Add test for expression filter pushdown

Author: patricklucas

data/persistent/expression_filter/data/00000-0-1406cdaa-c3e4-4e6d-a22b-d85e4a813169-00001.parquet

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+{"format-version":2,"table-uuid":"d6293bed-4757-4504-9342-f69a447b7759","location":"data/persistent/expression_filter","last-sequence-number":0,"last-updated-ms":1757676428493,"last-column-id":2,"current-schema-id":0,"schemas":[{"type":"struct","schema-id":0,"fields":[{"id":1,"name":"id","required":true,"type":"long"},{"id":2,"name":"value","required":false,"type":"string"}]}],"default-spec-id":0,"partition-specs":[{"spec-id":0,"fields":[]}],"last-partition-id":999,"default-sort-order-id":0,"sort-orders":[{"order-id":0,"fields":[]}],"properties":{"write.parquet.compression-codec":"zstd"},"current-snapshot-id":-1,"refs":{},"snapshots":[],"statistics":[],"partition-statistics":[],"snapshot-log":[],"metadata-log":[]}

data/persistent/expression_filter/metadata/00000-acdf842e-3a9d-4b9b-ad87-daf78583a550.metadata.json

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+{"format-version":2,"table-uuid":"d6293bed-4757-4504-9342-f69a447b7759","location":"data/persistent/expression_filter","last-sequence-number":1,"last-updated-ms":1757676429141,"last-column-id":2,"current-schema-id":0,"schemas":[{"type":"struct","schema-id":0,"fields":[{"id":1,"name":"id","required":true,"type":"long"},{"id":2,"name":"value","required":false,"type":"string"}]}],"default-spec-id":0,"partition-specs":[{"spec-id":0,"fields":[]}],"last-partition-id":999,"default-sort-order-id":0,"sort-orders":[{"order-id":0,"fields":[]}],"properties":{"write.parquet.compression-codec":"zstd"},"current-snapshot-id":8096310958539014181,"refs":{"main":{"snapshot-id":8096310958539014181,"type":"branch"}},"snapshots":[{"sequence-number":1,"snapshot-id":8096310958539014181,"timestamp-ms":1757676429141,"summary":{"operation":"append","added-data-files":"1","added-records":"3","added-files-size":"705","changed-partition-count":"1","total-records":"3","total-files-size":"705","total-data-files":"1","total-delete-files":"0","total-position-deletes":"0","total-equality-deletes":"0","iceberg-version":"Apache Iceberg 1.9.2 (commit 071d5606bc6199a0be9b3f274ec7fbf111d88821)"},"manifest-list":"data/persistent/expression_filter/metadata/snap-8096310958539014181-1-8d30f58e-7333-4451-983d-eaf657a21a11.avro","schema-id":0}],"statistics":[],"partition-statistics":[],"snapshot-log":[{"timestamp-ms":1757676429141,"snapshot-id":8096310958539014181}],"metadata-log":[{"timestamp-ms":1757676428493,"metadata-file":"data/persistent/expression_filter/metadata/00000-acdf842e-3a9d-4b9b-ad87-daf78583a550.metadata.json"}]}

data/persistent/expression_filter/metadata/00001-19739cda-f528-4429-84cc-377ffdd24c75.metadata.json

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+00001-19739cda-f528-4429-84cc-377ffdd24c75

data/persistent/expression_filter/metadata/8d30f58e-7333-4451-983d-eaf657a21a11-m0.avro

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+# name: test/sql/local/iceberg_scans/expression_filter.test
+# group: [iceberg_scans]
+
+require-env DUCKDB_ICEBERG_HAVE_GENERATED_DATA
+
+require avro
+
+require parquet
+
+require iceberg
+
+statement ok
+attach ':memory:' as my_datalake;
+
+statement ok
+create schema my_datalake.default;
+
+statement ok
+create view my_datalake.default.expression_filter as select * from ICEBERG_SCAN('__WORKING_DIRECTORY__/data/persistent/expression_filter');
+
+# baseline: select all rows
+query II
+SELECT * FROM my_datalake.default.expression_filter ORDER BY id ASC;
+----
+1	foo
+2	bar
+3	baz
+
+# CASE expression should not exclude any data files (prior to #464, IS NULL on CASE expression column resulted in exclusion)
+query II
+SELECT id, CASE WHEN value = 'foo' THEN 'not null' ELSE NULL END AS role FROM my_datalake.default.expression_filter WHERE role IS NULL ORDER BY id ASC;
+----
+2	NULL
+3	NULL
+
+# Complement to previous query
+query II
+SELECT id, CASE WHEN value = 'foo' THEN 'not null' ELSE NULL END AS role FROM my_datalake.default.expression_filter WHERE role IS NOT NULL ORDER BY id ASC;
+----
+1	not null