fix MySQL enum type lookup with values matching another type. Closes #17402.

The MySQLAdapter type map used the lowest priority for enum types.
This was the result of a recent refactoring and lead to some broken lookups
for enums with values that match other types. Like `8bit`.

This patch restores the priority to what we had before the refactoring.

/cc @sgrif

3 files changed, 17 insertions, 6 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 79dc390f0a..ad4ee0f489 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   MySQL enum type lookups, with values matching another type, no longer result
+    in an endless loop.
+
+    Fixes #17402.
+
+    *Yves Senn*
+
 *   Raise `ArgumentError` when the body of a scope is not callable.
 
     *Mauro George*
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 c5dd93ee89..9077a9cfe3 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -656,12 +656,6 @@ module ActiveRecord
       def initialize_type_map(m) # :nodoc:
         super
 
-        m.register_type(%r(enum)i) do |sql_type|
-          limit = sql_type[/^enum\((.+)\)/i, 1]
-            .split(',').map{|enum| enum.strip.length - 2}.max
-          Type::String.new(limit: limit)
-        end
-
         m.register_type %r(tinytext)i,   Type::Text.new(limit: 2**8 - 1)
         m.register_type %r(tinyblob)i,   Type::Binary.new(limit: 2**8 - 1)
         m.register_type %r(text)i,       Type::Text.new(limit: 2**16 - 1)
@@ -682,6 +676,12 @@ module ActiveRecord
         m.alias_type %r(set)i,           'varchar'
         m.alias_type %r(year)i,          'integer'
         m.alias_type %r(bit)i,           'binary'
+
+        m.register_type(%r(enum)i) do |sql_type|
+          limit = sql_type[/^enum\((.+)\)/i, 1]
+            .split(',').map{|enum| enum.strip.length - 2}.max
+          Type::String.new(limit: limit)
+        end
       end
 
       # MySQL is too stupid to create a temporary table for use subquery, so we have
diff --git a/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb b/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
index d4d67487db..80244d1439 100644
--- a/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
+++ b/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
@@ -22,6 +22,10 @@ module ActiveRecord
         assert_lookup_type :string, "SET('one', 'two', 'three')"
       end
 
+      def test_enum_type_with_value_matching_other_type
+        assert_lookup_type :string, "ENUM('unicode', '8bit', 'none')"
+      end
+
       def test_binary_types
         assert_lookup_type :binary, 'bit'
         assert_lookup_type :binary, 'BIT'