Propagate type filters through variables

lib/crystal/type_inference.rb

@@ -312,14 +312,16 @@ def visit_var(node)
       var = lookup_var node.name
       filter = build_var_filter var
       node.bind_to(filter || var)
-      node.type_filters = {node.name => NotNilFilter}
+      node.type_filters = and_type_filters({node.name => NotNilFilter}, var.type_filters)
     end
 
     def build_var_filter(var)
       filters = @type_filter_stack.map { |hash| hash[var.name] }.compact
       return if filters.empty?
 
-      filtered_node = TypeFilteredNode.new(filters.last)
+      final_filter = filters.length == 1 ? filters[0] : AndTypeFilter.new(*filters)
+
+      filtered_node = TypeFilteredNode.new(final_filter)
       filtered_node.bind_to var
       filtered_node
     end
@@ -409,7 +411,7 @@ def type_assign(target, value, node = nil)
           var.bind_to value
         end
 
-        node.type_filters = and_type_filters({target.name => NotNilFilter}, node.value.type_filters) if node
+        var.type_filters = node.type_filters = and_type_filters({target.name => NotNilFilter}, node.value.type_filters) if node
       when InstanceVar
         value.accept self
 

lib/crystal/type_inference/filters.rb

@@ -38,17 +38,20 @@ def to_s
   end
 
   class AndTypeFilter
-    def initialize(filter1, filter2)
-      @filter1 = filter1
-      @filter2 = filter2
+    def initialize(*filters)
+      @filters = filters.uniq
     end
 
     def apply(other)
-      @filter2.apply(@filter1.apply(other))
+      type = other
+      @filters.each do |filter|
+        type = filter.apply(type)
+      end
+      type
     end
 
     def to_s
-      "(#{@filter1} && #{@filter2})"
+      "(#{@filters.join ' && '})"
     end
   end
 

spec/type_inference/nil_spec.rb

@@ -179,4 +179,22 @@ def bar
       1
       )) { int }
   end
+
+  it "restricts type when using previously assigned var" do
+    assert_type(%q(
+      class Foo
+        def bar
+          1
+        end
+      end
+
+      f = Foo.new || nil
+      x = f
+      if x
+        f.bar
+      else
+        2
+      end
+      )) { int }
+  end
 end