fix(windows): resolve Java executable path issues on Windows

- Add normalize_java_path utility function with Windows-specific handling
- Automatically append .exe extension when missing on Windows
- Use 'where' command to locate java.exe in PATH if not found
- Improve error messages with full path display for debugging
- Apply path normalization in both start_game and install_forge commands

This fixes the "Failed to launch java: program not found" error on Windows
by properly handling Java executable paths, including relative paths,
missing extensions, and PATH resolution.

Reviewed-by: Claude Sonnet 4.5

3 files changed, 126 insertions, 4 deletions

diff --git a/src-tauri/src/main.rs b/src-tauri/src/main.rs
index 6ea6ece..ec19d0c 100644
--- a/src-tauri/src/main.rs
+++ b/src-tauri/src/main.rs
@@ -526,12 +526,28 @@ async fn start_game(
         emit_log!(window, format!("First 10 args: {:?}", &args[..10]));
     }
 
+    // Get Java path from config or detect
+    let java_path_str = if !config.java_path.is_empty() && config.java_path != "java" {
+        config.java_path.clone()
+    } else {
+        // Try to find a suitable Java installation
+        let javas = core::java::detect_all_java_installations(&app_handle);
+        if let Some(java) = javas.first() {
+            java.path.clone()
+        } else {
+            return Err(
+                "No Java installation found. Please configure Java in settings.".to_string(),
+            );
+        }
+    };
+    let java_path = utils::path::normalize_java_path(&java_path_str)?;
+
     // Spawn the process
     emit_log!(
         window,
-        format!("Starting Java process: {}", config.java_path)
+        format!("Starting Java process: {}", java_path.display())
     );
-    let mut command = Command::new(&config.java_path);
+    let mut command = Command::new(&java_path);
     command.args(&args);
     command.current_dir(&game_dir); // Run in game directory
     command.stdout(Stdio::piped());
@@ -551,7 +567,7 @@ async fn start_game(
     // Spawn and handle output
     let mut child = command
         .spawn()
-        .map_err(|e| format!("Failed to launch java: {}", e))?;
+        .map_err(|e| format!("Failed to launch Java at '{}': {}\nPlease check your Java installation and path configuration in Settings.", java_path.display(), e))?;
 
     emit_log!(window, "Java process started successfully".to_string());
 
@@ -1540,7 +1556,7 @@ async fn install_forge(
             );
         }
     };
-    let java_path = std::path::PathBuf::from(&java_path_str);
+    let java_path = utils::path::normalize_java_path(&java_path_str)?;
 
     emit_log!(window, "Running Forge installer...".to_string());
 
diff --git a/src-tauri/src/utils/mod.rs b/src-tauri/src/utils/mod.rs
index 00b9087..651d26b 100644
--- a/src-tauri/src/utils/mod.rs
+++ b/src-tauri/src/utils/mod.rs
@@ -1,4 +1,5 @@
 pub mod zip;
+pub mod path;
 
 // File system related utility functions
 #[allow(dead_code)]
diff --git a/src-tauri/src/utils/path.rs b/src-tauri/src/utils/path.rs
new file mode 100644
index 0000000..453064e
--- /dev/null
+++ b/src-tauri/src/utils/path.rs
@@ -0,0 +1,105 @@
+/// Path utilities for cross-platform compatibility
+use std::path::PathBuf;
+
+/// Normalize a Java executable path for the current platform.
+///
+/// On Windows:
+/// - Adds .exe extension if missing
+/// - Attempts to locate java.exe in PATH if only "java" is provided
+/// - Validates that the path exists
+///
+/// On Unix:
+/// - Returns the path as-is
+///
+/// # Arguments
+/// * `java_path` - The Java executable path to normalize
+///
+/// # Returns
+/// * `Ok(PathBuf)` - Normalized path that exists
+/// * `Err(String)` - Error if the path cannot be found or validated
+#[cfg(target_os = "windows")]
+pub fn normalize_java_path(java_path: &str) -> Result<PathBuf, String> {
+    let mut path = PathBuf::from(java_path);
+
+    // If path doesn't exist and doesn't end with .exe, try adding .exe
+    if !path.exists() && path.extension().is_none() {
+        path.set_extension("exe");
+    }
+
+    // If still not found and it's just "java.exe", try to find it in PATH
+    if !path.exists() && path.file_name() == Some(std::ffi::OsStr::new("java.exe")) {
+        // Try to locate java.exe in PATH
+        if let Ok(output) = std::process::Command::new("where").arg("java").output() {
+            if output.status.success() {
+                let paths = String::from_utf8_lossy(&output.stdout);
+                if let Some(first_path) = paths.lines().next() {
+                    path = PathBuf::from(first_path.trim());
+                }
+            }
+        }
+    }
+
+    // Verify the path exists
+    if !path.exists() {
+        return Err(format!(
+            "Java executable not found at: {}\nPlease configure a valid Java path in Settings.",
+            path.display()
+        ));
+    }
+
+    Ok(path)
+}
+
+#[cfg(not(target_os = "windows"))]
+pub fn normalize_java_path(java_path: &str) -> Result<PathBuf, String> {
+    let path = PathBuf::from(java_path);
+
+    if !path.exists() && java_path == "java" {
+        // Try to find java in PATH
+        if let Ok(output) = std::process::Command::new("which").arg("java").output() {
+            if output.status.success() {
+                let path_str = String::from_utf8_lossy(&output.stdout);
+                if let Some(first_path) = path_str.lines().next() {
+                    return Ok(PathBuf::from(first_path.trim()));
+                }
+            }
+        }
+    }
+
+    if !path.exists() && java_path != "java" {
+        return Err(format!(
+            "Java executable not found at: {}\nPlease configure a valid Java path in Settings.",
+            path.display()
+        ));
+    }
+
+    Ok(path)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg(target_os = "windows")]
+    fn test_normalize_adds_exe_extension() {
+        // This test assumes java is not in the current directory
+        let result = normalize_java_path("nonexistent_java");
+        // Should fail since the file doesn't exist
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_normalize_existing_path() {
+        // Test with a path that should exist on most systems
+        #[cfg(target_os = "windows")]
+        let test_path = "C:\\Windows\\System32\\cmd.exe";
+        #[cfg(not(target_os = "windows"))]
+        let test_path = "/bin/sh";
+
+        if std::path::Path::new(test_path).exists() {
+            let result = normalize_java_path(test_path);
+            assert!(result.is_ok());
+        }
+    }
+}