Use the error variance for unused generic args

Author: oli-obk

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1802,8 +1802,8 @@ fn receiver_is_implemented<'tcx>(
 pub fn check_variances_for_type_defn<'tcx>(
     tcx: TyCtxt<'tcx>,
     item: LocalDefId,
-    variances: &[ty::Variance],
-) -> Result<(), ErrorGuaranteed> {
+    variances: &'tcx [ty::Variance],
+) -> Result<&'tcx [ty::Variance], ErrorGuaranteed> {
     let identity_args = ty::GenericArgs::identity_for_item(tcx, item);
 
     match tcx.def_kind(item) {
@@ -1819,7 +1819,7 @@ pub fn check_variances_for_type_defn<'tcx>(
             );
             tcx.type_of(item).skip_binder().error_reported()?;
         }
-        _ => return Ok(()),
+        _ => return Ok(variances),
     }
 
     let ty_predicates = tcx.predicates_of(item);
@@ -1856,7 +1856,7 @@ pub fn check_variances_for_type_defn<'tcx>(
 
     let ty_generics = tcx.generics_of(item);
 
-    let mut res = Ok(());
+    let mut variances = variances;
 
     for (index, _) in variances.iter().enumerate() {
         let parameter = Parameter(index as u32);
@@ -1868,30 +1868,30 @@ pub fn check_variances_for_type_defn<'tcx>(
         let ty_param = &ty_generics.own_params[index];
         let hir_param = &hir_generics.params[index];
 
-        if ty_param.def_id != hir_param.def_id.into() {
+        let guar = if ty_param.def_id != hir_param.def_id.into() {
             // Valid programs always have lifetimes before types in the generic parameter list.
             // ty_generics are normalized to be in this required order, and variances are built
             // from ty generics, not from hir generics. but we need hir generics to get
             // a span out.
             //
             // If they aren't in the same order, then the user has written invalid code, and already
             // got an error about it (or I'm wrong about this).
-            tcx.dcx().span_delayed_bug(
-                hir_param.span,
-                "hir generics and ty generics in different order",
-            );
-            continue;
-        }
-
-        match hir_param.name {
-            hir::ParamName::Error(guar) => res = Err(guar),
-            _ => {
-                let has_explicit_bounds = explicitly_bounded_params.contains(&parameter);
-                res = Err(report_bivariance(tcx, hir_param, has_explicit_bounds, item));
+            tcx.dcx()
+                .span_delayed_bug(hir_param.span, "hir generics and ty generics in different order")
+        } else {
+            match hir_param.name {
+                hir::ParamName::Error(guar) => guar,
+                _ => {
+                    let has_explicit_bounds = explicitly_bounded_params.contains(&parameter);
+                    report_bivariance(tcx, hir_param, has_explicit_bounds, item)
+                }
             }
-        }
+        };
+        let mut v = variances.to_vec();
+        v[index] = ty::Variance::Errvariant(guar);
+        variances = tcx.arena.alloc_slice(&v);
     }
-    res
+    Ok(variances)
 }
 
 fn report_bivariance(

compiler/rustc_hir_analysis/src/variance/mod.rs

@@ -72,8 +72,10 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
         }
     };
 
-    let _ = crate::check::wfcheck::check_variances_for_type_defn(tcx, item_def_id, variances);
-    variances
+    match crate::check::wfcheck::check_variances_for_type_defn(tcx, item_def_id, variances) {
+        Ok(variances) => variances,
+        Err(guar) => tcx.arena.alloc_from_iter(variances.iter().map(|_| ty::Errvariant(guar))),
+    }
 }
 
 #[instrument(level = "trace", skip(tcx), ret)]

compiler/rustc_infer/src/infer/relate/glb.rs

@@ -40,8 +40,10 @@ impl<'tcx> TypeRelation<'tcx> for Glb<'_, '_, 'tcx> {
         match variance {
             ty::Invariant => self.fields.equate(StructurallyRelateAliases::No).relate(a, b),
             ty::Covariant => self.relate(a, b),
-            // TODO: report a new error kind
-            ty::Errvariant(_) => Ok(a),
+            ty::Errvariant(guar) => {
+                self.fields.infcx.set_tainted_by_errors(guar);
+                Ok(a)
+            }
             // FIXME(#41044) -- not correct, need test
             ty::Bivariant => Ok(a),
             ty::Contravariant => self.fields.lub().relate(a, b),

compiler/rustc_infer/src/infer/relate/lub.rs

@@ -40,8 +40,10 @@ impl<'tcx> TypeRelation<'tcx> for Lub<'_, '_, 'tcx> {
         match variance {
             ty::Invariant => self.fields.equate(StructurallyRelateAliases::No).relate(a, b),
             ty::Covariant => self.relate(a, b),
-            // TODO: report a new kind of type error that preserves the `ErrorGuaranteed`?
-            ty::Errvariant(_) => Ok(a),
+            ty::Errvariant(guar) => {
+                self.fields.infcx.set_tainted_by_errors(guar);
+                Ok(a)
+            }
             // FIXME(#41044) -- not correct, need test
             ty::Bivariant => Ok(a),
             ty::Contravariant => self.fields.glb().relate(a, b),

compiler/rustc_infer/src/infer/relate/type_relating.rs

@@ -117,7 +117,11 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
                     ty::Invariant => {
                         infcx.inner.borrow_mut().type_variables().equate(a_id, b_id);
                     }
-                    ty::Errvariant(_) | ty::Bivariant => {
+                    ty::Errvariant(guar) => {
+                        infcx.set_tainted_by_errors(guar);
+                        return Ok(Ty::new_error(self.tcx(), guar));
+                    }
+                    ty::Bivariant => {
                         unreachable!("Expected bivariance to be handled in relate_with_variance")
                     }
                 }
@@ -204,7 +208,11 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
                     .unwrap_region_constraints()
                     .make_eqregion(origin, a, b);
             }
-            ty::Errvariant(_) | ty::Bivariant => {
+            ty::Errvariant(guar) => {
+                self.fields.infcx.set_tainted_by_errors(guar);
+                return Ok(ty::Region::new_error(self.tcx(), guar));
+            }
+            ty::Bivariant => {
                 unreachable!("Expected bivariance to be handled in relate_with_variance")
             }
         }

tests/ui/associated-consts/wrong-projection-self-ty-on-invalid-type.rs

@@ -0,0 +1,11 @@
+struct Fail<T>;
+//~^ ERROR: type parameter `T` is never used
+
+impl Fail<i32> {
+    const C: () = ();
+}
+
+fn main() {
+    Fail::<()>::C
+    //~^ ERROR: no associated item named `C` found for struct `Fail<()>`
+}

tests/ui/associated-consts/wrong-projection-self-ty-on-invalid-type.stderr

@@ -0,0 +1,25 @@
+error[E0392]: type parameter `T` is never used
+  --> $DIR/wrong-projection-self-ty-on-invalid-type.rs:1:13
+   |
+LL | struct Fail<T>;
+   |             ^ unused type parameter
+   |
+   = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
+   = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
+
+error[E0599]: no associated item named `C` found for struct `Fail<()>` in the current scope
+  --> $DIR/wrong-projection-self-ty-on-invalid-type.rs:9:17
+   |
+LL | struct Fail<T>;
+   | -------------- associated item `C` not found for this struct
+...
+LL |     Fail::<()>::C
+   |                 ^ associated item not found in `Fail<()>`
+   |
+   = note: the associated item was found for
+           - `Fail<i32>`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0392, E0599.
+For more information about an error, try `rustc --explain E0392`.

tests/ui/inference/dont-collect-stmts-from-parent-body.rs

@@ -8,7 +8,6 @@ fn main() {
         impl<T> Type<T> {
             fn new() -> Type<T> {
                 Type
-                //~^ ERROR type annotations needed
             }
         }
     };

tests/ui/inference/dont-collect-stmts-from-parent-body.stderr

@@ -7,18 +7,6 @@ LL | struct Type<T>;
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
    = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
 
-error[E0282]: type annotations needed
-  --> $DIR/dont-collect-stmts-from-parent-body.rs:10:17
-   |
-LL |                 Type
-   |                 ^^^^ cannot infer type of the type parameter `T` declared on the struct `Type`
-   |
-help: consider specifying the generic argument
-   |
-LL |                 Type::<T>
-   |                     +++++
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0282, E0392.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0392`.

tests/ui/traits/trait-selection-ice-84727.rs

@@ -20,6 +20,7 @@ where
 {
     fn over(self) -> Cell<NewFg> {
     //~^ ERROR mismatched types
+    //~| ERROR `over` has an incompatible type for trait
         self.over();
     }
 }