src/tools/clippy/clippy_utils/src/usage.rs

use crate as utils;
use crate::visitors::{expr_visitor, expr_visitor_no_bodies};
use rustc_hir as hir;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::HirIdSet;
use rustc_hir::{Expr, ExprKind, HirId};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_middle::mir::FakeReadCause;
use rustc_middle::ty;
use rustc_typeck::expr_use_visitor::{Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};

/// Returns a set of mutated local variable IDs, or `None` if mutations could not be determined.
pub fn mutated_variables<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> Option<HirIdSet> {
    let mut delegate = MutVarsDelegate {
        used_mutably: HirIdSet::default(),
        skip: false,
    };
    cx.tcx.infer_ctxt().enter(|infcx| {
        ExprUseVisitor::new(
            &mut delegate,
            &infcx,
            expr.hir_id.owner,
            cx.param_env,
            cx.typeck_results(),
        )
        .walk_expr(expr);
    });

    if delegate.skip {
        return None;
    }
    Some(delegate.used_mutably)
}

pub fn is_potentially_mutated<'tcx>(variable: HirId, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
    mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&variable))
}

struct MutVarsDelegate {
    used_mutably: HirIdSet,
    skip: bool,
}

impl<'tcx> MutVarsDelegate {
    #[allow(clippy::similar_names)]
    fn update(&mut self, cat: &PlaceWithHirId<'tcx>) {
        match cat.place.base {
            PlaceBase::Local(id) => {
                self.used_mutably.insert(id);
            },
            PlaceBase::Upvar(_) => {
                //FIXME: This causes false negatives. We can't get the `NodeId` from
                //`Categorization::Upvar(_)`. So we search for any `Upvar`s in the
                //`while`-body, not just the ones in the condition.
                self.skip = true;
            },
            _ => {},
        }
    }
}

impl<'tcx> Delegate<'tcx> for MutVarsDelegate {
    fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId) {}

    fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId, bk: ty::BorrowKind) {
        if bk == ty::BorrowKind::MutBorrow {
            self.update(cmt);
        }
    }

    fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
        self.update(cmt);
    }

    fn fake_read(&mut self, _: rustc_typeck::expr_use_visitor::Place<'tcx>, _: FakeReadCause, _: HirId) {}
}

pub struct ParamBindingIdCollector {
    pub binding_hir_ids: Vec<hir::HirId>,
}
impl<'tcx> ParamBindingIdCollector {
    fn collect_binding_hir_ids(body: &'tcx hir::Body<'tcx>) -> Vec<hir::HirId> {
        let mut hir_ids: Vec<hir::HirId> = Vec::new();
        for param in body.params.iter() {
            let mut finder = ParamBindingIdCollector {
                binding_hir_ids: Vec::new(),
            };
            finder.visit_param(param);
            for hir_id in &finder.binding_hir_ids {
                hir_ids.push(*hir_id);
            }
        }
        hir_ids
    }
}
impl<'tcx> intravisit::Visitor<'tcx> for ParamBindingIdCollector {
    type Map = Map<'tcx>;

    fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) {
        if let hir::PatKind::Binding(_, hir_id, ..) = pat.kind {
            self.binding_hir_ids.push(hir_id);
        }
        intravisit::walk_pat(self, pat);
    }

    fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
        intravisit::NestedVisitorMap::None
    }
}

pub struct BindingUsageFinder<'a, 'tcx> {
    cx: &'a LateContext<'tcx>,
    binding_ids: Vec<hir::HirId>,
    usage_found: bool,
}
impl<'a, 'tcx> BindingUsageFinder<'a, 'tcx> {
    pub fn are_params_used(cx: &'a LateContext<'tcx>, body: &'tcx hir::Body<'tcx>) -> bool {
        let mut finder = BindingUsageFinder {
            cx,
            binding_ids: ParamBindingIdCollector::collect_binding_hir_ids(body),
            usage_found: false,
        };
        finder.visit_body(body);
        finder.usage_found
    }
}
impl<'a, 'tcx> intravisit::Visitor<'tcx> for BindingUsageFinder<'a, 'tcx> {
    type Map = Map<'tcx>;

    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
        if !self.usage_found {
            intravisit::walk_expr(self, expr);
        }
    }

    fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
        if let hir::def::Res::Local(id) = path.res {
            if self.binding_ids.contains(&id) {
                self.usage_found = true;
            }
        }
    }

    fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
        intravisit::NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
    }
}

pub fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool {
    let mut seen_return_break_continue = false;
    expr_visitor_no_bodies(|ex| {
        if seen_return_break_continue {
            return false;
        }
        match &ex.kind {
            ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => {
                seen_return_break_continue = true;
            },
            // Something special could be done here to handle while or for loop
            // desugaring, as this will detect a break if there's a while loop
            // or a for loop inside the expression.
            _ => {
                if ex.span.from_expansion() {
                    seen_return_break_continue = true;
                }
            },
        }
        !seen_return_break_continue
    })
    .visit_expr(expression);
    seen_return_break_continue
}

pub fn local_used_after_expr(cx: &LateContext<'_>, local_id: HirId, after: &Expr<'_>) -> bool {
    let Some(block) = utils::get_enclosing_block(cx, local_id) else { return false };
    let mut used_after_expr = false;
    let mut past_expr = false;
    expr_visitor(cx, |expr| {
        if used_after_expr {
            return false;
        }

        if expr.hir_id == after.hir_id {
            past_expr = true;
        } else if past_expr && utils::path_to_local_id(expr, local_id) {
            used_after_expr = true;
        }
        !used_after_expr
    })
    .visit_block(block);
    used_after_expr
}