Filter out all non-source files before feeding to javac.

README.md

@@ -43,6 +43,4 @@ raven run main.Main
     will be implemented should there arise a need.
 - [ ] Wrap errors properly, instead of hap-hazardly using `anyhow`
 - [ ] Maybe proper logging?
-- [ ] Make `fs::expand_files()` skip over non-`.java` files or properly handle
-    that.
 - [ ] Fix using hashes to avoid unnesscesary recompilation.

src/main.rs

@@ -185,7 +185,13 @@ fn new(project_name: String) -> anyhow::Result<()> {
 }
 
 fn build() -> anyhow::Result<()> {
-    let mut targets = crate::fs::expand_files(DIR_SRC.as_path())?;
+    let mut targets: Vec<PathBuf> = crate::fs::expand_files(DIR_SRC.as_path())?
+        .into_iter()
+        .filter(|f| {
+            f.extension()
+                .is_some_and(|ext| ext.to_str().is_some_and(|ext| ext == JAVA_EXT_SOURCE))
+        })
+        .collect();
     let mut nest_lock = NestLock::load().unwrap_or_default();
 
     nest_lock.update();