DRILL-7377: Nested schemas for dynamic EVF columns The Result Set Loader (part of EVF) allows adding columns up-front before reading rows (s…
DRILL-7377: Nested schemas for dynamic EVF columnsThe Result Set Loader (part of EVF) allows adding columns up-frontbefore reading rows (so-called "early schema.") Such schemas allownested columns (maps with members, repeated lists with a type, etc.)The Result Set Loader also allows adding columns dynamicallywhile loading data (so-called "late schema".) Previously, the codeassumed that columns would be added top-down: first the map, thenthe map's contents, etc.Charles found a need to allow adding a nested column (a repeatedlist with a declared list type.)This patch revises the code to use the same mechanism in both theearly- and late-schema cases, allowing adding nested columns atany time.Testing: Added a new unit test case for the repeated list lateschema with content case.