fixes #2404

compiler/semexprs.nim

@@ -2011,7 +2011,7 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   case n.kind
   of nkIdent, nkAccQuoted:
     var s = lookUp(c, n)
-    semCaptureSym(s, c.p.owner)
+    if c.inTypeClass == 0: semCaptureSym(s, c.p.owner)
     result = semSym(c, n, s, flags)
     if s.kind in {skProc, skMethod, skConverter}+skIterators:
       #performProcvarCheck(c, n, s)

tests/concepts/mvarconcept.nim

@@ -0,0 +1,13 @@
+type RNG* = concept var rng
+  rng.randomUint32() is uint32
+
+type MersenneTwister* = object
+
+proc randomUint32*(self: var MersenneTwister): uint32 = 5
+
+proc randomInt*(rng: var RNG; max: Positive): Natural = 5
+
+var mersenneTwisterInst = MersenneTwister()
+
+proc randomInt*(max: Positive): Natural =
+  mersenneTwisterInst.randomInt(max)

tests/concepts/tvarconcept.nim

@@ -1,15 +1,9 @@
+discard """
+  output: "5"
+"""
 
-# bug #2346
+# bug #2346, bug #2404
 
-type RNG64 = concept var rng
+import mvarconcept
-  rng.randomUint64() is uint64
 
-proc randomInt*(rng: var RNG64; max: int): int = 4
+echo randomInt(5)
-
-
-type MyRNG* = object
-
-proc randomUint64*(self: var MyRNG): uint64 = 4
-
-var r = MyRNG()
-echo r.randomInt(5)