 @@ impl Default for BindgenOptions {
     }
 }
 
+#[cfg(feature = "runtime")]
 fn ensure_libclang_is_loaded() {
     if clang_sys::is_loaded() {
         return;
@@ -1707,7 +1707,7 @@ fn ensure_libclang_is_loaded() {
     // across different threads.
 
     lazy_static! {
-        static ref LIBCLANG: Arc<clang_sys::SharedLibrary> = {
+        static ref LIBCLANG: std::sync::Arc<clang_sys::SharedLibrary> = {
             clang_sys::load().expect("Unable to find libclang");
             clang_sys::get_library()
                 .expect("We just loaded libclang and it had better still be \
@@ -1718,6 +1718,10 @@ fn ensure_libclang_is_loaded() {
     clang_sys::set_library(Some(LIBCLANG.clone()));
 }
 
+#[cfg(not(feature = "runtime"))]
+fn ensure_libclang_is_loaded() {
+}
+
 /// Generated Rust bindings.
 #[derive(Debug)]
 pub struct Bindings {
@@ -1732,7 +1736,10 @@ impl Bindings {
     ) -> Result<Bindings, ()> {
         ensure_libclang_is_loaded();
 
+        #[cfg(feature = "runtime")]
         debug!("Generating bindings, libclang at {}", clang_sys::get_library().unwrap().path().display());
+        #[cfg(not(feature = "runtime"))]
+        debug!("Generating bindings, libclang linked");
 
         options.build();
 
@@ -2066,10 +2073,7 @@ pub struct ClangVersion {
 
 /// Get the major and the minor semver numbers of Clang's version
 pub fn clang_version() -> ClangVersion {
-    if !clang_sys::is_loaded() {
-        // TODO(emilio): Return meaningful error (breaking).
-        clang_sys::load().expect("Unable to find libclang");
-    }
+    ensure_libclang_is_loaded();
 
     let raw_v: String = clang::extract_clang_version();
     let split_v: Option<Vec<&str>> = raw_v.split_whitespace().nth(2).map(|v| {