Add a NULL test when compiling iterator expressions (#3012)

Otherwise an iterator over a missing pointer could produce output

edb/pgsql/compiler/clauses.py

@@ -26,6 +26,7 @@
 from edb.pgsql import ast as pgast
 from edb.pgsql import types as pg_types
 
+from . import astutils
 from . import context
 from . import dispatch
 from . import output
@@ -215,6 +216,17 @@ def compile_iterator_expr(
             query, iterator_expr.path_id, aspect='value', ctx=ctx)
         iterator_query = iterator_rvar.query
 
+        # If the iterator value is nullable, add a null test. This
+        # makes sure that we don't spuriously produce output when
+        # iterating over options pointers.
+        assert isinstance(iterator_query, pgast.SelectStmt)
+        iterator_var = pathctx.get_path_value_var(
+            iterator_query, path_id=iterator_expr.path_id, env=ctx.env)
+        if iterator_var.nullable:
+            iterator_query.where_clause = astutils.extend_binop(
+                iterator_query.where_clause,
+                pgast.NullTest(arg=iterator_var, negated=True))
+
         # Regardless of result type, we use transient identity,
         # for path identity of the iterator expression.  This is
         # necessary to maintain correct correlation for the state

tests/test_edgeql_select.py

@@ -5475,6 +5475,23 @@ async def test_edgeql_select_for_03(self):
             sort=lambda x: x['number'],
         )
 
+    async def test_edgeql_select_for_04(self):
+        await self.assert_query_result(
+            r'''
+                SELECT Issue {
+                    asdf := (
+                        FOR z IN {.due_date} UNION (1)
+                    )
+                }
+                FILTER .name = 'Release EdgeDB';
+            ''',
+            [
+                {
+                    'asdf': None
+                }
+            ],
+        )
+
     async def test_edgeql_select_json_01(self):
         await self.assert_query_result(
             r'''