fixes nested gensym'ed parameters; fixes #9476

tests/template/tparams_gensymed.nim

@@ -70,3 +70,43 @@ proc genericProc(x: any) =
 
 concreteProc(7) # This works
 genericProc(7)  # This doesn't compile
+
+import tables
+
+# bug #9476
+proc getTypeInfo*(T: typedesc): pointer =
+  var dummy: T
+  getTypeInfo(dummy)
+
+
+macro implementUnary(op: untyped): untyped =
+  result = newStmtList()
+
+  template defineTable(tableSymbol) =
+    var tableSymbol = initTable[pointer, pointer]()
+  let tableSymbol = genSym(nskVar, "registeredProcs")
+  result.add(getAst(defineTable(tableSymbol)))
+
+  template defineRegisterInstantiation(tableSym, regTemplSym, instSym, op) =
+    template regTemplSym*(T: typedesc) =
+      let ti = getTypeInfo(T)
+
+      proc instSym(xOrig: int): int {.gensym, cdecl.} =
+        let x {.inject.} = xOrig
+        op
+
+      tableSym[ti] = cast[pointer](instSym)
+
+  let regTemplSymbol = ident("registerInstantiation")
+  let instSymbol = ident("instantiation")
+  result.add(getAst(defineRegisterInstantiation(
+    tableSymbol, regTemplSymbol, instSymbol, op
+  )))
+
+  echo result.repr
+
+
+implementUnary(): x*x
+
+registerInstantiation(int)
+registerInstantiation(float)