if let clauses #5218Description
This code
if let Some(start) = (1_usize).checked_add(5) {
if let Some(end) = (2_usize).checked_add(5) {
// ...
}
}could be written like this
if let (Some(start), Some(end)) = ((1_usize).checked_add(5), (2_usize).checked_add(5)) {
// ...
}which would remove a layer of nesting.
The lint should only lint nested if let clauses, that are independent of each other.
For example this must be ignored (or handled like in #2521):
if let Some(start) = (1_usize).checked_add(5) {
if let Some(end) = call_fn(start) {
// ...
}
}but it should not matter, if there is code in between the if let clauses, as long as it does not influence the other if let clause(s):
if let Some(start) = (1_usize).checked_add(5) {
let x = 13_usize;
if let Some(end) = (2_usize).checked_add(5) {
// ...
}
let y = 15_usize;
}I think that there should not be a limit on how many nested if let clauses should be linted, because it would improve the readability either way.
Another thing to consider would be else clauses. I think this lint should only trigger, if the nested else clauses have the same body:
if let Some(start) = (1_usize).checked_add(5) {
if let Some(end) = (2_usize).checked_add(5) {
// ...
} else {
call_x();
}
} else {
call_x();
}would become
if let (Some(start), Some(end)) = ((1_usize).checked_add(5), (2_usize).checked_add(5)) {
// ...
} else {
call_x();
}It might be too difficult (for clippy), but it would be possible to refactor nested if let-clauses with different else-clauses too
if let Some(start) = (1_usize).checked_add(5) {
if let Some(end) = (2_usize).checked_add(5) {
// ...
} else {
call_z(start);
}
} else {
call_y();
}->
match ((1_usize).checked_add(5), (2_usize).checked_add(5)) {
(Some(start), Some(end)) => {
// ...
}
(Some(start), None) => {
call_z(start);
}
(None, None) => {
call_y();
}
_ => {
// this was not reachable in the original code (end would only be matched if Some(start))
}
}Should I move this issue in to several smaller ones?