//! Contains utility functions to generate suggestions.
#![deny(clippy::missing_docs_in_private_items)]

use crate::higher;
use crate::source::{snippet, snippet_opt, snippet_with_context, snippet_with_macro_callsite};
use rustc_ast::util::parser::AssocOp;
use rustc_ast::{ast, token};
use rustc_ast_pretty::pprust::token_kind_to_string;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::{EarlyContext, LateContext, LintContext};
use rustc_span::source_map::{CharPos, Span};
use rustc_span::{BytePos, Pos, SyntaxContext};
use std::borrow::Cow;
use std::convert::TryInto;
use std::fmt::Display;
use std::ops::{Add, Neg, Not, Sub};

/// A helper type to build suggestion correctly handling parenthesis.
#[derive(Clone, PartialEq)]
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 `0`, for convenience.
pub const ZERO: Sugg<'static> = Sugg::NonParen(Cow::Borrowed("0"));
/// Literal constant `1`, for convenience.
pub const ONE: Sugg<'static> = Sugg::NonParen(Cow::Borrowed("1"));
/// a constant represents an empty string, for convenience.
pub const EMPTY: Sugg<'static> = Sugg::NonParen(Cow::Borrowed(""));

impl Display for Sugg<'_> {
    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),
        }
    }
}

#[allow(clippy::wrong_self_convention)] // ok, because of the function `as_ty` method
impl<'a> Sugg<'a> {
    /// Prepare a suggestion from an expression.
    pub fn hir_opt(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<Self> {
        snippet_opt(cx, expr.span).map(|snippet| {
            let snippet = Cow::Owned(snippet);
            Self::hir_from_snippet(expr, snippet)
        })
    }

    /// Convenience function around `hir_opt` for suggestions with a default
    /// text.
    pub fn hir(cx: &LateContext<'_>, expr: &hir::Expr<'_>, default: &'a str) -> Self {
        Self::hir_opt(cx, expr).unwrap_or(Sugg::NonParen(Cow::Borrowed(default)))
    }

    /// Same as `hir`, but it adapts the applicability level by following rules:
    ///
    /// - Applicability level `Unspecified` will never be changed.
    /// - If the span is inside a macro, change the applicability level to `MaybeIncorrect`.
    /// - If the default value is used and the applicability level is `MachineApplicable`, change it
    ///   to
    /// `HasPlaceholders`
    pub fn hir_with_applicability(
        cx: &LateContext<'_>,
        expr: &hir::Expr<'_>,
        default: &'a str,
        applicability: &mut Applicability,
    ) -> Self {
        if *applicability != Applicability::Unspecified && expr.span.from_expansion() {
            *applicability = Applicability::MaybeIncorrect;
        }
        Self::hir_opt(cx, expr).unwrap_or_else(|| {
            if *applicability == Applicability::MachineApplicable {
                *applicability = Applicability::HasPlaceholders;
            }
            Sugg::NonParen(Cow::Borrowed(default))
        })
    }

    /// Same as `hir`, but will use the pre expansion span if the `expr` was in a macro.
    pub fn hir_with_macro_callsite(cx: &LateContext<'_>, expr: &hir::Expr<'_>, default: &'a str) -> Self {
        let snippet = snippet_with_macro_callsite(cx, expr.span, default);

        Self::hir_from_snippet(expr, snippet)
    }

    /// Same as `hir`, but first walks the span up to the given context. This will result in the
    /// macro call, rather then the expansion, if the span is from a child context. If the span is
    /// not from a child context, it will be used directly instead.
    ///
    /// e.g. Given the expression `&vec![]`, getting a snippet from the span for `vec![]` as a HIR
    /// node would result in `box []`. If given the context of the address of expression, this
    /// function will correctly get a snippet of `vec![]`.
    pub fn hir_with_context(
        cx: &LateContext<'_>,
        expr: &hir::Expr<'_>,
        ctxt: SyntaxContext,
        default: &'a str,
        applicability: &mut Applicability,
    ) -> Self {
        let (snippet, in_macro) = snippet_with_context(cx, expr.span, ctxt, default, applicability);

        if in_macro {
            Sugg::NonParen(snippet)
        } else {
            Self::hir_from_snippet(expr, snippet)
        }
    }

    /// Generate a suggestion for an expression with the given snippet. This is used by the `hir_*`
    /// function variants of `Sugg`, since these use different snippet functions.
    fn hir_from_snippet(expr: &hir::Expr<'_>, snippet: Cow<'a, str>) -> Self {
        if let Some(range) = higher::range(expr) {
            let op = match range.limits {
                ast::RangeLimits::HalfOpen => AssocOp::DotDot,
                ast::RangeLimits::Closed => AssocOp::DotDotEq,
            };
            return Sugg::BinOp(op, snippet);
        }

        match expr.kind {
            hir::ExprKind::AddrOf(..)
            | hir::ExprKind::Box(..)
            | hir::ExprKind::If(..)
            | hir::ExprKind::Closure(..)
            | hir::ExprKind::Unary(..)
            | hir::ExprKind::Match(..) => Sugg::MaybeParen(snippet),
            hir::ExprKind::Continue(..)
            | hir::ExprKind::Yield(..)
            | hir::ExprKind::Array(..)
            | hir::ExprKind::Block(..)
            | hir::ExprKind::Break(..)
            | hir::ExprKind::Call(..)
            | hir::ExprKind::Field(..)
            | hir::ExprKind::Index(..)
            | hir::ExprKind::InlineAsm(..)
            | hir::ExprKind::LlvmInlineAsm(..)
            | hir::ExprKind::ConstBlock(..)
            | hir::ExprKind::Lit(..)
            | hir::ExprKind::Loop(..)
            | hir::ExprKind::MethodCall(..)
            | hir::ExprKind::Path(..)
            | hir::ExprKind::Repeat(..)
            | hir::ExprKind::Ret(..)
            | hir::ExprKind::Struct(..)
            | hir::ExprKind::Tup(..)
            | hir::ExprKind::DropTemps(_)
            | hir::ExprKind::Err => Sugg::NonParen(snippet),
            hir::ExprKind::Assign(..) => Sugg::BinOp(AssocOp::Assign, snippet),
            hir::ExprKind::AssignOp(op, ..) => Sugg::BinOp(hirbinop2assignop(op), snippet),
            hir::ExprKind::Binary(op, ..) => Sugg::BinOp(AssocOp::from_ast_binop(higher::binop(op.node)), snippet),
            hir::ExprKind::Cast(..) => Sugg::BinOp(AssocOp::As, snippet),
            hir::ExprKind::Type(..) => Sugg::BinOp(AssocOp::Colon, snippet),
        }
    }

    /// Prepare a suggestion from an expression.
    pub fn ast(cx: &EarlyContext<'_>, expr: &ast::Expr, default: &'a str) -> Self {
        use rustc_ast::ast::RangeLimits;

        let snippet = if expr.span.from_expansion() {
            snippet_with_macro_callsite(cx, expr.span, default)
        } else {
            snippet(cx, expr.span, default)
        };

        match expr.kind {
            ast::ExprKind::AddrOf(..)
            | ast::ExprKind::Box(..)
            | ast::ExprKind::Closure(..)
            | ast::ExprKind::If(..)
            | ast::ExprKind::Let(..)
            | ast::ExprKind::Unary(..)
            | ast::ExprKind::Match(..) => Sugg::MaybeParen(snippet),
            ast::ExprKind::Async(..)
            | ast::ExprKind::Block(..)
            | ast::ExprKind::Break(..)
            | ast::ExprKind::Call(..)
            | ast::ExprKind::Continue(..)
            | ast::ExprKind::Yield(..)
            | ast::ExprKind::Field(..)
            | ast::ExprKind::ForLoop(..)
            | ast::ExprKind::Index(..)
            | ast::ExprKind::InlineAsm(..)
            | ast::ExprKind::LlvmInlineAsm(..)
            | ast::ExprKind::ConstBlock(..)
            | ast::ExprKind::Lit(..)
            | ast::ExprKind::Loop(..)
            | ast::ExprKind::MacCall(..)
            | ast::ExprKind::MethodCall(..)
            | ast::ExprKind::Paren(..)
            | ast::ExprKind::Underscore
            | ast::ExprKind::Path(..)
            | ast::ExprKind::Repeat(..)
            | ast::ExprKind::Ret(..)
            | ast::ExprKind::Struct(..)
            | ast::ExprKind::Try(..)
            | ast::ExprKind::TryBlock(..)
            | ast::ExprKind::Tup(..)
            | ast::ExprKind::Array(..)
            | ast::ExprKind::While(..)
            | ast::ExprKind::Await(..)
            | ast::ExprKind::Err => Sugg::NonParen(snippet),
            ast::ExprKind::Range(.., RangeLimits::HalfOpen) => Sugg::BinOp(AssocOp::DotDot, snippet),
            ast::ExprKind::Range(.., RangeLimits::Closed) => Sugg::BinOp(AssocOp::DotDotEq, 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 `<lhs> & <rhs>` suggestion.
    pub fn bit_and(self, rhs: &Self) -> Sugg<'static> {
        make_binop(ast::BinOpKind::BitAnd, &self, rhs)
    }

    /// Convenience method to create the `<lhs> as <rhs>` suggestion.
    pub fn as_ty<R: Display>(self, rhs: R) -> Sugg<'static> {
        make_assoc(AssocOp::As, &self, &Sugg::NonParen(rhs.to_string().into()))
    }

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

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

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

    /// Convenience method to create the `&*<expr>` suggestion. Currently this
    /// is needed because `sugg.deref().addr()` produces an unnecessary set of
    /// parentheses around the deref.
    pub fn addr_deref(self) -> Sugg<'static> {
        make_unop("&*", self)
    }

    /// Convenience method to create the `&mut *<expr>` suggestion. Currently
    /// this is needed because `sugg.deref().mut_addr()` produces an unnecessary
    /// set of parentheses around the deref.
    pub fn mut_addr_deref(self) -> Sugg<'static> {
        make_unop("&mut *", self)
    }

    /// Convenience method to transform suggestion into a return call
    pub fn make_return(self) -> Sugg<'static> {
        Sugg::NonParen(Cow::Owned(format!("return {}", self)))
    }

    /// Convenience method to transform suggestion into a block
    /// where the suggestion is a trailing expression
    pub fn blockify(self) -> Sugg<'static> {
        Sugg::NonParen(Cow::Owned(format!("{{ {} }}", self)))
    }

    /// Convenience method to create the `<lhs>..<rhs>` or `<lhs>...<rhs>`
    /// suggestion.
    #[allow(dead_code)]
    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::DotDotEq, &self, end),
        }
    }

    /// Adds parenthesis to any expression that might need them. Suitable to the
    /// `self` argument of a method call
    /// (e.g., to build `bar.foo()` or `(1 + 2).foo()`).
    pub fn maybe_par(self) -> Self {
        match self {
            Sugg::NonParen(..) => self,
            // `(x)` and `(x).y()` both don't need additional parens.
            Sugg::MaybeParen(sugg) => {
                if has_enclosing_paren(&sugg) {
                    Sugg::MaybeParen(sugg)
                } else {
                    Sugg::NonParen(format!("({})", sugg).into())
                }
            },
            Sugg::BinOp(_, sugg) => {
                if has_enclosing_paren(&sugg) {
                    Sugg::NonParen(sugg)
                } else {
                    Sugg::NonParen(format!("({})", sugg).into())
                }
            },
        }
    }
}

/// Return `true` if `sugg` is enclosed in parenthesis.
fn has_enclosing_paren(sugg: impl AsRef<str>) -> bool {
    let mut chars = sugg.as_ref().chars();
    if let Some('(') = chars.next() {
        let mut depth = 1;
        for c in &mut chars {
            if c == '(' {
                depth += 1;
            } else if c == ')' {
                depth -= 1;
            }
            if depth == 0 {
                break;
            }
        }
        chars.next().is_none()
    } else {
        false
    }
}

// Copied from the rust standart library, and then edited
macro_rules! forward_binop_impls_to_ref {
    (impl $imp:ident, $method:ident for $t:ty, type Output = $o:ty) => {
        impl $imp<$t> for &$t {
            type Output = $o;

            fn $method(self, other: $t) -> $o {
                $imp::$method(self, &other)
            }
        }

        impl $imp<&$t> for $t {
            type Output = $o;

            fn $method(self, other: &$t) -> $o {
                $imp::$method(&self, other)
            }
        }

        impl $imp for $t {
            type Output = $o;

            fn $method(self, other: $t) -> $o {
                $imp::$method(&self, &other)
            }
        }
    };
}

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

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

forward_binop_impls_to_ref!(impl Add, add for Sugg<'_>, type Output = Sugg<'static>);
forward_binop_impls_to_ref!(impl Sub, sub for Sugg<'_>, type Output = Sugg<'static>);

impl Neg for Sugg<'_> {
    type Output = Sugg<'static>;
    fn neg(self) -> Sugg<'static> {
        make_unop("-", self)
    }
}

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

/// Helper type to display either `foo` or `(foo)`.
struct ParenHelper<T> {
    /// `true` if parentheses are needed.
    paren: bool,
    /// The main thing to display.
    wrapped: T,
}

impl<T> ParenHelper<T> {
    /// Builds a `ParenHelper`.
    fn new(paren: bool, wrapped: T) -> Self {
        Self { paren, wrapped }
    }
}

impl<T: Display> 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)
        }
    }
}

/// Builds 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())
}

/// Builds 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> {
    /// Returns `true` if the operator is a shift operator `<<` or `>>`.
    fn is_shift(op: AssocOp) -> bool {
        matches!(op, AssocOp::ShiftLeft | AssocOp::ShiftRight)
    }

    /// Returns `true` if the operator is a arithmetic operator
    /// (i.e., `+`, `-`, `*`, `/`, `%`).
    fn is_arith(op: AssocOp) -> bool {
        matches!(
            op,
            AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide | AssocOp::Modulus
        )
    }

    /// Returns `true` if the operator `op` needs parenthesis with the operator
    /// `other` in the direction `dir`.
    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(lop, _) = *lhs {
        needs_paren(op, lop, Associativity::Left)
    } else {
        false
    };

    let rhs_paren = if let Sugg::BinOp(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::Assign => format!("{} = {}", lhs, rhs),
        AssocOp::AssignOp(op) => format!("{} {}= {}", lhs, token_kind_to_string(&token::BinOp(op)), rhs),
        AssocOp::As => format!("{} as {}", lhs, rhs),
        AssocOp::DotDot => format!("{}..{}", lhs, rhs),
        AssocOp::DotDotEq => format!("{}..={}", lhs, rhs),
        AssocOp::Colon => format!("{}: {}", lhs, rhs),
    };

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

/// Convenience wrapper around `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, Clone, Copy)]
/// Operator associativity.
enum Associativity {
    /// The operator is both left-associative and right-associative.
    Both,
    /// The operator is left-associative.
    Left,
    /// The operator is not associative.
    None,
    /// The operator is right-associative.
    Right,
}

/// Returns 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.
#[must_use]
fn associativity(op: AssocOp) -> Associativity {
    use rustc_ast::util::parser::AssocOp::{
        Add, As, Assign, AssignOp, BitAnd, BitOr, BitXor, Colon, Divide, DotDot, DotDotEq, Equal, Greater,
        GreaterEqual, LAnd, LOr, Less, LessEqual, Modulus, Multiply, NotEqual, ShiftLeft, ShiftRight, Subtract,
    };

    match op {
        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 | DotDotEq => Associativity::None,
    }
}

/// Converts a `hir::BinOp` to the corresponding assigning binary operator.
fn hirbinop2assignop(op: hir::BinOp) -> AssocOp {
    use rustc_ast::token::BinOpToken::{And, Caret, Minus, Or, Percent, Plus, Shl, Shr, Slash, Star};

    AssocOp::AssignOp(match op.node {
        hir::BinOpKind::Add => Plus,
        hir::BinOpKind::BitAnd => And,
        hir::BinOpKind::BitOr => Or,
        hir::BinOpKind::BitXor => Caret,
        hir::BinOpKind::Div => Slash,
        hir::BinOpKind::Mul => Star,
        hir::BinOpKind::Rem => Percent,
        hir::BinOpKind::Shl => Shl,
        hir::BinOpKind::Shr => Shr,
        hir::BinOpKind::Sub => Minus,

        hir::BinOpKind::And
        | hir::BinOpKind::Eq
        | hir::BinOpKind::Ge
        | hir::BinOpKind::Gt
        | hir::BinOpKind::Le
        | hir::BinOpKind::Lt
        | hir::BinOpKind::Ne
        | hir::BinOpKind::Or => panic!("This operator does not exist"),
    })
}

/// Converts an `ast::BinOp` to the corresponding assigning binary operator.
fn astbinop2assignop(op: ast::BinOp) -> AssocOp {
    use rustc_ast::ast::BinOpKind::{
        Add, And, BitAnd, BitOr, BitXor, Div, Eq, Ge, Gt, Le, Lt, Mul, Ne, Or, Rem, Shl, Shr, Sub,
    };
    use rustc_ast::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"),
    })
}

/// Returns the indentation before `span` if there are nothing but `[ \t]`
/// before it on its line.
fn indentation<T: LintContext>(cx: &T, span: Span) -> Option<String> {
    let lo = cx.sess().source_map().lookup_char_pos(span.lo());
    lo.file
        .get_line(lo.line - 1 /* line numbers in `Loc` are 1-based */)
        .and_then(|line| {
            if let Some((pos, _)) = line.char_indices().find(|&(_, c)| c != ' ' && c != '\t') {
                // We can mix char and byte positions here because we only consider `[ \t]`.
                if lo.col == CharPos(pos) {
                    Some(line[..pos].into())
                } else {
                    None
                }
            } else {
                None
            }
        })
}

/// Convenience extension trait for `DiagnosticBuilder`.
pub trait DiagnosticBuilderExt<T: LintContext> {
    /// Suggests to add an attribute to an item.
    ///
    /// Correctly handles indentation of the attribute and item.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// diag.suggest_item_with_attr(cx, item, "#[derive(Default)]");
    /// ```
    fn suggest_item_with_attr<D: Display + ?Sized>(
        &mut self,
        cx: &T,
        item: Span,
        msg: &str,
        attr: &D,
        applicability: Applicability,
    );

    /// Suggest to add an item before another.
    ///
    /// The item should not be indented (except for inner indentation).
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// diag.suggest_prepend_item(cx, item,
    /// "fn foo() {
    ///     bar();
    /// }");
    /// ```
    fn suggest_prepend_item(&mut self, cx: &T, item: Span, msg: &str, new_item: &str, applicability: Applicability);

    /// Suggest to completely remove an item.
    ///
    /// This will remove an item and all following whitespace until the next non-whitespace
    /// character. This should work correctly if item is on the same indentation level as the
    /// following item.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// diag.suggest_remove_item(cx, item, "remove this")
    /// ```
    fn suggest_remove_item(&mut self, cx: &T, item: Span, msg: &str, applicability: Applicability);
}

impl<T: LintContext> DiagnosticBuilderExt<T> for rustc_errors::DiagnosticBuilder<'_> {
    fn suggest_item_with_attr<D: Display + ?Sized>(
        &mut self,
        cx: &T,
        item: Span,
        msg: &str,
        attr: &D,
        applicability: Applicability,
    ) {
        if let Some(indent) = indentation(cx, item) {
            let span = item.with_hi(item.lo());

            self.span_suggestion(span, msg, format!("{}\n{}", attr, indent), applicability);
        }
    }

    fn suggest_prepend_item(&mut self, cx: &T, item: Span, msg: &str, new_item: &str, applicability: Applicability) {
        if let Some(indent) = indentation(cx, item) {
            let span = item.with_hi(item.lo());

            let mut first = true;
            let new_item = new_item
                .lines()
                .map(|l| {
                    if first {
                        first = false;
                        format!("{}\n", l)
                    } else {
                        format!("{}{}\n", indent, l)
                    }
                })
                .collect::<String>();

            self.span_suggestion(span, msg, format!("{}\n{}", new_item, indent), applicability);
        }
    }

    fn suggest_remove_item(&mut self, cx: &T, item: Span, msg: &str, applicability: Applicability) {
        let mut remove_span = item;
        let hi = cx.sess().source_map().next_point(remove_span).hi();
        let fmpos = cx.sess().source_map().lookup_byte_offset(hi);

        if let Some(ref src) = fmpos.sf.src {
            let non_whitespace_offset = src[fmpos.pos.to_usize()..].find(|c| c != ' ' && c != '\t' && c != '\n');

            if let Some(non_whitespace_offset) = non_whitespace_offset {
                remove_span = remove_span
                    .with_hi(remove_span.hi() + BytePos(non_whitespace_offset.try_into().expect("offset too large")));
            }
        }

        self.span_suggestion(remove_span, msg, String::new(), applicability);
    }
}

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

    use rustc_ast::util::parser::AssocOp;
    use std::borrow::Cow;

    const SUGGESTION: Sugg<'static> = Sugg::NonParen(Cow::Borrowed("function_call()"));

    #[test]
    fn make_return_transform_sugg_into_a_return_call() {
        assert_eq!("return function_call()", SUGGESTION.make_return().to_string());
    }

    #[test]
    fn blockify_transforms_sugg_into_a_block() {
        assert_eq!("{ function_call() }", SUGGESTION.blockify().to_string());
    }

    #[test]
    fn binop_maybe_par() {
        let sugg = Sugg::BinOp(AssocOp::Add, "(1 + 1)".into());
        assert_eq!("(1 + 1)", sugg.maybe_par().to_string());

        let sugg = Sugg::BinOp(AssocOp::Add, "(1 + 1) + (1 + 1)".into());
        assert_eq!("((1 + 1) + (1 + 1))", sugg.maybe_par().to_string());
    }
}