Log SDK environment variable messages only when values differ

src/Build/Instance/ProjectInstance.cs

@@ -1390,13 +1390,13 @@ public void AddSdkResolvedEnvironmentVariable(string name, string value)
             // If the property has already been set as an environment variable, we do not overwrite it.
             if (_environmentVariableProperties.Contains(name))
             {
-                _loggingContext.LogComment(MessageImportance.Low, "SdkEnvironmentVariableAlreadySet", name, value);
+                LogIfValueDiffers(_environmentVariableProperties, name, value, "SdkEnvironmentVariableAlreadySet");
                 return;
             }
             // If another SDK already set it, we do not overwrite it.
             else if (_sdkResolvedEnvironmentVariableProperties?.Contains(name) == true)
             {
-                _loggingContext.LogComment(MessageImportance.Low, "SdkEnvironmentVariableAlreadySetBySdk", name, value);
+                LogIfValueDiffers(_sdkResolvedEnvironmentVariableProperties, name, value, "SdkEnvironmentVariableAlreadySetBySdk");
                 return;
             }
 
@@ -1412,8 +1412,18 @@ public void AddSdkResolvedEnvironmentVariable(string name, string value)
                 ((IEvaluatorData<ProjectPropertyInstance, ProjectItemInstance, ProjectMetadataInstance, ProjectItemDefinitionInstance>)this)
                    .SetProperty(name, value, isGlobalProperty: false, mayBeReserved: false, loggingContext: _loggingContext, isEnvironmentVariable: true, isCommandLineProperty: false);
             }
+        }
 
-            _loggingContext.LogComment(MessageImportance.Low, "SdkEnvironmentVariableSet", name, value);
+        /// <summary>
+        /// Helper method to log a message if the attempted value differs from the existing value.
+        /// </summary>
+        private void LogIfValueDiffers(PropertyDictionary<ProjectPropertyInstance> propertyDictionary, string name, string attemptedValue, string messageResourceName)
+        {
+            ProjectPropertyInstance existingProperty = propertyDictionary.GetProperty(name);
+            if (existingProperty != null && !string.Equals(existingProperty.EvaluatedValue, attemptedValue, StringComparison.Ordinal))
+            {
+                _loggingContext.LogComment(MessageImportance.Low, messageResourceName, name, attemptedValue, existingProperty.EvaluatedValue);
+            }
         }
 
         /// <summary>

src/Build/Resources/Strings.resx

@@ -1384,14 +1384,12 @@ Errors: {3}</value>
     <comment>{StrBegin="MSB4238: "}</comment>
   </data>
   <data name="SdkEnvironmentVariableAlreadySet" xml:space="preserve">
-    <value>An SDK attempted to set the environment variable "{0}" to "{1}" but it was already set as an environment variable.</value>
+    <value>An SDK attempted to set the environment variable "{0}" to "{1}" but it was already set to "{2}" as an environment variable.</value>
   </data>
   <data name="SdkEnvironmentVariableAlreadySetBySdk" xml:space="preserve">
-    <value>An SDK attempted to set the environment variable "{0}" to "{1}" but it was already set by another SDK.</value>
-  </data>
-  <data name="SdkEnvironmentVariableSet" xml:space="preserve">
-    <value>An SDK attempted set the environment variable "{0}" to "{1}".</value>
+    <value>An SDK attempted to set the environment variable "{0}" to "{1}" but it was already set to "{2}" by another SDK.</value>
   </data>
+
   <data name="UnrecognizedParentElement" xml:space="preserve">
     <value>MSB4189: &lt;{1}&gt; is not a valid child of the &lt;{0}&gt; element.</value>
     <comment>{StrBegin="MSB4189: "}</comment>