From a26d60902e1833514c9386583213abd114c915ac Mon Sep 17 00:00:00 2001
From: Brezak <bezak.adamko@gmail.com>
Date: Tue, 20 Aug 2024 20:53:49 +0200
Subject: [PATCH] Check that `#[pointee]` is applied only to generic arguments

---
 compiler/rustc_builtin_macros/messages.ftl    |  2 ++
 .../src/deriving/smart_ptr.rs                 | 25 +++++++++++++++++++
 compiler/rustc_builtin_macros/src/errors.rs   |  7 ++++++
 .../ui/deriving/deriving-smart-pointer-neg.rs |  8 ++++++
 .../deriving-smart-pointer-neg.stderr         |  8 +++++-
 5 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index 9695df9c87e8a..8bd07027da46f 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -235,6 +235,8 @@ builtin_macros_non_exhaustive_default = default variant must be exhaustive
     .label = declared `#[non_exhaustive]` here
     .help = consider a manual implementation of `Default`
 
+builtin_macros_non_generic_pointee = the `#[pointee]` attribute may only be used on generic parameters
+
 builtin_macros_non_unit_default = the `#[default]` attribute may only be used on unit enum variants
     .help = consider a manual implementation of `Default`
 
diff --git a/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs b/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
index bc41d33a609e3..ecf232bac5ce8 100644
--- a/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
@@ -13,6 +13,8 @@ use rustc_span::symbol::{sym, Ident};
 use rustc_span::{Span, Symbol};
 use thin_vec::{thin_vec, ThinVec};
 
+use crate::errors;
+
 macro_rules! path {
     ($span:expr, $($part:ident)::*) => { vec![$(Ident::new(sym::$part, $span),)*] }
 }
@@ -25,6 +27,8 @@ pub(crate) fn expand_deriving_smart_ptr(
     push: &mut dyn FnMut(Annotatable),
     _is_const: bool,
 ) {
+    item.visit_with(&mut DetectNonGenericPointeeAttr { cx });
+
     let (name_ident, generics) = if let Annotatable::Item(aitem) = item
         && let ItemKind::Struct(struct_data, g) = &aitem.kind
     {
@@ -396,3 +400,24 @@ impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
         }
     }
 }
+
+struct DetectNonGenericPointeeAttr<'a, 'b> {
+    cx: &'a ExtCtxt<'b>,
+}
+
+impl<'a, 'b> rustc_ast::visit::Visitor<'a> for DetectNonGenericPointeeAttr<'a, 'b> {
+    fn visit_attribute(&mut self, attr: &'a rustc_ast::Attribute) -> Self::Result {
+        if attr.has_name(sym::pointee) {
+            self.cx.dcx().emit_err(errors::NonGenericPointee { span: attr.span });
+        }
+    }
+
+    fn visit_generic_param(&mut self, param: &'a rustc_ast::GenericParam) -> Self::Result {
+        match param.kind {
+            GenericParamKind::Type { .. } => return,
+            GenericParamKind::Lifetime | GenericParamKind::Const { .. } => {
+                rustc_ast::visit::walk_generic_param(self, param)
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 4fffffb91c8b4..625aa4f2b75de 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -937,3 +937,10 @@ pub(crate) struct NakedFunctionTestingAttribute {
     #[label]
     pub testing_span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(builtin_macros_non_generic_pointee)]
+pub(crate) struct NonGenericPointee {
+    #[primary_span]
+    pub span: Span,
+}
diff --git a/tests/ui/deriving/deriving-smart-pointer-neg.rs b/tests/ui/deriving/deriving-smart-pointer-neg.rs
index f02fb56130fa7..e7b45b2fd4b6c 100644
--- a/tests/ui/deriving/deriving-smart-pointer-neg.rs
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.rs
@@ -53,6 +53,14 @@ struct NoMaybeSized<'a, #[pointee] T> {
     ptr: &'a T,
 }
 
+#[derive(SmartPointer)]
+#[repr(transparent)]
+struct PointeeOnField<'a, #[pointee] T: ?Sized> {
+    #[pointee]
+    //~^ ERROR: the `#[pointee]` attribute may only be used on generic parameters
+    ptr: &'a T
+}
+
 // However, reordering attributes should work nevertheless.
 #[repr(transparent)]
 #[derive(SmartPointer)]
diff --git a/tests/ui/deriving/deriving-smart-pointer-neg.stderr b/tests/ui/deriving/deriving-smart-pointer-neg.stderr
index e7c2afc8b00c7..e84b2ee9a6c05 100644
--- a/tests/ui/deriving/deriving-smart-pointer-neg.stderr
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.stderr
@@ -58,6 +58,12 @@ error: `derive(SmartPointer)` requires T to be marked `?Sized`
 LL | struct NoMaybeSized<'a, #[pointee] T> {
    |                                    ^
 
+error: the `#[pointee]` attribute may only be used on generic parameters
+  --> $DIR/deriving-smart-pointer-neg.rs:59:5
+   |
+LL |     #[pointee]
+   |     ^^^^^^^^^^
+
 error[E0392]: lifetime parameter `'a` is never used
   --> $DIR/deriving-smart-pointer-neg.rs:15:16
    |
@@ -90,6 +96,6 @@ LL | struct NoFieldUnit<'a, #[pointee] T: ?Sized>();
    |
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
 
-error: aborting due to 12 previous errors
+error: aborting due to 13 previous errors
 
 For more information about this error, try `rustc --explain E0392`.