Allow SQL functions in SQL write queries

Closes #2751

docs/authentication.rst

@@ -1425,7 +1425,7 @@ See also :ref:`the default_allow_sql setting <setting_default_allow_sql>`.
 execute-write-sql
 -----------------
 
-Actor is allowed to run arbitrary writable SQL queries against a specific database, subject to table-level write permissions such as ``insert-row``, ``update-row`` and ``delete-row``.
+Actor is allowed to run arbitrary writable SQL queries against a specific database, subject to table-level write permissions such as ``insert-row``, ``update-row`` and ``delete-row``. SQL functions are allowed and are not separately restricted by Datasette permissions.
 
 ``resource`` - ``datasette.resources.DatabaseResource(database)``
     ``database`` is the name of the database (string)

docs/json_api.rst

@@ -531,7 +531,7 @@ The request body must include a ``"sql"`` string. Named SQL parameters can be pr
 
 The SQL must be writable. Read-only ``select`` queries should use the regular :ref:`custom SQL query API <sql>` instead.
 
-Datasette analyzes the SQL before executing it. The actor must have ``execute-write-sql`` permission for the database, and must also have any permissions required by the operations in the SQL. For example, inserts and updates against a table require ``insert-row``, ``update-row`` and ``delete-row`` permissions for that table. Reads performed as part of the write, such as ``insert into dogs select ... from other_table``, require ``view-table`` permission on the source table.
+Datasette analyzes the SQL before executing it. The actor must have ``execute-write-sql`` permission for the database, and must also have any permissions required by the operations in the SQL. For example, inserts and updates against a table require ``insert-row``, ``update-row`` and ``delete-row`` permissions for that table. Reads performed as part of the write, such as ``insert into dogs select ... from other_table``, require ``view-table`` permission on the source table. SQL functions are allowed and are not separately restricted by Datasette permissions.
 
 A successful response includes a message, the SQLite ``rowcount`` and a summary of the operations that were executed:
 

docs/sql_queries.rst

@@ -140,7 +140,7 @@ Datasette stores both configured queries and user-created queries in the ``queri
 
 Stored queries created by users default to private. Private stored queries can only be viewed, updated or deleted by the actor that created them. Broad ``view-query``, ``update-query`` or ``delete-query`` permission grants still do not allow other actors to access another actor's private stored queries.
 
-Stored queries created by users are untrusted. This means they execute using the permissions of the actor who runs them, as if that actor had pasted the SQL into the regular custom SQL interface or write SQL interface. Read-only stored queries require ``execute-sql``. Writable stored queries require ``execute-write-sql`` plus the relevant table-level write permissions.
+Stored queries created by users are untrusted. This means they execute using the permissions of the actor who runs them, as if that actor had pasted the SQL into the regular custom SQL interface or write SQL interface. Read-only stored queries require ``execute-sql``. Writable stored queries require ``execute-write-sql`` plus the relevant table-level write permissions. SQL functions are allowed and are not separately restricted by Datasette permissions.
 
 .. _trusted_stored_queries:
 .. _trusted_saved_queries: