clippy_lints/src/methods/map_unwrap_or.rs

use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::res::{MaybeDef as _, MaybeResPath as _};
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::is_copy;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::intravisit::{Visitor, walk_expr, walk_path};
use rustc_hir::{ExprKind, HirId, LangItem, Node, PatKind, Path, QPath};
use rustc_lint::LateContext;
use rustc_middle::hir::nested_filter;
use rustc_span::{Span, sym};
use std::ops::ControlFlow;

use super::MAP_UNWRAP_OR;

/// lint use of `map().unwrap_or()` for `Option`s and `Result`s
#[expect(clippy::too_many_arguments)]
pub(super) fn check<'tcx>(
    cx: &LateContext<'tcx>,
    expr: &rustc_hir::Expr<'_>,
    recv: &rustc_hir::Expr<'_>,
    map_arg: &'tcx rustc_hir::Expr<'_>,
    unwrap_recv: &rustc_hir::Expr<'_>,
    unwrap_arg: &'tcx rustc_hir::Expr<'_>,
    map_span: Span,
    msrv: Msrv,
) {
    let recv_ty = cx.typeck_results().expr_ty(recv).peel_refs();
    let recv_ty_kind = match recv_ty.opt_diag_name(cx) {
        Some(sym::Option) => sym::Option,
        Some(sym::Result) if msrv.meets(cx, msrvs::RESULT_MAP_OR) => sym::Result,
        _ => return,
    };

    let unwrap_arg_ty = cx.typeck_results().expr_ty(unwrap_arg);
    if !is_copy(cx, unwrap_arg_ty) {
        // Replacing `.map(<f>).unwrap_or(<a>)` with `.map_or(<a>, <f>)` can sometimes lead to
        // borrowck errors, see #10579 for one such instance.
        // In particular, if `a` causes a move and `f` references that moved binding, then we cannot lint:
        // ```
        // let x = vec![1, 2];
        // x.get(0..1).map(|s| s.to_vec()).unwrap_or(x);
        // ```
        // This compiles, but changing it to `map_or` will produce a compile error:
        // ```
        // let x = vec![1, 2];
        // x.get(0..1).map_or(x, |s| s.to_vec())
        //                    ^ moving `x` here
        // ^^^^^^^^^^^ while it is borrowed here (and later used in the closure)
        // ```
        // So, we have to check that `a` is not referenced anywhere (even outside of the `.map` closure!)
        // before the call to `unwrap_or`.

        let mut unwrap_visitor = UnwrapVisitor {
            cx,
            identifiers: FxHashSet::default(),
        };
        unwrap_visitor.visit_expr(unwrap_arg);

        let mut reference_visitor = ReferenceVisitor {
            cx,
            identifiers: unwrap_visitor.identifiers,
            unwrap_or_span: unwrap_arg.span,
        };

        let body = cx.tcx.hir_body_owned_by(cx.tcx.hir_enclosing_body_owner(expr.hir_id));

        // Visit the body, and return if we've found a reference
        if reference_visitor.visit_body(body).is_break() {
            return;
        }
    }

    if !unwrap_arg.span.eq_ctxt(map_span) {
        return;
    }

    let mut applicability = Applicability::MachineApplicable;
    // get snippet for unwrap_or()
    let unwrap_snippet = snippet_with_applicability(cx, unwrap_arg.span, "..", &mut applicability);
    // lint message

    let suggest_kind = if recv_ty_kind == sym::Option
        && unwrap_arg
            .basic_res()
            .ctor_parent(cx)
            .is_lang_item(cx, LangItem::OptionNone)
    {
        SuggestedKind::AndThen
    }
    // is_some_and is stabilised && `unwrap_or` argument is false; suggest `is_some_and` instead
    else if matches!(&unwrap_arg.kind, ExprKind::Lit(lit)
            if matches!(lit.node, rustc_ast::LitKind::Bool(false)))
        && msrv.meets(cx, msrvs::OPTION_RESULT_IS_VARIANT_AND)
    {
        SuggestedKind::IsVariantAnd
    } else {
        SuggestedKind::Other
    };

    let arg = match suggest_kind {
        SuggestedKind::AndThen => "None",
        SuggestedKind::IsVariantAnd => "false",
        SuggestedKind::Other => "<a>",
    };

    let suggest = match (suggest_kind, recv_ty_kind) {
        (SuggestedKind::AndThen, _) => "and_then(<f>)",
        (SuggestedKind::IsVariantAnd, sym::Result) => "is_ok_and(<f>)",
        (SuggestedKind::IsVariantAnd, sym::Option) => "is_some_and(<f>)",
        _ => "map_or(<a>, <f>)",
    };

    let msg = format!(
        "called `map(<f>).unwrap_or({arg})` on {} `{recv_ty_kind}` value",
        if recv_ty_kind == sym::Option { "an" } else { "a" }
    );

    span_lint_and_then(cx, MAP_UNWRAP_OR, expr.span, msg, |diag| {
        let map_arg_span = map_arg.span;

        let mut suggestion = vec![
            (
                map_span,
                String::from(match (suggest_kind, recv_ty_kind) {
                    (SuggestedKind::AndThen, _) => "and_then",
                    (SuggestedKind::IsVariantAnd, sym::Result) => "is_ok_and",
                    (SuggestedKind::IsVariantAnd, sym::Option) => "is_some_and",
                    (SuggestedKind::Other, _)
                        if unwrap_arg_ty.peel_refs().is_array()
                            && cx.typeck_results().expr_ty_adjusted(unwrap_arg).peel_refs().is_slice() =>
                    {
                        return;
                    },
                    _ => "map_or",
                }),
            ),
            (expr.span.with_lo(unwrap_recv.span.hi()), String::new()),
        ];

        if matches!(suggest_kind, SuggestedKind::Other) {
            suggestion.push((map_arg_span.with_hi(map_arg_span.lo()), format!("{unwrap_snippet}, ")));
        }

        diag.multipart_suggestion(format!("use `{suggest}` instead"), suggestion, applicability);
    });
}

#[derive(Clone, Copy, PartialEq, Eq)]
enum SuggestedKind {
    AndThen,
    IsVariantAnd,
    Other,
}

struct UnwrapVisitor<'a, 'tcx> {
    cx: &'a LateContext<'tcx>,
    identifiers: FxHashSet<HirId>,
}

impl<'tcx> Visitor<'tcx> for UnwrapVisitor<'_, 'tcx> {
    type NestedFilter = nested_filter::All;

    fn visit_path(&mut self, path: &Path<'tcx>, _: HirId) {
        if let Res::Local(local_id) = path.res
            && let Node::Pat(pat) = self.cx.tcx.hir_node(local_id)
            && let PatKind::Binding(_, local_id, ..) = pat.kind
        {
            self.identifiers.insert(local_id);
        }
        walk_path(self, path);
    }

    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
        self.cx.tcx
    }
}

struct ReferenceVisitor<'a, 'tcx> {
    cx: &'a LateContext<'tcx>,
    identifiers: FxHashSet<HirId>,
    unwrap_or_span: Span,
}

impl<'tcx> Visitor<'tcx> for ReferenceVisitor<'_, 'tcx> {
    type NestedFilter = nested_filter::All;
    type Result = ControlFlow<()>;
    fn visit_expr(&mut self, expr: &'tcx rustc_hir::Expr<'_>) -> ControlFlow<()> {
        // If we haven't found a reference yet, check if this references
        // one of the locals that was moved in the `unwrap_or` argument.
        // We are only interested in exprs that appear before the `unwrap_or` call.
        if expr.span < self.unwrap_or_span
            && let ExprKind::Path(ref path) = expr.kind
            && let QPath::Resolved(_, path) = path
            && let Res::Local(local_id) = path.res
            && let Node::Pat(pat) = self.cx.tcx.hir_node(local_id)
            && let PatKind::Binding(_, local_id, ..) = pat.kind
            && self.identifiers.contains(&local_id)
        {
            return ControlFlow::Break(());
        }
        walk_expr(self, expr)
    }

    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
        self.cx.tcx
    }
}