reference implementation of a vector swizzle library

This also provides the initial steps towards support for type class "filtered" type inference
fixes an "ordinal type expected" ICE, related to the use of static params

12 files changed, 225 insertions, 58 deletions

diff --git a/compiler/ast.nim b/compiler/ast.nim
index 00fe3b246..ae1b34fd9 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -435,6 +435,8 @@ type
     tfUnresolved,     # marks unresolved typedesc/static params: e.g.
                       # proc foo(T: typedesc, list: seq[T]): var T
                       # proc foo(L: static[int]): array[L, int]
+                      # can be attached to ranges to indicate that the range
+                      # depends on unresolved static params.
     tfRetType,        # marks return types in proc (used to detect type classes 
                       # used as return types for return type inference)
     tfCapturesEnv,    # whether proc really captures some environment
diff --git a/compiler/sem.nim b/compiler/sem.nim
index 093fc9452..c35cff027 100644
--- a/compiler/sem.nim
+++ b/compiler/sem.nim
@@ -66,6 +66,9 @@ proc fitNode(c: PContext, formal: PType, arg: PNode): PNode =
       result = copyTree(arg)
       result.typ = formal
 
+proc inferWithMetatype(c: PContext, formal: PType,
+                       arg: PNode, coerceDistincts = false): PNode
+
 var commonTypeBegin = PType(kind: tyExpr)
 
 proc commonType*(x, y: PType): PType =
diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index 5d480bc98..b994a94d7 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -228,12 +228,25 @@ proc indexTypesMatch(c: PContext, f, a: PType, arg: PNode): PNode =
   if m.genericConverter and result != nil:
     instGenericConvertersArg(c, result, m)
 
-proc convertTo*(c: PContext, f: PType, n: PNode): PNode = 
+proc inferWithMetatype(c: PContext, formal: PType,
+                       arg: PNode, coerceDistincts = false): PNode =
   var m: TCandidate
-  initCandidate(c, m, f)
-  result = paramTypesMatch(m, f, n.typ, n, nil)
+  initCandidate(c, m, formal)
+  m.coerceDistincts = coerceDistincts
+  result = paramTypesMatch(m, formal, arg.typ, arg, nil)
   if m.genericConverter and result != nil:
     instGenericConvertersArg(c, result, m)
+  if result != nil:
+    # This almost exactly replicates the steps taken by the compiler during
+    # param matching. It performs an embarassing ammount of back-and-forth
+    # type jugling, but it's the price to pay for consistency and correctness
+    result.typ = generateTypeInstance(c, m.bindings, arg.info,
+                                      formal.skipTypes({tyCompositeTypeClass}))
+  else:
+    typeMismatch(arg, formal, arg.typ)
+    # error correction:
+    result = copyTree(arg)
+    result.typ = formal
 
 proc semResolvedCall(c: PContext, n: PNode, x: TCandidate): PNode =
   assert x.state == csMatch
diff --git a/compiler/semdata.nim b/compiler/semdata.nim
index 088b93fae..5ec66b51c 100644
--- a/compiler/semdata.nim
+++ b/compiler/semdata.nim
@@ -251,6 +251,27 @@ proc makeNotType*(c: PContext, t1: PType): PType =
   propagateToOwner(result, t1)
   result.flags.incl(t1.flags * {tfHasStatic})
 
+proc nMinusOne*(n: PNode): PNode =
+  result = newNode(nkCall, n.info, @[
+    newSymNode(getSysMagic("<", mUnaryLt)),
+    n])
+
+# Remember to fix the procs below this one when you make changes!
+proc makeRangeWithStaticExpr*(c: PContext, n: PNode): PType =
+  let intType = getSysType tyInt
+  result = newTypeS(tyRange, c)
+  result.sons = @[intType]
+  result.n = newNode(nkRange, n.info, @[
+    newIntTypeNode(nkIntLit, 0, intType),
+    makeStaticExpr(c, n.nMinusOne)])
+
+template rangeHasStaticIf*(t: PType): bool =
+  # this accepts the ranges's node
+  t.n[1].kind == nkStaticExpr
+
+template getStaticTypeFromRange*(t: PType): PType =
+  t.n[1][0][1].typ
+
 proc newTypeS(kind: TTypeKind, c: PContext): PType =
   result = newType(kind, getCurrOwner())
 
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index a6e2eaa23..b8c4f3297 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -121,6 +121,8 @@ proc semSym(c: PContext, n: PNode, s: PSym, flags: TExprFlags): PNode =
       return n
   of skType:
     markUsed(n, s)
+    if s.typ.kind == tyStatic and s.typ.n != nil:
+      return s.typ.n
     result = newSymNode(s, n.info)
     result.typ = makeTypeDesc(c, s.typ)
   else:
@@ -191,15 +193,35 @@ proc isCastable(dst, src: PType): bool =
 proc isSymChoice(n: PNode): bool {.inline.} =
   result = n.kind in nkSymChoices
 
+proc maybeLiftType(t: var PType, c: PContext, info: TLineInfo) =
+  # XXX: liftParamType started to perform addDecl
+  # we could do that instead in semTypeNode by snooping for added
+  # gnrc. params, then it won't be necessary to open a new scope here
+  openScope(c)
+  var lifted = liftParamType(c, skType, newNodeI(nkArgList, info),
+                         t, ":anon", info)
+  closeScope(c)
+  if lifted != nil: t = lifted
+
 proc semConv(c: PContext, n: PNode): PNode =
   if sonsLen(n) != 2:
     localError(n.info, errConvNeedsOneArg)
     return n
+
   result = newNodeI(nkConv, n.info)
-  result.typ = semTypeNode(c, n.sons[0], nil).skipTypes({tyGenericInst})
-  addSon(result, copyTree(n.sons[0]))
-  addSon(result, semExprWithType(c, n.sons[1]))
-  var op = result.sons[1]
+  var targetType = semTypeNode(c, n.sons[0], nil)
+  maybeLiftType(targetType, c, n[0].info)
+  result.addSon copyTree(n.sons[0])
+  var op = semExprWithType(c, n.sons[1])
+  
+  if targetType.isMetaType:
+    let final = inferWithMetatype(c, targetType, op, true)
+    result.addSon final
+    result.typ = final.typ
+    return
+
+  result.typ = targetType
+  addSon(result, op)
   
   if not isSymChoice(op):
     let status = checkConvertible(c, result.typ, op.typ)
@@ -221,7 +243,7 @@ proc semConv(c: PContext, n: PNode): PNode =
     for i in countup(0, sonsLen(op) - 1):
       let it = op.sons[i]
       let status = checkConvertible(c, result.typ, it.typ)
-      if status == convOK:
+      if status in {convOK, convNotNeedeed}:
         markUsed(n, it.sym)
         markIndirect(c, it.sym)
         return it
@@ -325,14 +347,7 @@ proc isOpImpl(c: PContext, n: PNode): PNode =
                                         tfIterator notin t.flags))
   else:
     var t2 = n[2].typ.skipTypes({tyTypeDesc})
-    # XXX: liftParamType started to perform addDecl
-    # we could do that instead in semTypeNode by snooping for added
-    # gnrc. params, then it won't be necessary to open a new scope here
-    openScope(c)
-    let lifted = liftParamType(c, skType, newNodeI(nkArgList, n.info),
-                               t2, ":anon", n.info)
-    closeScope(c)
-    if lifted != nil: t2 = lifted
+    maybeLiftType(t2, c, n.info)
     var m: TCandidate
     initCandidate(c, m, t2)
     let match = typeRel(m, t2, t1) != isNone
@@ -1202,7 +1217,7 @@ proc semAsgn(c: PContext, n: PNode): PNode =
         if lhsIsResult: {efAllowDestructor} else: {})
     if lhsIsResult:
       n.typ = enforceVoidContext
-      if resultTypeIsInferrable(lhs.sym.typ):
+      if c.p.owner.kind != skMacro and resultTypeIsInferrable(lhs.sym.typ):
         if cmpTypes(c, lhs.typ, rhs.typ) == isGeneric:
           internalAssert c.p.resultSym != nil
           lhs.typ = rhs.typ
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 15bfaab10..38854bc8a 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -12,9 +12,6 @@
 
 var enforceVoidContext = PType(kind: tyStmt)
 
-proc semCommand(c: PContext, n: PNode): PNode =
-  result = semExprNoType(c, n)
-  
 proc semDiscard(c: PContext, n: PNode): PNode = 
   result = n
   checkSonsLen(n, 1)
@@ -133,6 +130,7 @@ proc fixNilType(n: PNode) =
   n.typ = nil
 
 proc discardCheck(c: PContext, result: PNode) =
+  if c.inTypeClass > 0: return
   if result.typ != nil and result.typ.kind notin {tyStmt, tyEmpty}:
     if result.kind == nkNilLit:
       result.typ = nil
@@ -143,11 +141,6 @@ proc discardCheck(c: PContext, result: PNode) =
       while n.kind in skipForDiscardable:
         n = n.lastSon
         n.typ = nil
-    elif c.inTypeClass > 0:
-      if result.typ.kind == tyBool:
-        let verdict = semConstExpr(c, result)
-        if verdict.intVal == 0:
-          localError(result.info, "type class predicate failed")
     elif result.typ.kind != tyError and gCmd != cmdInteractive:
       if result.typ.kind == tyNil:
         fixNilType(result)
@@ -1324,13 +1317,17 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
       return
     else:
       n.sons[i] = semExpr(c, n.sons[i])
+      if c.inTypeClass > 0 and n[i].typ != nil and n[i].typ.kind == tyBool:
+        let verdict = semConstExpr(c, n[i])
+        if verdict.intVal == 0:
+          localError(result.info, "type class predicate failed")
       if n.sons[i].typ == enforceVoidContext or usesResult(n.sons[i]):
         voidContext = true
         n.typ = enforceVoidContext
       if i == last and (length == 1 or efWantValue in flags):
         n.typ = n.sons[i].typ
         if not isEmptyType(n.typ): n.kind = nkStmtListExpr
-      elif i != last or voidContext or c.inTypeClass > 0:
+      elif i != last or voidContext:
         discardCheck(c, n.sons[i])
       else:
         n.typ = n.sons[i].typ
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index f0ef43be4..269676624 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -198,19 +198,6 @@ proc semRange(c: PContext, n: PNode, prev: PType): PType =
     localError(n.info, errXExpectsOneTypeParam, "range")
     result = newOrPrevType(tyError, prev, c)
 
-proc nMinusOne(n: PNode): PNode =
-  result = newNode(nkCall, n.info, @[
-    newSymNode(getSysMagic("<", mUnaryLt)),
-    n])
-
-proc makeRangeWithStaticExpr(c: PContext, n: PNode): PType =
-  let intType = getSysType(tyInt)
-  result = newTypeS(tyRange, c)
-  result.sons = @[intType]
-  result.n = newNode(nkRange, n.info, @[
-    newIntTypeNode(nkIntLit, 0, intType),
-    makeStaticExpr(c, n.nMinusOne)])
-
 proc semArray(c: PContext, n: PNode, prev: PType): PType = 
   var indx, base: PType
   result = newOrPrevType(tyArray, prev, c)
@@ -229,6 +216,7 @@ proc semArray(c: PContext, n: PNode, prev: PType): PType =
         if not isOrdinalType(e.typ.lastSon):
           localError(n[1].info, errOrdinalTypeExpected)
         indx = makeRangeWithStaticExpr(c, e)
+        indx.flags.incl tfUnresolved
       elif e.kind in nkCallKinds and hasGenericArguments(e):
         if not isOrdinalType(e.typ):
           localError(n[1].info, errOrdinalTypeExpected)
@@ -628,17 +616,28 @@ proc semObjectNode(c: PContext, n: PNode, prev: PType): PType =
   if base == nil and tfInheritable notin result.flags:
     incl(result.flags, tfFinal)
 
+proc findEnforcedStaticType(t: PType): PType =
+  # This handles types such as `static[T] and Foo`,
+  # which are subset of `static[T]`, hence they could
+  # be treated in the same way
+  if t.kind == tyStatic: return t
+  if t.kind == tyAnd:
+    for s in t.sons:
+      let t = findEnforcedStaticType(s)
+      if t != nil: return t
+
 proc addParamOrResult(c: PContext, param: PSym, kind: TSymKind) =
   template addDecl(x) =
     if sfGenSym notin x.flags: addDecl(c, x)
 
   if kind == skMacro:
-    if param.typ.kind == tyTypeDesc:
-      addDecl(param)
-    elif param.typ.kind == tyStatic:
+    let staticType = findEnforcedStaticType(param.typ)
+    if staticType != nil:
       var a = copySym(param)
-      a.typ = param.typ.base
+      a.typ = staticType.base
       addDecl(a)
+    elif param.typ.kind == tyTypeDesc:
+      addDecl(param)
     else:
       # within a macro, every param has the type PNimrodNode!
       let nn = getSysSym"PNimrodNode"
@@ -944,14 +943,18 @@ proc semBlockType(c: PContext, n: PNode, prev: PType): PType =
 proc semGenericParamInInvokation(c: PContext, n: PNode): PType =
   result = semTypeNode(c, n, nil)
 
-proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType = 
+proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
   if s.typ == nil:
     localError(n.info, "cannot instantiate the '$1' $2" %
                        [s.name.s, ($s.kind).substr(2).toLower])
     return newOrPrevType(tyError, prev, c)
   
+  var t = s.typ
+  if t.kind == tyCompositeTypeClass and t.base.kind == tyGenericBody:
+    t = t.base
+
   result = newOrPrevType(tyGenericInvokation, prev, c)
-  addSonSkipIntLit(result, s.typ)
+  addSonSkipIntLit(result, t)
 
   template addToResult(typ) =
     if typ.isNil:
@@ -959,23 +962,24 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
       rawAddSon(result, typ)
     else: addSonSkipIntLit(result, typ)
 
-  if s.typ.kind == tyForward:
+  if t.kind == tyForward:
     for i in countup(1, sonsLen(n)-1):
       var elem = semGenericParamInInvokation(c, n.sons[i])
       addToResult(elem)
-  elif s.typ.kind != tyGenericBody:
+    return
+  elif t.kind != tyGenericBody:
     #we likely got code of the form TypeA[TypeB] where TypeA is
     #not generic.
     localError(n.info, errNoGenericParamsAllowedForX, s.name.s)
     return newOrPrevType(tyError, prev, c)
   else:
-    var m = newCandidate(c, s, n)
+    var m = newCandidate(c, t)
     matches(c, n, copyTree(n), m)
     
     if m.state != csMatch:
-      var err = "cannot instantiate " & typeToString(s.typ) & "\n" &
+      var err = "cannot instantiate " & typeToString(t) & "\n" &
                 "got: (" & describeArgs(c, n) & ")\n" &
-                "but expected: (" & describeArgs(c, s.typ.n, 0) & ")"
+                "but expected: (" & describeArgs(c, t.n, 0) & ")"
       localError(n.info, errGenerated, err)
       return newOrPrevType(tyError, prev, c)
 
@@ -987,7 +991,8 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
       addToResult(typ)
    
     if isConcrete:
-      if s.ast == nil:
+      if s.ast == nil and s.typ.kind != tyCompositeTypeClass:
+        # XXX: What kind of error is this? is it still relevant?
         localError(n.info, errCannotInstantiateX, s.name.s)
         result = newOrPrevType(tyError, prev, c)
       else:
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 662268380..56490dfe3 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -40,6 +40,8 @@ type
     proxyMatch*: bool        # to prevent instantiations
     genericConverter*: bool  # true if a generic converter needs to
                              # be instantiated
+    coerceDistincts*: bool   # this is an explicit coercion that can strip away
+                             # a distrinct type
     typedescMatched: bool
     inheritancePenalty: int  # to prefer closest father object type
     errors*: seq[string]     # additional clarifications to be displayed to the
@@ -114,6 +116,9 @@ proc newCandidate*(ctx: PContext, callee: PSym,
                    binding: PNode, calleeScope = -1): TCandidate =
   initCandidate(ctx, result, callee, binding, calleeScope)
 
+proc newCandidate*(ctx: PContext, callee: PType): TCandidate =
+  initCandidate(ctx, result, callee)
+
 proc copyCandidate(a: var TCandidate, b: TCandidate) = 
   a.c = b.c
   a.exactMatches = b.exactMatches
@@ -460,7 +465,8 @@ proc matchUserTypeClass*(c: PContext, m: var TCandidate,
     
     if param.kind == nkVarTy:
       dummyName = param[0]
-      dummyType = makeVarType(c, a)
+      dummyType = if a.kind != tyVar: makeVarType(c, a)
+                  else: a
     else:
       dummyName = param
       dummyType = a
@@ -470,7 +476,7 @@ proc matchUserTypeClass*(c: PContext, m: var TCandidate,
     dummyParam.typ = dummyType
     addDecl(c, dummyParam)
 
-  var checkedBody = c.semTryExpr(c, copyTree(body.n[3]), bufferErrors = false)
+  var checkedBody = c.semTryExpr(c, body.n[3].copyTree, bufferErrors = false)
   m.errors = bufferedMsgs
   clearBufferedMsgs()
   if checkedBody == nil: return isNone
@@ -623,6 +629,20 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
       result = typeRel(c, f.sons[1], a.sons[1])
       if result < isGeneric:
         result = isNone
+      elif tfUnresolved in fRange.flags and
+           rangeHasStaticIf(fRange):
+        # This is a range from an array instantiated with a generic
+        # static param. We must extract the static param here and bind
+        # it to the size of the currently supplied array.
+        var
+          rangeStaticT = fRange.getStaticTypeFromRange
+          replacementT = newTypeWithSons(c.c, tyStatic, @[tyInt.getSysType])
+          inputUpperBound = a.sons[0].n[1].intVal
+        # we must correct for the off-by-one discrepancy between
+        # ranges and static params:
+        replacementT.n = newIntNode(nkIntLit, inputUpperBound + 1)
+        put(c.bindings, rangeStaticT, replacementT)
+        result = isGeneric
       elif lengthOrd(fRange) != lengthOrd(a):
         result = isNone
     else: discard
@@ -686,6 +706,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
           result = isSubtype
   of tyDistinct:
     if (a.kind == tyDistinct) and sameDistinctTypes(f, a): result = isEqual
+    elif c.coerceDistincts: result = typeRel(c, f.base, a)
   of tySet: 
     if a.kind == tySet: 
       if (f.sons[0].kind != tyGenericParam) and (a.sons[0].kind == tyEmpty): 
@@ -848,7 +869,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
 
   of tyUserTypeClass, tyUserTypeClassInst:
     considerPreviousT:
-      result = matchUserTypeClass(c.c, c, f, a)
+      result = matchUserTypeClass(c.c, c, f, aOrig)
       if result == isGeneric:
         put(c.bindings, f, a)
 
@@ -863,7 +884,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
   of tyGenericParam:
     var x = PType(idTableGet(c.bindings, f))
     if x == nil:
-      if c.calleeSym != nil and c.calleeSym.kind == skType and
+      if c.calleeSym != nil and c.callee.kind == tyGenericBody and
          f.kind == tyGenericParam and not c.typedescMatched:
         # XXX: The fact that generic types currently use tyGenericParam for 
         # their parameters is really a misnomer. tyGenericParam means "match
@@ -1051,7 +1072,7 @@ proc paramTypesMatchAux(m: var TCandidate, f, argType: PType,
     # XXX: When implicit statics are the default
     # this will be done earlier - we just have to
     # make sure that static types enter here
-    
+     
     # XXX: weaken tyGenericParam and call it tyGenericPlaceholder
     # and finally start using tyTypedesc for generic types properly.
     if argType.kind == tyGenericParam and tfWildcard in argType.flags:
@@ -1060,7 +1081,7 @@ proc paramTypesMatchAux(m: var TCandidate, f, argType: PType,
       return argSemantized
 
     if argType.kind == tyStatic:
-      if m.calleeSym.kind == skType:
+      if m.callee.kind == tyGenericBody:
         result = newNodeI(nkType, argOrig.info)
         result.typ = makeTypeFromExpr(c, arg)
         return
diff --git a/compiler/types.nim b/compiler/types.nim
index 89b15c4a8..d7410c67a 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -436,6 +436,7 @@ proc typeToString(typ: PType, prefer: TPreferedDesc = preferName): string =
   of tyStatic:
     internalAssert t.len > 0
     result = "static[" & typeToString(t.sons[0]) & "]"
+    if t.n != nil: result.add "(" & renderTree(t.n) & ")"
   of tyUserTypeClass:
     internalAssert t.sym != nil and t.sym.owner != nil
     return t.sym.owner.name.s
diff --git a/tests/bind/tinvalidbindtypedesc.nim b/tests/bind/tinvalidbindtypedesc.nim
index 7d97d2e0d..5b2f51110 100644
--- a/tests/bind/tinvalidbindtypedesc.nim
+++ b/tests/bind/tinvalidbindtypedesc.nim
@@ -1,5 +1,5 @@
 discard """
-  line: 11
+  line: 10
   errormsg: "type mismatch: got (typedesc[float], string)"
 """
 
diff --git a/tests/metatype/swizzle.nim b/tests/metatype/swizzle.nim
new file mode 100644
index 000000000..ce18fa234
--- /dev/null
+++ b/tests/metatype/swizzle.nim
@@ -0,0 +1,79 @@
+discard """
+  output: '''3
+[1, 3]
+[2, 1, 2]
+'''
+"""
+
+import macros, strutils
+
+template accept(e: expr) =
+  static: assert(compiles(e))
+
+template reject(e: expr) =
+  static: assert(not compiles(e))
+
+proc swizzleIdx(c: char): int =
+  return case c
+    of 'x': 0
+    of 'y': 1
+    of 'z': 2
+    of 'w': 3    
+    of 'r': 0
+    of 'g': 1
+    of 'b': 2
+    of 'a': 3    
+    else: 0
+
+proc isSwizzle(s: string): bool =
+  template trySet(name, set) =
+    block search:
+      for c in s:
+        if c notin set:
+          break search
+      return true
+
+  trySet coords, {'x', 'y', 'z', 'w'}
+  trySet colors, {'r', 'g', 'b', 'a'}
+  
+  return false
+
+type 
+  StringIsSwizzle = generic value
+    value.isSwizzle
+
+  SwizzleStr = static[string] and StringIsSwizzle
+
+proc foo(x: SwizzleStr) =
+  echo "sw"
+
+accept foo("xx")
+reject foo("xe")
+
+type 
+  Vec[N: static[int]; T] = array[N, T]
+
+
+proc card(x: Vec): int = x.N
+proc `$`(x: Vec): string = x.repr.strip
+
+macro `.`(x: Vec, swizzle: SwizzleStr): expr =
+  var
+    cardinality = swizzle.len
+    values = newNimNode(nnkBracket)
+    v = genSym()
+
+  for c in swizzle:
+    values.add newNimNode(nnkBracketExpr).add(
+      v, c.swizzleIdx.newIntLitNode)
+  
+  return quote do:
+    let `v` = `x`
+    Vec[`cardinality`, `v`.T](`values`)
+
+var z = Vec([1, 2, 3])
+
+echo z.card
+echo z.xz
+echo z.yxy
+
diff --git a/tests/metatype/typeclassinference.nim b/tests/metatype/typeclassinference.nim
new file mode 100644
index 000000000..72b5aca96
--- /dev/null
+++ b/tests/metatype/typeclassinference.nim
@@ -0,0 +1,10 @@
+import typetraits
+
+type
+  Vec[N: static[int]; T] = distinct array[N, T]
+
+var x = Vec([1, 2, 3])
+
+static:
+  assert x.type.name == "Vec[static[int](3), int]"
+