Add the `block_on`/`block_on_result`/`block_on_next` helpers the Postgres
backend uses to drive its async `tokio-postgres` futures to completion from
sync, GIL-holding Python methods, releasing the GIL for the wait. They take
a `tokio::runtime::Handle` and block on it from the calling (Python) thread.
Rather than give the DB backend a runtime of its own, they use the
extension's existing shared runtime (`tokio_runtime::PyTokioRuntime`, stored
on the reactor). `start` is made idempotent and a `runtime_handle` accessor
starts it on demand, so a caller that needs a connection before the reactor
is running still gets a handle; once the reactor runs, its
`callWhenRunning(start)` hook is a no-op.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RPEeXx2fAG67o6u4CnmC8W
Introduce the Python<->Postgres value-mapping layer that the forthcoming
Rust DBAPI2 backend will build on, plus the module scaffolding to hang it
off (`synapse_rust.database.postgres`).
`PgValue` is an owned representation of a bound parameter that implements
`tokio_postgres::types::ToSql`, encoding into Postgres' binary wire format
according to the column type from the prepared statement (so a single
Python `int` becomes INT2/INT4/INT8 as appropriate, with range checks).
`PythonPgFromSql` is the decode counterpart, turning a column's wire bytes
back into the natural Python object (and SQL NULL into `None`). The two
`accepts` lists are kept in sync via tests.
The `value` submodule is exposed as `pub` for now so its
not-yet-consumed public items don't trip clippy's `dead_code` lint; later
changes that wire it into the cursor/connection code tighten that back up.
Covers int / float / bool / str / bytes / None; lists and richer types
(json, decimal, timestamps) are left to a follow-up.
The unit tests exercise the whole mapping without a live Postgres server,
including the float4 lossy narrowing, integer width boundaries, the
WrongType and out-of-range paths, and the unsupported/non-UTF-8 decode
errors.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Erik Johnston