Clone trait of TreeCursor might not be correctedly implemented

[Enter-tainer]

Many thanks to your awesome project!

After adding a dummy implementation to utf8_text(see silvanshade/tree-sitter-facade#34). I'm still experiencing errors.

index_bg.js:272 wasm-bindgen: imported JS function that was not marked as `catch` threw an error: memory access out of bounds

Stack:
RuntimeError: memory access out of bounds
    at http://localhost:5000/tree-sitter.wasm:wasm-function[22]:0x41ec
    at http://localhost:5000/tree-sitter.wasm:wasm-function[191]:0x2569c
    at TreeCursor.currentNode (webpack:///./node_modules/web-tree-sitter/tree-sitter.js?:4:42057)
    at eval (webpack:///./pkg/index_bg.js?:366:31)
    at logError (webpack:///./pkg/index_bg.js?:263:18)
    at Module.__wbg_currentNode_04cfbe6cd11c8027 (webpack:///./pkg/index_bg.js?:365:56)
    at __wbg_currentNode_04cfbe6cd11c8027 (http://localhost:5000/index.js:86:106)
    at web_tree_sitter_sys::TreeCursor::current_node::he854676394a58e9d (http://localhost:5000/7d4a6f82fcb2b88088ae.module.wasm:wasm-function[1074]:0x48d39)
    at tree_sitter_facade::tree_cursor::wasm::TreeCursor::node::h5ea81ee2cf927f75 (http://localhost:5000/7d4a6f82fcb2b88088ae.module.wasm:wasm-function[1156]:0x4a6de)
    at cxx2flow::parser::parse_stat::h1ee01db538459ef5 (http://localhost:5000/7d4a6f82fcb2b88088ae.module.wasm:wasm-function[37]:0x3e21)

After some debugging, I found that I have an invalid TreeCursor, which result in the failure of TreeCursor.currentNode.

https://docs.rs/web-tree-sitter-sys/0.2.6/src/web_tree_sitter_sys/lib.rs.html#626 says that TreeCursor has clone trait, but it seems that TreeCursor has no members. I'm not really familiar with wasm-bindgen. IIRC, the derived clone() function will call clone on every member of the struct. But given that TreeCursor has no members, I guess this will result in an empty clone function. Thus nothing is really cloned when calling TreeCursor::clone

[Enter-tainer]

After reading wasm-bindgen's guide, I realized that Clone trait is forwarded to inner types. Maybe my error is related to other issues.

[silvanshade]

It is actually possible that this is implemented incorrectly. Looking at the tree-sitter source, it seems that there is a special ts_tree_cursor_copy function that is used to copy a TreeCursor on the C binding side of things.

I can look into this but if it's implemented incorrectly it will probably require an update to the bindings upstream to expose a proper copy method that we can wrap.

[Enter-tainer]

Many thanks! I will try to provide a minimal reproducible example.

[silvanshade]

@Enter-tainer Apologies for the delay in addressing this.

I was just recently trying to expose the internal ts_tree_cursor_copy to the web bindings but it doesn't seem to be working correctly so I might have to try a different approach.

Do you happen to have a small example that demonstrates this behavior?

It would be interesting to verify that TreeCursor::clone on the native rust side works okay but that the wasm-bindgen version does not.

[Enter-tainer]

I will have a try this week. Thank you for your help!