chore: implement deleting custom roles (#14101)

* chore: implement deleting custom roles

* add trigger to delete role from organization members on delete
* chore: add comments to explain populated field

coderd/database/migrations/000241_delete_user_roles.down.sql

@@ -0,0 +1,2 @@
+DROP TRIGGER IF EXISTS remove_organization_member_custom_role ON custom_roles;
+DROP FUNCTION IF EXISTS remove_organization_member_role;

coderd/database/migrations/000241_delete_user_roles.up.sql

@@ -0,0 +1,35 @@
+-- When a custom role is deleted, we need to remove the assigned role
+-- from all organization members that have it.
+-- This action cannot be reverted, so deleting a custom role should be
+-- done with caution.
+CREATE OR REPLACE FUNCTION remove_organization_member_role()
+	RETURNS TRIGGER AS
+$$
+BEGIN
+	-- Delete the role from all organization members that have it.
+	-- TODO: When site wide custom roles are supported, if the
+	--	organization_id is null, we should remove the role from the 'users'
+	--	table instead.
+	IF OLD.organization_id IS NOT NULL THEN
+		UPDATE organization_members
+		-- this is a noop if the role is not assigned to the member
+		SET roles = array_remove(roles, OLD.name)
+		WHERE
+			-- Scope to the correct organization
+			organization_members.organization_id = OLD.organization_id;
+	END IF;
+	RETURN OLD;
+END;
+$$ LANGUAGE plpgsql;
+
+
+-- Attach the function to deleting the custom role
+CREATE TRIGGER remove_organization_member_custom_role
+	BEFORE DELETE ON custom_roles FOR EACH ROW
+	EXECUTE PROCEDURE remove_organization_member_role();
+
+
+COMMENT ON TRIGGER
+	remove_organization_member_custom_role
+	ON custom_roles IS
+		'When a custom_role is deleted, this trigger removes the role from all organization members.';