SQL: Enchance output of explain for optimized plan

x-pack/plugin/sql/qa/single-node/src/test/java/org/elasticsearch/xpack/sql/qa/single_node/CliExplainIT.java

@@ -160,4 +160,22 @@ public void testExplainWithCount() throws IOException {
         assertThat(readLine(), startsWith("}]"));
         assertEquals("", readLine());
     }
+
+    public void testOptimizedPlanWithFoldableLiteralExpressions() throws IOException {
+        index("test", body -> body.field("test_field", "test_value1").field("i", 1));
+        index("test", body -> body.field("test_field", "test_value2").field("i", 2));
+
+        assertThat(command("EXPLAIN (PLAN OPTIMIZED) SELECT POWER(i, (1 + 2)) FROM test"), containsString("plan"));
+        assertThat(readLine(), startsWith("----------"));
+        assertEquals("Project[[POWER(i,3)]]", readLine().replaceAll("#\\d+", ""));
+        assertThat(readLine(), startsWith("\\_EsRelation[test][i{f}"));
+        assertEquals("", readLine());
+
+        assertThat(command("EXPLAIN (PLAN OPTIMIZED) SELECT POWER(i, (1 - 2)) * ABS(10 + 20) FROM test"),
+            containsString("plan"));
+        assertThat(readLine(), startsWith("----------"));
+        assertEquals("Project[[MUL(POWER(i,-1),30)]]", readLine().replaceAll("#\\d+", ""));
+        assertThat(readLine(), startsWith("\\_EsRelation[test][i{f}#"));
+        assertEquals("", readLine());
+    }
 }

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/function/Function.java

@@ -8,11 +8,13 @@
 import org.elasticsearch.xpack.sql.expression.Expression;
 import org.elasticsearch.xpack.sql.expression.ExpressionId;
 import org.elasticsearch.xpack.sql.expression.Expressions;
+import org.elasticsearch.xpack.sql.expression.Literal;
 import org.elasticsearch.xpack.sql.expression.NamedExpression;
 import org.elasticsearch.xpack.sql.tree.Location;
 import org.elasticsearch.xpack.sql.util.StringUtils;
 
 import java.util.List;
+import java.util.Objects;
 import java.util.StringJoiner;
 
 /**
@@ -51,7 +53,7 @@ public boolean nullable() {
 
     @Override
     public String toString() {
-        return name() + "#" + id();
+        return functionName + functionArgsForToString() + "#" + id();
     }
 
     public String functionName() {
@@ -75,4 +77,31 @@ protected String functionArgs() {
     public boolean functionEquals(Function f) {
         return f != null && getClass() == f.getClass() && arguments().equals(f.arguments());
     }
+
+    /**
+     * Build the string representation of the function arguments for the {@link #toString()}.
+     *  - If an argument is a Function call {@code toString()} to work recursively
+     *  - If an argument is a Literal then just use the evaluated value.
+     *  - If an argument is a NamedExpression then use it's {@code name()} to avoid long confusing output
+     *  - If none of those resolve to the {@code toString()} method of the argument
+     *
+     * @return String representation of the function args for the {@link #toString} representation
+     */
+    private String functionArgsForToString() {
+        StringJoiner sj = new StringJoiner(",", "(", ")");
+        for (Expression child : children()) {
+            String val;
+            if (child instanceof Function) {
+                val = child.toString();
+            } else if (child instanceof Literal) {
+                val = Objects.toString(((Literal) child).value());
+            } else if (child instanceof NamedExpression && child.resolved()) {
+                val = Expressions.name(child);
+            } else {
+                val = child.toString();
+            }
+            sj.add(val);
+        }
+        return sj.toString();
+    }
 }

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/parser/ExpressionTests.java

@@ -16,8 +16,6 @@
 import org.elasticsearch.xpack.sql.expression.predicate.operator.arithmetic.Sub;
 import org.elasticsearch.xpack.sql.type.DataType;
 
-import static org.hamcrest.core.StringStartsWith.startsWith;
-
 public class ExpressionTests extends ESTestCase {
 
     private final SqlParser parser = new SqlParser();
@@ -137,7 +135,7 @@ public void testComplexArithmetic() {
         Expression expr = parser.createExpression("-(((a-2)-(-3))+b)");
         assertEquals(Neg.class, expr.getClass());
         Neg neg = (Neg) expr;
-        assertThat(neg.name(), startsWith("-(((a) - 2) - -3) + (b)#"));
+        assertEquals("-ADD(SUB(SUB(?a,2),-3),?b)", neg.name().replaceAll("#\\d+", ""));
         assertEquals(1, neg.children().size());
         assertEquals(Add.class, neg.children().get(0).getClass());
         Add add = (Add) neg.children().get(0);