Add pre/post build events to the Build page

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/Properties/InterceptedProjectProperties/AbstractBuildEventValueProvider.AbstractBuildEventHelper.cs

@@ -31,7 +31,7 @@ protected AbstractBuildEventHelper(string buildEvent,
             private string BuildEvent { get; }
             private string TargetName { get; }
 
-            public async Task<(bool success, string? property)> TryGetPropertyAsync(IProjectProperties defaultProperties)
+            public async Task<(bool success, string? value)> TryGetUnevaluatedPropertyValueAsync(IProjectProperties defaultProperties)
             {
                 // check if value already exists
                 string? unevaluatedPropertyValue = await defaultProperties.GetUnevaluatedPropertyValueAsync(BuildEvent);
@@ -43,9 +43,34 @@ protected AbstractBuildEventHelper(string buildEvent,
                 return (false, null);
             }
 
-            public string? GetProperty(ProjectRootElement projectXml)
+            public async Task<(bool success, string value)> TryGetEvaluatedPropertyValueAsync(IProjectProperties defaultProperties)
             {
-                return GetFromTargets(projectXml);
+                string? unevaluatedPropertyValue = await defaultProperties.GetUnevaluatedPropertyValueAsync(BuildEvent);
+
+                if (unevaluatedPropertyValue is null)
+                {
+                    return (false, "");
+                }
+
+                string evaluatedPropertyValue = await defaultProperties.GetEvaluatedPropertyValueAsync(BuildEvent);
+                return (true, evaluatedPropertyValue);
+            }
+
+            public string? TryGetValueFromTarget(ProjectRootElement projectXml)
+            {
+                ProjectTaskElement? execTask = FindExecTaskInTargets(projectXml);
+
+                if (execTask == null)
+                {
+                    return null;
+                }
+
+                if (execTask.Parameters.TryGetValue(Command, out string commandText))
+                {
+                    return commandText.Replace("%25", "%");
+                }
+
+                return null; // exec task as written in the project file is invalid, we should be resilient to this case.
             }
 
             public async Task<bool> TrySetPropertyAsync(string unevaluatedPropertyValue, IProjectProperties defaultProperties)
@@ -82,23 +107,6 @@ public void SetProperty(string unevaluatedPropertyValue, ProjectRootElement proj
                 SetParameter(projectXml, unevaluatedPropertyValue);
             }
 
-            private string? GetFromTargets(ProjectRootElement projectXml)
-            {
-                ProjectTaskElement? execTask = FindExecTaskInTargets(projectXml);
-
-                if (execTask == null)
-                {
-                    return null;
-                }
-
-                if (execTask.Parameters.TryGetValue(Command, out string commandText))
-                {
-                    return commandText.Replace("%25", "%");
-                }
-
-                return null; // exec task as written in the project file is invalid, we should be resilient to this case.
-            }
-
             private static bool OnlyWhitespaceCharacters(string unevaluatedPropertyValue)
                 => string.IsNullOrWhiteSpace(unevaluatedPropertyValue) &&
                    !unevaluatedPropertyValue.Contains("\n");

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/Properties/InterceptedProjectProperties/AbstractBuildEventValueProvider.cs

@@ -22,19 +22,68 @@ protected AbstractBuildEventValueProvider(
             _helper = helper;
         }
 
+        // There are two ways of storing pre/post build events in the project.
+        //
+        // 1. As MSBuild properties (PreBuildEvent / PostBuildEvent)
+        // 2. As MSBuild tasks (PreBuild / PostBuild)
+        //
+        // Properties were used in legacy projects.
+        //
+        // For SDK style projects, we should use tasks.
+        //
+        // In legacy projects, the properties were defined _after_ the import of common targets,
+        // meaning that the properties had access to a full range of property values for use in their
+        // bodies.
+        //
+        // In SDK projects, it's not possible to define a property in the project after the common
+        // targets, so an MSBuild task is used instead.
+        //
+        // Some projects still define these events using properties, and the below code will work
+        // with such properties when they exist. However if these properties are absent, then
+        // tasks are used instead.
+        //
+        // Examples of MSBuild properties that are not available to PreBuildEvent/PostBuildEvent
+        // properties (but which are available to PreBuild/PostBuild targets) are ProjectExt,
+        // PlatformName, ProjectDir, TargetDir, TargetFileName, TargetExt, ProjectFileName,
+        // ProjectPath, TargetPath, TargetName, ProjectName, ConfigurationName, and OutDir.
+        //
+        // Tasks are defined as:
+        //
+        // <Target Name="PreBuild" AfterTargets="PreBuildEvent">
+        //   <Exec Command="echo Hello World" />
+        // </Target>
+        // <Target Name="PostBuild" AfterTargets="PostBuildEvent">
+        //   <Exec Command="echo Hello World" />
+        // </Target>
+
+        public override async Task<string> OnGetUnevaluatedPropertyValueAsync(
+            string propertyName,
+            string unevaluatedPropertyValue,
+            IProjectProperties defaultProperties)
+        {
+            (bool success, string? property) = await _helper.TryGetUnevaluatedPropertyValueAsync(defaultProperties);
+
+            if (success)
+            {
+                return property ?? string.Empty;
+            }
+
+            return await _projectAccessor.OpenProjectXmlForReadAsync(_unconfiguredProject, projectXml => _helper.TryGetValueFromTarget(projectXml)) ?? string.Empty;
+        }
+
         public override async Task<string> OnGetEvaluatedPropertyValueAsync(
             string propertyName,
             string evaluatedPropertyValue,
             IProjectProperties defaultProperties)
         {
-            (bool success, string? property) = await _helper.TryGetPropertyAsync(defaultProperties);
+            (bool success, string property) = await _helper.TryGetEvaluatedPropertyValueAsync(defaultProperties);
 
             if (success)
             {
-                return property ?? string.Empty;
+                return property;
             }
 
-            return await _projectAccessor.OpenProjectXmlForReadAsync(_unconfiguredProject, projectXml => _helper.GetProperty(projectXml)) ?? string.Empty;
+            return await _projectAccessor.OpenProjectXmlForReadAsync(_unconfiguredProject, projectXml => _helper.TryGetValueFromTarget(projectXml)) ?? string.Empty;
         }
 
         public override async Task<string?> OnSetPropertyValueAsync(

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

@@ -19,6 +19,10 @@
               Description="Configures the output options for the build process."
               DisplayName="Output" />
 
+    <Category Name="Events"
+              Description="Configures custom events that run before and after build."
+              DisplayName="Events" />
+
     <Category Name="StrongNaming"
               Description="Configures strong name signing of build outputs."
               DisplayName="Strong naming" />
@@ -275,6 +279,63 @@
     </StringProperty.Metadata>
   </StringProperty>
 
+  <!-- TODO create fwlink -->
+  <StringProperty Name="PreBuildEvent"
+                  DisplayName="Pre-build event"
+                  Description="Specifies commands that run before the build starts. Does not run if the project is up-to-date. A non-zero exit code will fail the build before it runs."
+                  HelpUrl="https://docs.microsoft.com/en-us/visualstudio/ide/how-to-specify-build-events-csharp?view=vs-2019"
+                  Category="Events">
+    <StringProperty.DataSource>
+      <DataSource HasConfigurationCondition="False"
+                  Persistence="ProjectFileWithInterception"
+                  SourceOfDefaultValue="AfterContext" />
+    </StringProperty.DataSource>
+    <StringProperty.ValueEditors>
+      <ValueEditor EditorType="MultiLineString">
+        <ValueEditor.Metadata>
+          <NameValuePair Name="UseMonospaceFont" Value="True" />
+        </ValueEditor.Metadata>
+      </ValueEditor>
+    </StringProperty.ValueEditors>
+  </StringProperty>
+
+  <!-- TODO create fwlink -->
+  <StringProperty Name="PostBuildEvent"
+                  DisplayName="Post-build event"
+                  Description="Specifies commands that run after the build completes. Does not run if the build failed. Use 'call' to invoke .bat files. A non-zero exit code will fail the build."
+                  HelpUrl="https://docs.microsoft.com/en-us/visualstudio/ide/how-to-specify-build-events-csharp?view=vs-2019"
+                  Category="Events">
+    <StringProperty.DataSource>
+      <DataSource HasConfigurationCondition="False"
+                  Persistence="ProjectFileWithInterception"
+                  SourceOfDefaultValue="AfterContext" />
+    </StringProperty.DataSource>
+    <StringProperty.ValueEditors>
+      <ValueEditor EditorType="MultiLineString">
+        <ValueEditor.Metadata>
+          <NameValuePair Name="UseMonospaceFont" Value="True" />
+        </ValueEditor.Metadata>
+      </ValueEditor>
+    </StringProperty.ValueEditors>
+  </StringProperty>
+
+  <!-- TODO create fwlink -->
+  <EnumProperty Name="RunPostBuildEvent"
+                DisplayName="When to run the post-build event"
+                Description="Specifies under which condition the post-build event will be executed."
+                HelpUrl="https://docs.microsoft.com/en-us/visualstudio/ide/how-to-specify-build-events-csharp?view=vs-2019"
+                Category="Events">
+    <EnumProperty.DataSource>
+      <DataSource HasConfigurationCondition="False"
+                  PersistedName="RunPostBuildEvent"
+                  Persistence="ProjectFile"
+                  SourceOfDefaultValue="AfterContext" />
+    </EnumProperty.DataSource>
+    <EnumValue Name="Always" />
+    <EnumValue Name="OnBuildSuccess" IsDefault="True" />
+    <EnumValue Name="OnOutputUpdated" />
+  </EnumProperty>
+
   <BoolProperty Name="SignAssembly"
                 Description="Sign the output assembly to give it a strong name."
                 HelpUrl="https://go.microsoft.com/fwlink/?linkid=2147136"