Size of Operator in binary

[thesuhas]

Is there anyway one can determine the size of a wasmparser::Operator in binary on encoding? I would like this information to find the offset of the instruction in the binary but I don't see how one could obtain it.
An idea is to create an empty wasm_encoder::Module and create an empty CodeSection. Encode the respective instruction in it and use the size of the code section before and after encoding the instruction to find the size in binary

[fitzgen]

I don't believe we expose an easier way of doing it now than what you've sketched but I don't think there is any fundamental reason we couldn't do better

[fitzgen]

Actually, we implement wasm_encoder::Encode for wasm_encoder::Instruction so I think it would be slightly easier (compared to your OP) to do something like

use wasm_encoder::{Encode, reencode::Reencode};

let op: wasmparser::Operator = todo!();
let inst: wasm_encoder::Instruction = wasm_encoder::RoundtripReencoder.instruction(op)?;

let mut buf = vec![];
inst.encode(&mut buf);

Ok(buf.len())

[fitzgen]

I don't think we could really do anything better than this for an arbitrary wasmparser::Operator.

If you are parsing the operator yourself, I think you could look at the OperatorReader's underlying BinaryReader's current offset before and after parsing, and then save that info somewhere.