From 3c1488d23311c6171540b6427470c8f6862d8244 Mon Sep 17 00:00:00 2001
From: Will Noble <wnoble@google.com>
Date: Wed, 3 Nov 2021 15:18:57 -0700
Subject: [PATCH] Add recursive digest helper method

---
 .../org/apache/calcite/plan/RelOptNode.java   |  9 ++++++++
 .../apache/calcite/plan/hep/HepRelVertex.java |  6 +++++
 .../java/org/apache/calcite/rel/RelNode.java  | 22 +++++++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptNode.java b/core/src/main/java/org/apache/calcite/plan/RelOptNode.java
index c21f745d4ea..0171ccfaccb 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptNode.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptNode.java
@@ -49,6 +49,15 @@ public interface RelOptNode {
    */
   String getDigest();
 
+  /**
+   * Like {@link #getDigest()} but describes this relational expression as well as all of it's
+   * inputs, with each digest separated by newlines and children indented according to depth.
+   * This is mainly useful for visual comparisons of rel node trees while debugging.
+   *
+   * @return Digest string of this {@code RelNode}, with input digests indented recursively underneath
+   */
+  String getDigestRecursive();
+
   /**
    * Retrieves this RelNode's traits. Note that although the RelTraitSet
    * returned is modifiable, it <b>must not</b> be modified during
diff --git a/core/src/main/java/org/apache/calcite/plan/hep/HepRelVertex.java b/core/src/main/java/org/apache/calcite/plan/hep/HepRelVertex.java
index 96d5f68856e..d4077e96dbf 100644
--- a/core/src/main/java/org/apache/calcite/plan/hep/HepRelVertex.java
+++ b/core/src/main/java/org/apache/calcite/plan/hep/HepRelVertex.java
@@ -114,4 +114,10 @@ public RelNode getCurrentRel() {
   @Override public String getDigest() {
     return "HepRelVertex(" + currentRel + ')';
   }
+
+  @Override public String getDigestRecursive() {
+    // For the purposes of the recursive digest (which is really only intended for debugging),
+    // pretend vertices don't exist.
+    return currentRel.getDigestRecursive();
+  }
 }
diff --git a/core/src/main/java/org/apache/calcite/rel/RelNode.java b/core/src/main/java/org/apache/calcite/rel/RelNode.java
index 21f6586cc2f..78536e40d8a 100644
--- a/core/src/main/java/org/apache/calcite/rel/RelNode.java
+++ b/core/src/main/java/org/apache/calcite/rel/RelNode.java
@@ -270,6 +270,28 @@ default String explain() {
     return getRelDigest().toString();
   }
 
+  /**
+   * Returns a digest string of this {@code RelNode}, as well as the digests of all its input rel
+   * nodes as an indented tree, useful for visual debugging.
+   *
+   * <p>Each call creates many new digest strings,
+   * so don't forget to cache the result if necessary.
+   *
+   * @return Digest string of this {@code RelNode} and all it's direct or indirect inputs.
+   *
+   * @see #getDigest()
+   */
+  @Override default String getDigestRecursive() {
+    final String indentedNewline = "\n  ";
+    final StringBuilder builder = new StringBuilder();
+    builder.append(getDigest());
+    for (RelNode input: getInputs()) {
+      builder.append(indentedNewline);
+      builder.append(input.getDigestRecursive().replace("\n", indentedNewline));
+    }
+    return builder.toString();
+  }
+
   /**
    * Returns a digest of this {@code RelNode}.
    *