rust/clippy_lints/src/methods/bind_instead_of_map.rs

use super::{contains_return, BIND_INSTEAD_OF_MAP};
use crate::utils::{
    in_macro, match_qpath, match_type, method_calls, multispan_sugg_with_applicability, paths, remove_blocks, snippet,
    snippet_with_macro_callsite, span_lint_and_sugg, span_lint_and_then, visitors::find_all_ret_expressions,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_span::Span;

pub(crate) struct OptionAndThenSome;

impl BindInsteadOfMap for OptionAndThenSome {
    const TYPE_NAME: &'static str = "Option";
    const TYPE_QPATH: &'static [&'static str] = &paths::OPTION;

    const BAD_METHOD_NAME: &'static str = "and_then";
    const BAD_VARIANT_NAME: &'static str = "Some";
    const BAD_VARIANT_QPATH: &'static [&'static str] = &paths::OPTION_SOME;

    const GOOD_METHOD_NAME: &'static str = "map";
}

pub(crate) struct ResultAndThenOk;

impl BindInsteadOfMap for ResultAndThenOk {
    const TYPE_NAME: &'static str = "Result";
    const TYPE_QPATH: &'static [&'static str] = &paths::RESULT;

    const BAD_METHOD_NAME: &'static str = "and_then";
    const BAD_VARIANT_NAME: &'static str = "Ok";
    const BAD_VARIANT_QPATH: &'static [&'static str] = &paths::RESULT_OK;

    const GOOD_METHOD_NAME: &'static str = "map";
}

pub(crate) struct ResultOrElseErrInfo;

impl BindInsteadOfMap for ResultOrElseErrInfo {
    const TYPE_NAME: &'static str = "Result";
    const TYPE_QPATH: &'static [&'static str] = &paths::RESULT;

    const BAD_METHOD_NAME: &'static str = "or_else";
    const BAD_VARIANT_NAME: &'static str = "Err";
    const BAD_VARIANT_QPATH: &'static [&'static str] = &paths::RESULT_ERR;

    const GOOD_METHOD_NAME: &'static str = "map_err";
}

pub(crate) trait BindInsteadOfMap {
    const TYPE_NAME: &'static str;
    const TYPE_QPATH: &'static [&'static str];

    const BAD_METHOD_NAME: &'static str;
    const BAD_VARIANT_NAME: &'static str;
    const BAD_VARIANT_QPATH: &'static [&'static str];

    const GOOD_METHOD_NAME: &'static str;

    fn no_op_msg() -> String {
        format!(
            "using `{}.{}({})`, which is a no-op",
            Self::TYPE_NAME,
            Self::BAD_METHOD_NAME,
            Self::BAD_VARIANT_NAME
        )
    }

    fn lint_msg() -> String {
        format!(
            "using `{}.{}(|x| {}(y))`, which is more succinctly expressed as `{}(|x| y)`",
            Self::TYPE_NAME,
            Self::BAD_METHOD_NAME,
            Self::BAD_VARIANT_NAME,
            Self::GOOD_METHOD_NAME
        )
    }

    fn lint_closure_autofixable(
        cx: &LateContext<'_>,
        expr: &hir::Expr<'_>,
        args: &[hir::Expr<'_>],
        closure_expr: &hir::Expr<'_>,
        closure_args_span: Span,
    ) -> bool {
        if_chain! {
            if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
            if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
            if match_qpath(qpath, Self::BAD_VARIANT_QPATH);
            if some_args.len() == 1;
            then {
                let inner_expr = &some_args[0];

                if contains_return(inner_expr) {
                    return false;
                }

                let some_inner_snip = if inner_expr.span.from_expansion() {
                    snippet_with_macro_callsite(cx, inner_expr.span, "_")
                } else {
                    snippet(cx, inner_expr.span, "_")
                };

                let closure_args_snip = snippet(cx, closure_args_span, "..");
                let option_snip = snippet(cx, args[0].span, "..");
                let note = format!("{}.{}({} {})", option_snip, Self::GOOD_METHOD_NAME, closure_args_snip, some_inner_snip);
                span_lint_and_sugg(
                    cx,
                    BIND_INSTEAD_OF_MAP,
                    expr.span,
                    Self::lint_msg().as_ref(),
                    "try this",
                    note,
                    Applicability::MachineApplicable,
                );
                true
            } else {
                false
            }
        }
    }

    fn lint_closure(cx: &LateContext<'_>, expr: &hir::Expr<'_>, closure_expr: &hir::Expr<'_>) -> bool {
        let mut suggs = Vec::new();
        let can_sugg: bool = find_all_ret_expressions(cx, closure_expr, |ret_expr| {
            if_chain! {
                if !in_macro(ret_expr.span);
                if let hir::ExprKind::Call(ref func_path, ref args) = ret_expr.kind;
                if let hir::ExprKind::Path(ref qpath) = func_path.kind;
                if match_qpath(qpath, Self::BAD_VARIANT_QPATH);
                if args.len() == 1;
                if !contains_return(&args[0]);
                then {
                    suggs.push((ret_expr.span, args[0].span.source_callsite()));
                    true
                } else {
                    false
                }
            }
        });

        if can_sugg {
            span_lint_and_then(cx, BIND_INSTEAD_OF_MAP, expr.span, Self::lint_msg().as_ref(), |diag| {
                multispan_sugg_with_applicability(
                    diag,
                    "try this",
                    Applicability::MachineApplicable,
                    std::iter::once((*method_calls(expr, 1).2.get(0).unwrap(), Self::GOOD_METHOD_NAME.into())).chain(
                        suggs
                            .into_iter()
                            .map(|(span1, span2)| (span1, snippet(cx, span2, "_").into())),
                    ),
                )
            });
        }
        can_sugg
    }

    /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
    fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) -> bool {
        if !match_type(cx, cx.typeck_results().expr_ty(&args[0]), Self::TYPE_QPATH) {
            return false;
        }

        match args[1].kind {
            hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
                let closure_body = cx.tcx.hir().body(body_id);
                let closure_expr = remove_blocks(&closure_body.value);

                if Self::lint_closure_autofixable(cx, expr, args, closure_expr, closure_args_span) {
                    true
                } else {
                    Self::lint_closure(cx, expr, closure_expr)
                }
            },
            // `_.and_then(Some)` case, which is no-op.
            hir::ExprKind::Path(ref qpath) if match_qpath(qpath, Self::BAD_VARIANT_QPATH) => {
                span_lint_and_sugg(
                    cx,
                    BIND_INSTEAD_OF_MAP,
                    expr.span,
                    Self::no_op_msg().as_ref(),
                    "use the expression directly",
                    snippet(cx, args[0].span, "..").into(),
                    Applicability::MachineApplicable,
                );
                true
            },
            _ => false,
        }
    }
}