correctly check for unique params

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -352,12 +352,7 @@ fn check_opaque_type_parameter_valid<'tcx>(
     opaque_type_key: OpaqueTypeKey<'tcx>,
     span: Span,
 ) -> Result<(), ErrorGuaranteed> {
-    let opaque_ty_hir = tcx.hir().expect_item(opaque_type_key.def_id);
-    let is_ty_alias = match opaque_ty_hir.expect_opaque_ty().origin {
-        OpaqueTyOrigin::TyAlias { .. } => true,
-        OpaqueTyOrigin::AsyncFn(..) | OpaqueTyOrigin::FnReturn(..) => false,
-    };
-
+    let opaque_env = LazyOpaqueTyEnv::new(tcx, opaque_type_key.def_id);
     let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
     let mut seen_params: FxIndexMap<_, Vec<_>> = FxIndexMap::default();
     for (i, arg) in opaque_type_key.iter_captured_args(tcx) {
@@ -367,20 +362,17 @@ fn check_opaque_type_parameter_valid<'tcx>(
 
         let arg_is_param = match arg.unpack() {
             GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
-            GenericArgKind::Lifetime(lt) => match is_ty_alias {
-                true => matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_)),
-                // FIXME(#111935, #113916): For RPIT, we currently accept ReStatic as well.
-                // This is a back-compat hack, see the issue for more.
-                false => matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic),
-            },
+            GenericArgKind::Lifetime(lt) => {
+                matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_))
+                    || (lt.is_static() && opaque_env.param_equal_static(i))
+            }
             GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)),
         };
 
         if arg_is_param {
-            // FIXME(#113916): For RPIT, we can't currently check for unique lifetime
-            // params, see that issue for more. We limit this to TAIT for now.
-            if is_ty_alias {
-                seen_params.entry(arg).or_default().push(i);
+            let seen_where = seen_params.entry(arg).or_default();
+            if !seen_where.first().is_some_and(|&prev_i| opaque_env.params_equal(i, prev_i)) {
+                seen_where.push(i);
             }
         } else {
             // Prevent `fn foo() -> Foo<u32>` from being defining.
@@ -413,3 +405,81 @@ fn check_opaque_type_parameter_valid<'tcx>(
 
     Ok(())
 }
+
+struct LazyOpaqueTyEnv<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    def_id: LocalDefId,
+    canonical_args: std::cell::Cell<Option<ty::GenericArgsRef<'tcx>>>,
+}
+
+impl<'tcx> LazyOpaqueTyEnv<'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
+        Self { tcx, def_id, canonical_args: std::cell::Cell::new(None) }
+    }
+
+    pub fn param_equal_static(&self, param_index: usize) -> bool {
+        self.get_canonical_args()[param_index].expect_region().is_static()
+    }
+
+    pub fn params_equal(&self, param1: usize, param2: usize) -> bool {
+        let canonical_args = self.get_canonical_args();
+        canonical_args[param1] == canonical_args[param2]
+    }
+
+    fn get_canonical_args(&self) -> ty::GenericArgsRef<'tcx> {
+        use rustc_hir as hir;
+        use rustc_infer::infer::outlives::env::OutlivesEnvironment;
+        use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
+
+        if let Some(canonical_args) = self.canonical_args.get() {
+            return canonical_args;
+        }
+
+        let &Self { tcx, def_id, .. } = self;
+        let origin = tcx.opaque_type_origin(def_id);
+        let defining_use_anchor = match origin {
+            hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
+            hir::OpaqueTyOrigin::TyAlias { .. } => tcx.impl_trait_parent(def_id),
+        };
+        let param_env = tcx.param_env(defining_use_anchor);
+
+        let infcx = tcx.infer_ctxt().build();
+        let ocx = ObligationCtxt::new(&infcx);
+
+        let args = match origin {
+            hir::OpaqueTyOrigin::FnReturn(parent) | hir::OpaqueTyOrigin::AsyncFn(parent) => {
+                GenericArgs::identity_for_item(tcx, parent).extend_to(
+                    tcx,
+                    def_id.to_def_id(),
+                    |param, _| {
+                        tcx.map_rpit_lifetime_to_fn_lifetime(param.def_id.expect_local()).into()
+                    },
+                )
+            }
+            hir::OpaqueTyOrigin::TyAlias { .. } => GenericArgs::identity_for_item(tcx, def_id),
+        };
+
+        let wf_tys = ocx.assumed_wf_types(param_env, defining_use_anchor).unwrap_or_else(|_| {
+            tcx.sess.delay_span_bug(tcx.def_span(def_id), "error getting implied bounds");
+            Default::default()
+        });
+        let implied_bounds = infcx.implied_bounds_tys(param_env, defining_use_anchor, wf_tys);
+        let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+
+        let mut seen = vec![tcx.lifetimes.re_static];
+        let canonical_args = tcx.fold_regions(args, |r1, _| {
+            if let Some(&r2) = seen.iter().find(|&&r2| {
+                let free_regions = outlives_env.free_region_map();
+                free_regions.sub_free_regions(tcx, r1, r2)
+                    && free_regions.sub_free_regions(tcx, r2, r1)
+            }) {
+                r2
+            } else {
+                seen.push(r1);
+                r1
+            }
+        });
+        self.canonical_args.set(Some(canonical_args));
+        canonical_args
+    }
+}

tests/ui/impl-trait/defining-use-captured-non-universal-region.infer.stderr

@@ -1,5 +1,5 @@
 error[E0792]: expected generic lifetime parameter, found `'_`
-  --> $DIR/defining-use-captured-non-universal-region.rs:15:18
+  --> $DIR/defining-use-captured-non-universal-region.rs:14:18
    |
 LL | fn foo<'a>() -> impl Sized + 'a {
    |                              -- this generic parameter must be used with a generic lifetime parameter

tests/ui/impl-trait/defining-use-captured-non-universal-region.rs

@@ -1,15 +1,14 @@
 // This was an ICE. See #110726.
-//
-// FIXME(#111935) revision `statik` should not pass.
 
 // revisions: statik infer fixed
 //[fixed] check-pass
-//[statik] check-pass
+//[statik] check-fail
 #![allow(unconditional_recursion)]
 
 fn foo<'a>() -> impl Sized + 'a {
     #[cfg(statik)]
     let i: i32 = foo::<'static>();
+    //[statik]~^ ERROR expected generic lifetime parameter, found `'static`
 
     #[cfg(infer)]
     let i: i32 = foo::<'_>();

tests/ui/impl-trait/defining-use-captured-non-universal-region.statik.stderr

@@ -0,0 +1,12 @@
+error[E0792]: expected generic lifetime parameter, found `'static`
+  --> $DIR/defining-use-captured-non-universal-region.rs:10:18
+   |
+LL | fn foo<'a>() -> impl Sized + 'a {
+   |                              -- cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
+LL |     #[cfg(statik)]
+LL |     let i: i32 = foo::<'static>();
+   |                  ^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0792`.

tests/ui/impl-trait/in-trait/bad-item-bound-within-rpitit-2.rs

@@ -5,6 +5,7 @@ trait Foo {
     fn bar<'other: 'a>() -> impl Sized + 'a {}
     //~^ ERROR use of undeclared lifetime name `'a`
     //~| ERROR use of undeclared lifetime name `'a`
+    //~| ERROR expected generic lifetime parameter, found `'static`
 }
 
 fn main() {}

tests/ui/impl-trait/in-trait/bad-item-bound-within-rpitit-2.stderr

@@ -28,6 +28,15 @@ help: consider introducing lifetime `'a` here
 LL | trait Foo<'a> {
    |          ++++
 
-error: aborting due to 2 previous errors
+error[E0792]: expected generic lifetime parameter, found `'static`
+  --> $DIR/bad-item-bound-within-rpitit-2.rs:5:45
+   |
+LL |     fn bar<'other: 'a>() -> impl Sized + 'a {}
+   |            ------                           ^^
+   |            |
+   |            cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
+
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0261`.
+Some errors have detailed explanations: E0261, E0792.
+For more information about an error, try `rustc --explain E0261`.

tests/ui/impl-trait/rpit/non-defining-use-lifetimes.rs

@@ -0,0 +1,37 @@
+// issue: #111935
+
+#![allow(unconditional_recursion)]
+
+// Lt indirection is necessary to make the lifetime of the function late-bound,
+// in order to bypass some other bugs.
+type Lt<'lt> = Option<*mut &'lt ()>;
+
+mod statik {
+    use super::*;
+    // invalid defining use: Opaque<'static> := ()
+    fn foo<'a>(_: Lt<'a>) -> impl Sized + 'a {
+        let _: () = foo(Lt::<'static>::None);
+        //~^ ERROR expected generic lifetime parameter, found `'static`
+    }
+}
+
+mod infer {
+    use super::*;
+    // invalid defining use: Opaque<'_> := ()
+    fn foo<'a>(_: Lt<'a>) -> impl Sized + 'a {
+        let _: () = foo(Lt::<'_>::None);
+        //~^ ERROR expected generic lifetime parameter, found `'_`
+    }
+}
+
+mod equal {
+    use super::*;
+    // invalid defining use: Opaque<'a, 'a> := ()
+    // because of the use of equal lifetimes in args
+    fn foo<'a, 'b>(_: Lt<'a>, _: Lt<'b>) -> impl Sized + 'a + 'b {
+        let _: () = foo(Lt::<'a>::None, Lt::<'a>::None);
+        //~^ ERROR non-defining opaque type use in defining scope
+    }
+}
+
+fn main() {}

tests/ui/impl-trait/rpit/non-defining-use-lifetimes.stderr

@@ -0,0 +1,31 @@
+error[E0792]: expected generic lifetime parameter, found `'static`
+  --> $DIR/non-defining-use-lifetimes.rs:13:16
+   |
+LL |     fn foo<'a>(_: Lt<'a>) -> impl Sized + 'a {
+   |                                           -- cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
+LL |         let _: () = foo(Lt::<'static>::None);
+   |                ^^
+
+error[E0792]: expected generic lifetime parameter, found `'_`
+  --> $DIR/non-defining-use-lifetimes.rs:22:16
+   |
+LL |     fn foo<'a>(_: Lt<'a>) -> impl Sized + 'a {
+   |                                           -- this generic parameter must be used with a generic lifetime parameter
+LL |         let _: () = foo(Lt::<'_>::None);
+   |                ^^
+
+error: non-defining opaque type use in defining scope
+  --> $DIR/non-defining-use-lifetimes.rs:32:16
+   |
+LL |         let _: () = foo(Lt::<'a>::None, Lt::<'a>::None);
+   |                ^^
+   |
+note: lifetime used multiple times
+  --> $DIR/non-defining-use-lifetimes.rs:31:58
+   |
+LL |     fn foo<'a, 'b>(_: Lt<'a>, _: Lt<'b>) -> impl Sized + 'a + 'b {
+   |                                                          ^^   ^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0792`.

tests/ui/type-alias-impl-trait/equal-lifetime-params-ok.rs

@@ -0,0 +1,50 @@
+// FIXME: description
+// issue: #113916
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+#![feature(impl_trait_in_assoc_type)]
+
+trait Trait<'a, 'b> {}
+impl<T> Trait<'_, '_> for T {}
+
+mod equal_params {
+    type Opaque<'a: 'b, 'b: 'a> = impl super::Trait<'a, 'b>;
+    fn test<'a: 'b, 'b: 'a>() -> Opaque<'a, 'b> {
+        let _ = None::<&'a &'b &'a ()>;
+        0u8
+    }
+}
+
+mod equal_static {
+    type Opaque<'a: 'static> = impl Sized + 'a;
+    fn test<'a: 'static>() -> Opaque<'a> {
+        let _ = None::<&'static &'a ()>;
+        0u8
+    }
+}
+
+mod implied_bounds {
+    trait Traitor {
+        type Assoc;
+        fn define(self) -> Self::Assoc;
+    }
+
+    impl<'a> Traitor for &'static &'a () {
+        type Assoc = impl Sized + 'a;
+        fn define(self) -> Self::Assoc {
+            let _ = None::<&'static &'a ()>;
+            0u8
+        }
+    }
+
+    impl<'a, 'b> Traitor for (&'a &'b (), &'b &'a ()) {
+        type Assoc = impl Sized + 'a + 'b;
+        fn define(self) -> Self::Assoc {
+            let _ = None::<(&'a &'b (), &'b &'a ())>;
+            0u8
+        }
+    }
+}
+
+fn main() {}