crates/ra_assists/src/handlers/introduce_variable.rs

use ra_syntax::{
    ast::{self, AstNode},
    SyntaxKind::{
        BLOCK_EXPR, BREAK_EXPR, COMMENT, LAMBDA_EXPR, LOOP_EXPR, MATCH_ARM, PATH_EXPR, RETURN_EXPR,
        WHITESPACE,
    },
    SyntaxNode, TextUnit,
};
use stdx::format_to;
use test_utils::tested_by;

use crate::{Assist, AssistCtx, AssistId};

// Assist: introduce_variable
//
// Extracts subexpression into a variable.
//
// ```
// fn main() {
//     <|>(1 + 2)<|> * 4;
// }
// ```
// ->
// ```
// fn main() {
//     let var_name = (1 + 2);
//     var_name * 4;
// }
// ```
pub(crate) fn introduce_variable(ctx: AssistCtx) -> Option<Assist> {
    if ctx.frange.range.is_empty() {
        return None;
    }
    let node = ctx.covering_element();
    if node.kind() == COMMENT {
        tested_by!(introduce_var_in_comment_is_not_applicable);
        return None;
    }
    let expr = node.ancestors().find_map(valid_target_expr)?;
    let (anchor_stmt, wrap_in_block) = anchor_stmt(expr.clone())?;
    let indent = anchor_stmt.prev_sibling_or_token()?.as_token()?.clone();
    if indent.kind() != WHITESPACE {
        return None;
    }
    ctx.add_assist(AssistId("introduce_variable"), "Extract into variable", move |edit| {
        let mut buf = String::new();

        let cursor_offset = if wrap_in_block {
            buf.push_str("{ let var_name = ");
            TextUnit::of_str("{ let ")
        } else {
            buf.push_str("let var_name = ");
            TextUnit::of_str("let ")
        };
        format_to!(buf, "{}", expr.syntax());
        let full_stmt = ast::ExprStmt::cast(anchor_stmt.clone());
        let is_full_stmt = if let Some(expr_stmt) = &full_stmt {
            Some(expr.syntax().clone()) == expr_stmt.expr().map(|e| e.syntax().clone())
        } else {
            false
        };
        if is_full_stmt {
            tested_by!(test_introduce_var_expr_stmt);
            if full_stmt.unwrap().semicolon_token().is_none() {
                buf.push_str(";");
            }
            edit.replace(expr.syntax().text_range(), buf);
        } else {
            buf.push_str(";");

            // We want to maintain the indent level,
            // but we do not want to duplicate possible
            // extra newlines in the indent block
            let text = indent.text();
            if text.starts_with('\n') {
                buf.push_str("\n");
                buf.push_str(text.trim_start_matches('\n'));
            } else {
                buf.push_str(text);
            }

            edit.target(expr.syntax().text_range());
            edit.replace(expr.syntax().text_range(), "var_name".to_string());
            edit.insert(anchor_stmt.text_range().start(), buf);
            if wrap_in_block {
                edit.insert(anchor_stmt.text_range().end(), " }");
            }
        }
        edit.set_cursor(anchor_stmt.text_range().start() + cursor_offset);
    })
}

/// Check whether the node is a valid expression which can be extracted to a variable.
/// In general that's true for any expression, but in some cases that would produce invalid code.
fn valid_target_expr(node: SyntaxNode) -> Option<ast::Expr> {
    match node.kind() {
        PATH_EXPR | LOOP_EXPR => None,
        BREAK_EXPR => ast::BreakExpr::cast(node).and_then(|e| e.expr()),
        RETURN_EXPR => ast::ReturnExpr::cast(node).and_then(|e| e.expr()),
        BLOCK_EXPR => {
            ast::BlockExpr::cast(node).filter(|it| it.is_standalone()).map(ast::Expr::from)
        }
        _ => ast::Expr::cast(node),
    }
}

/// Returns the syntax node which will follow the freshly introduced var
/// and a boolean indicating whether we have to wrap it within a { } block
/// to produce correct code.
/// It can be a statement, the last in a block expression or a wanna be block
/// expression like a lambda or match arm.
fn anchor_stmt(expr: ast::Expr) -> Option<(SyntaxNode, bool)> {
    expr.syntax().ancestors().find_map(|node| {
        if let Some(expr) = node.parent().and_then(ast::Block::cast).and_then(|it| it.expr()) {
            if expr.syntax() == &node {
                tested_by!(test_introduce_var_last_expr);
                return Some((node, false));
            }
        }

        if let Some(parent) = node.parent() {
            if parent.kind() == MATCH_ARM || parent.kind() == LAMBDA_EXPR {
                return Some((node, true));
            }
        }

        if ast::Stmt::cast(node.clone()).is_some() {
            return Some((node, false));
        }

        None
    })
}

#[cfg(test)]
mod tests {
    use test_utils::covers;

    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};

    use super::*;

    #[test]
    fn test_introduce_var_simple() {
        check_assist(
            introduce_variable,
            "
fn foo() {
    foo(<|>1 + 1<|>);
}",
            "
fn foo() {
    let <|>var_name = 1 + 1;
    foo(var_name);
}",
        );
    }

    #[test]
    fn introduce_var_in_comment_is_not_applicable() {
        covers!(introduce_var_in_comment_is_not_applicable);
        check_assist_not_applicable(introduce_variable, "fn main() { 1 + /* <|>comment<|> */ 1; }");
    }

    #[test]
    fn test_introduce_var_expr_stmt() {
        covers!(test_introduce_var_expr_stmt);
        check_assist(
            introduce_variable,
            "
fn foo() {
    <|>1 + 1<|>;
}",
            "
fn foo() {
    let <|>var_name = 1 + 1;
}",
        );
        check_assist(
            introduce_variable,
            "
fn foo() {
    <|>{ let x = 0; x }<|>
    something_else();
}",
            "
fn foo() {
    let <|>var_name = { let x = 0; x };
    something_else();
}",
        );
    }

    #[test]
    fn test_introduce_var_part_of_expr_stmt() {
        check_assist(
            introduce_variable,
            "
fn foo() {
    <|>1<|> + 1;
}",
            "
fn foo() {
    let <|>var_name = 1;
    var_name + 1;
}",
        );
    }

    #[test]
    fn test_introduce_var_last_expr() {
        covers!(test_introduce_var_last_expr);
        check_assist(
            introduce_variable,
            "
fn foo() {
    bar(<|>1 + 1<|>)
}",
            "
fn foo() {
    let <|>var_name = 1 + 1;
    bar(var_name)
}",
        );
        check_assist(
            introduce_variable,
            "
fn foo() {
    <|>bar(1 + 1)<|>
}",
            "
fn foo() {
    let <|>var_name = bar(1 + 1);
    var_name
}",
        )
    }

    #[test]
    fn test_introduce_var_in_match_arm_no_block() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let x = true;
    let tuple = match x {
        true => (<|>2 + 2<|>, true)
        _ => (0, false)
    };
}
",
            "
fn main() {
    let x = true;
    let tuple = match x {
        true => { let <|>var_name = 2 + 2; (var_name, true) }
        _ => (0, false)
    };
}
",
        );
    }

    #[test]
    fn test_introduce_var_in_match_arm_with_block() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let x = true;
    let tuple = match x {
        true => {
            let y = 1;
            (<|>2 + y<|>, true)
        }
        _ => (0, false)
    };
}
",
            "
fn main() {
    let x = true;
    let tuple = match x {
        true => {
            let y = 1;
            let <|>var_name = 2 + y;
            (var_name, true)
        }
        _ => (0, false)
    };
}
",
        );
    }

    #[test]
    fn test_introduce_var_in_closure_no_block() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let lambda = |x: u32| <|>x * 2<|>;
}
",
            "
fn main() {
    let lambda = |x: u32| { let <|>var_name = x * 2; var_name };
}
",
        );
    }

    #[test]
    fn test_introduce_var_in_closure_with_block() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let lambda = |x: u32| { <|>x * 2<|> };
}
",
            "
fn main() {
    let lambda = |x: u32| { let <|>var_name = x * 2; var_name };
}
",
        );
    }

    #[test]
    fn test_introduce_var_path_simple() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let o = <|>Some(true)<|>;
}
",
            "
fn main() {
    let <|>var_name = Some(true);
    let o = var_name;
}
",
        );
    }

    #[test]
    fn test_introduce_var_path_method() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let v = <|>bar.foo()<|>;
}
",
            "
fn main() {
    let <|>var_name = bar.foo();
    let v = var_name;
}
",
        );
    }

    #[test]
    fn test_introduce_var_return() {
        check_assist(
            introduce_variable,
            "
fn foo() -> u32 {
    <|>return 2 + 2<|>;
}
",
            "
fn foo() -> u32 {
    let <|>var_name = 2 + 2;
    return var_name;
}
",
        );
    }

    #[test]
    fn test_introduce_var_does_not_add_extra_whitespace() {
        check_assist(
            introduce_variable,
            "
fn foo() -> u32 {


    <|>return 2 + 2<|>;
}
",
            "
fn foo() -> u32 {


    let <|>var_name = 2 + 2;
    return var_name;
}
",
        );

        check_assist(
            introduce_variable,
            "
fn foo() -> u32 {

        <|>return 2 + 2<|>;
}
",
            "
fn foo() -> u32 {

        let <|>var_name = 2 + 2;
        return var_name;
}
",
        );

        check_assist(
            introduce_variable,
            "
fn foo() -> u32 {
    let foo = 1;

    // bar


    <|>return 2 + 2<|>;
}
",
            "
fn foo() -> u32 {
    let foo = 1;

    // bar


    let <|>var_name = 2 + 2;
    return var_name;
}
",
        );
    }

    #[test]
    fn test_introduce_var_break() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let result = loop {
        <|>break 2 + 2<|>;
    };
}
",
            "
fn main() {
    let result = loop {
        let <|>var_name = 2 + 2;
        break var_name;
    };
}
",
        );
    }

    #[test]
    fn test_introduce_var_for_cast() {
        check_assist(
            introduce_variable,
            "
fn main() {
    let v = <|>0f32 as u32<|>;
}
",
            "
fn main() {
    let <|>var_name = 0f32 as u32;
    let v = var_name;
}
",
        );
    }

    #[test]
    fn test_introduce_var_for_return_not_applicable() {
        check_assist_not_applicable(introduce_variable, "fn foo() { <|>return<|>; } ");
    }

    #[test]
    fn test_introduce_var_for_break_not_applicable() {
        check_assist_not_applicable(introduce_variable, "fn main() { loop { <|>break<|>; }; }");
    }

    // FIXME: This is not quite correct, but good enough(tm) for the sorting heuristic
    #[test]
    fn introduce_var_target() {
        check_assist_target(introduce_variable, "fn foo() -> u32 { <|>return 2 + 2<|>; }", "2 + 2");

        check_assist_target(
            introduce_variable,
            "
fn main() {
    let x = true;
    let tuple = match x {
        true => (<|>2 + 2<|>, true)
        _ => (0, false)
    };
}
",
            "2 + 2",
        );
    }
}