Precompile SQL as PRQL

[aljazerzen]

Proof of concept of PRQL support in EdgeDB.

Compiles prqlc from source via cargo and provides a cpython extension module edb._prql. Alternatively, we could use prql-python package from PyPi, which comes with prqlc precompiled, but this limits supported architectures and has a restricted API.

➜  edgedb git:(prql-sql) ✗ edb cli
EdgeDB 4.0-dev.7779+local (repl 3.5.0-dev)
Applied /home/aljaz/.config/edgedb/cli.toml configuration file
Type \help for help, \quit to quit.
edgedb> insert Post { title := 'hello world' };
edgedb> configure current database set allow_bare_ddl := 'AlwaysAllow';
OK: CONFIGURE DATABASE
edgedb> create type Movie {
....... create property title: str;
....... create property release_year: int32;
....... };
OK: CREATE TYPE
edgedb> insert Movie { title := "Hello world", release_year := 2014 };
{Object {id: 24f1c89e-5092-11ee-aad6-73d5cf1de13c}}
edgedb> insert Movie { title := "Hell over the world", release_year := 2020 };
{Object {id: 2c44ed92-5092-11ee-aad6-d7c93fe6cb80}}
edgedb>
➜  edgedb git:(prql-sql) ✗ psql -h localhost -p 5656 -U edgedb -d edgedb
psql (14.8, server 13.9)
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

edgedb=# from Movie | select {id, title, release_year} #;
                  id                  |        title        | release_year
--------------------------------------+---------------------+--------------
 24f1c89e-5092-11ee-aad6-73d5cf1de13c | Hello world         |         2014
 2c44ed92-5092-11ee-aad6-d7c93fe6cb80 | Hell over the world |         2020
(2 rows)

edgedb=#

(psql is looking for ; to issue the query, but ; is invalid PRQL. As a workaround, one can end queries with a comment #;)

TODO:

• some kind of switch to enable PRQL compiler (currently all queries over the pgsql wire protocol are treated as PRQL)
• figure out why the edb._prql cpython extension is 256MB, instead of, say, 23MB (which is the size of edb._edgeql_parser). It's probably just the debug symbols because --release build of the cli is 17MB.
• error handling - right now, error messages are converted to JSON and thrown as ValueError, which should be caught and converted into edb.errors.Error

Possible improvements:

• for better UX, edgedb could generate table definitions, so prqlc would have the information about what columns exist and what are their types. This would allow it to fail early, before passing SQL to Posrgres, which reports errors within the generated SQL, not PRQL source.