Style Guide

Style Guide for Rust in Polkadot

• Indent using tabs
• Never have spaces on a line prior to a non-whitespace character
• Follow-on lines are only ever a single indent from the original line.

fn long_simple_calculation(some_long_variable_a: i8, some_long_variable_b: i8) -> bool {
	let x = some_long_variable_a * some_long_variable_b
		- some_long_variable_b / some_long_variable_a
		+ sqrt(some_long_variable_a) - sqrt(some_long_variable_b);
	x > 10
}

• Indent level should follow open parens/brackets, but should be collapsed to the smallest number of levels actually used:

fn calculate(some_long_variable_a: f32, some_long_variable_b: f32, some_long_variable_c: f32) -> f32 {
	(-some_long_variable_b + sqrt(
		// two parens open, but since we close them both on the same line, only one indent level is used
		some_long_variable_b * some_long_variable_b
		- 4 * some_long_variable_a * some_long_variable_c
	// both closed here at beginning of line, so back to the original indent level
	)) / (2 * some_long_variable_a)
}

• where is indented, and its items are indented one further
• Long arg lists or function calls are indented similarly to code blocks, and once one param is indented in such a way, all others should be, too. Run-on parameter lists are also acceptable for single-line run-ons of basic function calls.

fn foo(
	really_long_parameter_name_1: SomeLongTypeName,
	really_long_parameter_name_2: SomeLongTypeName,
	shrt_nm_1: u8,
	shrt_nm_2: u8
) {
	// Complex line (not just a function call, also a let statement). Full structure.
	let (a, b) = bar(
		really_long_parameter_name_1,
		really_long_parameter_name_2,
		shrt_nm_1,
		shrt_nm_2,
	);
	// Long, simple function call that fits onto two lines. Inline with a run-on.
	waz(really_long_parameter_name_1, really_long_parameter_name_2,
		shrt_nm_1, shrt_nm_2);
	// Short function call. Inline.
	baz(a, b);
}

• Always end last item of a multi-line comma-delimited set with , when legal:

struct Point<T> {
	x: T,
	y: T,    // <-- Multiline comma-delimited lists end with a trailing ,
}

// Single line comma-delimited items do not have a trailing `,`
enum Meal { Breakfast, Lunch, Dinner };

• Avoid trailing ;s where unneeded.

if condition {
	return 1    // <-- no ; here
}

• match arms may be either blocks or have a trailing , but not both.
• Blocks should not be used unnecessarily.

match meal {
	Meal::Breakfast => "eggs",
	Meal::Lunch => { check_diet(); recipe() }
//	Meal::Dinner => { return Err("Fasting") }   // WRONG
	Meal::Dinner => return Err("Fasting"),
}