fix: change AggregateFunctionConverter to accept Calcite function ins…

…tances

isthmus/src/main/java/io/substrait/isthmus/expression/AggregateFunctionConverter.java

@@ -6,6 +6,7 @@
 import io.substrait.expression.ExpressionCreator;
 import io.substrait.expression.FunctionArg;
 import io.substrait.extension.SimpleExtension;
+import io.substrait.isthmus.AggregateFunctions;
 import io.substrait.isthmus.SubstraitRelVisitor;
 import io.substrait.isthmus.TypeConverter;
 import io.substrait.type.Type;
@@ -21,7 +22,12 @@
 import org.apache.calcite.rex.RexBuilder;
 import org.apache.calcite.rex.RexNode;
 import org.apache.calcite.sql.SqlAggFunction;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.fun.SqlAvgAggFunction;
+import org.apache.calcite.sql.fun.SqlMinMaxAggFunction;
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
+import org.apache.calcite.sql.fun.SqlSumAggFunction;
+import org.apache.calcite.sql.fun.SqlSumEmptyIsZeroAggFunction;
 
 public class AggregateFunctionConverter
     extends FunctionConverter<
@@ -86,6 +92,20 @@ public Optional<AggregateFunctionInvocation> convert(
     if (aggFunction == SqlStdOperatorTable.COUNT && call.isDistinct() && call.isApproximate()) {
       aggFunction = SqlStdOperatorTable.APPROX_COUNT_DISTINCT;
     }
+
+    // Substrait has replaced those function classes with their own counterparts (which are
+    // subclasses of the Calcite ones), but some Calcite rules might still use the original
+    // functions during optimization (for example, at AggregateExpandDistinctAggregatesRule)
+    if (aggFunction instanceof SqlSumEmptyIsZeroAggFunction) {
+      aggFunction = AggregateFunctions.SUM0;
+    } else if (aggFunction instanceof SqlMinMaxAggFunction fun) {
+      aggFunction = fun.getKind() == SqlKind.MIN ? AggregateFunctions.MIN : AggregateFunctions.MAX;
+    } else if (aggFunction instanceof SqlAvgAggFunction) {
+      aggFunction = AggregateFunctions.AVG;
+    } else if (aggFunction instanceof SqlSumAggFunction) {
+      aggFunction = AggregateFunctions.SUM;
+    }
+
     FunctionFinder m = signatures.get(aggFunction);
     if (m == null) {
       return Optional.empty();