change to a LatePass lint, ignore doc_hidden and PhantomData fields

Author: ParkMyCar

clippy_lints/src/lib.rs

@@ -1124,7 +1124,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     store.register_late_pass(move |_| Box::new(manual_hash_one::ManualHashOne::new(msrv())));
     store.register_late_pass(|_| Box::new(iter_without_into_iter::IterWithoutIntoIter));
-    store.register_early_pass(|| Box::new(pub_underscore_fields::PubUnderscoreFields));
+    store.register_late_pass(|_| Box::new(pub_underscore_fields::PubUnderscoreFields));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/pub_underscore_fields.rs

@@ -1,6 +1,10 @@
+use clippy_utils::attrs::is_doc_hidden;
 use clippy_utils::diagnostics::span_lint_and_help;
-use rustc_ast::ast::{Item, ItemKind, VisibilityKind};
-use rustc_lint::{EarlyContext, EarlyLintPass};
+use clippy_utils::is_path_lang_item;
+// use rustc_ast::ast::{Item, ItemKind, VisibilityKind};
+use rustc_hir::{FieldDef, Item, ItemKind, LangItem};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::Visibility;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 
 declare_clippy_lint! {
@@ -20,13 +24,15 @@ declare_clippy_lint! {
     /// ```
     /// Use instead:
     /// ```rust
-    /// struct FileHandle_Foo {
+    /// struct FileHandle {
     ///     _descriptor: usize,
     /// }
-    /// 
+    /// ```
+    ///
     /// // OR
-    /// 
-    /// struct FileHandle_Bar {
+    ///
+    /// ```
+    /// struct FileHandle {
     ///     pub descriptor: usize,
     /// }
     /// ```
@@ -37,21 +43,36 @@ declare_clippy_lint! {
 }
 declare_lint_pass!(PubUnderscoreFields => [PUB_UNDERSCORE_FIELDS]);
 
-impl EarlyLintPass for PubUnderscoreFields {
-    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
-        // this only pertains to structs
-        let ItemKind::Struct(ref st, _) = item.kind else {
+impl<'tcx> LateLintPass<'tcx> for PubUnderscoreFields {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
+        // This lint only pertains to structs.
+        let ItemKind::Struct(var, _) = &item.kind else {
             return;
         };
 
-        for field in st.fields() {
-            if let Some(ident) = field.ident.as_ref()
-            && ident.as_str().starts_with('_')
-            && !matches!(field.vis.kind, VisibilityKind::Inherited) {
+        let is_visible = |field: &FieldDef<'_>| {
+            let parent = cx.tcx.parent_module_from_def_id(field.def_id);
+            let grandparent = cx.tcx.parent_module_from_def_id(parent.into());
+            let visibility = cx.tcx.visibility(field.def_id);
+
+            let case_1 = parent == grandparent && !field.vis_span.is_empty();
+            let case_2 = visibility != Visibility::Restricted(parent.to_def_id());
+
+            case_1 || case_2
+        };
+
+        for field in var.fields() {
+            // Only pertains to fields that start with an underscore, and are visible publically.
+            if field.ident.as_str().starts_with('_') && is_visible(&field)
+                // We ignore fields that have `#[doc(hidden)]`.
+                && !is_doc_hidden(cx.tcx.hir().attrs(field.hir_id))
+                // We ignore fields that are `PhantomData`.
+                && !is_path_lang_item(cx, field.ty, LangItem::PhantomData)
+            {
                 span_lint_and_help(
                     cx,
                     PUB_UNDERSCORE_FIELDS,
-                    field.vis.span.to(ident.span),
+                    field.vis_span.to(field.ident.span),
                     "field marked as public but also inferred as unused because it's prefixed with `_`",
                     None,
                     "consider removing the underscore, or making the field private",