Add option to prefer static linking (#143)

README.md

@@ -94,9 +94,11 @@ are passed through to shaderc-sys when building shaderc-rs:
 1. Building from source, if the native shaderc library is not found via the
    above steps.
 
-For each library directory, the build script will try to fine and link to the
+For each library directory, the build script will try to find and link to the
 dynamic native shaderc library `shaderc_shared` first and the static native
-shaderc library `shaderc_combined` next.
+shaderc library `shaderc_combined` next. To prefer searching for the static
+library first and the dynamic library next, the option
+`--features prefer-static-linking` may be used.
 
 Building from Source
 --------------------

shaderc-rs/Cargo.toml

@@ -21,3 +21,4 @@ assert_matches = "1.5"
 
 [features]
 build-from-source = ["shaderc-sys/build-from-source"]
+prefer-static-linking = ["shaderc-sys/prefer-static-linking"]

shaderc-sys/Cargo.toml

@@ -16,6 +16,7 @@ name = "shaderc_sys"
 
 [features]
 build-from-source = []
+prefer-static-linking = []
 
 [dependencies]
 libc = "0.2"

shaderc-sys/build/build.rs

@@ -169,6 +169,7 @@ fn main() {
     let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
     let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
     let config_build_from_source = env::var("CARGO_FEATURE_BUILD_FROM_SOURCE").is_ok();
+    let config_prefer_static_linking = env::var("CARGO_FEATURE_PREFER_STATIC_LINKING").is_ok();
     let has_explicit_set_search_dir = env::var("SHADERC_LIB_DIR").is_ok();
 
     // Initialize explicit shaderc search directory first.
@@ -275,12 +276,17 @@ fn main() {
         let dylib_path = search_dir.join(dylib_name);
 
         if let Some((lib_name, lib_kind)) = {
-            if dylib_path.exists() {
-                Some((SHADERC_SHARED_LIB, "dylib"))
-            } else if static_lib_path.exists() {
-                Some((SHADERC_STATIC_LIB, "static"))
-            } else {
-                None
+            match (
+                dylib_path.exists(),
+                static_lib_path.exists(),
+                config_prefer_static_linking,
+            ) {
+                // If dylib not exist OR prefer static lib and static lib exist, static.
+                (false, true, _) | (_, true, true) => Some((SHADERC_STATIC_LIB, "static")),
+                // Otherwise, if dylib exist, dynamic.
+                (true, _, _) => Some((SHADERC_SHARED_LIB, "dylib")),
+                // Neither dylib nor static lib exist.
+                _ => None,
             }
         } {
             match (target_os.as_str(), target_env.as_str()) {