feature: Add Replace if let else with Option::map_or_else assist

[Emilgardis]

Implements the option_if_let_else clippy lint.

Screen.Recording.2023-12-05.at.18.30.03.webm

[Emilgardis]

This works fine, however we don't check for control flow like break, return or continue. I think that's fine.

I want to also implement the reverse but I had trouble implementing it.

[Emilgardis]

I don't know if this is needed, stolen from

rust-analyzer/crates/ide-assists/src/handlers/replace_if_let_with_match.rs

Lines 82 to 88 in b2f6fd4

	// FIXME: If one `let` is wrapped in parentheses and the second is not,
	// we'll exit here.
	if scrutinee_to_be_expr.syntax().text() != expr.syntax().text() {
	// Only if all condition expressions are equal we can merge them into a match
	return None;
	}
	pat_seen = true;

[Veykril]

I don't think this applies here

[Emilgardis]

this doesn't seem to handle

if let Some(ref field) = self.field {
    field.eq_ignore_ascii_case(other)
} else $0if let Some(field2) = self.field2 {
    self.something()
} else {
    false
}

well, it becomes

if let Some(ref field) = self.field {
    field.eq_ignore_ascii_case(other)
} else self.field2.map_or_else(|| {
    false
}, |field2| {
    self.something()
})

which is obviously wrong.

[Emilgardis]

We also need to prevent

let _ = if $0let Some(ref mut field) = self.field2 {
    *field = "".to_owned();
    field == other
} else {
    true
}

or make it change to

let _ = self.field2.as_mut().map_or_else(|| {
    true
}, |field| {
    *field = "".to_owned();
    field == other
})

however I can't figure out how to get the bindings inside the pattern

[Veykril]

Looks like we can just ? on the result of single_let

[Veykril]

I don't think this applies here

[Veykril]

this doesn't seem to handle

if let Some(ref field) = self.field {
    field.eq_ignore_ascii_case(other)
} else $0if let Some(field2) = self.field2 {
    self.something()
} else {
    false
}

well, it becomes

if let Some(ref field) = self.field {
    field.eq_ignore_ascii_case(other)
} else self.field2.map_or_else(|| {
    false
}, |field2| {
    self.something()
})

which is obviously wrong.

It's fine if we just don't offer the assist in that case for the time being. better than creating these syntax errors.

[Veykril]

We also need to prevent

let _ = if $0let Some(ref mut field) = self.field2 {
    *field = "".to_owned();
    field == other
} else {
    true
}

or make it change to

let _ = self.field2.as_mut().map_or_else(|| {
    true
}, |field| {
    *field = "".to_owned();
    field == other
})

however I can't figure out how to get the bindings inside the pattern

You can get the binding for that here https://github.com/rust-lang/rust-analyzer/pull/16031/files#diff-74f54460a4549ebe1f552b2513663b9eac476eef5399254c8895d6177094baa0R70-R72

tuple_pat is your pattern in that case, you just gotta inspect it there (ref mut ident in that case would be an IdentPat with ref and mut keyword being some)

[Veykril]

Closing due to inactivity, feel free to come back to this if you find the time