rust/crates/assists/src/handlers/replace_if_let_with_match.rs

use syntax::{
    ast::{
        self,
        edit::{AstNodeEdit, IndentLevel},
        make,
    },
    AstNode,
};

use crate::{utils::unwrap_trivial_block, AssistContext, AssistId, AssistKind, Assists};
use ide_db::ty_filter::TryEnum;

// Assist: replace_if_let_with_match
//
// Replaces `if let` with an else branch with a `match` expression.
//
// ```
// enum Action { Move { distance: u32 }, Stop }
//
// fn handle(action: Action) {
//     <|>if let Action::Move { distance } = action {
//         foo(distance)
//     } else {
//         bar()
//     }
// }
// ```
// ->
// ```
// enum Action { Move { distance: u32 }, Stop }
//
// fn handle(action: Action) {
//     match action {
//         Action::Move { distance } => foo(distance),
//         _ => bar(),
//     }
// }
// ```
pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
    let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
    let cond = if_expr.condition()?;
    let pat = cond.pat()?;
    let expr = cond.expr()?;
    let then_block = if_expr.then_branch()?;
    let else_block = match if_expr.else_branch()? {
        ast::ElseBranch::Block(it) => it,
        ast::ElseBranch::IfExpr(_) => return None,
    };

    let target = if_expr.syntax().text_range();
    acc.add(
        AssistId("replace_if_let_with_match", AssistKind::RefactorRewrite),
        "Replace with match",
        target,
        move |edit| {
            let match_expr = {
                let then_arm = {
                    let then_block = then_block.reset_indent().indent(IndentLevel(1));
                    let then_expr = unwrap_trivial_block(then_block);
                    make::match_arm(vec![pat.clone()], then_expr)
                };
                let else_arm = {
                    let pattern = ctx
                        .sema
                        .type_of_pat(&pat)
                        .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty))
                        .map(|it| it.sad_pattern())
                        .unwrap_or_else(|| make::wildcard_pat().into());
                    let else_expr = unwrap_trivial_block(else_block);
                    make::match_arm(vec![pattern], else_expr)
                };
                let match_expr =
                    make::expr_match(expr, make::match_arm_list(vec![then_arm, else_arm]));
                match_expr.indent(IndentLevel::from_node(if_expr.syntax()))
            };

            edit.replace_ast::<ast::Expr>(if_expr.into(), match_expr);
        },
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::tests::{check_assist, check_assist_target};

    #[test]
    fn test_replace_if_let_with_match_unwraps_simple_expressions() {
        check_assist(
            replace_if_let_with_match,
            r#"
impl VariantData {
    pub fn is_struct(&self) -> bool {
        if <|>let VariantData::Struct(..) = *self {
            true
        } else {
            false
        }
    }
}           "#,
            r#"
impl VariantData {
    pub fn is_struct(&self) -> bool {
        match *self {
            VariantData::Struct(..) => true,
            _ => false,
        }
    }
}           "#,
        )
    }

    #[test]
    fn test_replace_if_let_with_match_doesnt_unwrap_multiline_expressions() {
        check_assist(
            replace_if_let_with_match,
            r#"
fn foo() {
    if <|>let VariantData::Struct(..) = a {
        bar(
            123
        )
    } else {
        false
    }
}           "#,
            r#"
fn foo() {
    match a {
        VariantData::Struct(..) => {
            bar(
                123
            )
        }
        _ => false,
    }
}           "#,
        )
    }

    #[test]
    fn replace_if_let_with_match_target() {
        check_assist_target(
            replace_if_let_with_match,
            r#"
impl VariantData {
    pub fn is_struct(&self) -> bool {
        if <|>let VariantData::Struct(..) = *self {
            true
        } else {
            false
        }
    }
}           "#,
            "if let VariantData::Struct(..) = *self {
            true
        } else {
            false
        }",
        );
    }

    #[test]
    fn special_case_option() {
        check_assist(
            replace_if_let_with_match,
            r#"
enum Option<T> { Some(T), None }
use Option::*;

fn foo(x: Option<i32>) {
    <|>if let Some(x) = x {
        println!("{}", x)
    } else {
        println!("none")
    }
}
           "#,
            r#"
enum Option<T> { Some(T), None }
use Option::*;

fn foo(x: Option<i32>) {
    match x {
        Some(x) => println!("{}", x),
        None => println!("none"),
    }
}
           "#,
        );
    }

    #[test]
    fn special_case_result() {
        check_assist(
            replace_if_let_with_match,
            r#"
enum Result<T, E> { Ok(T), Err(E) }
use Result::*;

fn foo(x: Result<i32, ()>) {
    <|>if let Ok(x) = x {
        println!("{}", x)
    } else {
        println!("none")
    }
}
           "#,
            r#"
enum Result<T, E> { Ok(T), Err(E) }
use Result::*;

fn foo(x: Result<i32, ()>) {
    match x {
        Ok(x) => println!("{}", x),
        Err(_) => println!("none"),
    }
}
           "#,
        );
    }

    #[test]
    fn nested_indent() {
        check_assist(
            replace_if_let_with_match,
            r#"
fn main() {
    if true {
        <|>if let Ok(rel_path) = path.strip_prefix(root_path) {
            let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
            Some((*id, rel_path))
        } else {
            None
        }
    }
}
"#,
            r#"
fn main() {
    if true {
        match path.strip_prefix(root_path) {
            Ok(rel_path) => {
                let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
                Some((*id, rel_path))
            }
            _ => None,
        }
    }
}
"#,
        )
    }
}