more test cases for generic object impl AST (#22077)

closes #9899, closes #14708, refs #21017

tests/generics/timpl_ast.nim

@@ -0,0 +1,49 @@
+discard """
+  action: compile
+"""
+
+import std/macros
+import std/assertions
+
+block: # issue #16639
+  type Foo[T] = object
+    when true:
+      x: float
+
+  type Bar = object
+    when true:
+      x: float
+
+  macro test() =
+    let a = getImpl(bindSym"Foo")[^1]
+    let b = getImpl(bindSym"Bar")[^1]
+    doAssert treeRepr(a) == treeRepr(b)
+
+  test()
+
+import strutils
+
+block: # issues #9899, ##14708
+  macro implRepr(a: typed): string =
+    result = newLit(repr(a.getImpl))
+
+  type
+    Option[T] = object
+      when false: discard # issue #14708
+      when false: x: int
+      when T is (ref | ptr):
+        val: T
+      else:
+        val: T
+        has: bool
+
+  static: # check information is retained
+    let r = implRepr(Option)
+    doAssert "when T is" in r
+    doAssert r.count("val: T") == 2
+    doAssert "has: bool" in r
+
+  block: # try to compile the output
+    macro parse(s: static string) =
+      result = parseStmt(s)
+    parse("type " & implRepr(Option))