drill

2224ee10 - DRILL-7293: Convert the regex ("log") plugin to use EVF

DRILL-7293: Convert the regex ("log") plugin to use EVF Converts the log format plugin (which uses a regex for parsing) to work with the Extended Vector Format. User-visible behavior changes added to the README file. * Use the plugin config object to pass config to the Easy framework. * Use the EVF scan mechanism in place of the legacy "ScanBatch" mechanism. * Minor code and README cleanup. * Replace ad-hoc type conversion with builtin conversions The provided schema support in the enhanced vector framework (EVF) provides automatic conversions from VARCHAR to most types. The log format plugin was created before EVF was available and provided its own conversion mechanism. This commit removes the ad-hoc conversion code and instead uses the log plugin config schema information to create an "output schema" just as if it was provided by the provided schema framework. Because we need the schema in the plugin (rather than the reader), moved the schema-parsing code out of the reader into the plugin. The plugin creates two schemas: an "output schema" with the desired output types, and a "reader schema" that uses only VARCHAR. This causes the EVF to perform conversions. * Enable provided schema support Allows the user to specify types using either the format config (as previously) or a provided schema. If a schema is provided, it will match columns using names specified in the format config. The provided schema can specify both types and modes (nullable or not null.) If a schema is provided, then the types specified in the plugin config are ignored. No attempt is made to merge schemas. If a schema is provided, but a column is omitted from the schema, the type defaults to VARCHAR. * Added ability to specify regex in table properties Allows the user to specify the regex, and the column schema, using a CREATE SCHEMA statement. The README file provides the details. Unit tests demonstrate and verify the functionality. * Used the custom error context provided by EVF to enhance the log format reader error messages. * Added user name to default EVF error context * Added support for table functions Can set the regex and maxErrors fields, but not the schema. Schema will default to "field_0", "field_1", etc. of type VARCHAR. * Added unit tests to verify the functionality. * Added a check, and a test, for a regex with no groups. * Added columns array support When the log regex plugin is given no schema, it previously created a list of columns "field_0", "field_1", etc. After this change, the plugin instead follows the pattern set by the text plugin: it will place all fields into the columns array. (The two special fields are still separate.) A few adjustments were necessary to the columns array framework to allow use of the special columns along with the `columns` column. Modified unit tests and the README to reflect this change. The change should be backward compatible because few users are likely relying on the dummy field names. Added unit tests to verify that schema-based table functions work. A test shows that, due to the unforunate config property name "schema", users of this plugin cannot combine a config table function with the schema attribute in the way promised in DRILL-6965.