Support endless ranges in where

This commit adds support for endless ranges, e.g. (1..), that were added
in Ruby 2.6. They're functionally equivalent to explicitly specifying
Float::INFINITY as the end of the range.

3 files changed, 18 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index ca072be5e1..e468cc3169 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add support for endless ranges introduces in Ruby 2.6.
+
+    *Greg Navis*
+
 *   Deprecate passing `migrations_paths` to `connection.assume_migrated_upto_version`.
 
     *Ryuta Kamizono*
diff --git a/activerecord/lib/arel/predications.rb b/activerecord/lib/arel/predications.rb
index 28679ae892..0c03e93138 100644
--- a/activerecord/lib/arel/predications.rb
+++ b/activerecord/lib/arel/predications.rb
@@ -36,14 +36,14 @@ module Arel # :nodoc: all
 
     def between(other)
       if infinity?(other.begin)
-        if infinity?(other.end)
+        if other.end.nil? || infinity?(other.end)
           not_in([])
         elsif other.exclude_end?
           lt(other.end)
         else
           lteq(other.end)
         end
-      elsif infinity?(other.end)
+      elsif other.end.nil? || infinity?(other.end)
         gteq(other.begin)
       elsif other.exclude_end?
         gteq(other.begin).and(lt(other.end))
diff --git a/activerecord/test/cases/arel/attributes/attribute_test.rb b/activerecord/test/cases/arel/attributes/attribute_test.rb
index 671e273543..6ad54ab5df 100644
--- a/activerecord/test/cases/arel/attributes/attribute_test.rb
+++ b/activerecord/test/cases/arel/attributes/attribute_test.rb
@@ -639,6 +639,18 @@ module Arel
           )
         end
 
+        if Gem::Version.new("2.6.0") <= Gem::Version.new(RUBY_VERSION)
+          it "can be constructed with a range implicitly ending at Infinity" do
+            attribute = Attribute.new nil, nil
+            node = attribute.between(eval("0..")) # Use eval for compatibility with Ruby < 2.6 parser
+
+            node.must_equal Nodes::GreaterThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            )
+          end
+        end
+
         it "can be constructed with a quoted range ending at Infinity" do
           attribute = Attribute.new nil, nil
           node = attribute.between(quoted_range(0, ::Float::INFINITY, false))