fixes #1783

compiler/semtypes.nim

@@ -1057,7 +1057,12 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
     var isConcrete = true
 
     for i in 1 .. <m.call.len:
-      let typ = m.call[i].typ.skipTypes({tyTypeDesc})
+      var typ = m.call[i].typ
+      if typ.kind == tyTypeDesc and typ.sons[0].kind == tyNone:
+        isConcrete = false
+        addToResult(typ)
+      else:
+        typ = typ.skipTypes({tyTypeDesc})
         if containsGenericType(typ): isConcrete = false
         addToResult(typ)
 

compiler/semtypinst.nim

@@ -89,6 +89,7 @@ type
     info*: TLineInfo
     allowMetaTypes*: bool     # allow types such as seq[Number]
                               # i.e. the result contains unresolved generics
+    skipTypedesc*: bool       # wether we should skip typeDescs
 
 proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType
 proc replaceTypeVarsS(cl: var TReplTypeVars, s: PSym): PSym
@@ -276,6 +277,8 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   else:
     idTablePut(cl.localCache, t, result)
 
+  let oldSkipTypedesc = cl.skipTypedesc
+  cl.skipTypedesc = true
   for i in countup(1, sonsLen(t) - 1):
     var x = replaceTypeVarsT(cl, t.sons[i])
     assert x.kind != tyGenericInvocation
@@ -289,6 +292,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
     rawAddSon(result, header.sons[i])
 
   var newbody = replaceTypeVarsT(cl, lastSon(body))
+  cl.skipTypedesc = oldSkipTypedesc
   newbody.flags = newbody.flags + (t.flags + body.flags - tfInstClearedFlags)
   result.flags = result.flags + newbody.flags - tfInstClearedFlags
   # This is actually wrong: tgeneric_closure fails with this line:
@@ -400,7 +404,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
     let lookup = PType(idTableGet(cl.typeMap, t)) # lookupTypeVar(cl, t)
     if lookup != nil:
       result = lookup
-      if tfUnresolved in t.flags: result = result.base
+      if tfUnresolved in t.flags or cl.skipTypedesc: result = result.base
     elif t.sons[0].kind != tyNone:
       result = makeTypeDesc(cl.c, replaceTypeVarsT(cl, t.sons[0]))
 

tests/metatype/ttypedesc2.nim

@@ -0,0 +1,37 @@
+discard """
+  output: "(x: a)"
+"""
+
+type
+  Bar[T] = object
+    x: T
+
+proc infer(T: typeDesc): Bar[T] = Bar[T](x: 'a')
+
+let foo = infer(char)
+echo foo
+
+when true:
+  # bug #1783
+
+  type
+      uoffset_t* = uint32
+      FlatBufferBuilder* = object
+
+      uarray* {.unchecked.} [T]  = array [0..0, T]
+      Array* [T] = object
+          o*: uoffset_t
+          len*: int
+          data*: ptr uarray[T]
+
+  proc ca* (fbb: ptr FlatBufferBuilder, T: typedesc, len: int): Array[T] {.noinit.} =
+      result.len = len
+
+  var fbb: ptr FlatBufferBuilder
+  let boolarray = ca(fbb, bool, 2)
+  let boolarray2 = fbb.ca(bool, 2)
+
+# bug #1664
+type Point[T] = tuple[x, y: T]
+proc origin(T: typedesc): Point[T] = discard
+discard origin(int)