feat(isthmus): true, false, distinct comparator scalar fn mappings

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

@@ -78,7 +78,12 @@ public class FunctionMappings {
               s(SqlStdOperatorTable.BITXOR, "bitwise_xor"),
               s(SqlStdOperatorTable.RADIANS, "radians"),
               s(SqlStdOperatorTable.DEGREES, "degrees"),
-              s(SqlLibraryOperators.FACTORIAL, "factorial"))
+              s(SqlLibraryOperators.FACTORIAL, "factorial"),
+              s(SqlStdOperatorTable.IS_TRUE, "is_true"),
+              s(SqlStdOperatorTable.IS_FALSE, "is_false"),
+              s(SqlStdOperatorTable.IS_NOT_TRUE, "is_not_true"),
+              s(SqlStdOperatorTable.IS_NOT_FALSE, "is_not_false"),
+              s(SqlStdOperatorTable.IS_DISTINCT_FROM, "is_distinct_from"))
           .build();
 
   public static final ImmutableList<Sig> AGGREGATE_SIGS =

isthmus/src/test/java/io/substrait/isthmus/ComparisonFunctionsTest.java

@@ -0,0 +1,49 @@
+package io.substrait.isthmus;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+public class ComparisonFunctionsTest extends PlanTestBase {
+  static String CREATES =
+      "CREATE TABLE numbers (int_a INT, int_b INT, double_a DOUBLE, double_b DOUBLE)";
+
+  @Test
+  void is_true() throws Exception {
+    String query = "SELECT ((int_a > int_b) IS TRUE) FROM numbers";
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+
+  @Test
+  void is_false() throws Exception {
+    String query = "SELECT ((int_a > int_b) IS FALSE) FROM numbers";
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+
+  @Test
+  void is_not_true() throws Exception {
+    String query = "SELECT ((int_a > int_b) IS NOT TRUE) FROM numbers";
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+
+  @Test
+  void is_not_false() throws Exception {
+    String query = "SELECT ((int_a > int_b) IS NOT FALSE) FROM numbers";
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+
+  @ParameterizedTest
+  @CsvSource({"int_a, int_b", "int_b, int_a", "double_a, double_b", "double_b, double_a"})
+  void is_distinct_from(String left, String right) throws Exception {
+    String query = String.format("SELECT (%s IS DISTINCT FROM %s) FROM numbers", left, right);
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+
+  @ParameterizedTest
+  @ValueSource(strings = {"int_a", "int_b", "double_a", "double_b"})
+  void is_distinct_from_null_vs_col(String column) throws Exception {
+    String query = String.format("SELECT (NULL IS DISTINCT FROM %s) FROM numbers", column);
+    assertSqlSubstraitRelRoundTrip(query, CREATES);
+  }
+}