usage.rs

use crate::visitors::{for_each_expr, for_each_expr_with_closures, Descend, Visitable};
use crate::{self as utils, get_enclosing_loop_or_multi_call_closure};
use core::ops::ControlFlow;
use hir::def::Res;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{self as hir, Expr, ExprKind, HirId, HirIdSet};
use rustc_hir_typeck::expr_use_visitor::{Delegate, ExprUseVisitor, Place, PlaceBase, PlaceWithHirId};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::hir::nested_filter;
use rustc_middle::mir::FakeReadCause;
use rustc_middle::ty;

/// 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,
    };
    let infcx = cx.tcx.infer_ctxt().build();
    ExprUseVisitor::new(
        &mut delegate,
        &infcx,
        expr.hir_id.owner.def_id,
        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))
}

pub fn is_potentially_local_place(local_id: HirId, place: &Place<'_>) -> bool {
    match place.base {
        PlaceBase::Local(id) => id == local_id,
        PlaceBase::Upvar(_) => {
            // Conservatively assume yes.
            true
        },
        _ => false,
    }
}

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

impl<'tcx> MutVarsDelegate {
    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, _: &PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {}
}

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

pub struct BindingUsageFinder<'a, 'tcx> {
    cx: &'a LateContext<'tcx>,
    binding_ids: Vec<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> Visitor<'tcx> for BindingUsageFinder<'a, 'tcx> {
    type NestedFilter = nested_filter::OnlyBodies;

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

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

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

pub fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool {
    for_each_expr(expression, |e| {
        match e.kind {
            ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => ControlFlow::Break(()),
            // 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 e.span.from_expansion() => ControlFlow::Break(()),
            _ => ControlFlow::Continue(()),
        }
    })
    .is_some()
}

pub fn local_used_in<'tcx>(cx: &LateContext<'tcx>, local_id: HirId, v: impl Visitable<'tcx>) -> bool {
    for_each_expr_with_closures(cx, v, |e| {
        if utils::path_to_local_id(e, local_id) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_some()
}

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;
    };

    // for _ in 1..3 {
    //    local
    // }
    //
    // let closure = || local;
    // closure();
    // closure();
    let loop_start = get_enclosing_loop_or_multi_call_closure(cx, after).map(|e| e.hir_id);

    let mut past_expr = false;
    for_each_expr_with_closures(cx, block, |e| {
        if past_expr {
            if utils::path_to_local_id(e, local_id) {
                ControlFlow::Break(())
            } else {
                ControlFlow::Continue(Descend::Yes)
            }
        } else if e.hir_id == after.hir_id {
            past_expr = true;
            ControlFlow::Continue(Descend::No)
        } else {
            past_expr = Some(e.hir_id) == loop_start;
            ControlFlow::Continue(Descend::Yes)
        }
    })
    .is_some()
}