Unwrap in I2C transaction

Let's say I have an I2C transaction like this one below. Clearly, any of the operations can fail and in this case error should be returned (At least I2c interface allows this). To simulate such failed operation, I was expecting with_error approach to work (Line 3).

let mut i2c = Mock::new(&[
    I2cTransaction::transaction_start(0x76),
    I2cTransaction::write(0x76, vec![0x88]), // .with_error(I2cErrorKind::Other),
    I2cTransaction::read(0x76, vec![0xCC, 0x6D, 0x1B, 0x68, 0x32, 0x00]),
    I2cTransaction::write(0x76, vec![0xA1]),
    I2cTransaction::read(0x76, vec![0x4B]),
    I2cTransaction::write(0x76, vec![0xE1]),
    I2cTransaction::read(0x76, vec![0x70, 0x01, 0x00, 0x13, 0x21, 0x03, 0x1E]),
    I2cTransaction::write(0x76, vec![0xFA]),
    I2cTransaction::read(0x76, vec![0x7E, 0x9B, 0x00, 0x5D, 0xC2])
        .with_error(I2cErrorKind::Other),
    I2cTransaction::transaction_end(0x76),
])

But it does not and causes panic instead. This panic originates from unwrap on the following line:
https://github.com/dbrgn/embedded-hal-mock/blob/e11348e9d34ef5809eb3b13979bab0efd7d92a44/src/eh1/i2c.rs#L273
For me it seems ? would be more appropriate.

[simonsso]

Sounds reasonable

[simonsso]

I tried this one-line fix and it does not work exactly as you describe in this ticket. (I simplified your example above)

When the error is propagated from line 273 the entire transaction is aborted and transaction_end is not consumed. Not sure what should be the expected behaviour here.

    #[test]
    fn write() {
        use Transaction as I2cTransaction;
        let expectations = [
            I2cTransaction::transaction_start(0x76),
            I2cTransaction::write(0x76, vec![0x88]).with_error(ErrorKind::Other),
            // I2cTransaction::transaction_end(0x76),  // This token never gets consumed
        ];
        let mut i2c = Mock::new(&expectations);

        let mut operations = [Operation::Write(
            &[0x88])];
        let x = i2c.transaction(0x76, &mut operations);
        assert!(x.is_err());

        i2c.done();
    }