Do leak check after function pointer coercion

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1442,6 +1442,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// the message in `secondary_span` as the primary label, and apply the message that would
     /// otherwise be used for the primary label on the `secondary_span` `Span`. This applies on
     /// E0271, like `src/test/ui/issues/issue-39970.stderr`.
+    #[tracing::instrument(
+        level = "debug",
+        skip(self, diag, secondary_span, swap_secondary_and_primary, force_label)
+    )]
     pub fn note_type_err(
         &self,
         diag: &mut Diagnostic,
@@ -1453,7 +1457,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         force_label: bool,
     ) {
         let span = cause.span(self.tcx);
-        debug!("note_type_err cause={:?} values={:?}, terr={:?}", cause, values, terr);
 
         // For some types of errors, expected-found does not make
         // sense, so just ignore the values we were given.
@@ -1621,9 +1624,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             }
         };
 
-        // Ignore msg for object safe coercion
-        // since E0038 message will be printed
         match terr {
+            // Ignore msg for object safe coercion
+            // since E0038 message will be printed
             TypeError::ObjectUnsafeCoercion(_) => {}
             _ => {
                 let mut label_or_note = |span: Span, msg: &str| {
@@ -1774,6 +1777,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         // It reads better to have the error origin as the final
         // thing.
         self.note_error_origin(diag, cause, exp_found, terr);
+
+        debug!(?diag);
     }
 
     fn suggest_tuple_pattern(

compiler/rustc_middle/src/ty/error.rs

@@ -135,11 +135,10 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
             ArgCount => write!(f, "incorrect number of function parameters"),
             FieldMisMatch(adt, field) => write!(f, "field type mismatch: {}.{}", adt, field),
             RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
-            RegionsInsufficientlyPolymorphic(br, _) => write!(
-                f,
-                "expected bound lifetime parameter{}, found concrete lifetime",
-                br_string(br)
-            ),
+            // Actually naming the region here is a bit confusing because context is lacking
+            RegionsInsufficientlyPolymorphic(..) => {
+                write!(f, "one type is more general than the other")
+            }
             RegionsOverlyPolymorphic(br, _) => write!(
                 f,
                 "expected concrete lifetime, found bound lifetime parameter{}",

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -151,6 +151,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     ///
     /// * From each pre-binding block to the next pre-binding block.
     /// * From each otherwise block to the next pre-binding block.
+    #[tracing::instrument(level = "debug", skip(self, arms))]
     pub(crate) fn match_expr(
         &mut self,
         destination: Place<'tcx>,

compiler/rustc_mir_build/src/thir/cx/block.rs

@@ -75,6 +75,7 @@ impl<'tcx> Cx<'tcx> {
                         };
 
                         let mut pattern = self.pattern_from_hir(local.pat);
+                        debug!(?pattern);
 
                         if let Some(ty) = &local.ty {
                             if let Some(&user_ty) =

compiler/rustc_mir_build/src/thir/cx/mod.rs

@@ -98,6 +98,7 @@ impl<'tcx> Cx<'tcx> {
         }
     }
 
+    #[tracing::instrument(level = "debug", skip(self))]
     pub(crate) fn pattern_from_hir(&mut self, p: &hir::Pat<'_>) -> Pat<'tcx> {
         let p = match self.tcx.hir().get(p.hir_id) {
             Node::Pat(p) | Node::Binding(p) => p,

compiler/rustc_typeck/src/check/_match.rs

@@ -56,6 +56,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut all_arms_diverge = Diverges::WarnedAlways;
 
         let expected = orig_expected.adjust_for_branches(self);
+        debug!(?expected);
 
         let mut coercion = {
             let coerce_first = match expected {
@@ -127,6 +128,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Some(&arm.body),
                 arm_ty,
                 Some(&mut |err: &mut Diagnostic| {
+                    let Some(ret) = self.ret_type_span else {
+                        return;
+                    };
+                    let Expectation::IsLast(stmt) = orig_expected else {
+                        return
+                    };
                     let can_coerce_to_return_ty = match self.ret_coercion.as_ref() {
                         Some(ret_coercion) if self.in_tail_expr => {
                             let ret_ty = ret_coercion.borrow().expected_ty();
@@ -138,38 +145,38 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                         _ => false,
                     };
-                    if let (Expectation::IsLast(stmt), Some(ret), true) =
-                        (orig_expected, self.ret_type_span, can_coerce_to_return_ty)
-                    {
-                        let semi_span = expr.span.shrink_to_hi().with_hi(stmt.hi());
-                        let mut ret_span: MultiSpan = semi_span.into();
-                        ret_span.push_span_label(
-                            expr.span,
-                            "this could be implicitly returned but it is a statement, not a \
-                                tail expression"
-                                .to_owned(),
-                        );
-                        ret_span.push_span_label(
-                            ret,
-                            "the `match` arms can conform to this return type".to_owned(),
-                        );
-                        ret_span.push_span_label(
-                            semi_span,
-                            "the `match` is a statement because of this semicolon, consider \
-                                removing it"
-                                .to_owned(),
-                        );
-                        err.span_note(
-                            ret_span,
-                            "you might have meant to return the `match` expression",
-                        );
-                        err.tool_only_span_suggestion(
-                            semi_span,
-                            "remove this semicolon",
-                            String::new(),
-                            Applicability::MaybeIncorrect,
-                        );
+                    if !can_coerce_to_return_ty {
+                        return;
                     }
+
+                    let semi_span = expr.span.shrink_to_hi().with_hi(stmt.hi());
+                    let mut ret_span: MultiSpan = semi_span.into();
+                    ret_span.push_span_label(
+                        expr.span,
+                        "this could be implicitly returned but it is a statement, not a \
+                            tail expression"
+                            .to_owned(),
+                    );
+                    ret_span.push_span_label(
+                        ret,
+                        "the `match` arms can conform to this return type".to_owned(),
+                    );
+                    ret_span.push_span_label(
+                        semi_span,
+                        "the `match` is a statement because of this semicolon, consider \
+                            removing it"
+                            .to_owned(),
+                    );
+                    err.span_note(
+                        ret_span,
+                        "you might have meant to return the `match` expression",
+                    );
+                    err.tool_only_span_suggestion(
+                        semi_span,
+                        "remove this semicolon",
+                        String::new(),
+                        Applicability::MaybeIncorrect,
+                    );
                 }),
                 false,
             );
@@ -199,7 +206,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // We won't diverge unless the scrutinee or all arms diverge.
         self.diverges.set(scrut_diverges | all_arms_diverge);
 
-        coercion.complete(self)
+        let match_ty = coercion.complete(self);
+        debug!(?match_ty);
+        match_ty
     }
 
     fn get_appropriate_arm_semicolon_removal_span(

compiler/rustc_typeck/src/check/coercion.rs

@@ -737,14 +737,27 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
         G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
     {
-        if let ty::FnPtr(fn_ty_b) = b.kind()
-            && let (hir::Unsafety::Normal, hir::Unsafety::Unsafe) =
-                (fn_ty_a.unsafety(), fn_ty_b.unsafety())
-        {
-            let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
-            return self.unify_and(unsafe_a, b, to_unsafe);
-        }
-        self.unify_and(a, b, normal)
+        self.commit_unconditionally(|snapshot| {
+            let result = if let ty::FnPtr(fn_ty_b) = b.kind()
+                && let (hir::Unsafety::Normal, hir::Unsafety::Unsafe) =
+                    (fn_ty_a.unsafety(), fn_ty_b.unsafety())
+            {
+                let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
+                self.unify_and(unsafe_a, b, to_unsafe)
+            } else {
+                self.unify_and(a, b, normal)
+            };
+
+            // FIXME(#73154): This is a hack. Currently LUB can generate
+            // unsolvable constraints. Additionally, it returns `a`
+            // unconditionally, even when the "LUB" is `b`. In the future, we
+            // want the coerced type to be the actual supertype of these two,
+            // but for now, we want to just error to ensure we don't lock
+            // ourselves into a specific behavior with NLL.
+            self.leak_check(false, snapshot)?;
+
+            result
+        })
     }
 
     fn coerce_from_fn_pointer(
@@ -1133,8 +1146,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let (adjustments, target) = self.register_infer_ok_obligations(ok);
                     self.apply_adjustments(new, adjustments);
                     debug!(
-                        "coercion::try_find_coercion_lub: was able to coerce from previous type {:?} to new type {:?}",
-                        prev_ty, new_ty,
+                        "coercion::try_find_coercion_lub: was able to coerce from new type {:?} to previous type {:?} ({:?})",
+                        new_ty, prev_ty, target
                     );
                     return Ok(target);
                 }
@@ -1190,15 +1203,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             Ok(ok) => {
-                debug!(
-                    "coercion::try_find_coercion_lub: was able to coerce previous type {:?} to new type {:?}",
-                    prev_ty, new_ty,
-                );
                 let (adjustments, target) = self.register_infer_ok_obligations(ok);
                 for expr in exprs {
                     let expr = expr.as_coercion_site();
                     self.apply_adjustments(expr, adjustments.clone());
                 }
+                debug!(
+                    "coercion::try_find_coercion_lub: was able to coerce previous type {:?} to new type {:?} ({:?})",
+                    prev_ty, new_ty, target
+                );
                 Ok(target)
             }
         }
@@ -1430,6 +1443,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                 })
         };
 
+        debug!(?result);
         match result {
             Ok(v) => {
                 self.final_ty = Some(v);
@@ -1520,7 +1534,10 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                     augment_error(&mut err);
                 }
 
-                if let Some(expr) = expression {
+                let is_insufficiently_polymorphic =
+                    matches!(coercion_error, TypeError::RegionsInsufficientlyPolymorphic(..));
+
+                if !is_insufficiently_polymorphic && let Some(expr) = expression {
                     fcx.emit_coerce_suggestions(
                         &mut err,
                         expr,

compiler/rustc_typeck/src/check/demand.rs

@@ -129,6 +129,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ///
     /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
     /// will be permitted if the diverges flag is currently "always".
+    #[tracing::instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
     pub fn demand_coerce_diag(
         &self,
         expr: &hir::Expr<'tcx>,
@@ -150,7 +151,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
 
-        self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr, Some(e));
+        let is_insufficiently_polymorphic =
+            matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
+
+        // FIXME(#73154): For now, we do leak check when coercing function
+        // pointers in typeck, instead of only during borrowck. This can lead
+        // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
+        if !is_insufficiently_polymorphic {
+            self.emit_coerce_suggestions(
+                &mut err,
+                expr,
+                expr_ty,
+                expected,
+                expected_ty_expr,
+                Some(e),
+            );
+        }
 
         (expected, Some(err))
     }

src/test/ui/hr-subtype/placeholder-pattern-fail.nll.stderr

@@ -1,37 +1,12 @@
 error[E0308]: mismatched types
-  --> $DIR/placeholder-pattern-fail.rs:9:12
+  --> $DIR/placeholder-pattern-fail.rs:9:47
    |
 LL |     let _: for<'a, 'b> fn(Inv<'a>, Inv<'b>) = sub;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |                                               ^^^ one type is more general than the other
    |
    = note: expected fn pointer `for<'a, 'b> fn(Inv<'a>, Inv<'b>)`
               found fn pointer `for<'a> fn(Inv<'a>, Inv<'a>)`
 
-error[E0308]: mismatched types
-  --> $DIR/placeholder-pattern-fail.rs:9:12
-   |
-LL |     let _: for<'a, 'b> fn(Inv<'a>, Inv<'b>) = sub;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
-   |
-   = note: expected fn pointer `for<'a, 'b> fn(Inv<'a>, Inv<'b>)`
-              found fn pointer `for<'a> fn(Inv<'a>, Inv<'a>)`
-
-error: lifetime may not live long enough
-  --> $DIR/placeholder-pattern-fail.rs:14:13
-   |
-LL | fn simple1<'c>(x: (&'c i32,)) {
-   |            -- lifetime `'c` defined here
-LL |     let _x: (&'static i32,) = x;
-   |             ^^^^^^^^^^^^^^^ type annotation requires that `'c` must outlive `'static`
-
-error: lifetime may not live long enough
-  --> $DIR/placeholder-pattern-fail.rs:19:12
-   |
-LL | fn simple2<'c>(x: (&'c i32,)) {
-   |            -- lifetime `'c` defined here
-LL |     let _: (&'static i32,) = x;
-   |            ^^^^^^^^^^^^^^^ type annotation requires that `'c` must outlive `'static`
-
-error: aborting due to 4 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0308`.

src/test/ui/hrtb/hrtb-exists-forall-fn.nll.stderr

@@ -1,8 +1,8 @@
 error[E0308]: mismatched types
-  --> $DIR/hrtb-exists-forall-fn.rs:17:12
+  --> $DIR/hrtb-exists-forall-fn.rs:17:34
    |
 LL |     let _: for<'b> fn(&'b u32) = foo();
-   |            ^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |                                  ^^^^^ one type is more general than the other
    |
    = note: expected fn pointer `for<'b> fn(&'b u32)`
               found fn pointer `fn(&u32)`

src/test/ui/lub-glb/old-lub-glb-hr-noteq1.stderr → src/test/ui/lub-glb/old-lub-glb-hr-noteq1.baseleak.stderr

@@ -1,12 +1,15 @@
 error[E0308]: `match` arms have incompatible types
-  --> $DIR/old-lub-glb-hr-noteq1.rs:11:14
+  --> $DIR/old-lub-glb-hr-noteq1.rs:17:14
    |
 LL |       let z = match 22 {
    |  _____________-
 LL | |         0 => x,
    | |              - this is found to be of type `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
 LL | |         _ => y,
    | |              ^ one type is more general than the other
+LL | |
+...  |
+LL | |
 LL | |     };
    | |_____- `match` arms have incompatible types
    |

src/test/ui/lub-glb/old-lub-glb-hr-noteq1.basenoleak.stderr

@@ -0,0 +1,21 @@
+error[E0308]: `match` arms have incompatible types
+  --> $DIR/old-lub-glb-hr-noteq1.rs:17:14
+   |
+LL |       let z = match 22 {
+   |  _____________-
+LL | |         0 => x,
+   | |              - this is found to be of type `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
+LL | |         _ => y,
+   | |              ^ one type is more general than the other
+LL | |
+...  |
+LL | |
+LL | |     };
+   | |_____- `match` arms have incompatible types
+   |
+   = note: expected fn pointer `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
+              found fn pointer `for<'a> fn(&'a u8, &'a u8) -> &'a u8`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.