Error::description() deprecated, should use Display trait

[Skaldebane]

Hi there! I just started using your library, and it worked perfectly well the first time I used it (2 days ago). The IDE was complaining about description() being deprecated, but it was only a warning and everything was working perfectly.

However now I'm getting a RuntimeException in Java whenever I try to call my JNI function, with the following message:

java.lang.RuntimeException: JNI call error!. Cause: description() is deprecated; use Display

This is quite confusing, because why on earth is this compile-time check inside the generated shared library file itself?! I couldn't really figure out what's causing this.

My only hypothesis for now is that the Error::description() function is automatically populated with that message to get the attention of developers to use Display instead, which makes it useless to understand what's going on under-the-hood.

[Skaldebane]

I checked the source code for Error in the standard lib, and yeah, description() is indeed hardcoded to that string.

From error.rs:

[Skaldebane]

It's been buried for a while: rust-lang/rfcs#2230

[giovanniberti]

Thank you for the issue! I'll try to fix it ASAP as it seems it impacts already other users #29

[Skaldebane]

I guess a recent version of Rust just shot that function off of std, since it's been deprecated for long enough :p

But yeah, using Display will make errors actually print something useful to make debugging easier, since description was made useless for quite some time now with the hardcoded message.

P.S.: Thanks a lot for this incredible crate! It makes JNI interop a breeze, alongside cargo-ndk which makes building for Android (with NDK) an easy one-line command!

[Skaldebane]

Hi! Any updates on this?

[EliseChouleur]

Hi !
Could you check with darling update ? #31

[Skaldebane]

@EliseChouleur assuming you're asking me, it may take me some time, but I'll give the PR a shot on Android and desktop and reply with the results!

[Skaldebane]

Hi again! Sorry for my delay, but I can confirm that #31 fixes the issue on Android.

Now instead of the confusing:
java.lang.RuntimeException: JNI call error!. Cause: description() is deprecated; use Display
it correctly reports the error message
java.lang.RuntimeException: JNI call error!. Cause: Java exception was thrown

So updating darling is a valid fix. I don't expect there to be any difference on the desktop (JVM) side, since this bug is purely from the Rust side.

[Skaldebane]

This makes me wonder, however, that it should be possible to pass a custom message to JniError::JavaException type, so that error messages are generally more helpful.

For example in this case, if I want information about the cause of the error, I'd have to log it right before returning the JniError::JavaException to keep those details.

However this should be its own issue.