Add the generic_associated_types_extended feature

Cargo.lock

@@ -320,7 +320,7 @@ dependencies = [
  "cargo-test-macro",
  "cargo-test-support",
  "cargo-util",
- "clap 3.1.1",
+ "clap 3.1.6",
  "crates-io",
  "crossbeam-utils",
  "curl",
@@ -598,17 +598,17 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "3.1.1"
+version = "3.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d76c22c9b9b215eeb8d016ad3a90417bd13cb24cf8142756e6472445876cab7"
+checksum = "d8c93436c21e4698bacadf42917db28b23017027a4deccb35dbe47a7e7840123"
 dependencies = [
  "atty",
  "bitflags",
  "indexmap",
  "os_str_bytes",
  "strsim 0.10.0",
  "termcolor",
- "textwrap 0.14.2",
+ "textwrap 0.15.0",
 ]
 
 [[package]]
@@ -1502,9 +1502,9 @@ dependencies = [
 
 [[package]]
 name = "git2"
-version = "0.14.1"
+version = "0.14.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6e7d3b96ec1fcaa8431cf04a4f1ef5caafe58d5cf7bcc31f09c1626adddb0ffe"
+checksum = "3826a6e0e2215d7a41c2bfc7c9244123969273f3476b939a226aac0ab56e9e3c"
 dependencies = [
  "bitflags",
  "libc",
@@ -1974,9 +1974,9 @@ dependencies = [
 
 [[package]]
 name = "libgit2-sys"
-version = "0.13.1+1.4.2"
+version = "0.13.2+1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "43e598aa7a4faedf1ea1b4608f582b06f0f40211eec551b7ef36019ae3f62def"
+checksum = "3a42de9a51a5c12e00fc0e4ca6bc2ea43582fc6418488e8f615e905d886f258b"
 dependencies = [
  "cc",
  "libc",
@@ -5024,9 +5024,9 @@ dependencies = [
 
 [[package]]
 name = "textwrap"
-version = "0.14.2"
+version = "0.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0066c8d12af8b5acd21e00547c3797fde4e8677254a7ee429176ccebbe93dd80"
+checksum = "b1141d4d61095b28419e22cb0bbf02755f5e54e0526f97f1e3d1d160e60885fb"
 
 [[package]]
 name = "thiserror"

compiler/rustc_feature/src/active.rs

@@ -398,6 +398,8 @@ declare_features! (
     (active, generic_arg_infer, "1.55.0", Some(85077), None),
     /// Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
     (active, generic_associated_types, "1.23.0", Some(44265), None),
+    /// An extension to the `generic_associated_types` feature, allowing incomplete features.
+    (incomplete, generic_associated_types_extended, "1.61.0", Some(44265), None),
     /// Allows non-trivial generic constants which have to have wfness manually propagated to callers
     (incomplete, generic_const_exprs, "1.56.0", Some(76560), None),
     /// Allows using `..X`, `..=X`, `...X`, and `X..` as a pattern.

compiler/rustc_middle/src/ty/fold.rs

@@ -1375,3 +1375,50 @@ impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
         ControlFlow::CONTINUE
     }
 }
+
+/// Finds the max universe present
+pub struct MaxUniverse {
+    max_universe: ty::UniverseIndex,
+}
+
+impl MaxUniverse {
+    pub fn new() -> Self {
+        MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
+    }
+
+    pub fn max_universe(self) -> ty::UniverseIndex {
+        self.max_universe
+    }
+}
+
+impl<'tcx> TypeVisitor<'tcx> for MaxUniverse {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+        if let ty::Placeholder(placeholder) = t.kind() {
+            self.max_universe = ty::UniverseIndex::from_u32(
+                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
+            );
+        }
+
+        t.super_visit_with(self)
+    }
+
+    fn visit_const(&mut self, c: ty::consts::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
+        if let ty::ConstKind::Placeholder(placeholder) = c.val() {
+            self.max_universe = ty::UniverseIndex::from_u32(
+                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
+            );
+        }
+
+        c.super_visit_with(self)
+    }
+
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
+        if let ty::RePlaceholder(placeholder) = *r {
+            self.max_universe = ty::UniverseIndex::from_u32(
+                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
+            );
+        }
+
+        ControlFlow::CONTINUE
+    }
+}

compiler/rustc_span/src/symbol.rs

@@ -723,6 +723,7 @@ symbols! {
         generators,
         generic_arg_infer,
         generic_associated_types,
+        generic_associated_types_extended,
         generic_const_exprs,
         generic_param_attrs,
         get_context,

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -5,6 +5,7 @@ use super::*;
 
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::InferCtxt;
+use crate::traits::project::ProjectAndUnifyResult;
 use rustc_middle::ty::fold::TypeFolder;
 use rustc_middle::ty::{Region, RegionVid, Term};
 
@@ -733,19 +734,19 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                     debug!("Projecting and unifying projection predicate {:?}", predicate);
 
                     match project::poly_project_and_unify_type(select, &obligation.with(p)) {
-                        Err(e) => {
+                        ProjectAndUnifyResult::MismatchedProjectionTypes(e) => {
                             debug!(
                                 "evaluate_nested_obligations: Unable to unify predicate \
                                  '{:?}' '{:?}', bailing out",
                                 ty, e
                             );
                             return false;
                         }
-                        Ok(Err(project::InProgress)) => {
+                        ProjectAndUnifyResult::Recursive => {
                             debug!("evaluate_nested_obligations: recursive projection predicate");
                             return false;
                         }
-                        Ok(Ok(Some(v))) => {
+                        ProjectAndUnifyResult::Holds(v) => {
                             // We only care about sub-obligations
                             // when we started out trying to unify
                             // some inference variables. See the comment above
@@ -764,7 +765,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                                 }
                             }
                         }
-                        Ok(Ok(None)) => {
+                        ProjectAndUnifyResult::FailedNormalization => {
                             // It's ok not to make progress when have no inference variables -
                             // in that case, we were only performing unifcation to check if an
                             // error occurred (which would indicate that it's impossible for our

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty::{self, Binder, Const, Ty, TypeFoldable};
 use std::marker::PhantomData;
 
 use super::const_evaluatable;
-use super::project;
+use super::project::{self, ProjectAndUnifyResult};
 use super::select::SelectionContext;
 use super::wf;
 use super::CodeAmbiguity;
@@ -752,8 +752,8 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         }
 
         match project::poly_project_and_unify_type(self.selcx, &project_obligation) {
-            Ok(Ok(Some(os))) => ProcessResult::Changed(mk_pending(os)),
-            Ok(Ok(None)) => {
+            ProjectAndUnifyResult::Holds(os) => ProcessResult::Changed(mk_pending(os)),
+            ProjectAndUnifyResult::FailedNormalization => {
                 stalled_on.clear();
                 stalled_on.extend(substs_infer_vars(
                     self.selcx,
@@ -762,10 +762,12 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                 ProcessResult::Unchanged
             }
             // Let the caller handle the recursion
-            Ok(Err(project::InProgress)) => ProcessResult::Changed(mk_pending(vec![
+            ProjectAndUnifyResult::Recursive => ProcessResult::Changed(mk_pending(vec![
                 project_obligation.with(project_obligation.predicate.to_predicate(tcx)),
             ])),
-            Err(e) => ProcessResult::Error(CodeProjectionError(e)),
+            ProjectAndUnifyResult::MismatchedProjectionTypes(e) => {
+                ProcessResult::Error(CodeProjectionError(e))
+            }
         }
     }
 }

compiler/rustc_trait_selection/src/traits/project.rs

@@ -27,6 +27,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
+use rustc_middle::ty::fold::MaxUniverse;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
@@ -143,6 +144,18 @@ impl<'tcx> ProjectionCandidateSet<'tcx> {
     }
 }
 
+/// Takes the place of a
+/// Result<
+///     Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
+///     MismatchedProjectionTypes<'tcx>,
+/// >
+pub(super) enum ProjectAndUnifyResult<'tcx> {
+    Holds(Vec<PredicateObligation<'tcx>>),
+    FailedNormalization,
+    Recursive,
+    MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>),
+}
+
 /// Evaluates constraints of the form:
 ///
 ///     for<...> <T as Trait>::U == V
@@ -166,19 +179,39 @@ impl<'tcx> ProjectionCandidateSet<'tcx> {
 pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &PolyProjectionObligation<'tcx>,
-) -> Result<
-    Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
-    MismatchedProjectionTypes<'tcx>,
-> {
+) -> ProjectAndUnifyResult<'tcx> {
     let infcx = selcx.infcx();
-    infcx.commit_if_ok(|_snapshot| {
+    let r = infcx.commit_if_ok(|_snapshot| {
+        let old_universe = infcx.universe();
         let placeholder_predicate =
             infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+        let new_universe = infcx.universe();
 
         let placeholder_obligation = obligation.with(placeholder_predicate);
-        let result = project_and_unify_type(selcx, &placeholder_obligation)?;
-        Ok(result)
-    })
+        match project_and_unify_type(selcx, &placeholder_obligation) {
+            ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
+            ProjectAndUnifyResult::Holds(obligations)
+                if old_universe != new_universe
+                    && selcx.tcx().features().generic_associated_types_extended =>
+            {
+                let new_obligations = obligations
+                    .into_iter()
+                    .filter(|obligation| {
+                        let mut visitor = MaxUniverse::new();
+                        obligation.predicate.visit_with(&mut visitor);
+                        visitor.max_universe() < new_universe
+                    })
+                    .collect();
+                Ok(ProjectAndUnifyResult::Holds(new_obligations))
+            }
+            other => Ok(other),
+        }
+    });
+
+    match r {
+        Ok(inner) => inner,
+        Err(err) => ProjectAndUnifyResult::MismatchedProjectionTypes(err),
+    }
 }
 
 /// Evaluates constraints of the form:
@@ -188,15 +221,11 @@ pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
 /// If successful, this may result in additional obligations.
 ///
 /// See [poly_project_and_unify_type] for an explanation of the return value.
+#[tracing::instrument(level = "debug", skip(selcx))]
 fn project_and_unify_type<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionObligation<'tcx>,
-) -> Result<
-    Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
-    MismatchedProjectionTypes<'tcx>,
-> {
-    debug!(?obligation, "project_and_unify_type");
-
+) -> ProjectAndUnifyResult<'tcx> {
     let mut obligations = vec![];
 
     let infcx = selcx.infcx();
@@ -209,8 +238,8 @@ fn project_and_unify_type<'cx, 'tcx>(
         &mut obligations,
     ) {
         Ok(Some(n)) => n,
-        Ok(None) => return Ok(Ok(None)),
-        Err(InProgress) => return Ok(Err(InProgress)),
+        Ok(None) => return ProjectAndUnifyResult::FailedNormalization,
+        Err(InProgress) => return ProjectAndUnifyResult::Recursive,
     };
     debug!(?normalized, ?obligations, "project_and_unify_type result");
     match infcx
@@ -219,11 +248,11 @@ fn project_and_unify_type<'cx, 'tcx>(
     {
         Ok(InferOk { obligations: inferred_obligations, value: () }) => {
             obligations.extend(inferred_obligations);
-            Ok(Ok(Some(obligations)))
+            ProjectAndUnifyResult::Holds(obligations)
         }
         Err(err) => {
-            debug!("project_and_unify_type: equating types encountered error {:?}", err);
-            Err(MismatchedProjectionTypes { err })
+            debug!("equating types encountered error {:?}", err);
+            ProjectAndUnifyResult::MismatchedProjectionTypes(MismatchedProjectionTypes { err })
         }
     }
 }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -25,6 +25,7 @@ use super::{ObligationCause, PredicateObligation, TraitObligation};
 
 use crate::infer::{InferCtxt, InferOk, TypeFreshener};
 use crate::traits::error_reporting::InferCtxtExt;
+use crate::traits::project::ProjectAndUnifyResult;
 use crate::traits::project::ProjectionCacheKeyExt;
 use crate::traits::ProjectionCacheKey;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -551,7 +552,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     let data = bound_predicate.rebind(data);
                     let project_obligation = obligation.with(data);
                     match project::poly_project_and_unify_type(self, &project_obligation) {
-                        Ok(Ok(Some(mut subobligations))) => {
+                        ProjectAndUnifyResult::Holds(mut subobligations) => {
                             'compute_res: {
                                 // If we've previously marked this projection as 'complete', thne
                                 // use the final cached result (either `EvaluatedToOk` or
@@ -599,9 +600,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                 res
                             }
                         }
-                        Ok(Ok(None)) => Ok(EvaluatedToAmbig),
-                        Ok(Err(project::InProgress)) => Ok(EvaluatedToRecur),
-                        Err(_) => Ok(EvaluatedToErr),
+                        ProjectAndUnifyResult::FailedNormalization => Ok(EvaluatedToAmbig),
+                        ProjectAndUnifyResult::Recursive => Ok(EvaluatedToRecur),
+                        ProjectAndUnifyResult::MismatchedProjectionTypes(_) => Ok(EvaluatedToErr),
                     }
                 }
 

src/test/ui/feature-gates/feature-gate-generic_associated_types_extended.rs

@@ -0,0 +1,6 @@
+#![feature(generic_associated_types)]
+
+// This feature doesn't *currently* fire on any specific code; it's just a
+// behavior change. Future changes might.
+#[rustc_error] //~ the
+fn main() {}

src/test/ui/feature-gates/feature-gate-generic_associated_types_extended.stderr

@@ -0,0 +1,11 @@
+error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
+  --> $DIR/feature-gate-generic_associated_types_extended.rs:5:1
+   |
+LL | #[rustc_error]
+   | ^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.