make new concepts match themselves (#24244)

fixes #22839

compiler/sigmatch.nim

@@ -1899,8 +1899,11 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
         else:
           result = isNone
   of tyConcept:
-    result = if concepts.conceptMatch(c.c, f, a, c.bindings, nil): isGeneric
-             else: isNone
+    if a.kind == tyConcept and sameType(f, a):
+      result = isGeneric
+    else:
+      result = if concepts.conceptMatch(c.c, f, a, c.bindings, nil): isGeneric
+               else: isNone
   of tyCompositeTypeClass:
     considerPreviousT:
       let roota = a.skipGenericAlias

tests/concepts/tintypesection.nim

@@ -0,0 +1,22 @@
+# issues with concepts in type section types
+
+block: # issue #22839
+  type
+    Comparable = concept
+      proc `<`(a, b: Self): bool
+    
+    # Works with this.
+    # Comparable = concept a
+    #   `<`(a, a) is bool
+    
+    # Doesn't work with the new style concept.
+    Node[T: Comparable] = object
+      data: T
+      next: ref Node[T]
+
+  var x: Node[int]
+  type NotComparable = object
+  doAssert not (compiles do:
+    var y: Node[NotComparable])
+  proc `<`(a, b: NotComparable): bool = false
+  var z: Node[NotComparable]