fixes #7092

compiler/ccgexprs.nim

@@ -59,7 +59,7 @@ proc genLiteral(p: BProc, n: PNode, ty: PType): Rope =
     else:
       result = rope("NIM_NIL")
   of nkStrLit..nkTripleStrLit:
-    case skipTypes(ty, abstractVarRange + {tyStatic}).kind
+    case skipTypes(ty, abstractVarRange + {tyStatic, tyUserTypeClass, tyUserTypeClassInst}).kind
     of tyNil:
       result = genNilStringLiteral(p.module, n.info)
     of tyString:

tests/concepts/tusertypeclasses.nim

@@ -4,6 +4,7 @@ Sortable
 Container
 TObj
 int
+111 111
 '''
 """
 
@@ -97,3 +98,12 @@ proc testFoo(x: TFoo) =
 
 testFoo(TObj(x: 10))
 
+# bug #7092
+
+type stringTest = concept x
+  x is string
+
+let usedToFail: stringTest = "111"
+let working: string = "111"
+
+echo usedToFail, " ", working