rust/clippy_lints/src/utils/sugg.rs

use rustc::hir;
use rustc::lint::{EarlyContext, LateContext};
use std::borrow::Cow;
use std;
use syntax::ast;
use syntax::util::parser::AssocOp;
use utils::{higher, snippet};

/// A helper type to build suggestion correctly handling parenthesis.
pub enum Sugg<'a> {
    /// An expression that never needs parenthesis such as `1337` or `[0; 42]`.
    NonParen(Cow<'a, str>),
    /// An expression that does not fit in other variants.
    MaybeParen(Cow<'a, str>),
    /// A binary operator expression, including `as`-casts and explicit type coercion.
    BinOp(AssocOp, Cow<'a, str>),
}

impl<'a> std::fmt::Display for Sugg<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        match *self {
            Sugg::NonParen(ref s) | Sugg::MaybeParen(ref s) | Sugg::BinOp(_, ref s) => {
                s.fmt(f)
            }
        }
    }
}

impl<'a> Sugg<'a> {
    pub fn hir(cx: &LateContext, expr: &'a hir::Expr, default: &'a str) -> Sugg<'a> {
        let snippet = snippet(cx, expr.span, default);

        match expr.node {
            hir::ExprAddrOf(..) |
            hir::ExprBox(..) |
            hir::ExprClosure(..) |
            hir::ExprIf(..) |
            hir::ExprUnary(..) |
            hir::ExprMatch(..) => Sugg::MaybeParen(snippet),
            hir::ExprAgain(..) |
            hir::ExprBlock(..) |
            hir::ExprBreak(..) |
            hir::ExprCall(..) |
            hir::ExprField(..) |
            hir::ExprIndex(..) |
            hir::ExprInlineAsm(..) |
            hir::ExprLit(..) |
            hir::ExprLoop(..) |
            hir::ExprMethodCall(..) |
            hir::ExprPath(..) |
            hir::ExprRepeat(..) |
            hir::ExprRet(..) |
            hir::ExprStruct(..) |
            hir::ExprTup(..) |
            hir::ExprTupField(..) |
            hir::ExprVec(..) |
            hir::ExprWhile(..) => Sugg::NonParen(snippet),
            hir::ExprAssign(..) => Sugg::BinOp(AssocOp::Assign, snippet),
            hir::ExprAssignOp(op, ..) => Sugg::BinOp(hirbinop2assignop(op), snippet),
            hir::ExprBinary(op, ..) => Sugg::BinOp(AssocOp::from_ast_binop(higher::binop(op.node)), snippet),
            hir::ExprCast(..) => Sugg::BinOp(AssocOp::As, snippet),
            hir::ExprType(..) => Sugg::BinOp(AssocOp::Colon, snippet),
        }
    }

    pub fn ast(cx: &EarlyContext, expr: &'a ast::Expr, default: &'a str) -> Sugg<'a> {
        use syntax::ast::RangeLimits;

        let snippet = snippet(cx, expr.span, default);

        match expr.node {
            ast::ExprKind::AddrOf(..) |
            ast::ExprKind::Box(..) |
            ast::ExprKind::Closure(..) |
            ast::ExprKind::If(..) |
            ast::ExprKind::IfLet(..) |
            ast::ExprKind::InPlace(..) |
            ast::ExprKind::Unary(..) |
            ast::ExprKind::Match(..) => Sugg::MaybeParen(snippet),
            ast::ExprKind::Block(..) |
            ast::ExprKind::Break(..) |
            ast::ExprKind::Call(..) |
            ast::ExprKind::Continue(..) |
            ast::ExprKind::Field(..) |
            ast::ExprKind::ForLoop(..) |
            ast::ExprKind::Index(..) |
            ast::ExprKind::InlineAsm(..) |
            ast::ExprKind::Lit(..) |
            ast::ExprKind::Loop(..) |
            ast::ExprKind::Mac(..) |
            ast::ExprKind::MethodCall(..) |
            ast::ExprKind::Paren(..) |
            ast::ExprKind::Path(..) |
            ast::ExprKind::Repeat(..) |
            ast::ExprKind::Ret(..) |
            ast::ExprKind::Struct(..) |
            ast::ExprKind::Try(..) |
            ast::ExprKind::Tup(..) |
            ast::ExprKind::TupField(..) |
            ast::ExprKind::Vec(..) |
            ast::ExprKind::While(..) |
            ast::ExprKind::WhileLet(..) => Sugg::NonParen(snippet),
            ast::ExprKind::Range(.., RangeLimits::HalfOpen) => Sugg::BinOp(AssocOp::DotDot, snippet),
            ast::ExprKind::Range(.., RangeLimits::Closed) => Sugg::BinOp(AssocOp::DotDotDot, snippet),
            ast::ExprKind::Assign(..) => Sugg::BinOp(AssocOp::Assign, snippet),
            ast::ExprKind::AssignOp(op, ..) => Sugg::BinOp(astbinop2assignop(op), snippet),
            ast::ExprKind::Binary(op, ..) => Sugg::BinOp(AssocOp::from_ast_binop(op.node), snippet),
            ast::ExprKind::Cast(..) => Sugg::BinOp(AssocOp::As, snippet),
            ast::ExprKind::Type(..) => Sugg::BinOp(AssocOp::Colon, snippet),
        }
    }

    /// Convenience method to create the `lhs && rhs` suggestion.
    pub fn and(&self, rhs: &Self) -> Sugg<'static> {
        make_binop(ast::BinOpKind::And, self, rhs)
    }

    /// Convenience method to create the `&<expr>` suggestion.
    pub fn addr(&self) -> Sugg<'static> {
        make_unop("&", self)
    }
}

impl<'a, 'b> std::ops::Sub<&'b Sugg<'b>> for &'a Sugg<'a> {
    type Output = Sugg<'static>;
    fn sub(self, rhs: &'b Sugg<'b>) -> Sugg<'static> {
        make_binop(ast::BinOpKind::Sub, self, rhs)
    }
}

impl<'a> std::ops::Not for &'a Sugg<'a> {
    type Output = Sugg<'static>;
    fn not(self) -> Sugg<'static> {
        make_unop("!", self)
    }
}

struct ParenHelper<T> {
    paren: bool,
    wrapped: T,
}

impl<T> ParenHelper<T> {
    fn new(paren: bool, wrapped: T) -> Self {
        ParenHelper {
            paren: paren,
            wrapped: wrapped,
        }
    }
}

impl<T: std::fmt::Display> std::fmt::Display for ParenHelper<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        if self.paren {
            write!(f, "({})", self.wrapped)
        } else {
            self.wrapped.fmt(f)
        }
    }
}

/// Build the string for `<op> <expr>` adding parenthesis when necessary.
///
/// For convenience, the operator is taken as a string because all unary operators have the same
/// precedence.
pub fn make_unop(op: &str, expr: &Sugg) -> Sugg<'static> {
    let needs_paren = !matches!(*expr, Sugg::NonParen(..));
    Sugg::MaybeParen(format!("{}{}", op, ParenHelper::new(needs_paren, expr)).into())
}

/// Build the string for `<lhs> <op> <rhs>` adding parenthesis when necessary.
///
/// Precedence of shift operator relative to other arithmetic operation is often confusing so
/// parenthesis will always be added for a mix of these.
pub fn make_binop(op: ast::BinOpKind, lhs: &Sugg, rhs: &Sugg) -> Sugg<'static> {
    fn is_shift(op: &AssocOp) -> bool {
        matches!(*op, AssocOp::ShiftLeft | AssocOp::ShiftRight)
    }

    fn is_arith(op: &AssocOp) -> bool {
        matches!(*op, AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide | AssocOp::Modulus)
    }

    fn needs_paren(op: &AssocOp, other: &AssocOp, dir: Associativity) -> bool {
        other.precedence() < op.precedence() ||
            (other.precedence() == op.precedence() &&
                ((op != other && associativity(op) != dir) ||
                 (op == other && associativity(op) != Associativity::Both))) ||
             is_shift(op) && is_arith(other) ||
             is_shift(other) && is_arith(op)
    }

    let aop = AssocOp::from_ast_binop(op);

    let lhs_paren = if let Sugg::BinOp(ref lop, _) = *lhs {
        needs_paren(&aop, lop, Associativity::Left)
    } else {
        false
    };

    let rhs_paren = if let Sugg::BinOp(ref rop, _) = *rhs {
        needs_paren(&aop, rop, Associativity::Right)
    } else {
        false
    };

    Sugg::BinOp(aop,
                format!("{} {} {}",
                        ParenHelper::new(lhs_paren, lhs),
                        op.to_string(),
                        ParenHelper::new(rhs_paren, rhs)).into())
}

#[derive(PartialEq, Eq)]
enum Associativity {
    Both,
    Left,
    None,
    Right,
}

/// Return the associativity/fixity of an operator. The difference with `AssocOp::fixity` is that
/// an operator can be both left and right associative (such as `+`:
/// `a + b + c == (a + b) + c == a + (b + c)`.
///
/// Chained `as` and explicit `:` type coercion never need inner parenthesis so they are considered
/// associative.
fn associativity(op: &AssocOp) -> Associativity {
    use syntax::util::parser::AssocOp::*;

    match *op {
        Inplace | Assign | AssignOp(_) => Associativity::Right,
        Add | BitAnd | BitOr | BitXor | LAnd | LOr | Multiply |
        As | Colon => Associativity::Both,
    Divide | Equal | Greater | GreaterEqual | Less | LessEqual | Modulus | NotEqual | ShiftLeft |
        ShiftRight | Subtract => Associativity::Left,
        DotDot | DotDotDot => Associativity::None
    }
}

/// Convert a `hir::BinOp` to the corresponding assigning binary operator.
fn hirbinop2assignop(op: hir::BinOp) -> AssocOp {
    use rustc::hir::BinOp_::*;
    use syntax::parse::token::BinOpToken::*;

    AssocOp::AssignOp(match op.node {
        BiAdd => Plus,
        BiBitAnd => And,
        BiBitOr => Or,
        BiBitXor => Caret,
        BiDiv => Slash,
        BiMul => Star,
        BiRem => Percent,
        BiShl => Shl,
        BiShr => Shr,
        BiSub => Minus,
        BiAnd | BiEq | BiGe | BiGt | BiLe | BiLt | BiNe | BiOr => panic!("This operator does not exist"),
    })
}

/// Convert an `ast::BinOp` to the corresponding assigning binary operator.
fn astbinop2assignop(op: ast::BinOp) -> AssocOp {
    use syntax::ast::BinOpKind::*;
    use syntax::parse::token::BinOpToken;

    AssocOp::AssignOp(match op.node {
        Add => BinOpToken::Plus,
        BitAnd => BinOpToken::And,
        BitOr => BinOpToken::Or,
        BitXor => BinOpToken::Caret,
        Div => BinOpToken::Slash,
        Mul => BinOpToken::Star,
        Rem => BinOpToken::Percent,
        Shl => BinOpToken::Shl,
        Shr => BinOpToken::Shr,
        Sub => BinOpToken::Minus,
        And | Eq | Ge | Gt | Le | Lt | Ne | Or => panic!("This operator does not exist"),
    })
}