fix typetraits.$ regression https://github.com/c-blake/cligen/issues/84 (#10131)

* fix typetraits.`$` regression https://github.com/c-blake/cligen/issues/84
* add test

compiler/semmagic.nim

@@ -129,7 +129,8 @@ proc evalTypeTrait(c: PContext; traitCall: PNode, operand: PType, context: PSym)
   template typeWithSonsResult(kind, sons): PNode =
     newTypeWithSons(context, kind, sons).toNode(traitCall.info)
 
-  case trait.sym.name.s
+  let s = trait.sym.name.s
+  case s
   of "or", "|":
     return typeWithSonsResult(tyOr, @[operand, operand2])
   of "and":
@@ -160,7 +161,7 @@ proc evalTypeTrait(c: PContext; traitCall: PNode, operand: PType, context: PSym)
                      hasDestructor(t)
     result = newIntNodeT(ord(not complexObj), traitCall, c.graph)
   else:
-    localError(c.config, traitCall.info, "unknown trait")
+    localError(c.config, traitCall.info, "unknown trait: " & s)
     result = newNodeI(nkEmpty, traitCall.info)
 
 proc semTypeTraits(c: PContext, n: PNode): PNode =

lib/pure/typetraits.nim

@@ -10,6 +10,8 @@
 ## This module defines compile-time reflection procs for
 ## working with types
 
+export system.`$`
+
 proc name*(t: typedesc): string {.magic: "TypeTrait".}
   ## Alias for system.`$`(t) since Nim v0.20.0.
 

tests/metatype/ttypetraits2.nim

@@ -0,0 +1,3 @@
+# todo: merge with $nimc_D/tests/metatype/ttypetraits.nim (currently disabled)
+
+from typetraits import `$` # checks fix for https://github.com/c-blake/cligen/issues/84