Improve error messages when ToolTask overrides exit code 0 to -1 due to logged errors

src/Tasks.UnitTests/Exec_Tests.cs

@@ -246,7 +246,18 @@ public void LoggedErrorsCauseFailureDespiteExitCode0()
             Assert.False(result);
             // Exitcode is set to -1
             Assert.Equal(-1, exec.ExitCode);
-            ((MockEngine)exec.BuildEngine).AssertLogContains("MSB3073");
+
+            MockEngine engine = (MockEngine)exec.BuildEngine;
+
+            // Should log the special "exited zero with errors" message
+            engine.AssertLogContains("MSB3077");
+
+            // Should not log other failure-related error codes
+            engine.AssertLogDoesntContain("MSB3073");
+            engine.AssertLogDoesntContain("MSB6006");
+
+            // Errors: canonical error from tool output + MSB3077 from HandleTaskExecutionErrors
+            engine.Errors.ShouldBe(2);
         }
 
         [Fact]

src/Tasks.UnitTests/XamlDataDrivenToolTask_Tests.cs

@@ -5,8 +5,14 @@
 using System.IO;
 using System.Reflection;
 using Microsoft.Build.Evaluation;
+using Microsoft.Build.Framework;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Tasks;
+using Microsoft.Build.Tasks.Xaml;
+using Microsoft.Build.Utilities;
+using Shouldly;
 using Xunit;
+using Xunit.Abstractions;
 
 #nullable disable
 
@@ -382,4 +388,65 @@ public void SquareBracketEscaping()
             logger.AssertLogContains("echo 14) [[notaproperty]] end");
         }
     }
+
+    /// <summary>
+    /// Tests for XamlDataDrivenToolTask error handling using direct task instantiation.
+    /// </summary>
+    public class ErrorHandlingTests
+    {
+        private readonly ITestOutputHelper _output;
+
+        public ErrorHandlingTests(ITestOutputHelper output)
+        {
+            _output = output;
+        }
+
+        /// <summary>
+        /// Tests that when a XamlDataDrivenTask's tool exits with code 0 but canonical errors
+        /// were logged during execution, the special "exited zero with errors" message (MSB3725)
+        /// is used instead of the normal command failure message (MSB3721).
+        /// </summary>
+        [Fact]
+        public void ExitCodeZeroWithLoggedErrors_LogsMSB3725()
+        {
+            var cmdLine = NativeMethodsShared.IsWindows
+                ? "echo myfile(88,37): error AB1234: thisisacanonicalerror"
+                : "echo \"myfile(88,37): error AB1234: thisisacanonicalerror\"";
+
+            var task = new TestableXamlDataDrivenToolTask();
+            task.BuildEngine = new MockEngine(_output);
+            task.CommandLineTemplate = cmdLine;
+            task.EchoOff = true;
+
+            bool result = task.Execute();
+
+            result.ShouldBeFalse();
+
+            MockEngine engine = (MockEngine)task.BuildEngine;
+
+            // Should log the special "exited zero with errors" message, not the normal command failure
+            engine.AssertLogContains("MSB3725");
+
+            // Should not log other error messages related to XamlDataDrivenToolTask command failure 
+            engine.AssertLogDoesntContain("MSB3721");
+            engine.AssertLogDoesntContain("MSB3722");
+
+            // Errors: canonical error from tool output + MSB3725 from HandleTaskExecutionErrors
+            engine.Errors.ShouldBe(2);
+        }
+    }
+
+    /// <summary>
+    /// A concrete subclass of XamlDataDrivenToolTask for direct unit testing
+    /// without requiring a project file or XamlTaskFactory.
+    /// </summary>
+    internal sealed class TestableXamlDataDrivenToolTask : XamlDataDrivenToolTask
+    {
+        public TestableXamlDataDrivenToolTask()
+            : base(Array.Empty<string>(), null)
+        {
+        }
+
+        protected override string ToolName => "unused";
+    }
 }

src/Tasks/Exec.cs

@@ -325,10 +325,15 @@ protected override bool HandleTaskExecutionErrors()
             {
                 Log.LogErrorWithCodeFromResources("Exec.CommandFailedAccessDenied", commandForLog, ExitCode);
             }
+            else if (ExitCodeOverriddenToIndicateErrors)
+            {
+                Log.LogErrorWithCodeFromResources("Exec.CommandExitedZeroWithErrors", commandForLog);
+            }
             else
             {
                 Log.LogErrorWithCodeFromResources("Exec.CommandFailed", commandForLog, ExitCode);
             }
+
             return false;
         }
 

src/Tasks/Resources/Strings.resx

@@ -408,6 +408,10 @@
   <data name="Exec.CommandFailedNoErrorCode">
     <value>The command "{0}" exited with code {1}.</value>
   </data>
+  <data name="Exec.CommandExitedZeroWithErrors">
+    <value>MSB3077: The command "{0}" exited with return value 0, but errors were detected during execution. ExitCode was set to -1.</value>
+    <comment>{StrBegin="MSB3077: "}</comment>
+  </data>
   <data name="Exec.InvalidRegex">
     <value>MSB3076: The regular expression "{0}" that was supplied is invalid. {1}</value>
     <comment>{StrBegin="MSB3076: "}</comment>
@@ -2311,6 +2315,10 @@
     <value>MSB3722: The command "{0}" exited with code {1}. Please verify that you have sufficient rights to run this command.</value>
     <comment>{StrBegin="MSB3722: "}</comment>
   </data>
+  <data name="Xaml.CommandExitedZeroWithErrors">
+    <value>MSB3725: The command "{0}" exited with return value 0, but errors were detected during execution. ExitCode was set to -1.</value>
+    <comment>{StrBegin="MSB3725: "}</comment>
+  </data>
   <data name="Xaml.MissingRequiredArgument">
     <value>MSB3723: The parameter "{0}" requires missing parameter "{1}" to be set.</value>
     <comment>{StrBegin="MSB3723: "}</comment>