X-Git-Url: http://nitlanguage.org

diff --git a/src/semantize/typing.nit b/src/semantize/typing.nit
index 4955eda..8fb3852 100644
--- a/src/semantize/typing.nit
+++ b/src/semantize/typing.nit
@@ -266,8 +266,13 @@ private class TypeVisitor
 
 		#debug("recv: {recvtype} (aka {unsafe_type})")
 		if recvtype isa MNullType then
-			self.error(node, "Error: Method '{name}' call on 'null'.")
-			return null
+			# `null` only accepts some methods of object.
+			if name == "==" or name == "!=" or name == "is_same_instance" then
+				unsafe_type = mmodule.object_type.as_nullable
+			else
+				self.error(node, "Error: Method '{name}' call on 'null'.")
+				return null
+			end
 		end
 
 		var mproperty = self.try_get_mproperty_by_name2(node, unsafe_type, name)
@@ -633,6 +638,12 @@ redef class AExpr
 	do
 		v.error(self, "no implemented accept_typing for {self.class_name}")
 	end
+
+	# Is non-null if `self` is a leaf of a comprehension array construction.
+	# In this case, the enclosing literal array node is designated.
+	# The result of the evaluation of `self` must be
+	# stored inside the designated array (there is an implicit `push`)
+	var comprehension: nullable AArrayExpr = null
 end
 
 redef class ABlockExpr
@@ -750,11 +761,6 @@ redef class AReassignFormExpr
 
 		self.read_type = readtype
 
-		if readtype isa MNullType then
-			v.error(self, "Error: Method '{reassign_name}' call on 'null'.")
-			return null
-		end
-
 		var callsite = v.get_method(self, readtype, reassign_name, false)
 		if callsite == null then return null # Skip error
 		self.reassign_callsite = callsite
@@ -857,7 +863,12 @@ redef class AIfExpr
 
 		v.visit_stmt(n_then)
 		v.visit_stmt(n_else)
+
 		self.is_typed = true
+
+		if n_then != null and n_else == null then
+			self.mtype = n_then.mtype
+		end
 	end
 end
 
@@ -964,7 +975,7 @@ redef class AForExpr
 			is_col = true
 		end
 
-		if mapit_cla != null and v.is_subtype(ittype, mapit_cla.get_mtype([objcla.mclass_type, objcla.mclass_type.as_nullable])) then
+		if mapit_cla != null and v.is_subtype(ittype, mapit_cla.get_mtype([objcla.mclass_type.as_nullable, objcla.mclass_type.as_nullable])) then
 			# Map Iterator
 			var coltype = ittype.supertype_to(v.mmodule, v.anchor, mapit_cla)
 			var variables = self.variables
@@ -1043,6 +1054,7 @@ redef class AForExpr
 		self.do_type_iterator(v, mtype)
 
 		v.visit_stmt(n_block)
+		self.mtype = n_block.mtype
 		self.is_typed = true
 	end
 end
@@ -1180,9 +1192,31 @@ redef class ASuperstringExpr
 end
 
 redef class AArrayExpr
+	# The `with_capacity` method on Array
 	var with_capacity_callsite: nullable CallSite
+
+	# The `push` method on arrays
 	var push_callsite: nullable CallSite
 
+	# The element of each type
+	var element_mtype: nullable MType
+
+	# Set that `self` is a part of comprehension array `na`
+	# If `self` is a `for`, or a `if`, then `set_comprehension` is recursively applied.
+	private fun set_comprehension(n: nullable AExpr)
+	do
+		if n == null then
+			return
+		else if n isa AForExpr then
+			set_comprehension(n.n_block)
+		else if n isa AIfExpr then
+			set_comprehension(n.n_then)
+			set_comprehension(n.n_else)
+		else
+			# is a leave
+			n.comprehension = self
+		end
+	end
 	redef fun accept_typing(v)
 	do
 		var mtype: nullable MType = null
@@ -1198,6 +1232,7 @@ redef class AArrayExpr
 			if t == null then
 				return # Skip error
 			end
+			set_comprehension(e)
 			if mtype != null then
 				if v.check_subtype(e, t, mtype) == null then return # Skip error
 				if t == mtype then useless = true
@@ -1208,7 +1243,7 @@ redef class AArrayExpr
 		if mtype == null then
 			mtype = v.merge_types(self, mtypes)
 		end
-		if mtype == null then
+		if mtype == null or mtype isa MNullType then
 			v.error(self, "Type Error: ambiguous array type {mtypes.join(" ")}")
 			return
 		end
@@ -1216,6 +1251,9 @@ redef class AArrayExpr
 			assert ntype != null
 			v.modelbuilder.warning(ntype, "useless-type", "Warning: useless type declaration `{mtype}` in literal Array since it can be inferred from the elements type.")
 		end
+
+		self.element_mtype = mtype
+
 		var mclass = v.get_mclass(self, "Array")
 		if mclass == null then return # Forward error
 		var array_mtype = mclass.get_mtype([mtype])
@@ -1369,10 +1407,6 @@ redef class ASendExpr
 		var name = self.property_name
 
 		if recvtype == null then return # Forward error
-		if recvtype isa MNullType then
-			v.error(self, "Error: Method '{name}' call on 'null'.")
-			return
-		end
 
 		var callsite = v.get_method(self, recvtype, name, self.n_expr isa ASelfExpr)
 		if callsite == null then return
@@ -1516,10 +1550,6 @@ redef class ASendReassignFormExpr
 		var name = self.property_name
 
 		if recvtype == null then return # Forward error
-		if recvtype isa MNullType then
-			v.error(self, "Error: Method '{name}' call on 'null'.")
-			return
-		end
 
 		var for_self = self.n_expr isa ASelfExpr
 		var callsite = v.get_method(self, recvtype, name, for_self)