only copy jar if it exists

build.rs

@@ -4,12 +4,15 @@ use std::env;
 use std::path::Path;
 
 fn main() {
+    // We copy the .gitignore'd mvn package output into jassets if it exists
     let input_path = Path::new(&env::var("CARGO_MANIFEST_DIR").unwrap())
         .join("java_wrapper/target/suntan-1.0-SNAPSHOT.jar");
-    dbg!(&input_path);
-    let output_path =
-        Path::new(&env::var("CARGO_MANIFEST_DIR").unwrap()).join("jassets/suntan.jar");
-    dbg!(&output_path);
-    let res = std::fs::copy(input_path, output_path).expect("must copy jar");
-    dbg!(res);
+    if input_path.exists() {
+        dbg!(&input_path);
+        let output_path =
+            Path::new(&env::var("CARGO_MANIFEST_DIR").unwrap()).join("jassets/suntan.jar");
+        dbg!(&output_path);
+        let res = std::fs::copy(input_path, output_path).expect("must copy jar");
+        dbg!(res);
+    }
 }

src/main.rs

@@ -56,9 +56,13 @@ fn run(
     // j4rs Rust -> Java setup
     // FIXME: is this the best way to handle the underlying java dependency?
     // the jar must be prebuilt already with maven, using mvn package, then build.rs moves it into jassets
-    let jassets_path =
-        Path::new(&env::var("CARGO_MANIFEST_DIR").unwrap()).join("jassets/suntan.jar");
-    let entry = ClasspathEntry::new(jassets_path.as_path().to_str().expect("valid path"));
+    let jassets_path = Path::new(&env!("CARGO_MANIFEST_DIR")).join("jassets/suntan.jar");
+    let entry = ClasspathEntry::new(
+        jassets_path
+            .as_path()
+            .to_str()
+            .expect("valid jassets classpath"),
+    );
     let jvm: Jvm = JvmBuilder::new()
         .classpath_entry(entry)
         .build()