Implement WarningsNotAsErrors in the new property pages

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/Properties/InterceptedProjectProperties/BuildPropertyPage/TreatWarningsAsErrorsValueProvider.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements. The .NET Foundation licenses this file to you under the MIT license. See the LICENSE.md file in the project root for more information.
+
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.Threading.Tasks;
+
+namespace Microsoft.VisualStudio.ProjectSystem.Properties
+{
+    [ExportInterceptingPropertyValueProvider("TreatWarningsAsErrors", ExportInterceptingPropertyValueProviderFile.ProjectFile)]
+    internal sealed class TreatWarningsAsErrorsValueProvider : InterceptingPropertyValueProviderBase
+    {
+        private const string WarningsAsErrorsProperty = "WarningsAsErrors";
+        private const string WarningsNotAsErrorsProperty = "WarningsNotAsErrors";
+        private readonly ITemporaryPropertyStorage _temporaryPropertyStorage;
+
+        [ImportingConstructor]
+        public TreatWarningsAsErrorsValueProvider(ITemporaryPropertyStorage temporaryPropertyStorage)
+        {
+            _temporaryPropertyStorage = temporaryPropertyStorage;
+        }
+
+        public override async Task<string?> OnSetPropertyValueAsync(string propertyName, string unevaluatedPropertyValue, IProjectProperties defaultProperties, IReadOnlyDictionary<string, string>? dimensionalConditions = null)
+        {
+            if (StringComparers.PropertyLiteralValues.Equals(unevaluatedPropertyValue, "true"))
+            {
+                // When setting this to "true", remove WarningsAsErrors
+                await defaultProperties.SaveValueIfCurrentlySetAsync(WarningsAsErrorsProperty, _temporaryPropertyStorage);
+                await defaultProperties.DeletePropertyAsync(WarningsAsErrorsProperty, dimensionalConditions);
+                await defaultProperties.RestoreValueIfNotCurrentlySetAsync(WarningsNotAsErrorsProperty, _temporaryPropertyStorage);
+            }
+            else
+            {
+                // When settings this to "false", remove WarningsNotAsErrors
+                await defaultProperties.SaveValueIfCurrentlySetAsync(WarningsNotAsErrorsProperty, _temporaryPropertyStorage);
+                await defaultProperties.DeletePropertyAsync(WarningsNotAsErrorsProperty, dimensionalConditions);
+                await defaultProperties.RestoreValueIfNotCurrentlySetAsync(WarningsAsErrorsProperty, _temporaryPropertyStorage);
+            }
+
+            return await base.OnSetPropertyValueAsync(propertyName, unevaluatedPropertyValue, defaultProperties, dimensionalConditions);
+        }
+    }
+}

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/Rules/PropertyPages/BuildPropertyPage.xaml

@@ -186,6 +186,11 @@
                 DisplayName="Treat warnings as errors"
                 Description="Used to specify which warnings are treated as errors."
                 Category="ErrorsAndWarnings" >
+
+    <EnumProperty.DataSource>
+      <DataSource Persistence="ProjectFileWithInterception" />
+    </EnumProperty.DataSource>
+
     <EnumValue Name="false"
                DisplayName="None" />
     <EnumValue Name="true"
@@ -196,7 +201,27 @@
                   DisplayName="Treat specific warnings as errors"
                   HelpUrl="https://go.microsoft.com/fwlink/?linkid=2147301"
                   Description="Treats the specified warnings as errors. Separate multiple warning numbers with a comma (',') or semicolon (';')."
-                  Category="ErrorsAndWarnings" />
+                  Category="ErrorsAndWarnings">
+    <StringProperty.Metadata>
+      <NameValuePair Name="DependsOn" Value="Build::TreatWarningsAsErrors" />
+      <NameValuePair Name="VisibilityCondition">
+        <NameValuePair.Value>(has-evaluated-value "Build" "TreatWarningsAsErrors" "false")</NameValuePair.Value>
+      </NameValuePair>
+    </StringProperty.Metadata>
+  </StringProperty>
+
+  <StringProperty Name="WarningsNotAsErrors"
+                  DisplayName="Exempt specific warnings from being treated as errors"
+                  HelpUrl="https://go.microsoft.com/fwlink/?linkid=2147301"
+                  Description="Exempts the specified warnings from being treated as errors. Separate multiple warning numbers with a comma (',') or semicolon (';')."
+                  Category="ErrorsAndWarnings">
+    <StringProperty.Metadata>
+      <NameValuePair Name="DependsOn" Value="Build::TreatWarningsAsErrors" />
+      <NameValuePair Name="VisibilityCondition">
+        <NameValuePair.Value>(has-evaluated-value "Build" "TreatWarningsAsErrors" "true")</NameValuePair.Value>
+      </NameValuePair>
+    </StringProperty.Metadata>
+  </StringProperty>
 
   <StringProperty Name="BaseOutputPath"
                   DisplayName="Base output path"