cargo-mend 0.16.1

//! HIR-level use-site collector.
//!
//! Walks every body in the local crate and emits one `UseSite` per
//! resolved expression-level path reference. The output is persisted with
//! the per-compilation findings so that, after every cargo target
//! compilation has run, `load_report` can compute the union of callers
//! for each item and suppress narrowing-style findings whose proposed
//! tighter visibility would block any actual caller.
//!
//! This catches every reference rustc itself sees, including paths inside
//! macro invocations and paths produced by proc-macro expansion — both
//! of which the source-level scanner cannot.

use std::collections::HashSet;

use rustc_hir::AmbigArg;
use rustc_hir::Expr;
use rustc_hir::ExprKind;
use rustc_hir::HirId;
use rustc_hir::ImplItem;
use rustc_hir::Item;
use rustc_hir::ItemKind;
use rustc_hir::Pat;
use rustc_hir::PatExprKind;
use rustc_hir::PatKind;
use rustc_hir::QPath;
use rustc_hir::TraitItem;
use rustc_hir::Ty;
use rustc_hir::TyKind;
use rustc_hir::def::DefKind;
use rustc_hir::def::Res;
use rustc_hir::def_id::CRATE_DEF_ID;
use rustc_hir::def_id::DefId;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::Visitor;
use rustc_hir::intravisit::walk_expr;
use rustc_hir::intravisit::walk_impl_item;
use rustc_hir::intravisit::walk_item;
use rustc_hir::intravisit::walk_trait_item;
use rustc_middle::hir::nested_filter::All;
use rustc_middle::ty;
use rustc_middle::ty::TyCtxt;
use rustc_middle::ty::Visibility;

use crate::compiler::persistence::UseSite;
use crate::rust_syntax::PathAnchor;

/// Walk the entire crate's HIR and append every resolved
/// expression/type/pattern path reference to `out`. The caller module is
/// the nearest enclosing module def (defaults to the crate root).
pub(super) fn collect_use_sites(tcx: TyCtxt<'_>, out: &mut Vec<UseSite>) {
    let mut collector = UseSiteCollector {
        tcx,
        current_module: CRATE_DEF_ID.to_def_id(),
        out,
    };
    let crate_items = tcx.hir_crate_items(());
    for item_id in crate_items.free_items() {
        let item = tcx.hir_item(item_id);
        collector.visit_item(item);
    }
    for impl_item_id in crate_items.impl_items() {
        let impl_item = tcx.hir_impl_item(impl_item_id);
        collector.visit_impl_item(impl_item);
    }
    for trait_item_id in crate_items.trait_items() {
        let trait_item = tcx.hir_trait_item(trait_item_id);
        collector.visit_trait_item(trait_item);
    }
}

struct UseSiteCollector<'a, 'tcx> {
    tcx:            TyCtxt<'tcx>,
    /// Def-id of the nearest enclosing module. Updated as the visitor
    /// descends into `mod` items so each call site is tagged with the
    /// module path it lives in (not the function or impl that contains
    /// it).
    current_module: DefId,
    out:            &'a mut Vec<UseSite>,
}

impl<'tcx> UseSiteCollector<'_, 'tcx> {
    fn record_target(&mut self, target: DefId) {
        // Skip references to items in other crates — narrowing decisions
        // only apply to local items.
        if target.is_local() {
            self.push_site(target);
        }
        match self.tcx.def_kind(target) {
            // A reference to a type alias also reaches every type the alias
            // names: `type M = Wrapper<Inner>` exposes `Inner` wherever `M`
            // is used, even though `Inner` never appears at the use site.
            // Record those component types under the same caller module so
            // narrowing findings see the reach that flows through the alias.
            // Foreign aliases can still name a local type, so this runs
            // regardless of where the alias itself lives.
            DefKind::TyAlias => self.record_alias_components(target),
            // Calling a function reaches every local type named in its
            // signature: `fn f() -> Guard` exposes `Guard` at the call site
            // even though `Guard` never appears there. Record those signature
            // types under the same caller module so narrowing findings see
            // the reach that flows through the call. Without this, removing
            // `pub` from a type returned by (or passed to) a `pub(crate)` fn
            // leaves a private type in that fn's signature (E0446) and rolls
            // `--fix` back.
            DefKind::Fn | DefKind::AssocFn => self.record_fn_signature_components(target),
            _ => {},
        }
    }

    /// Record every local type named in a function's signature as used from
    /// the current caller module, following each type's public field graph the
    /// same way alias components are. `fn_sig` yields the declared input and
    /// output types; a module-private field still caps reach, so genuinely
    /// internal types stay flagged.
    fn record_fn_signature_components(&mut self, func: DefId) {
        let signature = self.tcx.fn_sig(func).instantiate_identity();
        let mut seen = HashSet::new();
        for input_or_output in signature.skip_binder().inputs_and_output {
            for arg in input_or_output.walk() {
                if let Some(component) = arg.as_type()
                    && let ty::TyKind::Adt(adt_def, _) = component.kind()
                {
                    self.record_exposed_adt(adt_def.did(), &mut seen);
                }
            }
        }
    }

    /// Record every local type named in an alias's right-hand side as used
    /// from the current caller module. `type_of` returns the aliased type
    /// with nested eager aliases already expanded, so walking it yields the
    /// concrete types the alias exposes.
    fn record_alias_components(&mut self, alias: DefId) {
        let aliased = self.tcx.type_of(alias).instantiate_identity();
        let mut seen = HashSet::new();
        for arg in aliased.walk() {
            if let Some(component) = arg.as_type()
                && let ty::TyKind::Adt(adt_def, _) = component.kind()
            {
                self.record_exposed_adt(adt_def.did(), &mut seen);
            }
        }
    }

    /// Record a local type as used from the current caller module, then walk
    /// its public field graph: a `pub` field of an alias-exposed type makes
    /// the field's type reachable wherever the alias is used, so those types
    /// must keep matching visibility too. Fields that do not escape the
    /// type's own module are not followed — they expose nothing further.
    fn record_exposed_adt(&mut self, did: DefId, seen: &mut HashSet<DefId>) {
        let Some(local) = did.as_local() else {
            return;
        };
        if !seen.insert(did) {
            return;
        }
        self.push_site(did);
        let owning_module = self.tcx.parent_module_from_def_id(local).to_def_id();
        for field in self.tcx.adt_def(did).all_fields() {
            if !self.field_escapes_module(field.did, owning_module) {
                continue;
            }
            for arg in self.tcx.type_of(field.did).instantiate_identity().walk() {
                if let Some(component) = arg.as_type()
                    && let ty::TyKind::Adt(adt_def, _) = component.kind()
                {
                    self.record_exposed_adt(adt_def.did(), seen);
                }
            }
        }
    }

    /// Record every local ADT named in a trait impl's interface — trait-ref
    /// type arguments, associated type bindings, associated const types, and
    /// associated fn signatures — as used from the widest module the
    /// interface reaches. HIR holds post-expansion items, so this covers
    /// interface mentions that exist in no source file: `#[derive(AsBindGroup)]`
    /// on a `pub(crate)` type generates `type Data = TextExtensionKey;`,
    /// which requires `TextExtensionKey` to stay at least `pub(crate)`
    /// (E0446). Without these sites, `unused_pub` suggests removing `pub`
    /// and the `--fix` validation fails and rolls back.
    fn record_trait_impl_interface(&mut self, impl_def: LocalDefId) {
        if !matches!(
            self.tcx.def_kind(impl_def.to_def_id()),
            DefKind::Impl { of_trait: true }
        ) {
            return;
        }
        let trait_ref = self.tcx.impl_trait_ref(impl_def).instantiate_identity();
        let self_adt = trait_ref.self_ty().ty_adt_def().map(ty::AdtDef::did);

        let previous_module = self.current_module;
        self.current_module = self.interface_scope_module(trait_ref.def_id, self_adt);

        let mut seen = HashSet::new();
        for arg in trait_ref.args {
            if let Some(arg_type) = arg.as_type() {
                self.record_interface_component_types(arg_type, self_adt, &mut seen);
            }
        }
        for assoc_def_id in self.tcx.associated_item_def_ids(impl_def) {
            match self.tcx.def_kind(*assoc_def_id) {
                DefKind::AssocTy | DefKind::AssocConst { .. } => {
                    let assoc_type = self.tcx.type_of(*assoc_def_id).instantiate_identity();
                    self.record_interface_component_types(assoc_type, self_adt, &mut seen);
                },
                DefKind::AssocFn => {
                    let signature = self.tcx.fn_sig(*assoc_def_id).instantiate_identity();
                    for input_or_output in signature.skip_binder().inputs_and_output {
                        self.record_interface_component_types(input_or_output, self_adt, &mut seen);
                    }
                },
                _ => {},
            }
        }

        self.current_module = previous_module;
    }

    /// The widest module a trait impl's interface is usable from: the
    /// narrower of the trait's visibility and the self type's visibility.
    /// `Public` on both sides reaches the whole crate (and beyond), so the
    /// crate root stands in as the caller module.
    fn interface_scope_module(&self, trait_def_id: DefId, self_adt: Option<DefId>) -> DefId {
        let trait_visibility = self.tcx.visibility(trait_def_id);
        let self_visibility =
            self_adt.map_or(Visibility::Public, |adt_did| self.tcx.visibility(adt_did));
        match (trait_visibility, self_visibility) {
            (Visibility::Restricted(trait_scope), Visibility::Restricted(self_scope)) => {
                if self.tcx.is_descendant_of(trait_scope, self_scope) {
                    trait_scope
                } else {
                    self_scope
                }
            },
            (Visibility::Restricted(scope), Visibility::Public)
            | (Visibility::Public, Visibility::Restricted(scope)) => scope,
            (Visibility::Public, Visibility::Public) => CRATE_DEF_ID.to_def_id(),
        }
    }

    /// Record every local ADT mentioned in `component_type` as used from the
    /// current caller module. The impl's own self type is skipped: narrowing
    /// the self type narrows the interface with it, so the interface imposes
    /// no visibility floor on it.
    fn record_interface_component_types(
        &mut self,
        component_type: ty::Ty<'tcx>,
        self_adt: Option<DefId>,
        seen: &mut HashSet<DefId>,
    ) {
        for arg in component_type.walk() {
            if let Some(component) = arg.as_type()
                && let ty::TyKind::Adt(adt_def, _) = component.kind()
                && adt_def.did().is_local()
                && Some(adt_def.did()) != self_adt
                && seen.insert(adt_def.did())
            {
                self.push_site(adt_def.did());
            }
        }
    }

    /// True when `field` is visible beyond `owning_module` — i.e. its
    /// visibility is `pub` or restricted to a scope wider than the type's own
    /// module. A module-private field caps the reach of its type and is not
    /// followed.
    fn field_escapes_module(&self, field: DefId, owning_module: DefId) -> bool {
        match self.tcx.visibility(field) {
            Visibility::Public => true,
            Visibility::Restricted(scope) => scope != owning_module,
        }
    }

    fn push_site(&mut self, target: DefId) {
        self.out.push(UseSite {
            target_def_path:        self.tcx.def_path_str(target),
            caller_module_def_path: self.tcx.def_path_str(self.current_module),
        });
    }

    fn record_qpath(&mut self, qpath: &QPath<'_>, hir_id: HirId) {
        let res = match qpath {
            QPath::Resolved(_, path) => path.res,
            QPath::TypeRelative(..) => {
                // Type-relative paths (e.g. `Foo::method`) need typeck to
                // resolve. Best-effort lookup via typeck_results.
                let owner = hir_id.owner.def_id;
                if !self.tcx.has_typeck_results(owner) {
                    return;
                }
                let typeck = self.tcx.typeck(owner);
                typeck.qpath_res(qpath, hir_id)
            },
        };
        if let Res::Def(_, def_id) = res {
            self.record_target(def_id);
        }
    }
}

impl<'tcx> Visitor<'tcx> for UseSiteCollector<'_, 'tcx> {
    type NestedFilter = All;

    fn maybe_tcx(&mut self) -> TyCtxt<'tcx> { self.tcx }

    fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
        let prev = self.current_module;
        if matches!(item.kind, ItemKind::Mod(..)) {
            self.current_module = item.owner_id.def_id.to_def_id();
        } else {
            self.current_module = self
                .tcx
                .parent_module_from_def_id(item.owner_id.def_id)
                .to_def_id();
        }
        if matches!(item.kind, ItemKind::Impl(..)) {
            self.record_trait_impl_interface(item.owner_id.def_id);
        }
        walk_item(self, item);
        self.current_module = prev;
    }

    fn visit_impl_item(&mut self, item: &'tcx ImplItem<'tcx>) {
        let prev = self.current_module;
        self.current_module = self
            .tcx
            .parent_module_from_def_id(item.owner_id.def_id)
            .to_def_id();
        walk_impl_item(self, item);
        self.current_module = prev;
    }

    fn visit_trait_item(&mut self, item: &'tcx TraitItem<'tcx>) {
        let prev = self.current_module;
        self.current_module = self
            .tcx
            .parent_module_from_def_id(item.owner_id.def_id)
            .to_def_id();
        walk_trait_item(self, item);
        self.current_module = prev;
    }

    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
        match &expr.kind {
            ExprKind::Path(qpath) => self.record_qpath(qpath, expr.hir_id),
            ExprKind::MethodCall(..) => {
                // Method-call dispatch is type-dependent, not path-based.
                // The callee def-id lives in TypeckResults, not in any
                // QPath the visitor descends into.
                let owner = expr.hir_id.owner.def_id;
                if self.tcx.has_typeck_results(owner)
                    && let Some(def_id) = self.tcx.typeck(owner).type_dependent_def_id(expr.hir_id)
                {
                    self.record_target(def_id);
                }
            },
            ExprKind::Struct(qpath, ..) => self.record_qpath(qpath, expr.hir_id),
            _ => {},
        }
        walk_expr(self, expr);
    }

    fn visit_ty(&mut self, ty: &'tcx Ty<'tcx, AmbigArg>) {
        if let TyKind::Path(qpath) = &ty.kind {
            self.record_qpath(qpath, ty.hir_id);
        }
        rustc_hir::intravisit::walk_ty(self, ty);
    }

    fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) {
        if let PatKind::Expr(expr) = &pat.kind
            && let PatExprKind::Path(qpath) = &expr.kind
        {
            self.record_qpath(qpath, expr.hir_id);
        }
        rustc_hir::intravisit::walk_pat(self, pat);
    }
}

/// Returns the def-path of `LocalDefId` as a `String`, e.g.
/// `crate::tui::panes::cpu::cpu_required_pane_height`.
pub(super) fn def_path_string(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
    tcx.def_path_str(def_id.to_def_id())
}

/// Returns the def-path of the parent module of `def_id`. For a function
/// in `crate::tui::panes::cpu`, returns `crate::tui::panes::cpu`. Used
/// when synthesizing the proposed narrower scope for a `pub(super)`
/// suggestion.
pub(super) fn parent_module_def_path(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
    let parent = tcx.parent_module_from_def_id(def_id);
    tcx.def_path_str(parent.to_def_id())
}

pub(super) fn parent_module_path_segments(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Vec<String> {
    let mut segments = parent_module_def_path(tcx, def_id)
        .split("::")
        .filter(|segment| !segment.is_empty())
        .map(String::from)
        .collect::<Vec<_>>();
    if PathAnchor::first(&segments) == Some(PathAnchor::Crate) {
        segments.remove(0);
    }
    segments
}