config, db: support db_url setting to override the individual options

docs/source/configuration.rst

@@ -528,6 +528,13 @@ type of database, set :attr:`~CoreSection.db_type` to one of these values:
 * ``firebird``
 * ``sybase``
 
+.. note::
+
+    In certain environments, specifying the :attr:`~CoreSection.db_url`
+    setting via :ref:`environment variable <Overriding individual settings>`
+    may be more convenient. Doing so will supersede all of the other options
+    described in this section.
+
 SQLite
 ------
 

sopel/config/core_section.py

@@ -373,6 +373,23 @@ class CoreSection(StaticSection):
 
     """
 
+    db_url = ValidatedAttribute('db_url')
+    """A raw database URL.
+
+    If this option is present, Sopel will ignore **all** other ``db_*``
+    settings and use this option's value only.
+
+    .. note::
+
+        Specifying this option via the ``SOPEL_CORE_DB_URL`` :ref:`environment
+        variable <Overriding individual settings>` may prove especially useful
+        in certain cloud environments, avoiding the need to split a database
+        URI provided by the platform at runtime into its components with a
+        startup script.
+
+    .. versionadded:: 8.0
+    """
+
     db_user = ValidatedAttribute('db_user')
     """The user for Sopel's database.
 

sopel/db.py

@@ -9,7 +9,7 @@
 import traceback
 
 from sqlalchemy import Column, create_engine, ForeignKey, Integer, String
-from sqlalchemy.engine.url import URL
+from sqlalchemy.engine.url import make_url, URL
 from sqlalchemy.exc import OperationalError, SQLAlchemyError
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import scoped_session, sessionmaker
@@ -112,12 +112,17 @@ class SopelDB(object):
     """
 
     def __init__(self, config):
-        # MySQL - mysql://username:password@localhost/db
-        # SQLite - sqlite:////home/sopel/.sopel/default.db
-        self.type = config.core.db_type
-
-        # Handle SQLite explicitly as a default
-        if self.type == 'sqlite':
+        if config.core.db_url is not None:
+            self.url = make_url(config.core.db_url)
+
+            # TODO: there's no way to get `config.core.db_type.choices`, but
+            # it would be nice to validate this type name somehow. Shouldn't
+            # affect anything, since the only thing it's ever used for is
+            # checking whether the configured database is 'sqlite'.
+            self.type = self.url.drivername.split('+', 1)[0]
+        elif config.core.db_type == 'sqlite':
+            self.type = 'sqlite'
+            drivername = config.core.db_driver or 'sqlite'
             path = config.core.db_filename
             if path is None:
                 path = os.path.join(config.core.homedir, config.basename + '.db')
@@ -132,10 +137,10 @@ def __init__(self, config):
                     'core.db_filename is valid'.format(os.path.dirname(path)),
                     path
                 )
-            self.filename = path
-            self.url = 'sqlite:///%s' % path
-        # Otherwise, handle all other database engines
+            self.url = make_url('sqlite:///' + path)
         else:
+            self.type = config.core.db_type
+
             query = {}
             if self.type == 'mysql':
                 drivername = config.core.db_driver or 'mysql'
@@ -153,11 +158,11 @@ def __init__(self, config):
             else:
                 raise Exception('Unknown db_type')
 
-            db_user = config.core.db_user
-            db_pass = config.core.db_pass
-            db_host = config.core.db_host
+            db_user = config.core.db_user  # Sometimes empty
+            db_pass = config.core.db_pass  # Sometimes empty
+            db_host = config.core.db_host  # Sometimes empty
             db_port = config.core.db_port  # Optional
-            db_name = config.core.db_name  # Optional, depending on DB
+            db_name = config.core.db_name  # Sometimes optional
 
             # Ensure we have all our variables defined
             if db_user is None or db_pass is None or db_host is None: