Incoming crash reports from Rust/C/C++ code will include a minidump. During processing, minidump-stackwalk walks the stack in the minidump, symbolicates the frames in the stacks, and adds a json blob to the processed crash with stack trace structures in it.
Later in the processing pipeline, the signature generation rule will kick off, look at the json blob and generate a signature using the symbolicated frames and a bunch of processing around symbols-to-skip, sentinels, and all that.
Incoming crash reports from Java code are completely different. The Java stack trace is added as a string to the JavaStackTrace field. There's little to no information for those frames. Signature generation for Java stacks pretty much just look at the exception and the line it happened on. There's no processing, no symbols-to-skip, no sentinels, etc.
This tracker covers gauging interest in redoing signature generation for Java crash reports and if there's sufficient interest, figuring out how it should work. This might involve changing the crash reporter for Java crashes such that it includes more information to work with.