Revert to 4.1 behavior for casting PG arrays

The user is able to pass PG string literals in 4.1, and have it
converted to an array. This is also possible in 4.2, but it would remain
in string form until saving and reloading, which breaks our
`attr = save.reload.attr` contract. I think we should deprecate this in
5.0, and only allow array input from user sources. However, this
currently constitutes a breaking change to public API that did not go
through a deprecation cycle.

2 files changed, 23 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
index cd5efe2bb8..c203e6c604 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
@@ -34,6 +34,9 @@ module ActiveRecord
           end
 
           def type_cast_from_user(value)
+            if value.is_a?(::String)
+              value = parse_pg_array(value)
+            end
             type_cast_array(value, :type_cast_from_user)
           end
 
diff --git a/activerecord/test/cases/adapters/postgresql/array_test.rb b/activerecord/test/cases/adapters/postgresql/array_test.rb
index db302b6294..042beab23f 100644
--- a/activerecord/test/cases/adapters/postgresql/array_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/array_test.rb
@@ -264,11 +264,26 @@ class PostgresqlArrayTest < ActiveRecord::TestCase
 
   def test_assigning_non_array_value
     record = PgArray.new(tags: "not-an-array")
-    assert_equal "not-an-array", record.tags
-    e = assert_raises(ActiveRecord::StatementInvalid) do
-      record.save!
-    end
-    assert_instance_of PG::InvalidTextRepresentation, e.original_exception
+    assert_equal [], record.tags
+    assert_equal "not-an-array", record.tags_before_type_cast
+    assert record.save
+    assert_equal record.tags, record.reload.tags
+  end
+
+  def test_assigning_empty_string
+    record = PgArray.new(tags: "")
+    assert_equal [], record.tags
+    assert_equal "", record.tags_before_type_cast
+    assert record.save
+    assert_equal record.tags, record.reload.tags
+  end
+
+  def test_assigning_valid_pg_array_literal
+    record = PgArray.new(tags: "{1,2,3}")
+    assert_equal ["1", "2", "3"], record.tags
+    assert_equal "{1,2,3}", record.tags_before_type_cast
+    assert record.save
+    assert_equal record.tags, record.reload.tags
   end
 
   def test_uniqueness_validation