introduce a pre-processing pass for the concept bodies

fixes #4982
fixes #3805

close #3414

tests/concepts/t3414.nim

@@ -0,0 +1,22 @@
+type
+  View[T] = concept v
+    v.empty is bool
+    v.front is T
+    popFront v
+
+proc find(view: View; target: View.T): View =
+  result = view
+
+  while not result.empty:
+    if view.front == target:
+      return
+
+    mixin popFront
+    popFront result
+
+proc popFront[T](s: var seq[T]) = discard
+proc empty[T](s: seq[T]): bool = false
+
+var s1 = @[1, 2, 3]
+let s2 = s1.find(10)
+

tests/concepts/t4982.nim

@@ -0,0 +1,18 @@
+discard """
+errormsg: "undeclared identifier: 'x'"
+line: 10
+"""
+
+import typetraits # without this import the program compiles (and echos false)
+
+type
+  SomeTestConcept = concept t
+    x.name is string # typo: t.name was intended (which would result in echo true)
+
+type
+  TestClass = ref object of RootObj
+    name: string
+
+var test = TestClass(name: "mytest")
+echo $(test is SomeTestConcept)
+