fix(types): refine alias skipping logic in type comparison functions

compiler/semexprs.nim

@@ -578,7 +578,14 @@ proc isOpImpl(c: PContext, n: PNode, flags: TExprFlags): PNode =
     if efExplain in flags:
       m.diagnostics = @[]
       m.diagnosticsEnabled = true
-    res = typeRel(m, t2, t1) >= isSubtype # isNone
+    let rel = typeRel(m, t2, t1)
+    res = rel >= isSubtype # isNone
+    if res and rel == isEqual and
+        not compareTypes(t1, t2,
+                         flags = {ExactTypeDescValues,
+                                  PickyCAliases,
+                                  PickyBackendAliases}):
+      res = false
     # `res = sameType(t1, t2)` would be wrong, e.g. for `int is (int|float)`
 
   result = newIntNode(nkIntLit, ord(res))

compiler/types.nim

@@ -897,7 +897,11 @@ proc sameTypeAux(x, y: PType, c: var TSameTypeClosure): bool =
     c.flags = oldFlags
 
   if x == y: return true
-  let aliasSkipSet = maybeSkipRange({tyAlias, tyInferred})
+  let aliasSkipSet = maybeSkipRange(
+    if PickyBackendAliases in c.flags:
+      {tyInferred}
+    else:
+      {tyAlias, tyInferred})
   var a = skipTypes(x, aliasSkipSet)
   while a.kind == tyUserTypeClass and tfResolved in a.flags:
     a = skipTypes(a.last, aliasSkipSet)
@@ -1070,8 +1074,8 @@ proc sameBackendTypeIgnoreRange*(x, y: PType): bool =
   result = sameTypeAux(x, y, c)
 
 proc sameBackendTypePickyAliases*(x, y: PType): bool =
-  let x = x.skipTypes(abstractVar)
-  let y = y.skipTypes(abstractVar)
+  let x = x.skipTypes({tyVar, tyLent, tySink, tyOwned})
+  let y = y.skipTypes({tyVar, tyLent, tySink, tyOwned})
   var c = initSameTypeClosure()
   c.flags.incl {IgnoreTupleFields, IgnoreRangeShallow, PickyCAliases, PickyBackendAliases}
   c.cmp = dcEqIgnoreDistinct