Merge: model: introduce the bottom type

An old branch that was on some disk that I forgot to PR.

While the bottom type is useless now, it should be useful on future PR.
Type theorists and lattice fanboys might like it.

Pull-Request: #1374
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --git a/src/model/model.nit b/src/model/model.nit
index ff7bb48..94f11f2 100644 (file)
--- a/src/model/model.nit
+++ b/src/model/model.nit
@@ -1697,8 +1697,32 @@ class MNullType
        redef fun c_name do return "null"
        redef fun as_nullable do return self
 
-       # Aborts on `null`
-       redef fun as_notnull do abort # sorry...
+       redef var as_notnull = new MBottomType(model) is lazy
+       redef fun need_anchor do return false
+       redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual) do return self
+       redef fun can_resolve_for(mtype, anchor, mmodule) do return true
+
+       redef fun collect_mclassdefs(mmodule) do return new HashSet[MClassDef]
+
+       redef fun collect_mclasses(mmodule) do return new HashSet[MClass]
+
+       redef fun collect_mtypes(mmodule) do return new HashSet[MClassType]
+end
+
+# The special universal most specific type.
+#
+# This type is intended to be only used internally for type computation or analysis and should not be exposed to the user.
+# The bottom type can de used to denote things that are absurd, dead, or the absence of knowledge.
+#
+# Semantically it is the singleton `null.as_notnull`.
+class MBottomType
+       super MType
+       redef var model: Model
+       redef fun to_s do return "bottom"
+       redef fun full_name do return "bottom"
+       redef fun c_name do return "bottom"
+       redef fun as_nullable do return model.null_type
+       redef fun as_notnull do return self
        redef fun need_anchor do return false
        redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual) do return self
        redef fun can_resolve_for(mtype, anchor, mmodule) do return true