From 18d4f03c83979f29c80bec060587ff9d601af452 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 15 Jan 2026 15:38:23 +0000
Subject: [PATCH 1/4] Initial plan


From b67673e18e9875326e24ecaec07d1f6be6f18129 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 15 Jan 2026 16:06:11 +0000
Subject: [PATCH 2/4] Fix MSB1025 error when using DistributedFileLogger with
 null central logger

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
---
 src/MSBuild.UnitTests/XMake_Tests.cs | 38 ++++++++++++++++++++++++++++
 src/MSBuild/XMake.cs                 |  4 +--
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/src/MSBuild.UnitTests/XMake_Tests.cs b/src/MSBuild.UnitTests/XMake_Tests.cs
index 3ebfcae6615..cc492e9b4ed 100644
--- a/src/MSBuild.UnitTests/XMake_Tests.cs
+++ b/src/MSBuild.UnitTests/XMake_Tests.cs
@@ -2294,6 +2294,44 @@ public void TestProcessFileLoggerSwitch5()
             distributedLoggerRecords.Count.ShouldBe(0); // "Expected no distributed loggers to be attached"
             loggers.Count.ShouldBe(0); // "Expected no central loggers to be attached"
         }
+
+        /// <summary>
+        /// Verify that DistributedLoggerRecords with null CentralLogger don't cause exceptions when creating ProjectCollection
+        /// This is a regression test for the issue where -dfl flag caused MSB1025 error due to null logger not being filtered.
+        /// </summary>
+        [Fact]
+        public void TestNullCentralLoggerInDistributedLoggerRecord()
+        {
+            // Simulate the scenario when using -dfl flag
+            // ProcessDistributedFileLogger creates a DistributedLoggerRecord with null CentralLogger
+            var distributedLoggerRecords = new List<DistributedLoggerRecord>();
+            bool distributedFileLogger = true;
+            string[] fileLoggerParameters = null;
+
+            MSBuildApp.ProcessDistributedFileLogger(
+                distributedFileLogger,
+                fileLoggerParameters,
+                distributedLoggerRecords);
+
+            // Verify that we have a distributed logger record with null central logger
+            distributedLoggerRecords.Count.ShouldBe(1);
+            distributedLoggerRecords[0].CentralLogger.ShouldBeNull();
+
+            // This should not throw ArgumentNullException when creating ProjectCollection
+            // The fix filters out null central loggers from the evaluationLoggers array
+            var loggers = Array.Empty<ILogger>();
+            Should.NotThrow(() =>
+            {
+                using var projectCollection = new ProjectCollection(
+                    new Dictionary<string, string>(),
+                    loggers: [.. loggers, .. distributedLoggerRecords.Select(d => d.CentralLogger).Where(l => l is not null)],
+                    remoteLoggers: null,
+                    toolsetDefinitionLocations: ToolsetDefinitionLocations.Default,
+                    maxNodeCount: 1,
+                    onlyLogCriticalEvents: false,
+                    loadProjectsReadOnly: true);
+            });
+        }
         #endregion
 
         #region ProcessConsoleLoggerSwitches
diff --git a/src/MSBuild/XMake.cs b/src/MSBuild/XMake.cs
index 0bc9bd7aafd..181ae78179a 100644
--- a/src/MSBuild/XMake.cs
+++ b/src/MSBuild/XMake.cs
@@ -1392,8 +1392,8 @@ internal static bool BuildProject(
                         // all of the loggers that are single-node only
                         .. loggers,
                         // all of the central loggers for multi-node systems. These need to be resilient to multiple calls
-                        // to Initialize
-                        .. distributedLoggerRecords.Select(d => d.CentralLogger)
+                        // to Initialize. Filter out null loggers (e.g., DistributedFileLogger uses null central logger).
+                        .. distributedLoggerRecords.Select(d => d.CentralLogger).Where(l => l is not null)
                     ];
 
                 projectCollection = new ProjectCollection(

From 46c82d96492349e177a281c12acd7d67989d8f47 Mon Sep 17 00:00:00 2001
From: YuliiaKovalova <95473390+YuliiaKovalova@users.noreply.github.com>
Date: Fri, 16 Jan 2026 10:17:12 +0100
Subject: [PATCH 3/4] Update VersionPrefix to 18.3.1

---
 eng/Versions.props | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/eng/Versions.props b/eng/Versions.props
index 5ab5660455d..4ce8e50e5cc 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -3,7 +3,7 @@
   <Import Project="Version.Details.props" />
 
   <PropertyGroup>
-    <VersionPrefix>18.3.0</VersionPrefix>
+    <VersionPrefix>18.3.1</VersionPrefix>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
     <PackageValidationBaselineVersion>18.0.2</PackageValidationBaselineVersion>
     <AssemblyVersion>15.1.0.0</AssemblyVersion>

From 907ce02634ef1fd863ff6b957a8f2231342cfc17 Mon Sep 17 00:00:00 2001
From: YuliiaKovalova <95473390+YuliiaKovalova@users.noreply.github.com>
Date: Mon, 19 Jan 2026 10:32:33 +0100
Subject: [PATCH 4/4] Update VersionPrefix from 18.3.1 to 18.3.0

---
 eng/Versions.props | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/eng/Versions.props b/eng/Versions.props
index 4ce8e50e5cc..5ab5660455d 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -3,7 +3,7 @@
   <Import Project="Version.Details.props" />
 
   <PropertyGroup>
-    <VersionPrefix>18.3.1</VersionPrefix>
+    <VersionPrefix>18.3.0</VersionPrefix>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
     <PackageValidationBaselineVersion>18.0.2</PackageValidationBaselineVersion>
     <AssemblyVersion>15.1.0.0</AssemblyVersion>