Clarify database.yml DATABASE_URL instructions

From the instructions in database.yml, it is not clear that Rails will
automatically use ENV['DATABASE_URL'] if it is present.

This commit rewords the instructions to clarify that Rails will do so.

railties/lib/rails/generators/rails/app/templates/config/databases/frontbase.yml.tt

@@ -28,20 +28,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="frontbase://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/ibm_db.yml.tt

@@ -64,20 +64,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="ibm-db://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/jdbc.yml.tt

@@ -58,10 +58,9 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
+# Instead, provide the password as an environment variable when you boot the
+# app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   url: jdbc:db://localhost/<%= app_name %>_production

railties/lib/rails/generators/rails/app/templates/config/databases/jdbcmysql.yml.tt

@@ -31,20 +31,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="mysql://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/jdbcpostgresql.yml.tt

@@ -47,20 +47,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="postgres://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/mysql.yml.tt

@@ -36,20 +36,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/oracle.yml.tt

@@ -37,22 +37,23 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="oracle-enhanced://myuser:mypass@localhost/somedatabase"
 #
-# Note that the adapter name uses a dash instead of an underscore.
+# (Note that the adapter name uses a dash instead of an underscore.)
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml.tt

@@ -63,20 +63,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="postgres://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/sqlserver.yml.tt

@@ -30,20 +30,21 @@ test:
 # like your database password, in your source code. If your source code is
 # ever seen by anyone, they now have access to your database.
 #
-# Instead, provide the password as a unix environment variable when you boot
-# the app. Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
-# for a full rundown on how to provide these environment variables in a
-# production deployment.
-#
-# On Heroku and other platform providers, you may have a full connection URL
-# available as an environment variable. For example:
+# Instead, provide the password or a full connection URL as an environment
+# variable when you boot the app. For example:
 #
 #   DATABASE_URL="sqlserver://myuser:mypass@localhost/somedatabase"
 #
-# You can use this database configuration with:
+# If the connection URL is provided in the special DATABASE_URL environment
+# variable, Rails will automatically merge its configuration values on top of
+# the values provided in this file. Alternatively, you can specify a connection
+# URL environment variable explicitly:
 #
 #   production:
-#     url: <%%= ENV['DATABASE_URL'] %>
+#     url: <%%= ENV['MY_APP_DATABASE_URL'] %>
+#
+# Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# for a full overview on how database connection configuration can be specified.
 #
 production:
   <<: *default