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};
use syntax::print::pprust::binop_to_string;

/// 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>),
}

/// Literal constant `1`, for convenience.
pub const ONE: Sugg<'static> = Sugg::NonParen(Cow::Borrowed("1"));

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)
    }

    /// Convenience method to create the `<lhs>..<rhs>` or `<lhs>...<rhs>` suggestion.
    pub fn range(self, end: Self, limit: ast::RangeLimits) -> Sugg<'static> {
        match limit {
            ast::RangeLimits::HalfOpen => make_assoc(AssocOp::DotDot, &self, &end),
            ast::RangeLimits::Closed => make_assoc(AssocOp::DotDotDot, &self, &end),
        }
    }

    /// Add parenthesis to any expression that might need them. Suitable to the `self` argument of
    /// a method call (eg. to build `bar.foo()` or `(1 + 2).foo()`).
    pub fn maybe_par(self) -> Self {
        match self {
            Sugg::NonParen(..) => self,
            Sugg::MaybeParen(sugg) | Sugg::BinOp(_, sugg) => Sugg::NonParen(format!("({})", sugg).into()),
        }
    }
}

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

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

impl<'a> std::ops::Not for 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> {
    Sugg::MaybeParen(format!("{}{}", op, expr.maybe_par()).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_assoc(op: AssocOp, 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 lhs_paren = if let Sugg::BinOp(ref lop, _) = *lhs {
        needs_paren(&op, lop, Associativity::Left)
    } else {
        false
    };

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

    let lhs = ParenHelper::new(lhs_paren, lhs);
    let rhs = ParenHelper::new(rhs_paren, rhs);
    let sugg = match op {
        AssocOp::Add |
        AssocOp::BitAnd |
        AssocOp::BitOr |
        AssocOp::BitXor |
        AssocOp::Divide |
        AssocOp::Equal |
        AssocOp::Greater |
        AssocOp::GreaterEqual |
        AssocOp::LAnd |
        AssocOp::LOr |
        AssocOp::Less |
        AssocOp::LessEqual |
        AssocOp::Modulus |
        AssocOp::Multiply |
        AssocOp::NotEqual |
        AssocOp::ShiftLeft |
        AssocOp::ShiftRight |
        AssocOp::Subtract => format!("{} {} {}", lhs, op.to_ast_binop().expect("Those are AST ops").to_string(), rhs),
        AssocOp::Inplace => format!("in ({}) {}", lhs, rhs),
        AssocOp::Assign => format!("{} = {}", lhs, rhs),
        AssocOp::AssignOp(op) => format!("{} {}= {}", lhs, binop_to_string(op), rhs),
        AssocOp::As => format!("{} as {}", lhs, rhs),
        AssocOp::DotDot => format!("{}..{}", lhs, rhs),
        AssocOp::DotDotDot => format!("{}...{}", lhs, rhs),
        AssocOp::Colon => format!("{}: {}", lhs, rhs),
    };

    Sugg::BinOp(op, sugg.into())
}

/// Convinience wrapper arround `make_assoc` and `AssocOp::from_ast_binop`.
pub fn make_binop(op: ast::BinOpKind, lhs: &Sugg, rhs: &Sugg) -> Sugg<'static> {
    make_assoc(AssocOp::from_ast_binop(op), lhs, rhs)
}

#[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"),
    })
}