From 3813f5ab7c78b81d4bcfc78788e44609c6f8d636 Mon Sep 17 00:00:00 2001
From: Kartik Ganesh <gkart@amazon.com>
Date: Tue, 18 Apr 2023 11:38:35 -0700
Subject: [PATCH] Change the access modifier for the "expert" readLatestCommit
 API to public. (#12229)

This change also includes a unit test for this functionality.

Signed-off-by: Kartik Ganesh <gkart@amazon.com>
---
 .../backward_index/TestBackwardsCompatibility.java | 14 ++++++++++++++
 .../java/org/apache/lucene/index/SegmentInfos.java | 10 ++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/lucene/backward-codecs/src/test/org/apache/lucene/backward_index/TestBackwardsCompatibility.java b/lucene/backward-codecs/src/test/org/apache/lucene/backward_index/TestBackwardsCompatibility.java
index a2790d873c6..9eeebeefc62 100644
--- a/lucene/backward-codecs/src/test/org/apache/lucene/backward_index/TestBackwardsCompatibility.java
+++ b/lucene/backward-codecs/src/test/org/apache/lucene/backward_index/TestBackwardsCompatibility.java
@@ -2241,4 +2241,18 @@ public class TestBackwardsCompatibility extends LuceneTestCase {
       }
     }
   }
+
+  @Nightly
+  public void testReadNMinusTwoSegmentInfos() throws IOException {
+    for (String name : binarySupportedNames) {
+      Path oldIndexDir = createTempDir(name);
+      TestUtil.unzip(getDataInputStream("unsupported." + name + ".zip"), oldIndexDir);
+      try (BaseDirectoryWrapper dir = newFSDirectory(oldIndexDir)) {
+        expectThrows(
+            IndexFormatTooOldException.class,
+            () -> SegmentInfos.readLatestCommit(dir, Version.MIN_SUPPORTED_MAJOR));
+        SegmentInfos.readLatestCommit(dir, MIN_BINARY_SUPPORTED_MAJOR);
+      }
+    }
+  }
 }
diff --git a/lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java b/lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java
index ecd064ac875..d2cb1abaa8a 100644
--- a/lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java
+++ b/lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java
@@ -517,8 +517,14 @@ public final class SegmentInfos implements Cloneable, Iterable<SegmentCommitInfo
     return readLatestCommit(directory, Version.MIN_SUPPORTED_MAJOR);
   }
 
-  static final SegmentInfos readLatestCommit(Directory directory, int minSupportedMajorVersion)
-      throws IOException {
+  /**
+   * Find the latest commit ({@code segments_N file}) and load all {@link SegmentCommitInfo}s, as
+   * long as the commit's {@link SegmentInfos#getIndexCreatedVersionMajor()} is strictly greater
+   * than the provided minimum supported major version. If the commit's version is older, an {@link
+   * IndexFormatTooOldException} will be thrown.
+   */
+  public static final SegmentInfos readLatestCommit(
+      Directory directory, int minSupportedMajorVersion) throws IOException {
     return new FindSegmentsFile<SegmentInfos>(directory) {
       @Override
       protected SegmentInfos doBody(String segmentFileName) throws IOException {