Bugzilla

Okay, so I think I've figured this out: This occurs because we incorrectly "calculate" the deserialiser tags in Rust. We do this: 

https://searchfox.org/mozilla-central/rev/4a8bd8efdfaa43dd14a16d3cb15bf86796fd1def/tools/profiler/rust-api/src/marker/deserializer_tags_state.rs#64
```rust
let unique_marker_tag = &T::marker_type_name as *const _ as usize;
```
which //claims// to take the address of the `marker_type_name` method of the struct that we're trying to serialise. In reality, however, it does something different (I'm unsure of the specific semantics), and always returns a constant `1`. 

Because of this, when we come to deserialise, we always choose the deserialiser function of the //first// marker that we recorded. In my case, that involved trying to deserialise two integers (rather than an integer and a bool), which then panicked.

To fix this, we need to make it so that the `unique_marker_tag` is, well, unique. This seems to work instead: 

```rust
let unique_marker_tag = T::marker_type_name as *const () as usize;
```

Okay, so I think I've figured this out: This occurs because we incorrectly "calculate" the deserialiser tags in Rust. We do this: 

https://searchfox.org/mozilla-central/rev/4a8bd8efdfaa43dd14a16d3cb15bf86796fd1def/tools/profiler/rust-api/src/marker/deserializer_tags_state.rs#64
```rust
let unique_marker_tag = &T::marker_type_name as *const _ as usize;
```
which *claims* to take the address of the `marker_type_name` method of the struct that we're trying to serialise. In reality, however, it does something different (I'm unsure of the specific semantics), and always returns a constant `1`. 

Because of this, when we come to deserialise, we always choose the deserialiser function of the *first* marker that we recorded. In my case, that involved trying to deserialise two integers (rather than an integer and a bool), which then panicked.

To fix this, we need to make it so that the `unique_marker_tag` is, well, unique. This seems to work instead: 

```rust
let unique_marker_tag = T::marker_type_name as *const () as usize;
```