silently fails to format match expression if arm pat contains comment

[bradjc]

For Tock, we run rustfmt with Travis CI, and some PRs (example1 and example2) are passing a rustfmt check while still using tabs for indentation.

• No config options (we use defaults only).
• Noticed this on nightly-2020-03-06 and nightly-2020-04-10.

I've also tried manually running rustfmt in the relevant crate on my computer and see the same effect. Based on a question on discord, I am opening this issue.

One example (src):

impl Driver for L3gd20Spi<'a> {
    fn command(&self, command_num: usize, data1: usize, data2: usize, _: AppId) -> ReturnCode {
        match command_num {
            0 /* check if present */ => ReturnCode::SUCCESS,
            // Check is sensor is correctly connected
            1 => {
				if self.status.get () == L3gd20Status::Idle {
					self.is_present ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}

			}
			// Power On
            2 => {
				if self.status.get () == L3gd20Status::Idle {
					self.power_on ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			// Set Scale
            3 => {
				if self.status.get () == L3gd20Status::Idle {
					let scale = data1 as u8;
					self.set_scale (scale);
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
			// Enable High Pass Filter
            4 => {
				if self.status.get () == L3gd20Status::Idle {
					let mode = data1 as u8;
					let divider = data2 as u8;
					self.set_hpf_parameters (mode, divider);
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			// Set High Pass Filter Mode and Divider
            5 => {
				if self.status.get () == L3gd20Status::Idle {
					let enabled = if data1 == 1 { true } else { false };
					self.enable_hpf (enabled);
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
			// Read XYZ
            6 => {
				if self.status.get () == L3gd20Status::Idle {
					self.read_xyz ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			// Read Temperature
            7 => {
				if self.status.get () == L3gd20Status::Idle {
					self.read_temperature ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
            // default
            _ => ReturnCode::ENOSUPPORT,
        }
    }

    fn subscribe(
        &self,
        subscribe_num: usize,
        callback: Option<Callback>,
        _app_id: AppId,
    ) -> ReturnCode {
        match subscribe_num {
            0 /* set the one shot callback */ => {
				self.callback.insert (callback);
				ReturnCode::SUCCESS
			},
            // default
            _ => ReturnCode::ENOSUPPORT,
        }
    }
}

Another example (src):

impl Driver for Lsm303dlhcI2C<'a> {
    fn command(&self, command_num: usize, data1: usize, data2: usize, _: AppId) -> ReturnCode {
        match command_num {
            0 /* check if present */ => ReturnCode::SUCCESS,
            // Check is sensor is correctly connected
            1 => {
				if self.state.get () == State::Idle {
					self.is_present ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}

			}
			// Set Accelerometer Power Mode
            2 => {
				if self.state.get () == State::Idle {
                    if let Some (data_rate) = Lsm303dlhcAccelDataRate::from_usize (data1) {
                        self.set_power_mode(data_rate, if data2 != 0 { true } else { false });
                        ReturnCode::SUCCESS
                    }
                    else
                    {
                        ReturnCode::EINVAL
                    }
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			// Set Accelerometer Scale And Resolution
            3 => {
				if self.state.get () == State::Idle {
					if let Some (scale) = Lsm303dlhcScale::from_usize(data1) {
                        self.set_scale_and_resolution(scale, if data2 != 0 { true } else { false });
                        ReturnCode::SUCCESS
                    }
                    else
                    {
                        ReturnCode::EINVAL
                    }
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
            // Set Magnetometer Temperature Enable and Data Rate 
            4 => {
				if self.state.get () == State::Idle {
                    if let Some (data_rate) = Lsm303dlhcMagnetoDataRate::from_usize (data2) {
                        self.set_temperature_and_magneto_data_rate (if data1 != 0 { true } else { false }, data_rate);
                        ReturnCode::SUCCESS
                    }
                    else
                    {
                        ReturnCode::EINVAL
                    }
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			// Set Magnetometer Range
            5 => {
				if self.state.get () == State::Idle {
					if let Some (range) = Lsm303dlhcRange::from_usize(data1) {
                        self.set_range(range);
                        ReturnCode::SUCCESS
                    }
                    else
                    {
                        ReturnCode::EINVAL
                    }
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
			// Read Acceleration XYZ
            6 => {
				if self.state.get () == State::Idle {
					self.read_acceleration_xyz ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
            // Read Temperature
            7 => {
				if self.state.get () == State::Idle {
					self.read_temperature ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
			}
			8 => {
				if self.state.get () == State::Idle {
					self.read_magnetometer_xyz ();
					ReturnCode::SUCCESS
				}
				else
				{
					ReturnCode::EBUSY
				}
            }
            // default
            _ => ReturnCode::ENOSUPPORT,
        }
    }

    fn subscribe(
        &self,
        subscribe_num: usize,
        callback: Option<Callback>,
        _app_id: AppId,
    ) -> ReturnCode {
        match subscribe_num {
            0 /* set the one shot callback */ => {
				self.callback.insert (callback);
				ReturnCode::SUCCESS
			},
            // default
            _ => ReturnCode::ENOSUPPORT,
        }
    }
}

[calebcartwright]

Thanks for the report @bradjc. Looks like the problem is with the block comment in the match first match arm that's resulting in rustfmt failing to do any formatting within the match blocks (not just failing to convert the tabs).

This is definitely a bug, and as a temporary workaround you may want to consider changing those two block comments on the 0 arms to inline comments above the arms like was done for the others

[Wilfred]

I've been bitten by this too. This affects both the match bodies and the match patterns. The following code is unmodified by rustfmt, and no warnings are produced:

fn parse_term() {
    match x { |
       TokenKind::Name => {
                let qualified_name =1;
            }
            | TokenKind::Suspend
            // foo
            | _ => {}
        }
}