From 367041e2e65660c8f31706bb380bc667d22188ac Mon Sep 17 00:00:00 2001
From: Lawrence Lee <45837045+Lawrence37@users.noreply.github.com>
Date: Mon, 20 Jan 2025 12:49:36 -0800
Subject: [PATCH] Fix processing params clear when XMP sync enabled

Fix caching of XMP when clearing processing parameters so that it knows
if the pp3 can be deleted without affecting the rank and color labels.
---
 rtengine/utils.h   | 32 ++++++++++++++++++++++++++++++++
 rtgui/thumbnail.cc |  8 ++++----
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/rtengine/utils.h b/rtengine/utils.h
index 5dec93f51..f57163d1e 100644
--- a/rtengine/utils.h
+++ b/rtengine/utils.h
@@ -18,6 +18,7 @@
  */
 #pragma once
 
+#include <functional>
 #include <vector>
 
 #include <type_traits>
@@ -26,6 +27,37 @@
 namespace rtengine
 {
 
+/**
+ * A function object that supplies a value and returns the same value for
+ * subsequent calls.
+ */
+template <typename T>
+struct MemoizingSupplier {
+    using Supplier = std::function<T()>;
+
+    /**
+     * @param supplier The delegate supplier.
+     */
+    explicit MemoizingSupplier(const Supplier &supplier) :
+        supplier(supplier)
+    {
+    }
+
+    T operator()() const
+    {
+        if (!is_cached) {
+            value = supplier();
+            is_cached = true;
+        }
+        return value;
+    }
+
+private:
+    const Supplier supplier;
+    mutable T value;
+    mutable bool is_cached{false};
+};
+
 // Update a point of a Cairo::Surface by accessing the raw data
 void poke255_uc(unsigned char*& dest, unsigned char r, unsigned char g, unsigned char b);
 // Update a point of a Cairo::Surface by accessing the raw data
diff --git a/rtgui/thumbnail.cc b/rtgui/thumbnail.cc
index 26c96546e..b7f634b0e 100644
--- a/rtgui/thumbnail.cc
+++ b/rtgui/thumbnail.cc
@@ -37,6 +37,7 @@
 #include "rtengine/metadata.h"
 #include "rtengine/profilestore.h"
 #include "rtengine/settings.h"
+#include "rtengine/utils.h"
 #include "guiutils.h"
 #include "batchqueue.h"
 #include "extprog.h"
@@ -1418,10 +1419,9 @@ void Thumbnail::updateProcParamsProperties(bool forceUpdate)
         pparamsValid = true;
     }
 
-    const auto getXmpSidecar = [this]() {
-        static auto xmp = rtengine::Exiv2Metadata::getXmpSidecar(fname);
-        return xmp;
-    };
+    const rtengine::MemoizingSupplier<Exiv2::XmpData> getXmpSidecar([this]() {
+        return rtengine::Exiv2Metadata::getXmpSidecar(fname);
+    });
 
     // save procparams rank and color also when options.thumbnailRankColorMode == Options::ThumbnailPropertyMode::XMP
     // so they'll be kept in sync