From e928b885fbfd057e13e7fc242cb3665cde51da9a Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Fri, 31 Jan 2025 11:12:36 +1000
Subject: [PATCH] [pal] Always iterate through labeled layers in original layer
 order

Ensures that labeling solutions are deterministic
---
 src/core/pal/pal.cpp | 9 +++++++--
 src/core/pal/pal.h   | 2 +-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/core/pal/pal.cpp b/src/core/pal/pal.cpp
index dda39bd116bf..83d3b4831238 100644
--- a/src/core/pal/pal.cpp
+++ b/src/core/pal/pal.cpp
@@ -88,11 +88,16 @@ Layer *Pal::addLayer( QgsAbstractLabelProvider *provider, const QString &layerNa
 {
   mMutex.lock();
 
-  Q_ASSERT( mLayers.find( provider ) == mLayers.end() );
+#ifdef QGISDEBUG
+  for ( const auto &it : mLayers )
+  {
+    Q_ASSERT( it.first != provider );
+  }
+#endif
 
   std::unique_ptr< Layer > layer = std::make_unique< Layer >( provider, layerName, arrangement, defaultPriority, active, toLabel, this );
   Layer *res = layer.get();
-  mLayers.insert( std::pair<QgsAbstractLabelProvider *, std::unique_ptr< Layer >>( provider, std::move( layer ) ) );
+  mLayers.emplace_back( std::make_pair( provider, std::move( layer ) ) );
   mMutex.unlock();
 
   // cppcheck-suppress returnDanglingLifetime
diff --git a/src/core/pal/pal.h b/src/core/pal/pal.h
index 0f8a2192b351..dc9c5991a5c7 100644
--- a/src/core/pal/pal.h
+++ b/src/core/pal/pal.h
@@ -279,7 +279,7 @@ namespace pal
 
     private:
 
-      std::unordered_map< QgsAbstractLabelProvider *, std::unique_ptr< Layer > > mLayers;
+      std::vector< std::pair< QgsAbstractLabelProvider *, std::unique_ptr< Layer > > > mLayers;
 
       QList< QgsAbstractLabelingEngineRule * > mRules;