Auto merge of #118685 - compiler-errors:stack-dependent, r=lcnr

`EvaluatedToUnknown` -> `EvaluatedToAmbigStackDependent`, `EvaluatedToRecur` -> `EvaluatedToErrStackDependent`

Less confusing names, since the only difference between them and their parallel `EvalutedTo..` is that they are stack dependent.

r? lcnr

compiler/rustc_middle/src/traits/select.rs

@@ -180,8 +180,8 @@ pub enum SelectionCandidate<'tcx> {
 ///
 /// The evaluation results are ordered:
 ///     - `EvaluatedToOk` implies `EvaluatedToOkModuloRegions`
-///       implies `EvaluatedToAmbig` implies `EvaluatedToUnknown`
+///       implies `EvaluatedToAmbig` implies `EvaluatedToAmbigStackDependent`
-///     - `EvaluatedToErr` implies `EvaluatedToRecur`
+///     - `EvaluatedToErr` implies `EvaluatedToErrStackDependent`
 ///     - the "union" of evaluation results is equal to their maximum -
 ///     all the "potential success" candidates can potentially succeed,
 ///     so they are noops when unioned with a definite error, and within
@@ -199,7 +199,7 @@ pub enum EvaluationResult {
     /// Evaluation is known to be ambiguous -- it *might* hold for some
     /// assignment of inference variables, but it might not.
     ///
-    /// While this has the same meaning as `EvaluatedToUnknown` -- we can't
+    /// While this has the same meaning as `EvaluatedToAmbigStackDependent` -- we can't
     /// know whether this obligation holds or not -- it is the result we
     /// would get with an empty stack, and therefore is cacheable.
     EvaluatedToAmbig,
@@ -207,8 +207,8 @@ pub enum EvaluationResult {
     /// variables. We are somewhat imprecise there, so we don't actually
     /// know the real result.
     ///
-    /// This can't be trivially cached for the same reason as `EvaluatedToRecur`.
+    /// This can't be trivially cached for the same reason as `EvaluatedToErrStackDependent`.
-    EvaluatedToUnknown,
+    EvaluatedToAmbigStackDependent,
     /// Evaluation failed because we encountered an obligation we are already
     /// trying to prove on this branch.
     ///
@@ -247,12 +247,12 @@ pub enum EvaluationResult {
     /// does not hold, because of the bound (which can indeed be satisfied
     /// by `SomeUnsizedType` from another crate).
     //
-    // FIXME: when an `EvaluatedToRecur` goes past its parent root, we
+    // FIXME: when an `EvaluatedToErrStackDependent` goes past its parent root, we
     // ought to convert it to an `EvaluatedToErr`, because we know
     // there definitely isn't a proof tree for that obligation. Not
     // doing so is still sound -- there isn't any proof tree, so the
     // branch still can't be a part of a minimal one -- but does not re-enable caching.
-    EvaluatedToRecur,
+    EvaluatedToErrStackDependent,
     /// Evaluation failed.
     EvaluatedToErr,
 }
@@ -276,15 +276,15 @@ impl EvaluationResult {
             | EvaluatedToOk
             | EvaluatedToOkModuloRegions
             | EvaluatedToAmbig
-            | EvaluatedToUnknown => true,
+            | EvaluatedToAmbigStackDependent => true,
 
-            EvaluatedToErr | EvaluatedToRecur => false,
+            EvaluatedToErr | EvaluatedToErrStackDependent => false,
         }
     }
 
     pub fn is_stack_dependent(self) -> bool {
         match self {
-            EvaluatedToUnknown | EvaluatedToRecur => true,
+            EvaluatedToAmbigStackDependent | EvaluatedToErrStackDependent => true,
 
             EvaluatedToOkModuloOpaqueTypes
             | EvaluatedToOk

compiler/rustc_trait_selection/src/infer.rs

@@ -29,7 +29,7 @@ pub trait InferCtxtExt<'tcx> {
     /// - the parameter environment
     ///
     /// Invokes `evaluate_obligation`, so in the event that evaluating
-    /// `Ty: Trait` causes overflow, EvaluatedToRecur (or EvaluatedToUnknown)
+    /// `Ty: Trait` causes overflow, EvaluatedToErrStackDependent (or EvaluatedToAmbigStackDependent)
     /// will be returned.
     fn type_implements_trait(
         &self,

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

@@ -222,8 +222,8 @@ pub enum TreatInductiveCycleAs {
 impl From<TreatInductiveCycleAs> for EvaluationResult {
     fn from(treat: TreatInductiveCycleAs) -> EvaluationResult {
         match treat {
-            TreatInductiveCycleAs::Ambig => EvaluatedToUnknown,
+            TreatInductiveCycleAs::Ambig => EvaluatedToAmbigStackDependent,
-            TreatInductiveCycleAs::Recur => EvaluatedToRecur,
+            TreatInductiveCycleAs::Recur => EvaluatedToErrStackDependent,
         }
     }
 }
@@ -1231,7 +1231,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             })
         {
             debug!("evaluate_stack --> unbound argument, recursive --> giving up",);
-            return Ok(EvaluatedToUnknown);
+            return Ok(EvaluatedToAmbigStackDependent);
         }
 
         match self.candidate_from_obligation(stack) {