src/tools/clippy/clippy_lints/src/redundant_pub_crate.rs

use clippy_utils::diagnostics::span_lint_and_then;
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::{Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::def_id::CRATE_DEF_ID;
use rustc_span::hygiene::MacroKind;

declare_clippy_lint! {
    /// ### What it does
    /// Checks for items declared `pub(crate)` that are not crate visible because they
    /// are inside a private module.
    ///
    /// ### Why is this bad?
    /// Writing `pub(crate)` is misleading when it's redundant due to the parent
    /// module's visibility.
    ///
    /// ### Example
    /// ```no_run
    /// mod internal {
    ///     pub(crate) fn internal_fn() { }
    /// }
    /// ```
    /// This function is not visible outside the module and it can be declared with `pub` or
    /// private visibility
    /// ```no_run
    /// mod internal {
    ///     pub fn internal_fn() { }
    /// }
    /// ```
    #[clippy::version = "1.44.0"]
    pub REDUNDANT_PUB_CRATE,
    nursery,
    "Using `pub(crate)` visibility on items that are not crate visible due to the visibility of the module that contains them."
}

#[derive(Default)]
pub struct RedundantPubCrate {
    is_exported: Vec<bool>,
}

impl_lint_pass!(RedundantPubCrate => [REDUNDANT_PUB_CRATE]);

impl<'tcx> LateLintPass<'tcx> for RedundantPubCrate {
    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
        if_chain! {
            if cx.tcx.visibility(item.owner_id.def_id) == ty::Visibility::Restricted(CRATE_DEF_ID.to_def_id());
            if !cx.effective_visibilities.is_exported(item.owner_id.def_id) && self.is_exported.last() == Some(&false);
            if is_not_macro_export(item);
            then {
                let span = item.span.with_hi(item.ident.span.hi());
                let descr = cx.tcx.def_kind(item.owner_id).descr(item.owner_id.to_def_id());
                span_lint_and_then(
                    cx,
                    REDUNDANT_PUB_CRATE,
                    span,
                    &format!("pub(crate) {descr} inside private module"),
                    |diag| {
                        diag.span_suggestion(
                            item.vis_span,
                            "consider using",
                            "pub".to_string(),
                            Applicability::MachineApplicable,
                        );
                    },
                );
            }
        }

        if let ItemKind::Mod { .. } = item.kind {
            self.is_exported
                .push(cx.effective_visibilities.is_exported(item.owner_id.def_id));
        }
    }

    fn check_item_post(&mut self, _cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
        if let ItemKind::Mod { .. } = item.kind {
            self.is_exported.pop().expect("unbalanced check_item/check_item_post");
        }
    }
}

fn is_not_macro_export<'tcx>(item: &'tcx Item<'tcx>) -> bool {
    if let ItemKind::Use(path, _) = item.kind {
        if path
            .res
            .iter()
            .all(|res| matches!(res, Res::Def(DefKind::Macro(MacroKind::Bang), _)))
        {
            return false;
        }
    } else if let ItemKind::Macro(..) = item.kind {
        return false;
    }

    true
}