Gate direct pin-borrow ADT diagnostic on !Unpin

Author: P8L1

compiler/rustc_hir_typeck/src/expr.rs

@@ -36,6 +36,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::{Ident, Span, Spanned, Symbol, kw, sym};
 use rustc_trait_selection::infer::InferCtxtExt;
+use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt};
 use tracing::{debug, instrument, trace};
 
@@ -531,6 +532,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let ty = self.structurally_resolve_type(span, ty);
         if let Some(adt) = ty.ty_adt_def()
             && !adt.is_pin_project()
+            && self.type_known_to_not_be_unpin(ty, span)
         {
             let def_span = self.tcx.hir_span_if_local(adt.did());
             let sugg_span = def_span.map(|span| span.shrink_to_lo());
@@ -542,6 +544,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    fn type_known_to_not_be_unpin(&self, ty: Ty<'tcx>, span: Span) -> bool {
+        if ty.has_param() || ty.has_infer() || ty.has_aliases() || ty.has_placeholders() {
+            return false;
+        }
+
+        let unpin_def_id = self.tcx.require_lang_item(LangItem::Unpin, span);
+        let trait_ref = ty::TraitRef::new(self.tcx, unpin_def_id, [ty]);
+        let obligation =
+            traits::Obligation::new(self.tcx, self.misc(span), self.param_env, trait_ref);
+        self.evaluate_obligation(&obligation).is_ok_and(|result| !result.may_apply())
+    }
+
     /// Does this expression refer to a place that either:
     /// * Is based on a local or static.
     /// * Contains a dereference

tests/ui/pin-ergonomics/direct-borrow-requires-pin-v2.rs

@@ -1,17 +1,57 @@
 #![feature(pin_ergonomics)]
-#![allow(incomplete_features)]
+#![allow(dead_code, incomplete_features)]
 //@ normalize-stderr: "\n\n\z" -> "\n"
 
-struct NotPinV2;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
 
-fn direct_pin_mut(mut value: NotPinV2) {
-    let _ = &pin mut value;
+struct UnpinAdt;
+
+struct NotUnpin {
+    _pin: PhantomPinned,
+}
+
+#[pin_v2]
+struct PinV2NotUnpin {
+    _pin: PhantomPinned,
+}
+
+struct GenericAdt<T> {
+    value: T,
+}
+
+fn direct_pin_mut_unpin() {
+    let _: Pin<&mut _> = &pin mut UnpinAdt;
+}
+
+fn direct_pin_const_unpin() {
+    let _: Pin<&_> = &pin const UnpinAdt;
+}
+
+fn direct_pin_mut_not_unpin() {
+    let _ = &pin mut NotUnpin { _pin: PhantomPinned };
     //~^ ERROR cannot directly pin an ADT that is not `#[pin_v2]`
 }
 
-fn direct_pin_const(value: NotPinV2) {
-    let _ = &pin const value;
+fn direct_pin_const_not_unpin() {
+    let _ = &pin const NotUnpin { _pin: PhantomPinned };
     //~^ ERROR cannot directly pin an ADT that is not `#[pin_v2]`
 }
 
+fn direct_pin_mut_pin_v2_not_unpin() {
+    let _: Pin<&mut _> = &pin mut PinV2NotUnpin { _pin: PhantomPinned };
+}
+
+fn direct_pin_const_pin_v2_not_unpin() {
+    let _: Pin<&_> = &pin const PinV2NotUnpin { _pin: PhantomPinned };
+}
+
+fn direct_pin_mut_generic<T>(mut value: GenericAdt<T>) {
+    let _ = &pin mut value;
+}
+
+fn direct_pin_const_generic<T>(value: GenericAdt<T>) {
+    let _ = &pin const value;
+}
+
 fn main() {}

tests/ui/pin-ergonomics/direct-borrow-requires-pin-v2.stderr

@@ -1,35 +1,35 @@
 error: cannot directly pin an ADT that is not `#[pin_v2]`
-  --> $DIR/direct-borrow-requires-pin-v2.rs:8:13
+  --> $DIR/direct-borrow-requires-pin-v2.rs:32:13
    |
-LL |     let _ = &pin mut value;
-   |             ^^^^^^^^^^^^^^
+LL |     let _ = &pin mut NotUnpin { _pin: PhantomPinned };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: type defined here
-  --> $DIR/direct-borrow-requires-pin-v2.rs:5:1
+  --> $DIR/direct-borrow-requires-pin-v2.rs:10:1
    |
-LL | struct NotPinV2;
+LL | struct NotUnpin {
    | ^^^^^^^^^^^^^^^
 help: add `#[pin_v2]` here
    |
 LL + #[pin_v2]
-LL | struct NotPinV2;
+LL | struct NotUnpin {
    |
 
 error: cannot directly pin an ADT that is not `#[pin_v2]`
-  --> $DIR/direct-borrow-requires-pin-v2.rs:13:13
+  --> $DIR/direct-borrow-requires-pin-v2.rs:37:13
    |
-LL |     let _ = &pin const value;
-   |             ^^^^^^^^^^^^^^^^
+LL |     let _ = &pin const NotUnpin { _pin: PhantomPinned };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: type defined here
-  --> $DIR/direct-borrow-requires-pin-v2.rs:5:1
+  --> $DIR/direct-borrow-requires-pin-v2.rs:10:1
    |
-LL | struct NotPinV2;
+LL | struct NotUnpin {
    | ^^^^^^^^^^^^^^^
 help: add `#[pin_v2]` here
    |
 LL + #[pin_v2]
-LL | struct NotPinV2;
+LL | struct NotUnpin {
    |
 
 error: aborting due to 2 previous errors