IntelliJ and Gradle

[Julian Hyde]

After our migration to gradle, IntelliJ frequently fails to correctly load a 
project.

For example, I just switched to the amaliujia/rw-add_TVF_TUMBLE branch and 
opened SqlToRelConverterTest. The file starts with the following:

import org.apache.calcite.config.CalciteConnectionConfigImpl;
import org.apache.calcite.config.CalciteConnectionProperty;
import org.apache.calcite.config.NullCollation;
import org.apache.calcite.plan.Contexts;
import org.apache.calcite.plan.RelOptPlanner;
import org.apache.calcite.plan.RelOptUtil;
import org.apache.calcite.plan.RelTrait;
import org.apache.calcite.plan.RelTraitDef;
import org.apache.calcite.plan.RelTraitSet;
import org.apache.calcite.rel.RelCollationTraitDef;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.RelRoot;

Of these lines, lines 1, 2, 6, 7, 11, 12 are red, meaning IntelliJ cannot find 
the class definitions.

Is anyone else experiencing this flakiness? It is intensely frustrating.

Julian