Fix issues with empty sets leaking out of optional scopes

For the previous issues, see #5575 and #6526.

The issue here is that in queries like
```
select User filter .avatar ?= <Card>{} and .name = 'Bob'
```
we were returning an empty set, since we were deciding that the
optional wraper we grabbed `.avatar` in was also a reasonable source
for User itself. We have machinery to prevent that (introduced in
the mask of the statement that was a "tentative container" for the
relation, but in this case, that container statement was not being
used, so the masks had no effect.

Instead, set up the masks on the final main rvar before including it.

Fixes #6739.

edb/pgsql/compiler/relctx.py

@@ -792,9 +792,18 @@ def update_scope(
         assert p.path_id is not None
         ctx.path_scope[p.path_id] = stmt
 
+
+def update_scope_masks(
+        ir_set: irast.Set, rvar: pgast.PathRangeVar, *,
+        ctx: context.CompilerContextLevel) -> None:
+
+    if not isinstance(rvar, pgast.RangeSubselect):
+        return
+    stmt = rvar.subquery
+
     # Mark any paths under the scope tree as masked, so that they
     # won't get picked up by pull_path_namespace.
-    for child_path in scope_tree.get_all_paths():
+    for child_path in ctx.scope_tree.get_all_paths():
         pathctx.put_path_id_mask(stmt, child_path)
 
     # If this is an optional scope node, we need to be certain that
@@ -807,11 +816,11 @@ def update_scope(
     # with some DML linkprop cases (probably easy to fix) and a number
     # of materialization cases (possibly hard to fix), so I'm going
     # with a more conservative approach.
-    if scope_tree.is_optional(ir_set.path_id):
+    if ctx.scope_tree.is_optional(ir_set.path_id):
         # Since compilation is done, anything visible to us *will* be
         # up on the spine. Anything tucked away under a node must have
         # been pulled up.
-        for anc in scope_tree.ancestors:
+        for anc in ctx.scope_tree.ancestors:
             for direct_child in anc.path_children:
                 if not direct_child.optional:
                     pathctx.put_path_id_mask(stmt, direct_child.path_id)

edb/pgsql/compiler/relgen.py

@@ -240,6 +240,7 @@ def get_set_rvar(
                 null_query, (pgast.SelectStmt, pgast.NullRelation))
             null_query.where_clause = pgast.BooleanConstant(val=False)
 
+        relctx.update_scope_masks(ir_set, rvars.main.rvar, ctx=subctx)
         result_rvar = _include_rvars(rvars, scope_stmt=scope_stmt, ctx=subctx)
         for aspect in rvars.main.aspects:
             pathctx.put_path_rvar_if_not_exists(

tests/test_edgeql_scope.py

@@ -4112,3 +4112,22 @@ async def test_edgeql_scope_linkprop_assert_03(self):
                 }
             ],
         )
+
+    async def test_edgeql_scope_filter_qeq_01(self):
+        await self.assert_query_result(
+            r'''
+            select User filter .avatar ?= <Card>{} and .name = 'Bob';
+            ''',
+            [
+                {},
+            ],
+        )
+
+        await self.assert_query_result(
+            r'''
+            select User filter .name = 'Bob' and .avatar ?= <Card>{}
+            ''',
+            [
+                {},
+            ],
+        )