Merge pull request #8748 from LemonBoy/when-in-objects

Pervasive replacement of nkRecWhen in generic types

tests/objects/twhen1.nim

@@ -0,0 +1,51 @@
+const Z = 0
+
+type
+  Foo[T] = object
+   when true:
+     u: int
+   else:
+     v: int
+  Foo1[T] = object
+   when T is int:
+     x: T
+   elif true:
+     z: char
+  Foo2[x:static[int]] = object
+    when (x and 1) == 1:
+      x: array[x+1,int]
+    else:
+      x: array[x,int]
+
+  Foo3 = Foo2[128]
+
+  # #8417
+  Foo4[A: static[int]] = object
+    when Z == 0:
+      discard
+    else:
+      discard
+
+block:
+  var x: Foo[int] = Foo[int](u: 42)
+  doAssert x.u == 42
+
+# Don't evaluate `when` branches before the type is instantiated
+block:
+  var x: Foo1[bool] = Foo1[bool](z: 'o')
+  doAssert x.z == 'o'
+
+block:
+  var x: Foo2[3]
+  doAssert x.x.len == 4
+
+block:
+  var x: Foo2[4]
+  doAssert x.x.len == 4
+
+block:
+  var x: Foo3
+  doAssert x.x.len == 128
+
+block:
+  var x: Foo4[0]