Only find environment properties

src/Build/Definition/ProjectProperty.cs

@@ -204,6 +204,8 @@ string IValued.EscapedValue
             get => EvaluatedValueEscapedInternal;
         }
 
+        bool IProperty.IsEnvironmentProperty { get => IsEnvironmentProperty; set => throw new NotImplementedException(); }
+
         #region IEquatable<ProjectProperty> Members
 
         /// <summary>

src/Build/Evaluation/Expander.cs

@@ -1470,7 +1470,7 @@ private static object LookupProperty(IPropertyProvider<T> properties, string pro
             private static object LookupProperty(IPropertyProvider<T> properties, string propertyName, int startIndex, int endIndex, IElementLocation elementLocation, UsedUninitializedProperties usedUninitializedProperties)
             {
                 T property = properties.GetProperty(propertyName, startIndex, endIndex);
-                if (!string.IsNullOrEmpty(property?.EvaluatedValue))
+                if (!string.IsNullOrEmpty(property?.EvaluatedValue) && property.IsEnvironmentProperty)
                 {
                     EnvironmentUtilities.EnvironmentVariablesUsedAsProperties[property.Name] = property.EvaluatedValue;
                 }

src/Build/Evaluation/IProperty.cs

@@ -35,5 +35,11 @@ string EvaluatedValueEscaped
         {
             get;
         }
+
+        bool IsEnvironmentProperty
+        {
+            get;
+            set;
+        }
     }
 }

src/Build/Instance/ProjectInstance.cs

@@ -1478,7 +1478,7 @@ IItemDefinition<ProjectMetadataInstance> IEvaluatorData<ProjectPropertyInstance,
         ProjectPropertyInstance IEvaluatorData<ProjectPropertyInstance, ProjectItemInstance, ProjectMetadataInstance, ProjectItemDefinitionInstance>.SetProperty(string name, string evaluatedValueEscaped, bool isGlobalProperty, bool mayBeReserved, bool isEnvironmentVariable)
         {
             // Mutability not verified as this is being populated during evaluation
-            ProjectPropertyInstance property = ProjectPropertyInstance.Create(name, evaluatedValueEscaped, mayBeReserved, _isImmutable);
+            ProjectPropertyInstance property = ProjectPropertyInstance.Create(name, evaluatedValueEscaped, mayBeReserved, _isImmutable, isEnvironmentVariable);
             _properties.Set(property);
             return property;
         }
@@ -2966,7 +2966,7 @@ private void CreatePropertiesSnapshot(ICollection<ProjectProperty> properties, b
             {
                 // Allow reserved property names, since this is how they are added to the project instance. 
                 // The caller has prevented users setting them themselves.
-                ProjectPropertyInstance instance = ProjectPropertyInstance.Create(property.Name, ((IProperty)property).EvaluatedValueEscaped, true /* MAY be reserved name */, isImmutable);
+                ProjectPropertyInstance instance = ProjectPropertyInstance.Create(property.Name, ((IProperty)property).EvaluatedValueEscaped, true /* MAY be reserved name */, isImmutable, property.IsEnvironmentProperty);
                 _properties.Set(instance);
             }
         }

src/Build/Instance/ProjectPropertyInstance.cs

@@ -98,6 +98,8 @@ public string EvaluatedValue
         [DebuggerBrowsable(DebuggerBrowsableState.Never)]
         string IValued.EscapedValue => _escapedValue;
 
+        bool IProperty.IsEnvironmentProperty { get; set; }
+
         #region IEquatable<ProjectPropertyInstance> Members
 
         /// <summary>
@@ -182,9 +184,9 @@ internal static ProjectPropertyInstance Create(string name, string escapedValue,
         /// This flags should ONLY be set by the evaluator or by cloning; after the ProjectInstance is created, they must be illegal.
         /// If name is invalid or reserved, throws ArgumentException.
         /// </summary>
-        internal static ProjectPropertyInstance Create(string name, string escapedValue, bool mayBeReserved, bool isImmutable)
+        internal static ProjectPropertyInstance Create(string name, string escapedValue, bool mayBeReserved, bool isImmutable, bool isEnvironmentProperty = false)
         {
-            return Create(name, escapedValue, mayBeReserved, null, isImmutable);
+            return Create(name, escapedValue, mayBeReserved, null, isImmutable, isEnvironmentProperty);
         }
 
         /// <summary>
@@ -212,7 +214,7 @@ internal static ProjectPropertyInstance Create(string name, string escapedValue,
         /// </summary>
         internal static ProjectPropertyInstance Create(ProjectPropertyInstance that)
         {
-            return Create(that._name, that._escapedValue, mayBeReserved: true /* already validated */, isImmutable: that.IsImmutable);
+            return Create(that._name, that._escapedValue, mayBeReserved: true /* already validated */, isImmutable: that.IsImmutable, ((IProperty)that).IsEnvironmentProperty);
         }
 
         /// <summary>
@@ -221,7 +223,7 @@ internal static ProjectPropertyInstance Create(ProjectPropertyInstance that)
         /// </summary>
         internal static ProjectPropertyInstance Create(ProjectPropertyInstance that, bool isImmutable)
         {
-            return Create(that._name, that._escapedValue, mayBeReserved: true /* already validated */, isImmutable: isImmutable);
+            return Create(that._name, that._escapedValue, mayBeReserved: true /* already validated */, isImmutable: isImmutable, ((IProperty)that).IsEnvironmentProperty);
         }
 
         /// <summary>
@@ -278,7 +280,7 @@ internal ProjectPropertyElement ToProjectPropertyElement(ProjectElementContainer
         /// as it should never be needed for any subsequent messages, and is just extra bulk.
         /// Inherits mutability from project if any.
         /// </summary>
-        private static ProjectPropertyInstance Create(string name, string escapedValue, bool mayBeReserved, ElementLocation location, bool isImmutable)
+        private static ProjectPropertyInstance Create(string name, string escapedValue, bool mayBeReserved, ElementLocation location, bool isImmutable, bool isEnvironmentProperty = false)
         {
             // Does not check immutability as this is only called during build (which is already protected) or evaluation
             ErrorUtilities.VerifyThrowArgumentNull(escapedValue, nameof(escapedValue));
@@ -295,11 +297,9 @@ private static ProjectPropertyInstance Create(string name, string escapedValue,
                 XmlUtilities.VerifyThrowProjectValidElementName(name, location);
             }
 
-            if (isImmutable)
-            {
-                return new ProjectPropertyInstanceImmutable(name, escapedValue);
-            }
-            return new ProjectPropertyInstance(name, escapedValue);
+            ProjectPropertyInstance instance = isImmutable ? new ProjectPropertyInstanceImmutable(name, escapedValue) : new ProjectPropertyInstance(name, escapedValue);
+            ((IProperty)instance).IsEnvironmentProperty = isEnvironmentProperty;
+            return instance;
         }
 
         /// <summary>