Fix FIXME comment on FixupError.

`FixupError` is isomorphic with `TyOrConstInferVar`, so this commit
changes it to just be a wrapper around `TyOrConstInferVar`.

Also, move the `Display` impl for `FixupError` next to `FixupError`.

compiler/rustc_infer/src/infer/mod.rs

@@ -495,46 +495,41 @@ pub enum NllRegionVariableOrigin {
     },
 }
 
-// FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
 #[derive(Copy, Clone, Debug)]
-pub enum FixupError {
-    UnresolvedIntTy(IntVid),
-    UnresolvedFloatTy(FloatVid),
-    UnresolvedTy(TyVid),
-    UnresolvedConst(ConstVid),
-    UnresolvedEffect(EffectVid),
-}
-
-/// See the `region_obligations` field for more information.
-#[derive(Clone, Debug)]
-pub struct RegionObligation<'tcx> {
-    pub sub_region: ty::Region<'tcx>,
-    pub sup_type: Ty<'tcx>,
-    pub origin: SubregionOrigin<'tcx>,
+pub struct FixupError {
+    unresolved: TyOrConstInferVar,
 }
 
 impl fmt::Display for FixupError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        use self::FixupError::*;
+        use TyOrConstInferVar::*;
 
-        match *self {
-            UnresolvedIntTy(_) => write!(
+        match self.unresolved {
+            TyInt(_) => write!(
                 f,
                 "cannot determine the type of this integer; \
                  add a suffix to specify the type explicitly"
             ),
-            UnresolvedFloatTy(_) => write!(
+            TyFloat(_) => write!(
                 f,
                 "cannot determine the type of this number; \
                  add a suffix to specify the type explicitly"
             ),
-            UnresolvedTy(_) => write!(f, "unconstrained type"),
-            UnresolvedConst(_) => write!(f, "unconstrained const value"),
-            UnresolvedEffect(_) => write!(f, "unconstrained effect value"),
+            Ty(_) => write!(f, "unconstrained type"),
+            Const(_) => write!(f, "unconstrained const value"),
+            Effect(_) => write!(f, "unconstrained effect value"),
         }
     }
 }
 
+/// See the `region_obligations` field for more information.
+#[derive(Clone, Debug)]
+pub struct RegionObligation<'tcx> {
+    pub sub_region: ty::Region<'tcx>,
+    pub sup_type: Ty<'tcx>,
+    pub origin: SubregionOrigin<'tcx>,
+}
+
 /// Used to configure inference contexts before their creation.
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,

compiler/rustc_infer/src/infer/resolve.rs

@@ -138,11 +138,13 @@ impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
         if !t.has_infer() {
             Ok(t) // micro-optimize -- if there is nothing in this type that this fold affects...
         } else {
+            use super::TyOrConstInferVar::*;
+
             let t = self.infcx.shallow_resolve(t);
             match *t.kind() {
-                ty::Infer(ty::TyVar(vid)) => Err(FixupError::UnresolvedTy(vid)),
-                ty::Infer(ty::IntVar(vid)) => Err(FixupError::UnresolvedIntTy(vid)),
-                ty::Infer(ty::FloatVar(vid)) => Err(FixupError::UnresolvedFloatTy(vid)),
+                ty::Infer(ty::TyVar(vid)) => Err(FixupError { unresolved: Ty(vid) }),
+                ty::Infer(ty::IntVar(vid)) => Err(FixupError { unresolved: TyInt(vid) }),
+                ty::Infer(ty::FloatVar(vid)) => Err(FixupError { unresolved: TyFloat(vid) }),
                 ty::Infer(_) => {
                     bug!("Unexpected type in full type resolver: {:?}", t);
                 }
@@ -171,13 +173,13 @@ impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
             let c = self.infcx.shallow_resolve_const(c);
             match c.kind() {
                 ty::ConstKind::Infer(InferConst::Var(vid)) => {
-                    return Err(FixupError::UnresolvedConst(vid));
+                    return Err(FixupError { unresolved: super::TyOrConstInferVar::Const(vid) });
                 }
                 ty::ConstKind::Infer(InferConst::Fresh(_)) => {
                     bug!("Unexpected const in full const resolver: {:?}", c);
                 }
                 ty::ConstKind::Infer(InferConst::EffectVar(evid)) => {
-                    return Err(FixupError::UnresolvedEffect(evid));
+                    return Err(FixupError { unresolved: super::TyOrConstInferVar::Effect(evid) });
                 }
                 _ => {}
             }