From afc990cd2b43cb4731744ca867fb13173fd76dc8 Mon Sep 17 00:00:00 2001
From: Adrien Grand <jpountz@gmail.com>
Date: Fri, 13 Oct 2023 10:42:34 +0200
Subject: [PATCH] Fix lazy decoding of frequencies in `BlockImpactsDocsEnum`.
 (#12668)

The code was written as if frequencies should be lazily decoding, except that
when refilling buffers freqs were getting eagerly decoded instead of lazily.
---
 lucene/CHANGES.txt                                             | 3 +++
 .../apache/lucene/codecs/lucene90/Lucene90PostingsReader.java  | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index b9a3a35da05..5ed0623940b 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -183,6 +183,9 @@ Optimizations
 * GITHUB#12631: Write MSB VLong for better outputs sharing in block tree index, decreasing ~14% size
   of .tip file. (Guo Feng)
 
+* GITHUB#12668: ImpactsEnums now decode frequencies lazily like PostingsEnums.
+  (Adrien Grand)
+
 Changes in runtime behavior
 ---------------------
 
diff --git a/lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90PostingsReader.java b/lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90PostingsReader.java
index e2223598033..0f60ee29e49 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90PostingsReader.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90PostingsReader.java
@@ -1143,7 +1143,7 @@ public final class Lucene90PostingsReader extends PostingsReaderBase {
       if (left >= BLOCK_SIZE) {
         pforUtil.decodeAndPrefixSum(docIn, accum, docBuffer);
         if (indexHasFreqs) {
-          pforUtil.decode(docIn, freqBuffer);
+          isFreqsRead = false;
         }
         blockUpto += BLOCK_SIZE;
       } else {