Error on creating a resource with a list of tuples in variant

[Exotik850]

Working on this pr and whenever I create a resource with a list of tuples inside of a variant like so:

the wit representation of the resource:

interface toml {
  /// The handle for a `TomlValue`
  resource toml {
    /// Creates a value in table and returns the handle
    constructor(value: toml-value);
    /// Clones value from table
    get: func() -> toml-value;
    /// Sets value in table
    set: func(value: toml-value);
    /// Clones the value and makes a new handle
    clone: func() -> toml;
  }

  variant toml-value {
    %string(string),
    integer(s64),
    float(float64),
    boolean(bool),
    datetime(datetime),
    %array(array),
    %table(table),
  }

  record datetime {
    date: option<date>,
    time: option<time>,
    offset: option<offset>,
  }

  record date {
    year: u16,
    month: u8,
    day: u8,
  }

  record time {
    hour: u8,
    minute: u8, 
    second: u8,
    nanosecond: u32,
  }

  variant offset {
    z,
    custom(tuple<s8,u8>),
  }

  type array = list<toml>;
  type table = list<tuple<string, toml>>; // The problem child
}

This is the implementation of the resource, the bindings just call these functions:

impl PluginRuntimeState {
    pub fn get_toml(&self, value: Resource<Toml>) -> TomlValue {
        self.tomls
            .get(value.rep() as usize)
            .expect("Resource gaurantees existence")
            .clone()
    }

    pub fn set_toml(&mut self, key: Resource<Toml>, value: TomlValue) {
        *self
            .tomls
            .get_mut(key.rep() as usize)
            .expect("Resource gaurantees existence") = value;
    }

    pub fn insert_toml(&mut self, value: TomlValue) -> usize {
        self.tomls.insert(value)
    }

    pub fn new_toml(&mut self, value: TomlValue) -> Resource<Toml> {
        Resource::new_own(self.insert_toml(value) as u32)
    }

    pub fn clone_handle(&mut self, handle: &Resource<Toml>) -> Resource<Toml> {
        let new_toml = self.get_toml(Resource::new_own(handle.rep()));
        self.new_toml(new_toml)
    }
}

It throws this error when calling the constructor of the function with table values like so:

struct Plugin;

impl Guest for Plugin {
    fn get_default_config() -> Toml {
        let values = vec![(
            "Test".into(),
            Toml::new(TomlValue::String("THIS A TEST".into())),
        )];

        let table = TomlValue::Table(values);
        let toml = Toml::new(table); // The error occurs here

        let value = toml.get();
        log(&format!("{value:?}"));
        toml
    }
    ...

The error isn't very helpful as to what went wrong:

[WARN] Couldn't get default config from plugin: TestPlugin : error while executing at wasm backtrace:
   0: 0x2a0f8a - wit-component:shim!indirect-plugins:main/toml-[constructor]toml
   1: 0x979c - test_plugin::plugins::main::toml::Toml::new::he2c438c40e24e4ec
                   at D:\Code\Rust\dioxus\packages\cli-plugin\src\export_plugin.rs:4:9
   2: 0x168e2 - <test_plugin::Plugin as test_plugin::exports::plugins::main::definitions::Guest>::get_default_config::h924bfaae2c70a627
                   at D:\Code\Rust\dioxus\packages\cli-plugin\examples\test-plugin\src\lib.rs:21:20
   3: 0x11b99 - plugins:main/definitions#get-default-config
                   at D:\Code\Rust\dioxus\packages\cli-plugin\src\export_plugin.rs:4:9

I thought it was because it was a list of resources at first, but when it's initialized with an array object it works just fine, and
even when the implementation and signature are changed to be a list<tuple<string, string>>, it will cause the same error.

I would like to try and fix this if I can, but I don't even know where to start 😅

[alexcrichton]

Thanks for the report, but there's quite a lot behind this issue which isn't here and might be where the issue is from reading over this. Nothing looks awry from reading over this but I'm not sure for example where the [WARN] is coming from. Should the [WARN] not be printed? If so, could you show the logic that's printing it?

If you could provide a reproducible example for this that'd be a great start!

[Exotik850]

The [WARN] is just our own debugging when calling the binding, which is being called here

I've made a repo that reproduces the issue in as little code I could: https://github.com/Exotik850/wit-resource-fail
Just running the test-host example should do it, but all the other parts of the process are in there as well,
Thank you for your quick reply!

[alexcrichton]

How did you build test.wasm? I can reproduce with test.wasm as-is in the repository but if I run cargo build -p test-plugin --target wasm32-wasi and rebuild test.wasm myself with wasm-tools component new ./target/wasm32-wasi/debug/test_plugin.wasm --adapt wasi_snapshot_preview1.wasm -o test.wasm then the issue doesn't reproduce.

Also, to confirm, is the error you're seeing this:

thread 'main' panicked at examples/test-host/src/main.rs:101:10:
called `Result::unwrap()` on an `Err` value: error while executing at wasm backtrace:
    0: 0x259cbd - wit-component:shim!indirect-plugins:main/toml-[constructor]toml
    1: 0x6404 - <unknown>!test_plugin::plugins::main::toml::Toml::new::h40eba8924dad2660
    2: 0x137c - <unknown>!<test_plugin::Plugin as test_plugin::exports::plugins::main::definitions::Guest>::run::h82681d419b0799ec
    3: 0x1576 - <unknown>!plugins:main/definitions#run
note: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information

Caused by:
    invalid utf-8 sequence of 1 bytes from index 0

If so that indicates what's probably a bug in the guest and/or corruption there because invalid utf-8 is being passed somewhere by accident.

[Exotik850]

Hmm, that's quite strange, It works on my work laptop but not my home computer, both running windows 11.
I've added a readme that shows what we've done to make the wasm files and run it, so I'll dig a bit deeper once I get home and see if it isn't just an issue on my computer,
Thanks for all your help!

[Exotik850]

After a bit more testing I can't find what the exact difference would be in how each is being run, setting all of the toolchains to be the same, both have the latest version of wasm-tools, both have the same operating system version and everything, but when the exact same commands are run they both have different results:
Laptop output

Desktop output

With both building everything from scratch beforehand and making the wasm file into a component

Edit: It is also throwing the same error as my windows desktop when ran on mac

[Exotik850]

Turns out I forgot to have $env:CARGO_INCREMENTAL=true set on the desktop, once that was set it started building it correctly, not really sure how that would affect this particular issue but if it works it works 🤷‍♂️

[alexcrichton]

Hm I wonder if you're perhaps running into a rustc issue in that case? I'm also not sure how, though. Do you have a way to build test.wasm from source that reproduces the issue though?

[Exotik850]

After fiddling with it for a while I think I'm getting close to something, if I initialize the string that would go into the tomlvalue beforehand like this:

let val = "THIS A TEST".to_string();
log(&val);
let val = TomlValue::String(val);
let key = "Test".to_string();
log(&key);
let values: Vec<(String, Toml)> = vec![(
    key,
    Toml::new(val),
)];
let table = TomlValue::Table(values);
let toml = Toml::new(table);
let value = toml.get();
log(&format!("{value:?}"));
toml

it jumbles it before the variant is sent over to the host:

THIS A TEST
Test
INSERTING TOML : TomlValue::String("l \u{10}\0l \u{10}\0\u{10}\0\0")
New Resource : 0
INSERTING TOML : TomlValue::Table([("@\"\u{10}\0", Resource { rep: 0, state: "own (not in table)" })])
New Resource : 1
GETTING TOML Resource { rep: 1, state: "borrow" }
 Slab { len: 2, cap: 4 }
TomlValue::Table([("@\"\u{10}\0", Toml { handle: Resource { handle: 1 } })])
TomlValue::Table([("@\"\u{10}\0", Resource { rep: 0, state: "own (not in table)" })])

But when initialized in the same line as the tomlvalue like this:

let val = TomlValue::String("THIS A TEST".to_string());

It doesn't let the toml for the string be initialized at all:

Test
thread 'main' panicked at examples\test-host\src\main.rs:103:10:
called `Result::unwrap()` on an `Err` value: error while executing at wasm backtrace:
    0: 0x240ddf - wit-component:shim!indirect-plugins:main/toml-[constructor]toml
    1: 0x9dd5 - test_plugin::plugins::main::toml::Toml::new::hedffd76ba3fde429
                    at D:\Code\Rust\wit-resource-fail\src\export_plugin.rs:4:9
    2: 0x5c6c - <test_plugin::Plugin as test_plugin::exports::plugins::main::definitions::Guest>::run::h7c3d96060d2a60a7
                    at D:\Code\Rust\wit-resource-fail\examples\test-plugin\src\lib.rs:21:13
    3: 0x6010 - plugins:main/definitions#run
                    at D:\Code\Rust\wit-resource-fail\src\export_plugin.rs:4:9

Caused by:
    invalid utf-8 sequence of 1 bytes from index 0

This happens on both my laptop and my desktop, and the most recent changes have been pushed to the MRE

[alexcrichton]

Can you provide details on how to build this all from source to reproduce the error you're seeing on both systems? Basically what repos at what commits are used and what commands are done to run this.

[Exotik850]

There's a readme in this repo that has all of the commands to build the wasm and then run the host. Swapping between the commented out lines in the test-plugin example lib.rs file reproduces the errors on both systems

[alexcrichton]

Ah ok this is definitely a bug in the generated bindings and what's amounting to UB/use-after-free. Looking at the generated code I see:

 91             impl Toml {
 92                 #[allow(unused_unsafe, clippy::all)]
 93                 /// Creates a value in table and returns the handle
 94                 pub fn new(value: TomlValue) -> Self {
 95                     #[allow(unused_imports)]
 96                     use wit_bindgen::rt::{alloc, string::String, vec::Vec};
 97                     unsafe {
 98                         let mut cleanup_list = Vec::new();
 99                         let (result4_0, result4_1, result4_2) = match value {
100                             TomlValue::String(e) => {
101                                 let vec0 = e;
102                                 let ptr0 = vec0.as_ptr() as i32;
103                                 let len0 = vec0.len() as i32;
104                                 (0i32, ptr0, len0)
105                             }
...

where the string e is dropped before the ptr/len are ready by the imported function. This I think additionally applies to the other case as well.

[alexcrichton]

Ok I have gotten around to really digging into this and I've confirmed with your repository that it's fixed by #846. Thank you again for taking the time to open this issue and work with me debugging it, I very much appreciate it!

[Exotik850]

Absolutely! Glad I could be of help 😊