review

Author: lcnr

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -499,7 +499,7 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                         ty::Adt(def, ..) if !def.is_box() => {
                             // Again, only create type information if full debuginfo is enabled
                             if cx.sess().opts.debuginfo == DebugInfo::Full
-                                && !impl_self_ty.needs_subst(cx.tcx)
+                                && !impl_self_ty.definitely_needs_subst(cx.tcx)
                             {
                                 Some(type_metadata(cx, impl_self_ty, rustc_span::DUMMY_SP))
                             } else {

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -470,7 +470,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
     {
         let needs_canonical_flags = if canonicalize_region_mode.any() {
             TypeFlags::NEEDS_INFER |
-            TypeFlags::HAS_POTENTIAL_FREE_REGIONS | // `HAS_RE_PLACEHOLDER` implies `HAS_xxx_FREE_REGIONS`
+            TypeFlags::HAS_POTENTIAL_FREE_REGIONS | // `HAS_RE_PLACEHOLDER` implies `HAS_POTENTIAL_FREE_REGIONS`
             TypeFlags::HAS_TY_PLACEHOLDER |
             TypeFlags::HAS_CT_PLACEHOLDER
         } else {

compiler/rustc_lint/src/noop_method_call.rs

@@ -62,7 +62,7 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
             _ => return,
         };
         let substs = cx.typeck_results().node_substs(expr.hir_id);
-        if substs.needs_subst(cx.tcx) {
+        if substs.definitely_needs_subst(cx.tcx) {
             // We can't resolve on types that require monomorphization, so we don't handle them if
             // we need to perfom substitution.
             return;

compiler/rustc_middle/src/mir/mod.rs

@@ -285,7 +285,7 @@ impl<'tcx> Body<'tcx> {
             predecessor_cache: PredecessorCache::new(),
             is_cyclic: GraphIsCyclicCache::new(),
         };
-        body.is_polymorphic = body.has_param_types_or_consts(tcx);
+        body.is_polymorphic = body.definitely_has_param_types_or_consts(tcx);
         body
     }
 

compiler/rustc_middle/src/ty/flags.rs

@@ -311,9 +311,20 @@ impl FlagComputation {
     }
 
     fn add_unevaluated_const<P>(&mut self, ct: ty::Unevaluated<'tcx, P>) {
+        // The generic arguments of unevaluated consts are a bit special,
+        // see the `rustc-dev-guide` for more information.
+        //
+        // FIXME(@lcnr): Actually add a link here.
         if let Some(substs) = ct.substs_ {
+            // If they are available, we treat them as ordinary generic arguments.
             self.add_substs(substs);
         } else {
+            // Otherwise, we add `HAS_UNKNOWN_DEFAULT_CONST_SUBSTS` to signify
+            // that our const may potentially refer to generic parameters.
+            //
+            // Note that depending on which generic parameters are actually
+            // used in this constant, we may not actually refer to any generic
+            // parameters at all.
             self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
             self.add_flags(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS);
         }

compiler/rustc_middle/src/ty/fold.rs

@@ -92,14 +92,14 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
     fn references_error(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_ERROR)
     }
-    fn has_potential_param_types_or_consts(&self) -> bool {
+    fn potentially_has_param_types_or_consts(&self) -> bool {
         self.has_type_flags(
             TypeFlags::HAS_KNOWN_TY_PARAM
                 | TypeFlags::HAS_KNOWN_CT_PARAM
                 | TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS,
         )
     }
-    fn has_param_types_or_consts(&self, tcx: TyCtxt<'tcx>) -> bool {
+    fn definitely_has_param_types_or_consts(&self, tcx: TyCtxt<'tcx>) -> bool {
         self.definitely_has_type_flags(
             tcx,
             TypeFlags::HAS_KNOWN_TY_PARAM | TypeFlags::HAS_KNOWN_CT_PARAM,
@@ -129,7 +129,7 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
             TypeFlags::KNOWN_NEEDS_SUBST | TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS,
         )
     }
-    fn needs_subst(&self, tcx: TyCtxt<'tcx>) -> bool {
+    fn definitely_needs_subst(&self, tcx: TyCtxt<'tcx>) -> bool {
         self.definitely_has_type_flags(tcx, TypeFlags::KNOWN_NEEDS_SUBST)
     }
     /// "Free" regions in this context means that it has any region
@@ -227,10 +227,13 @@ pub trait TypeVisitor<'tcx>: Sized {
     /// Supplies the `tcx` for an unevaluated anonymous constant in case its default substs
     /// are not yet supplied.
     ///
-    /// Visitors which do not look into these substs may return `None` here, in which case
-    /// `super_visit_with` completely skips the default substs. Incorrectly returning
-    /// `None` can very quickly lead to ICE or other critical bugs, so be careful and
-    /// try to return an actual `tcx` if at all possible.
+    /// Returning `None` for this method is only recommended if the `TypeVisitor`
+    /// does not care about default anon const substs, as it ignores generic parameters,
+    /// and fetching the default substs would cause a query cycle.
+    ///
+    /// For visitors which return `None` we completely skip the default substs in `ty::Unevaluated::super_visit_with`.
+    /// This means that incorrectly returning `None` can very quickly lead to ICE or other critical bugs, so be careful and
+    /// try to return an actual `tcx` if possible.
     fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>;
 
     fn visit_binder<T: TypeFoldable<'tcx>>(

compiler/rustc_middle/src/ty/layout.rs

@@ -1727,7 +1727,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         // Ignore layouts that are done with non-empty environments or
         // non-monomorphic layouts, as the user only wants to see the stuff
         // resulting from the final codegen session.
-        if layout.ty.has_param_types_or_consts(self.tcx)
+        if layout.ty.definitely_has_param_types_or_consts(self.tcx)
             || !self.param_env.caller_bounds().is_empty()
         {
             return;
@@ -1896,7 +1896,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
                 let tail = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
                 match tail.kind() {
                     ty::Param(_) | ty::Projection(_) => {
-                        debug_assert!(tail.has_param_types_or_consts(tcx));
+                        debug_assert!(tail.definitely_has_param_types_or_consts(tcx));
                         Ok(SizeSkeleton::Pointer { non_zero, tail: tcx.erase_regions(tail) })
                     }
                     _ => bug!(

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -1193,7 +1193,7 @@ pub trait PrettyPrinter<'tcx>:
 
             // Aggregates, printed as array/tuple/struct/variant construction syntax.
             //
-            // NB: the `has_param_types_or_consts` check ensures that we can use
+            // NB: the `potentially_has_param_types_or_consts` check ensures that we can use
             // the `destructure_const` query with an empty `ty::ParamEnv` without
             // introducing ICEs (e.g. via `layout_of`) from missing bounds.
             // E.g. `transmute([0usize; 2]): (u8, *mut T)` needs to know `T: Sized`
@@ -1202,7 +1202,7 @@ pub trait PrettyPrinter<'tcx>:
             // FIXME(eddyb) for `--emit=mir`/`-Z dump-mir`, we should provide the
             // correct `ty::ParamEnv` to allow printing *all* constant values.
             (_, ty::Array(..) | ty::Tuple(..) | ty::Adt(..))
-                if !ty.has_potential_param_types_or_consts() =>
+                if !ty.potentially_has_param_types_or_consts() =>
             {
                 let contents = self.tcx().destructure_const(
                     ty::ParamEnv::reveal_all()

compiler/rustc_mir/src/interpret/util.rs

@@ -43,7 +43,7 @@ where
                         let is_used = unused_params.contains(index).map_or(true, |unused| !unused);
                         // Only recurse when generic parameters in fns, closures and generators
                         // are used and require substitution.
-                        match (is_used, subst.needs_subst(self.tcx)) {
+                        match (is_used, subst.definitely_needs_subst(self.tcx)) {
                             // Just in case there are closures or generators within this subst,
                             // recurse.
                             (true, true) => return subst.super_visit_with(self),

compiler/rustc_mir/src/monomorphize/polymorphize.rs

@@ -288,7 +288,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
     }
     #[instrument(skip(self))]
     fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        if !c.has_potential_param_types_or_consts() {
+        if !c.potentially_has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
         }
 
@@ -321,7 +321,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
 
     #[instrument(skip(self))]
     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-        if !ty.has_potential_param_types_or_consts() {
+        if !ty.potentially_has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
         }
 
@@ -363,7 +363,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for HasUsedGenericParams<'a, 'tcx> {
 
     #[instrument(skip(self))]
     fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-        if !c.has_potential_param_types_or_consts() {
+        if !c.potentially_has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
         }
 
@@ -381,7 +381,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for HasUsedGenericParams<'a, 'tcx> {
 
     #[instrument(skip(self))]
     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-        if !ty.has_potential_param_types_or_consts() {
+        if !ty.potentially_has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
         }