model: add new type `MNotNullType` to force that null is excluded from a type.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/model/model.nit b/src/model/model.nit
index 54c9edb..a391ea4 100644 (file)
--- a/src/model/model.nit
+++ b/src/model/model.nit
@@ -697,6 +697,8 @@ abstract class MType
                if sup isa MNullableType then
                        sup_accept_null = true
                        sup = sup.mtype
+               else if sup isa MNotNullType then
+                       sup = sup.mtype
                else if sup isa MNullType then
                        sup_accept_null = true
                end
@@ -704,9 +706,13 @@ abstract class MType
                # Can `sub` provide null or not?
                # Thus we can match with `sup_accept_null`
                # Also discard the nullable marker if it exists
+               var sub_reject_null = false
                if sub isa MNullableType then
                        if not sup_accept_null then return false
                        sub = sub.mtype
+               else if sub isa MNotNullType then
+                       sub_reject_null = true
+                       sub = sub.mtype
                else if sub isa MNullType then
                        return sup_accept_null
                end
@@ -721,12 +727,16 @@ abstract class MType
 
                        assert anchor != null
                        sub = sub.lookup_bound(mmodule, anchor)
+                       if sub_reject_null then sub = sub.as_notnull
 
                        #print "3.is {sub} a {sup}?"
 
                        # Manage the second layer of null/nullable
                        if sub isa MNullableType then
-                               if not sup_accept_null then return false
+                               if not sup_accept_null and not sub_reject_null then return false
+                               sub = sub.mtype
+                       else if sub isa MNotNullType then
+                               sub_reject_null = true
                                sub = sub.mtype
                        else if sub isa MNullType then
                                return sup_accept_null
@@ -734,7 +744,7 @@ abstract class MType
                end
                #print "4.is {sub} a {sup}? <- no more resolution"
 
-               assert sub isa MClassType # It is the only remaining type
+               assert sub isa MClassType else print "{sub} <? {sub}" # It is the only remaining type
 
                # A unfixed formal type can only accept itself
                if sup isa MFormalType then
@@ -998,6 +1008,13 @@ abstract class MType
                return self
        end
 
+       # Returns the not null version of the type.
+       # That is `self` minus the `null` value.
+       #
+       # For most types, this return `self`.
+       # For formal types, this returns a special `MNotNullType`
+       fun as_notnull: MType do return self
+
        private var as_nullable_cache: nullable MType = null
 
 
@@ -1265,6 +1282,8 @@ end
 # and need a context (anchor and mmodule) to be useful.
 abstract class MFormalType
        super MType
+
+       redef var as_notnull = new MNotNullType(self) is lazy
 end
 
 # A virtual formal type.
@@ -1519,7 +1538,7 @@ class MParameterType
        end
 end
 
-# A type that decorate an other type.
+# A type that decorates another type.
 #
 # The point of this class is to provide a common implementation of sevices that just forward to the original type.
 # Specific decorator are expected to redefine (or to extend) the default implementation as this suit them.
@@ -1531,6 +1550,7 @@ abstract class MProxyType
        redef fun model do return self.mtype.model
        redef fun need_anchor do return mtype.need_anchor
        redef fun as_nullable do return mtype.as_nullable
+       redef fun as_notnull do return mtype.as_notnull
        redef fun as_notnullable do return mtype.as_notnullable
        redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual)
        do
@@ -1603,6 +1623,33 @@ class MNullableType
        end
 end
 
+# A non-null version of a formal type.
+#
+# When a formal type in bounded to a nullable type, this is the type of the not null version of it.
+class MNotNullType
+       super MProxyType
+
+       redef fun to_s do return "not null {mtype}"
+       redef var full_name is lazy do return "not null {mtype.full_name}"
+       redef var c_name is lazy do return "notnull__{mtype.c_name}"
+
+       redef fun as_notnull do return self
+
+       redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual)
+       do
+               var res = super
+               return res.as_notnull
+       end
+
+       # Efficiently returns `mtype.lookup_fixed(mmodule, resolved_receiver).as_notnull`
+       redef fun lookup_fixed(mmodule, resolved_receiver)
+       do
+               var t = super
+               if t == mtype then return self
+               return t.as_notnull
+       end
+end
+
 # The type of the only value null
 #
 # The is only one null type per model, see `MModel::null_type`.
@@ -1613,6 +1660,9 @@ class MNullType
        redef fun full_name do return "null"
        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 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