Do not set DATABASE_URL if scheme is unknown (heroku#1715)

* Add support for `trilogy` adapter

When using the trilogy gem if you fail to supply a `DATABASE_URL` env variable you'll get an invalid database URL with no scheme. I figure that adding this in the Rails3 class is OK rather than duplicate this in Rails7 or add a Rails71 for it.

* Do not set DATABASE_URL if scheme is unknown

Reported in heroku#1714 when using a database adapter such as `trilogy`, the application will fail to boot because an invalid DATABASE_URL is constructed (because the `trilogy` adapter is unknown):

```
    remote: ensure you can run `$ bundle exec rake -P` against your app
       remote: and using the production group of your Gemfile.
       remote: rake aborted!
       remote: URI::InvalidURIError: bad URI (is not URI?): ://user:pass@127.0.0.1/dbname (URI::InvalidURIError)
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/uri-1.1.1/lib/uri/rfc2396_parser.rb:176:in `split'
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/uri-1.1.1/lib/uri/rfc2396_parser.rb:209:in `parse'
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/activerecord-8.1.2/lib/active_record/database_configurations/connection_url_resolver.rb:27:in `initialize'
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/activerecord-8.1.2/lib/active_record/database_configurations/url_config.rb:83:in `new'
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/activerecord-8.1.2/lib/active_record/database_configurations/url_config.rb:83:in `build_url_hash'
       remote: /tmp/build_b50909c5/vendor/bundle/ruby/3.3.0/gems/activerecord-8.1.2/lib/active_record/database_configurations/url_config.rb:44:in `initialize'
```

Rather than keeping track of all possible adapters we can guard against this case with Rails 4.1+ applications by having customers check in a `config/database.yml` https://devcenter.heroku.com/articles/rails-database-connection-behavior.

---------

Co-authored-by: Danny Fallon <danny.fallon.ie+github@gmail.com>

Author: schneems

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Fix bug where an invalid DATABASE_URL is set when the adapter is not known (https://github.com/heroku/heroku-buildpack-ruby/pull/1715).
 
 ## [v347] - 2026-02-02
 

hatchet.json

@@ -26,7 +26,8 @@
     "sharpstone/rails61",
     "sharpstone/rails-jsbundling",
     "sharpstone/rails_8_ruby_schema",
-    "sharpstone/rails_8_sql_schema"
+    "sharpstone/rails_8_sql_schema",
+    "sharpstone/rails_8_1_trilogy_db_minimal"
   ],
   "heroku": [
     "heroku/ruby-getting-started"

hatchet.lock

@@ -23,6 +23,8 @@
   - fbdaf031823f09d1514ec1d55dcb04ca2f4264ca
 - - "./repos/rails_versions/rails61"
   - 47828a3e8c79b7869ca0d9a3afa4be065fa46e96
+- - "./repos/rails_versions/rails_8_1_trilogy_db_minimal"
+  - 3a4ac8b53c68c504b980c4403f6b27b5cf57dd4b
 - - "./repos/rails_versions/rails_8_ruby_schema"
   - a993a3f00c8e09f733bc3b783f7e37148d0af1d4
 - - "./repos/rails_versions/rails_8_sql_schema"

lib/language_pack/rails3.rb

@@ -199,6 +199,9 @@ def database_url
       elsif bundler.has_gem?("sqlite3") || bundler.has_gem?("sqlite3-ruby")
         "sqlite3"
       end
-    "#{scheme}://user:pass@127.0.0.1/dbname"
+
+    if scheme
+      "#{scheme}://user:pass@127.0.0.1/dbname"
+    end
   end
 end

spec/hatchet/bugs_spec.rb

@@ -24,6 +24,14 @@
         end
       end
     end
+
+    it "does not generate an incorrect DATABASE_URL if adapter is not known" do
+      Hatchet::Runner.new("rails_8_1_trilogy_db_minimal").tap do |app|
+        app.deploy do
+          # Works
+        end
+      end
+    end
   end
 
   it "detect fails when no Gemfile is present" do