respect CUDA_PATH and friends in build.rs (with windows support)

build.rs

@@ -1,40 +1,39 @@
-#[cfg(unix)]
 fn main() {
-    let cuda_path = std::env::var("CUDA_PATH").unwrap_or_else(|_| "/usr/local/cuda".to_string());
+    let cuda_path = std::env::var("CUDA_PATH").map(std::path::PathBuf::from);
 
-    let cuda_include_path =
-        std::env::var("CUDA_INCLUDE_PATH").unwrap_or_else(|_| format!("{cuda_path}/include"));
+    #[cfg(not(windows))]
+    let cuda_path = cuda_path.unwrap_or_else(|_| std::path::PathBuf::from("/usr/local/cuda"));
+    #[cfg(windows)]
+    let cuda_path = cuda_path.expect("Missing environment variable `CUDA_PATH`.");
 
-    let cuda_lib_path =
-        std::env::var("CUDA_LIB_PATH").unwrap_or_else(|_| format!("{cuda_path}/lib64"));
+    let cuda_include_path = std::env::var("CUDA_INCLUDE_PATH")
+        .map(std::path::PathBuf::from)
+        .unwrap_or_else(|_| cuda_path.join("include"));
+
+    let cuda_lib_path = std::env::var("CUDA_LIB_PATH")
+        .map(std::path::PathBuf::from)
+        .unwrap_or_else(|_| {
+            #[cfg(not(windows))]
+            {
+                cuda_path.join("lib64")
+            }
+            #[cfg(windows)]
+            {
+                cuda_path.join("lib").join("x64")
+            }
+        });
 
     cpp_build::Config::new()
         .include(cuda_include_path)
         .build("src/lib.rs");
 
-    println!("cargo:rustc-link-search={cuda_lib_path}");
+    println!("cargo:rustc-link-search={}", cuda_lib_path.display());
     println!("cargo:rustc-link-lib=cudart");
 
     #[cfg(feature = "npp")]
     link_npp_libraries();
 }
 
-#[cfg(windows)]
-fn main() {
-    let cuda_path = std::env::var("CUDA_PATH").expect("Missing environment variable `CUDA_PATH`.");
-    let cuda_path = std::path::Path::new(&cuda_path);
-    cpp_build::Config::new()
-        .include(cuda_path.join("include"))
-        .build("src/lib.rs");
-    println!(
-        "cargo:rustc-link-search={}",
-        cuda_path.join("lib").join("x64").display()
-    );
-    println!("cargo:rustc-link-lib=cudart");
-    #[cfg(feature = "npp")]
-    link_npp_libraries();
-}
-
 #[cfg(feature = "npp")]
 fn link_npp_libraries() {
     println!("cargo:rustc-link-lib=nppc");