ryo_mutations/idiom/

manual_map.rs

//! ManualMapMutation: Convert manual Option/Result mapping patterns
//!
//! Transforms:
//! - `match opt { Some(x) => Some(f(x)), None => None }` → `opt.map(|x| f(x))`
//! - `if let Some(x) = opt { Some(f(x)) } else { None }` → `opt.map(|x| f(x))`
//!
//! Similar patterns for Result:
//! - `match res { Ok(x) => Ok(f(x)), Err(e) => Err(e) }` → `res.map(|x| f(x))`
//!
//! Corresponds to Clippy lint: `clippy::manual_map`
//!
//! # Note
//!
//! This mutation currently has limited pattern support due to PurePattern
//! not having a TupleStruct variant for patterns like `Some(x)`.
//! Full support requires AST enhancement.

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

use crate::Mutation;

/// Convert manual Option/Result mapping to .map() method
///
/// # Example
///
/// ```rust,ignore
/// use ryo_mutations::idiom::ManualMapMutation;
///
/// let mutation = ManualMapMutation::new();
/// // Transforms:
/// //   match opt {
/// //       Some(x) => Some(x.to_string()),
/// //       None => None,
/// //   }
/// // Into:
/// //   opt.map(|x| x.to_string())
/// ```
///
/// # Limitations
///
/// Currently only detects patterns where the AST represents `Some(x)` as
/// a Struct pattern with path "Some". Full TupleStruct pattern support
/// is planned for future AST enhancements.
#[derive(Debug, Clone, Default)]
pub struct ManualMapMutation {
    /// Target function SymbolId. If None, applies to all functions.
    pub target_fn: Option<SymbolId>,
}

impl ManualMapMutation {
    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
    }

    /// Check if pattern is Some(x) and extract the binding name
    ///
    /// Supports both Struct pattern `Some { 0: x }` (internal representation)
    /// and various other representations of tuple struct patterns.
    fn is_some_pattern(pattern: &PurePattern) -> Option<String> {
        match pattern {
            // Struct pattern: Some { 0: x } (how tuple struct patterns are represented)
            PurePattern::Struct { path, fields, .. } => {
                // Check for "Some" or "Option::Some" or "std::option::Option::Some"
                if (path == "Some" || path.ends_with("::Some")) && fields.len() == 1 {
                    // The field name is "0" for tuple structs
                    if let Some((_, PurePattern::Ident { name, .. })) = fields.first() {
                        return Some(name.clone());
                    }
                }
                None
            }
            _ => None,
        }
    }

    /// Check if pattern is None
    ///
    /// Note: `None` in a match arm is parsed by syn as `Pat::Ident` (not Pat::Path),
    /// so we need to check both Ident and Path variants.
    fn is_none_pattern(pattern: &PurePattern) -> bool {
        match pattern {
            PurePattern::Path(p) => p == "None" || p.ends_with("::None"),
            PurePattern::Ident { name, .. } => name == "None",
            _ => false,
        }
    }

    /// Check if pattern is Ok(x) and extract the binding name
    fn is_ok_pattern(pattern: &PurePattern) -> Option<String> {
        match pattern {
            PurePattern::Struct { path, fields, .. } => {
                if path == "Ok" && fields.len() == 1 {
                    if let (_, PurePattern::Ident { name, .. }) = &fields[0] {
                        return Some(name.clone());
                    }
                }
                None
            }
            _ => None,
        }
    }

    /// Check if pattern is Err(e) and extract the binding name
    fn is_err_pattern(pattern: &PurePattern) -> Option<String> {
        match pattern {
            PurePattern::Struct { path, fields, .. } => {
                if path == "Err" && fields.len() == 1 {
                    if let (_, PurePattern::Ident { name, .. }) = &fields[0] {
                        return Some(name.clone());
                    }
                }
                None
            }
            _ => None,
        }
    }

    /// Check if expression is Some(inner) and extract inner
    fn is_some_expr(expr: &PureExpr) -> Option<&PureExpr> {
        match expr {
            PureExpr::Call { func, args } => {
                if matches!(func.as_ref(), PureExpr::Path(p) if p == "Some" || p.ends_with("::Some"))
                    && args.len() == 1
                {
                    return Some(&args[0]);
                }
                None
            }
            _ => None,
        }
    }

    /// Check if expression is None
    fn is_none_expr(expr: &PureExpr) -> bool {
        matches!(expr, PureExpr::Path(p) if p == "None" || p.ends_with("::None"))
    }

    /// Check if expression is Ok(inner) and extract inner
    fn is_ok_expr(expr: &PureExpr) -> Option<&PureExpr> {
        match expr {
            PureExpr::Call { func, args } => {
                if matches!(func.as_ref(), PureExpr::Path(p) if p == "Ok") && args.len() == 1 {
                    return Some(&args[0]);
                }
                None
            }
            _ => None,
        }
    }

    /// Check if expression is Err(e) where e matches the given name
    fn is_err_passthrough(expr: &PureExpr, err_name: &str) -> bool {
        match expr {
            PureExpr::Call { func, args } => {
                if matches!(func.as_ref(), PureExpr::Path(p) if p == "Err") && args.len() == 1 {
                    return matches!(&args[0], PureExpr::Path(p) if p == err_name);
                }
                false
            }
            _ => false,
        }
    }

    /// Try to convert a match expression to .map() call
    fn try_convert_match(scrutinee: &PureExpr, arms: &[PureMatchArm]) -> Option<PureExpr> {
        if arms.len() != 2 {
            return None;
        }

        // Try Option pattern: Some(x) => Some(f(x)), None => None
        if let Some(var_name) = Self::is_some_pattern(&arms[0].pattern) {
            if Self::is_none_pattern(&arms[1].pattern) && Self::is_none_expr(&arms[1].body) {
                if let Some(inner) = Self::is_some_expr(&arms[0].body) {
                    return Some(Self::create_map_call(
                        scrutinee.clone(),
                        var_name,
                        inner.clone(),
                    ));
                }
            }
        }

        // Try reversed Option pattern: None => None, Some(x) => Some(f(x))
        if Self::is_none_pattern(&arms[0].pattern) && Self::is_none_expr(&arms[0].body) {
            if let Some(var_name) = Self::is_some_pattern(&arms[1].pattern) {
                if let Some(inner) = Self::is_some_expr(&arms[1].body) {
                    return Some(Self::create_map_call(
                        scrutinee.clone(),
                        var_name,
                        inner.clone(),
                    ));
                }
            }
        }

        // Try Result pattern: Ok(x) => Ok(f(x)), Err(e) => Err(e)
        if let Some(ok_var) = Self::is_ok_pattern(&arms[0].pattern) {
            if let Some(err_var) = Self::is_err_pattern(&arms[1].pattern) {
                if Self::is_err_passthrough(&arms[1].body, &err_var) {
                    if let Some(inner) = Self::is_ok_expr(&arms[0].body) {
                        return Some(Self::create_map_call(
                            scrutinee.clone(),
                            ok_var,
                            inner.clone(),
                        ));
                    }
                }
            }
        }

        None
    }

    /// Create a .map(|var| body) call
    fn create_map_call(receiver: PureExpr, var_name: String, body: PureExpr) -> PureExpr {
        PureExpr::MethodCall {
            receiver: Box::new(receiver),
            method: "map".to_string(),
            turbofish: None,
            args: vec![PureExpr::Closure {
                is_async: false,
                is_move: false,
                params: vec![PureClosureParam::untyped(PurePattern::Ident {
                    name: var_name,
                    is_mut: false,
                    by_ref: false,
                })],
                ret: None,
                body: Box::new(body),
            }],
        }
    }

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

        // Check for match pattern
        if let PureExpr::Match {
            expr: scrutinee,
            arms,
        } = expr
        {
            if let Some(map_call) = Self::try_convert_match(scrutinee, arms) {
                *expr = map_call;
                return 1;
            }
        }

        // Note: if let pattern support requires IfLet variant in PureExpr
        // which may not exist. For now, we focus on match expressions.
        // Future: if let Some(x) = opt { Some(f(x)) } else { None } → opt.map(|x| f(x))

        // 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::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);
            }
            _ => {}
        }

        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 ManualMapMutation {
    fn describe(&self) -> String {
        "Convert manual Option/Result map patterns to .map()".to_string()
    }

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

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

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

    #[test]
    fn test_is_some_pattern_struct() {
        // PurePattern::Struct is used to represent Some(x) patterns
        let pattern = PurePattern::Struct {
            path: "Some".to_string(),
            fields: vec![(
                "0".to_string(),
                PurePattern::Ident {
                    name: "x".to_string(),
                    is_mut: false,
                    by_ref: false,
                },
            )],
            rest: false,
        };
        assert_eq!(
            ManualMapMutation::is_some_pattern(&pattern),
            Some("x".to_string())
        );
    }

    #[test]
    fn test_is_none_pattern() {
        let pattern = PurePattern::Path("None".to_string());
        assert!(ManualMapMutation::is_none_pattern(&pattern));
    }

    #[test]
    fn test_is_some_expr() {
        let expr = PureExpr::Call {
            func: Box::new(PureExpr::Path("Some".to_string())),
            args: vec![PureExpr::Path("value".to_string())],
        };
        assert!(ManualMapMutation::is_some_expr(&expr).is_some());
    }

    #[test]
    fn test_is_none_expr() {
        let expr = PureExpr::Path("None".to_string());
        assert!(ManualMapMutation::is_none_expr(&expr));
    }

    #[test]
    fn test_try_convert_match_option() {
        let scrutinee = PureExpr::Path("opt".to_string());
        let arms = vec![
            PureMatchArm {
                pattern: PurePattern::Struct {
                    path: "Some".to_string(),
                    fields: vec![(
                        "0".to_string(),
                        PurePattern::Ident {
                            name: "x".to_string(),
                            is_mut: false,
                            by_ref: false,
                        },
                    )],
                    rest: false,
                },
                guard: None,
                body: PureExpr::Call {
                    func: Box::new(PureExpr::Path("Some".to_string())),
                    args: vec![PureExpr::Binary {
                        op: "+".to_string(),
                        left: Box::new(PureExpr::Path("x".to_string())),
                        right: Box::new(PureExpr::Lit("1".to_string())),
                    }],
                },
            },
            PureMatchArm {
                pattern: PurePattern::Path("None".to_string()),
                guard: None,
                body: PureExpr::Path("None".to_string()),
            },
        ];

        let result = ManualMapMutation::try_convert_match(&scrutinee, &arms);
        assert!(result.is_some());

        if let Some(PureExpr::MethodCall { method, .. }) = result {
            assert_eq!(method, "map");
        } else {
            panic!("Expected MethodCall");
        }
    }
}