7 files changed, 64 insertions, 7 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 184e881b25..b39f423700 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add support for beginless ranges, introduced in Ruby 2.7.
+
+    *Josh Goodall*
+
 *   Add database_exists? method to connection adapters to check if a database exists.
 
     *Guilherme Mansur*
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index e9ae8d159e..405fecb603 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -619,7 +619,11 @@ module ActiveRecord
           when ER_QUERY_INTERRUPTED
             QueryCanceled.new(message, sql: sql, binds: binds)
           else
-            super
+            if exception.is_a?(Mysql2::Error::TimeoutError)
+              ActiveRecord::AdapterTimeout.new(message, sql: sql, binds: binds)
+            else
+              super
+            end
           end
         end
 
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index c8c06375a3..20cc987d6e 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -353,16 +353,24 @@ module ActiveRecord
   class IrreversibleOrderError < ActiveRecordError
   end
 
+  # Superclass for errors that have been aborted (either by client or server).
+  class QueryAborted < StatementInvalid
+  end
+
   # LockWaitTimeout will be raised when lock wait timeout exceeded.
   class LockWaitTimeout < StatementInvalid
   end
 
   # StatementTimeout will be raised when statement timeout exceeded.
-  class StatementTimeout < StatementInvalid
+  class StatementTimeout < QueryAborted
   end
 
   # QueryCanceled will be raised when canceling statement due to user request.
-  class QueryCanceled < StatementInvalid
+  class QueryCanceled < QueryAborted
+  end
+
+  # AdapterTimeout will be raised when database clients times out while waiting from the server.
+  class AdapterTimeout < QueryAborted
   end
 
   # UnknownAttributeReference is raised when an unknown and potentially unsafe
diff --git a/activerecord/lib/arel/predications.rb b/activerecord/lib/arel/predications.rb
index dece478615..895d394363 100644
--- a/activerecord/lib/arel/predications.rb
+++ b/activerecord/lib/arel/predications.rb
@@ -37,7 +37,7 @@ module Arel # :nodoc: all
     def between(other)
       if unboundable?(other.begin) == 1 || unboundable?(other.end) == -1
         self.in([])
-      elsif open_ended?(other.begin)
+      elsif other.begin.nil? || open_ended?(other.begin)
         if other.end.nil? || open_ended?(other.end)
           not_in([])
         elsif other.exclude_end?
@@ -85,7 +85,7 @@ Passing a range to `#in` is deprecated. Call `#between`, instead.
     def not_between(other)
       if unboundable?(other.begin) == 1 || unboundable?(other.end) == -1
         not_in([])
-      elsif open_ended?(other.begin)
+      elsif other.begin.nil? || open_ended?(other.begin)
         if other.end.nil? || open_ended?(other.end)
           self.in([])
         elsif other.exclude_end?
diff --git a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
index df84a40f63..cfc1823773 100644
--- a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
@@ -225,6 +225,21 @@ class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
     end
   end
 
+  def test_read_timeout_exception
+    ActiveRecord::Base.establish_connection(
+      ActiveRecord::Base.configurations[:arunit].merge("read_timeout" => 1)
+    )
+
+    error = assert_raises(ActiveRecord::AdapterTimeout) do
+      ActiveRecord::Base.connection.execute("SELECT SLEEP(2)")
+    end
+    assert_kind_of ActiveRecord::QueryAborted, error
+
+    assert_equal Mysql2::Error::TimeoutError, error.cause.class
+  ensure
+    ActiveRecord::Base.establish_connection :arunit
+  end
+
   private
     def with_example_table(definition = "id int auto_increment primary key, number int, data varchar(255)", &block)
       super(@conn, "ex", definition, &block)
diff --git a/activerecord/test/cases/adapters/mysql2/transaction_test.rb b/activerecord/test/cases/adapters/mysql2/transaction_test.rb
index 52e283f247..2041cc308f 100644
--- a/activerecord/test/cases/adapters/mysql2/transaction_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/transaction_test.rb
@@ -92,7 +92,7 @@ module ActiveRecord
 
     test "raises StatementTimeout when statement timeout exceeded" do
       skip unless ActiveRecord::Base.connection.show_variable("max_execution_time")
-      assert_raises(ActiveRecord::StatementTimeout) do
+      error = assert_raises(ActiveRecord::StatementTimeout) do
         s = Sample.create!(value: 1)
         latch1 = Concurrent::CountDownLatch.new
         latch2 = Concurrent::CountDownLatch.new
@@ -117,10 +117,11 @@ module ActiveRecord
           thread.join
         end
       end
+      assert_kind_of ActiveRecord::QueryAborted, error
     end
 
     test "raises QueryCanceled when canceling statement due to user request" do
-      assert_raises(ActiveRecord::QueryCanceled) do
+      error = assert_raises(ActiveRecord::QueryCanceled) do
         s = Sample.create!(value: 1)
         latch = Concurrent::CountDownLatch.new
 
@@ -144,6 +145,7 @@ module ActiveRecord
           thread.join
         end
       end
+      assert_kind_of ActiveRecord::QueryAborted, error
     end
   end
 end
diff --git a/activerecord/test/cases/arel/attributes/attribute_test.rb b/activerecord/test/cases/arel/attributes/attribute_test.rb
index c7bd0a053b..7ebb90c6fd 100644
--- a/activerecord/test/cases/arel/attributes/attribute_test.rb
+++ b/activerecord/test/cases/arel/attributes/attribute_test.rb
@@ -638,6 +638,18 @@ module Arel
           )
         end
 
+        if Gem::Version.new("2.7.0") <= Gem::Version.new(RUBY_VERSION)
+          it "can be constructed with a range implicitly starting at Infinity" do
+            attribute = Attribute.new nil, nil
+            node = attribute.between(eval("..0")) # eval for backwards compatibility
+
+            node.must_equal Nodes::LessThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            )
+          end
+        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
@@ -839,6 +851,18 @@ module Arel
           )
         end
 
+        if Gem::Version.new("2.7.0") <= Gem::Version.new(RUBY_VERSION)
+          it "can be constructed with a range implicitly starting at Infinity" do
+            attribute = Attribute.new nil, nil
+            node = attribute.not_between(eval("..0")) # eval for backwards compatibility
+
+            node.must_equal Nodes::GreaterThan.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            )
+          end
+        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