Handle missing environment from non empty config

If using a `DATABASE_URL` and a `database.yml`. The connection information in `DATABASE_URL` should be merged into whatever environment we are in. As released in 4.1.0rc1 if someone has a database.yml but is missing a key like production:

```yml
development:
  host: localhost

```

Then the check for blank config will return false so the information from the `DATABASE_URL` will not be used when attempting to connect to the `production` database and the connection will incorrectly fail.

This commit fixes this problem and adds a test for the behavior.

In addition the ability to specify a connection url in a `database.yml` like this:

```
production: postgres://localhost/foo
```

Was introduced in 4.1.0rc1 though should not be used, instead using a url sub key

```
production:
  url: postgres://localhost/foo
```

This url sub key was also introduced in 4.1.0rc1 though the `production: postgres://localhost/foo` was not removed. As a result we should not test this behavior.

1 files changed, 5 insertions, 9 deletions

diff --git a/activerecord/lib/active_record/connection_handling.rb b/activerecord/lib/active_record/connection_handling.rb
index 11f6a47158..4ba4e09777 100644
--- a/activerecord/lib/active_record/connection_handling.rb
+++ b/activerecord/lib/active_record/connection_handling.rb
@@ -93,16 +93,12 @@ module ActiveRecord
         # the connection URL. This hash responds to any string key with
         # resolved connection information.
         def default_url_hash
-          if @raw_config.blank?
-            Hash.new do |hash, key|
-              hash[key] = if key.is_a? String
-                 ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(@url).to_hash
-              else
-                nil
-              end
+          Hash.new do |hash, key|
+            hash[key] = if key.is_a? String
+               ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(@url).to_hash
+            else
+              nil
             end
-          else
-            {}
           end
         end
     end