ryo-mutations 0.1.0

//! RedundantClosureMutation: Simplify redundant closures
//!
//! Transforms:
//! - `|x| foo(x)` → `foo`
//! - `|x| x.method()` → `Type::method` (when unambiguous)
//! - `|a, b| func(a, b)` → `func`
//!
//! Corresponds to Clippy lint: `clippy::redundant_closure`

use ryo_source::pure::{PureBlock, PureClosureParam, PureExpr, PurePattern, PureStmt};
use ryo_symbol::SymbolId;

use crate::Mutation;

/// Simplify redundant closures to function references
///
/// # Example
///
/// ```rust,ignore
/// use ryo_mutations::idiom::RedundantClosureMutation;
///
/// let mutation = RedundantClosureMutation::new();
/// // Transforms: items.map(|x| foo(x))
/// // Into:       items.map(foo)
/// ```
#[derive(Debug, Clone, Default)]
pub struct RedundantClosureMutation {
    /// Target function SymbolId. If None, applies to all functions.
    pub target_fn: Option<SymbolId>,
}

impl RedundantClosureMutation {
    pub fn new() -> Self {
        Self::default()
    }

    /// Only apply in a specific function
    pub fn in_function(mut self, id: SymbolId) -> Self {
        self.target_fn = Some(id);
        self
    }

    /// Extract parameter names from closure
    fn get_param_names(params: &[PureClosureParam]) -> Vec<String> {
        params
            .iter()
            .filter_map(|p| match &p.pattern {
                PurePattern::Ident { name, .. } => Some(name.clone()),
                _ => None,
            })
            .collect()
    }

    /// Check if expression is a simple path reference to the given name
    fn is_path_to(expr: &PureExpr, name: &str) -> bool {
        matches!(expr, PureExpr::Path(p) if p == name)
    }

    /// Check if closure body is a simple function call with params in order
    fn is_redundant_call(params: &[String], body: &PureExpr) -> Option<PureExpr> {
        match body {
            // |x| foo(x) or |a, b| foo(a, b)
            PureExpr::Call { func, args } => {
                if args.len() != params.len() {
                    return None;
                }

                // Check each argument matches corresponding param in order
                for (param, arg) in params.iter().zip(args.iter()) {
                    if !Self::is_path_to(arg, param) {
                        return None;
                    }
                }

                // Return the function reference
                Some(func.as_ref().clone())
            }
            // Handle blocks with single expression
            PureExpr::Block { block, .. } => {
                if block.stmts.len() == 1 {
                    match &block.stmts[0] {
                        PureStmt::Expr(e) => Self::is_redundant_call(params, e),
                        _ => None,
                    }
                } else {
                    None
                }
            }
            _ => None,
        }
    }

    /// Transform expressions, returns changes count
    fn transform_expr(&self, expr: &mut PureExpr) -> usize {
        let mut changes = 0;

        // Check for redundant closure pattern
        if let PureExpr::Closure { params, body, .. } = expr {
            let param_names = Self::get_param_names(params);

            // Only handle closures where all params are simple idents
            if param_names.len() == params.len() {
                if let Some(func_ref) = Self::is_redundant_call(&param_names, body) {
                    *expr = func_ref;
                    return 1;
                }
            }
        }

        // Recursively transform sub-expressions
        match expr {
            PureExpr::Binary { left, right, .. } => {
                changes += self.transform_expr(left);
                changes += self.transform_expr(right);
            }
            PureExpr::Unary { expr: inner, .. } => {
                changes += self.transform_expr(inner);
            }
            PureExpr::Call { func, args } => {
                changes += self.transform_expr(func);
                for arg in args {
                    changes += self.transform_expr(arg);
                }
            }
            PureExpr::MethodCall { receiver, args, .. } => {
                changes += self.transform_expr(receiver);
                for arg in args {
                    changes += self.transform_expr(arg);
                }
            }
            PureExpr::Field { expr: inner, .. } => {
                changes += self.transform_expr(inner);
            }
            PureExpr::Index { expr: inner, index } => {
                changes += self.transform_expr(inner);
                changes += self.transform_expr(index);
            }
            PureExpr::Block { block, .. } => {
                changes += self.transform_block(block);
            }
            PureExpr::If {
                cond,
                then_branch,
                else_branch,
            } => {
                changes += self.transform_expr(cond);
                changes += self.transform_block(then_branch);
                if let Some(else_expr) = else_branch {
                    changes += self.transform_expr(else_expr);
                }
            }
            PureExpr::Match { expr: e, arms } => {
                changes += self.transform_expr(e);
                for arm in arms {
                    changes += self.transform_expr(&mut arm.body);
                }
            }
            PureExpr::Loop { body: block, .. } | PureExpr::While { body: block, .. } => {
                changes += self.transform_block(block);
            }
            PureExpr::For {
                expr: iter_expr,
                body,
                ..
            } => {
                changes += self.transform_expr(iter_expr);
                changes += self.transform_block(body);
            }
            PureExpr::Closure { body, .. } => {
                changes += self.transform_expr(body);
            }
            PureExpr::Tuple(exprs) | PureExpr::Array(exprs) => {
                for e in exprs {
                    changes += self.transform_expr(e);
                }
            }
            PureExpr::Struct { fields, .. } => {
                for (_, e) in fields {
                    changes += self.transform_expr(e);
                }
            }
            PureExpr::Ref { expr: inner, .. } => {
                changes += self.transform_expr(inner);
            }
            PureExpr::Return(Some(inner)) => {
                changes += self.transform_expr(inner);
            }
            PureExpr::Try(inner) | PureExpr::Await(inner) => {
                changes += self.transform_expr(inner);
            }
            _ => {}
        }

        changes
    }

    pub fn transform_block(&self, block: &mut PureBlock) -> usize {
        let mut changes = 0;
        for stmt in &mut block.stmts {
            changes += self.transform_stmt(stmt);
        }
        changes
    }

    fn transform_stmt(&self, stmt: &mut PureStmt) -> usize {
        match stmt {
            PureStmt::Local { init: Some(e), .. } => self.transform_expr(e),
            PureStmt::Semi(e) | PureStmt::Expr(e) => self.transform_expr(e),
            _ => 0,
        }
    }
}

impl Mutation for RedundantClosureMutation {
    fn describe(&self) -> String {
        "Simplify redundant closures (|x| foo(x) → foo)".to_string()
    }

    fn mutation_type(&self) -> &'static str {
        "RedundantClosure"
    }

    fn box_clone(&self) -> Box<dyn Mutation> {
        Box::new(self.clone())
    }
}

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

    #[test]
    fn test_get_param_names() {
        let params = vec![
            PureClosureParam::untyped(PurePattern::Ident {
                name: "x".to_string(),
                is_mut: false,
            }),
            PureClosureParam::untyped(PurePattern::Ident {
                name: "y".to_string(),
                is_mut: false,
            }),
        ];
        let names = RedundantClosureMutation::get_param_names(&params);
        assert_eq!(names, vec!["x", "y"]);
    }

    #[test]
    fn test_is_redundant_call_single_param() {
        // |x| foo(x)
        let params = vec!["x".to_string()];
        let body = PureExpr::Call {
            func: Box::new(PureExpr::Path("foo".to_string())),
            args: vec![PureExpr::Path("x".to_string())],
        };

        let result = RedundantClosureMutation::is_redundant_call(&params, &body);
        assert!(result.is_some());
        assert!(matches!(result.unwrap(), PureExpr::Path(s) if s == "foo"));
    }

    #[test]
    fn test_is_redundant_call_multi_param() {
        // |a, b| func(a, b)
        let params = vec!["a".to_string(), "b".to_string()];
        let body = PureExpr::Call {
            func: Box::new(PureExpr::Path("func".to_string())),
            args: vec![
                PureExpr::Path("a".to_string()),
                PureExpr::Path("b".to_string()),
            ],
        };

        let result = RedundantClosureMutation::is_redundant_call(&params, &body);
        assert!(result.is_some());
    }

    #[test]
    fn test_is_not_redundant_wrong_order() {
        // |a, b| func(b, a) - params in wrong order
        let params = vec!["a".to_string(), "b".to_string()];
        let body = PureExpr::Call {
            func: Box::new(PureExpr::Path("func".to_string())),
            args: vec![
                PureExpr::Path("b".to_string()),
                PureExpr::Path("a".to_string()),
            ],
        };

        let result = RedundantClosureMutation::is_redundant_call(&params, &body);
        assert!(result.is_none());
    }

    #[test]
    fn test_is_not_redundant_extra_args() {
        // |x| foo(x, y) - extra argument
        let params = vec!["x".to_string()];
        let body = PureExpr::Call {
            func: Box::new(PureExpr::Path("foo".to_string())),
            args: vec![
                PureExpr::Path("x".to_string()),
                PureExpr::Path("y".to_string()),
            ],
        };

        let result = RedundantClosureMutation::is_redundant_call(&params, &body);
        assert!(result.is_none());
    }
}