Auto merge of #95526 - Dylan-DPC:rollup-0ikl5l5, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - #91416 (Specialize infinite-type "insert some indirection" suggestion for Option)
 - #95384 (Update target_has_atomic documentation for stabilization)
 - #95517 (small rustc_borrowck cleanup)
 - #95520 (Fix typos in core::ptr docs)
 - #95523 (remove unused field from `infcx`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 49 insertions, 12 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 468c7a3c55b..d83781170e8 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -2285,10 +2285,10 @@ impl<'v> Visitor<'v> for FindTypeParam {
     }
 }
 
-pub fn recursive_type_with_infinite_size_error(
-    tcx: TyCtxt<'_>,
+pub fn recursive_type_with_infinite_size_error<'tcx>(
+    tcx: TyCtxt<'tcx>,
     type_def_id: DefId,
-    spans: Vec<Span>,
+    spans: Vec<(Span, Option<hir::HirId>)>,
 ) {
     assert!(type_def_id.is_local());
     let span = tcx.hir().span_if_local(type_def_id).unwrap();
@@ -2297,7 +2297,7 @@ pub fn recursive_type_with_infinite_size_error(
     let mut err =
         struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size", path);
     err.span_label(span, "recursive type has infinite size");
-    for &span in &spans {
+    for &(span, _) in &spans {
         err.span_label(span, "recursive without indirection");
     }
     let msg = format!(
@@ -2305,16 +2305,25 @@ pub fn recursive_type_with_infinite_size_error(
         path,
     );
     if spans.len() <= 4 {
+        // FIXME(compiler-errors): This suggestion might be erroneous if Box is shadowed
         err.multipart_suggestion(
             &msg,
             spans
-                .iter()
-                .flat_map(|&span| {
-                    [
-                        (span.shrink_to_lo(), "Box<".to_string()),
-                        (span.shrink_to_hi(), ">".to_string()),
-                    ]
-                    .into_iter()
+                .into_iter()
+                .flat_map(|(span, field_id)| {
+                    if let Some(generic_span) = get_option_generic_from_field_id(tcx, field_id) {
+                        // If we match an `Option` and can grab the span of the Option's generic, then
+                        // suggest boxing the generic arg for a non-null niche optimization.
+                        vec![
+                            (generic_span.shrink_to_lo(), "Box<".to_string()),
+                            (generic_span.shrink_to_hi(), ">".to_string()),
+                        ]
+                    } else {
+                        vec![
+                            (span.shrink_to_lo(), "Box<".to_string()),
+                            (span.shrink_to_hi(), ">".to_string()),
+                        ]
+                    }
                 })
                 .collect(),
             Applicability::HasPlaceholders,
@@ -2325,6 +2334,34 @@ pub fn recursive_type_with_infinite_size_error(
     err.emit();
 }
 
+/// Extract the span for the generic type `T` of `Option<T>` in a field definition
+fn get_option_generic_from_field_id(tcx: TyCtxt<'_>, field_id: Option<hir::HirId>) -> Option<Span> {
+    let node = tcx.hir().find(field_id?);
+
+    // Expect a field from our field_id
+    let Some(hir::Node::Field(field_def)) = node
+        else { bug!("Expected HirId corresponding to FieldDef, found: {:?}", node) };
+
+    // Match a type that is a simple QPath with no Self
+    let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = &field_def.ty.kind
+        else { return None };
+
+    // Check if the path we're checking resolves to Option
+    let hir::def::Res::Def(_, did) = path.res
+        else { return None };
+
+    // Bail if this path doesn't describe `::core::option::Option`
+    if !tcx.is_diagnostic_item(sym::Option, did) {
+        return None;
+    }
+
+    // Match a single generic arg in the 0th path segment
+    let generic_arg = path.segments.last()?.args?.args.get(0)?;
+
+    // Take the span out of the type, if it's a type
+    if let hir::GenericArg::Type(generic_ty) = generic_arg { Some(generic_ty.span) } else { None }
+}
+
 /// Summarizes information
 #[derive(Clone)]
 pub enum ArgKind {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 505d78d800a..58e002b3360 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -1988,7 +1988,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ObligationCauseCode::Coercion { source: _, target } => {
                 err.note(&format!("required by cast to type `{}`", self.ty_to_string(target)));
             }
-            ObligationCauseCode::RepeatVec(is_const_fn) => {
+            ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
                 err.note(
                     "the `Copy` trait is required because the repeated element will be copied",
                 );