sqlite3: exception from a collation callback is replaced by SystemError #161837

Bug report

Summary

When a collation callback raises, sqlite3 returns 0 to SQLite and leaves the exception pending. SQLite keeps evaluating the row, and a later failure in the same step (here abs() of the smallest 64-bit integer, an integer overflow) makes sqlite3 build its own OperationalError with the collation's exception still set. The interpreter reports this as a SystemError, and the original exception is lost.

Expected: the collation's exception should propagate, or at least chain as the cause.

Reproducer

import sqlite3

def coll(a, b):
    if a == "boom":
        raise KeyError("collation raised")
    return (a > b) - (a < b)

con = sqlite3.connect(":memory:")
con.create_collation("c", coll)
con.execute("create table t(x, y)")
con.executemany("insert into t values (?, ?)",
                [(1, "a"), (-9223372036854775808, "boom")])
cur = con.execute("select case when y = 'q' collate c then abs(x) else 0 end from t")
cur.fetchone()

KeyError: 'collation raised'

The above exception was the direct cause of the following exception:

SystemError: <class 'sqlite3.OperationalError'> returned a result with an exception set

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-161837: Fix crashes in sqlite3 when a collation callback raises #161845