disable next-solver with higher-ranked-assumptions

compiler/rustc_ast_passes/src/diagnostics.rs

@@ -49,6 +49,15 @@ pub(crate) struct NextSolverDisabledForGenericConstExprs {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag("`-Zhigher-ranked-assumptions` is not supported with the next-generation trait solver")]
+#[note("the feature flag will be superseded by `-Zassumptions-on-binders`")]
+#[note("`-Znext-solver=globally` is currently enabled by default for testing")]
+#[note("reverted the setting to `-Znext-solver=coherence` for this crate")]
+#[note("the currently stable trait solver will be used for this crate")]
+#[note("see issues #160895 <https://github.com/rust-lang/rust/issues/160895> for more information")]
+pub(crate) struct NextSolverDisabledForHigherRankedAssumptions;
+
 #[derive(Diagnostic)]
 #[diag("functions in {$in_impl ->
         [true] trait impls

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -411,6 +411,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     check_incompatible_features(sess, features);
     check_dependent_features(sess, features);
     warn_next_solver_and_gce(sess, features);
+    warn_next_solver_and_higher_ranked_assumptions(sess);
     check_features_requiring_new_solver(sess, features);
 
     let mut visitor = PostExpansionVisitor { sess, features };
@@ -703,8 +704,8 @@ fn warn_next_solver_and_gce(sess: &Session, features: &Features) {
         return;
     }
 
-    // Warn people who uses GCE and -Znext-solver=globally
-    // that their trait solver was downgraded to -Znext-solver=no
+    // Warn people who use GCE and -Znext-solver=globally
+    // that their trait solver was downgraded to -Znext-solver=coherence
     if let Some(gce_span) = features
         .enabled_lang_features()
         .iter()
@@ -716,6 +717,16 @@ fn warn_next_solver_and_gce(sess: &Session, features: &Features) {
     }
 }
 
+fn warn_next_solver_and_higher_ranked_assumptions(sess: &Session) {
+    // Warn people who use -Zhigher-ranked-assumptions and -Znext-solver=globally
+    // that their trait solver was downgraded to -Znext-solver=coherence
+    if sess.opts.unstable_opts.next_solver == NextSolverConfig::Globally
+        && sess.opts.unstable_opts.higher_ranked_assumptions
+    {
+        sess.dcx().emit_warn(diagnostics::NextSolverDisabledForHigherRankedAssumptions);
+    }
+}
+
 fn check_features_requiring_new_solver(sess: &Session, features: &Features) {
     if sess.opts.unstable_opts.next_solver == NextSolverConfig::Globally {
         return;

compiler/rustc_middle/src/ty/context.rs

@@ -2818,6 +2818,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     pub fn next_trait_solver_globally(self) -> bool {
         self.sess.opts.unstable_opts.next_solver == NextSolverConfig::Globally
+            && !self.sess.opts.unstable_opts.higher_ranked_assumptions
             && !self.features().generic_const_exprs()
     }
 

compiler/rustc_traits/src/coroutine_witnesses.rs

@@ -54,7 +54,7 @@ fn compute_assumptions<'tcx>(
     def_id: DefId,
     bound_tys: &'tcx ty::List<Ty<'tcx>>,
 ) -> &'tcx ty::List<ty::ArgOutlivesClause<'tcx>> {
-    if tcx.next_trait_solver_globally() || !tcx.sess.opts.unstable_opts.higher_ranked_assumptions {
+    if !tcx.sess.opts.unstable_opts.higher_ranked_assumptions {
         return &ty::List::empty();
     }
 

tests/ui/async-await/witness-auto-trait/higher-ranked-auto-trait-1.assumptions_next.stderr

@@ -0,0 +1,10 @@
+warning: `-Zhigher-ranked-assumptions` is not supported with the next-generation trait solver
+   |
+   = note: the feature flag will be superseded by `-Zassumptions-on-binders`
+   = note: `-Znext-solver=globally` is currently enabled by default for testing
+   = note: reverted the setting to `-Znext-solver=coherence` for this crate
+   = note: the currently stable trait solver will be used for this crate
+   = note: see issues #160895 <https://github.com/rust-lang/rust/issues/160895> for more information
+
+warning: 1 warning emitted
+

tests/ui/async-await/witness-auto-trait/higher-ranked-auto-trait-1.no_assumptions.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/higher-ranked-auto-trait-1.rs:37:5
+  --> $DIR/higher-ranked-auto-trait-1.rs:43:5
    |
 LL | /     async {
 LL | |         let _y = &();
@@ -10,13 +10,13 @@ LL | |         drop(_x);
 LL | |     }
    | |_____^ one type is more general than the other
    |
-   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:40:19: 40:29}`
-              found `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:40:19: 40:29}`
+   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:46:19: 46:29}`
+              found `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:46:19: 46:29}`
    = note: no two async blocks, even if identical, have the same type
    = help: consider pinning your async block and casting it to a trait object
 
 error[E0308]: mismatched types
-  --> $DIR/higher-ranked-auto-trait-1.rs:37:5
+  --> $DIR/higher-ranked-auto-trait-1.rs:43:5
    |
 LL | /     async {
 LL | |         let _y = &();
@@ -27,8 +27,8 @@ LL | |         drop(_x);
 LL | |     }
    | |_____^ one type is more general than the other
    |
-   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:40:19: 40:29}`
-              found `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:40:19: 40:29}`
+   = note: expected `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:46:19: 46:29}`
+              found `async` block `{async block@$DIR/higher-ranked-auto-trait-1.rs:46:19: 46:29}`
    = note: no two async blocks, even if identical, have the same type
    = help: consider pinning your async block and casting it to a trait object
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

tests/ui/async-await/witness-auto-trait/higher-ranked-auto-trait-1.rs

@@ -1,10 +1,16 @@
 // Repro for <https://github.com/rust-lang/rust/issues/79648#issuecomment-749127947>.
 //@ edition: 2021
-//@ revisions: assumptions no_assumptions
+//@ revisions: assumptions no_assumptions assumptions_next
 //@[assumptions] compile-flags: -Zhigher-ranked-assumptions
+//@[assumptions_next] compile-flags: -Zhigher-ranked-assumptions -Znext-solver
 //@[assumptions] check-pass
+//@[assumptions_next] check-pass
 //@[no_assumptions] known-bug: #110338
 
+// We're using this test to just check the way -Zhigher-ranked-assumptions
+// interacts with the next-generation trait solver.
+//[assumptions_next]~? WARN `-Zhigher-ranked-assumptions` is not supported with the next-generation trait solver
+
 use std::future::Future;
 use std::marker::PhantomData;