More concept fixes

Fixes #7705, #7703, #7702

compiler/semexprs.nim

@@ -271,7 +271,7 @@ proc semLowHigh(c: PContext, n: PNode, m: TMagic): PNode =
     localError(c.config, n.info, errXExpectsTypeOrValue % opToStr[m])
   else:
     n.sons[1] = semExprWithType(c, n.sons[1], {efDetermineType})
-    var typ = skipTypes(n.sons[1].typ, abstractVarRange + {tyTypeDesc})
+    var typ = skipTypes(n.sons[1].typ, abstractVarRange + {tyTypeDesc, tyUserTypeClassInst})
     case typ.kind
     of tySequence, tyString, tyCString, tyOpenArray, tyVarargs:
       n.typ = getSysType(c.graph, n.info, tyInt)
@@ -1261,7 +1261,7 @@ proc semSubscript(c: PContext, n: PNode, flags: TExprFlags): PNode =
   # make sure we don't evaluate generic macros/templates
   n.sons[0] = semExprWithType(c, n.sons[0],
                               {efNoEvaluateGeneric})
-  let arr = skipTypes(n.sons[0].typ, {tyGenericInst,
+  let arr = skipTypes(n.sons[0].typ, {tyGenericInst, tyUserTypeClassInst,
                                       tyVar, tyLent, tyPtr, tyRef, tyAlias, tySink})
   case arr.kind
   of tyArray, tyOpenArray, tyVarargs, tySequence, tyString,

compiler/semfold.nim

@@ -619,7 +619,7 @@ proc getConstExpr(m: PSym, n: PNode; g: ModuleGraph): PNode =
       of mLow:
         result = newIntNodeT(firstOrd(g.config, n.sons[1].typ), n, g)
       of mHigh:
-        if skipTypes(n.sons[1].typ, abstractVar).kind notin
+        if skipTypes(n.sons[1].typ, abstractVar+{tyUserTypeClassInst}).kind notin
             {tySequence, tyString, tyCString, tyOpenArray, tyVarargs}:
           result = newIntNodeT(lastOrd(g.config, skipTypes(n[1].typ, abstractVar)), n, g)
         else:

compiler/types.nim

@@ -615,7 +615,7 @@ proc firstOrd*(conf: ConfigRef; t: PType): BiggestInt =
     else:
       assert(t.n.sons[0].kind == nkSym)
       result = t.n.sons[0].sym.position
-  of tyGenericInst, tyDistinct, tyTypeDesc, tyAlias, tyStatic, tyInferred:
+  of tyGenericInst, tyDistinct, tyTypeDesc, tyAlias, tyStatic, tyInferred, tyUserTypeClassInst:
     result = firstOrd(conf, lastSon(t))
   of tyOrdinal:
     if t.len > 0: result = firstOrd(conf, lastSon(t))

tests/concepts/treversable.nim

@@ -0,0 +1,31 @@
+# issue 7705, 7703, 7702
+discard """
+  output: '''
+z
+e
+  '''
+"""
+
+type
+  Reversable*[T] = concept a
+    a[int] is T
+    a.high is int
+    a.len is int
+    a.low is int
+
+proc get[T](s: Reversable[T], n: int): T =
+  s[n]
+
+proc hi[T](s: Reversable[T]): int =
+  s.high
+
+proc lo[T](s: Reversable[T]): int =
+  s.low
+
+iterator reverse*[T](s: Reversable[T]): T =
+  assert hi(s) - lo(s) == len(s) - 1
+  for z in hi(s).countdown(lo(s)):
+    yield s.get(z)
+
+for s in @["e", "z"].reverse:
+  echo s