Remove batching requirements placed on code and document generator providers

- #8419
- perform batching and `@(ServiceFileReference)` and `@(Compile)` additions in common code
  - take advantage of new simplicity in `DefaultDocumentGenerator` target
- add metadata serialization / deserialization in support of passing items into `<MSBuild />`
  - also ensure metadata values are escaped before calling `ITaskItem.SetMetadata(...)`
- correct typos in Microsoft.Extensions.ApiDescription.Client.* e.g. in comments and metadata names
- move last remaining `GenerationTasks` file

nits:
- combine `_ServiceProjectReferenceGenerator_Restore` and `_ServiceProjectReferenceGenerator_Build` targets
  - only build web sites projects once
- remove unused `buildMultiTargeting` targets
- remove qualification of metadata listed in an `<ItemDefinitionGroup />`; will always exist
- add / remove a few `Condition`s that were missing / redundant
- move properties users won't normally set to Microsoft.Extensions.ApiDescription.Client.targets
- shorten lines in MSBuild files

src/Microsoft.Extensions.ApiDescription.Client/GetCurrentItems.cs

@@ -0,0 +1,34 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.Extensions.ApiDescription.Client
+{
+    /// <summary>
+    /// Restore <see cref="ITaskItem"/>s from given property value.
+    /// </summary>
+    public class GetCurrentItems : Task
+    {
+        /// <summary>
+        /// The property value to deserialize.
+        /// </summary>
+        [Required]
+        public string Input { get; set; }
+
+        /// <summary>
+        /// The restored <see cref="ITaskItem"/>s. Will never contain more than one item.
+        /// </summary>
+        [Output]
+        public ITaskItem[] Outputs { get; set; }
+
+        /// <inheritdoc />
+        public override bool Execute()
+        {
+            Outputs = new[] { MetadataSerializer.DeserializeMetadata(Input) };
+
+            return true;
+        }
+    }
+}

src/Microsoft.Extensions.ApiDescription.Client/GetFileReferenceMetadata.cs

@@ -61,18 +61,21 @@ namespace Microsoft.Extensions.ApiDescription.Client
                 if (string.IsNullOrEmpty(@namespace))
                 {
                     @namespace = isTypeScript ? CSharpNamespace : TypeScriptNamespace;
-                    newItem.SetMetadata("Namespace", @namespace);
+                    MetadataSerializer.SetMetadata(newItem, "Namespace", @namespace);
                 }
 
                 var outputPath = item.GetMetadata("OutputPath");
                 if (string.IsNullOrEmpty(outputPath))
                 {
                     var className = item.GetMetadata("ClassName");
-                    outputPath = className + (isTypeScript ? ".ts" : ".cs");
+                    outputPath = $"{className}{(isTypeScript ? ".ts" : ".cs")}";
                 }
 
                 outputPath = GetFullPath(outputPath);
-                newItem.SetMetadata("OutputPath", outputPath);
+                MetadataSerializer.SetMetadata(newItem, "OutputPath", outputPath);
+
+                // Add metadata which may be used as a property and passed to an inner build.
+                newItem.SetMetadata("SerializedMetadata", MetadataSerializer.SerializeMetadata(newItem));
             }
 
             Outputs = outputs.ToArray();

src/Microsoft.Extensions.ApiDescription.Client/GetProjectReferenceMetadata.cs

@@ -52,6 +52,8 @@ namespace Microsoft.Extensions.ApiDescription.Client
                     outputPath = className + (isTypeScript ? ".ts" : ".cs");
                 }
 
+                // Add metadata which may be used as a property and passed to an inner build.
+                newItem.SetMetadata("SerializedMetadata", MetadataSerializer.SerializeMetadata(newItem));
                 outputPath = GetFullPath(outputPath);
                 newItem.SetMetadata("OutputPath", outputPath);
             }

src/Microsoft.Extensions.ApiDescription.Client/GetUriReferenceMetadata.cs

@@ -95,7 +95,7 @@ namespace Microsoft.Extensions.ApiDescription.Client
                 }
 
                 documentPath = GetFullPath(documentPath);
-                newItem.SetMetadata("DocumentPath", documentPath);
+                MetadataSerializer.SetMetadata(newItem, "DocumentPath", documentPath);
             }
 
             Outputs = outputs.ToArray();

src/Microsoft.Extensions.ApiDescription.Client/MetadataSerializer.cs

@@ -0,0 +1,147 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.Extensions.ApiDescription.Client
+{
+    /// <summary>
+    /// Utility methods to serialize and deserialize <see cref="ITaskItem"/> metadata.
+    /// </summary>
+    /// <remarks>
+    /// Based on and uses the same escaping as
+    /// https://github.com/Microsoft/msbuild/blob/e70a3159d64f9ed6ec3b60253ef863fa883a99b1/src/Shared/EscapingUtilities.cs
+    /// </remarks>
+    public static class MetadataSerializer
+    {
+        private static readonly char[] CharsToEscape = { '%', '*', '?', '@', '$', '(', ')', ';', '\'' };
+        private static readonly HashSet<char> CharsToEscapeHash = new HashSet<char>(CharsToEscape);
+
+        /// <summary>
+        /// Add the given <paramref name="key"/> and <paramref name="value"/> to the <paramref name="item"/>. Or,
+        /// modify existing value to be <paramref name="value"/>.
+        /// </summary>
+        /// <param name="item">The <see cref="ITaskItem"/> to update.</param>
+        /// <param name="key">The name of the new metadata.</param>
+        /// <param name="value">The value of the new metadata. Assumed to be unescaped.</param>
+        /// <remarks>Uses same hex-encoded format as MSBuild's EscapeUtilities.</remarks>
+        public static void SetMetadata(ITaskItem item, string key, string value)
+        {
+            if (item is ITaskItem2 item2)
+            {
+                item2.SetMetadataValueLiteral(key, value);
+                return;
+            }
+
+            if (value.IndexOfAny(CharsToEscape) == -1)
+            {
+                item.SetMetadata(key, value);
+                return;
+            }
+
+            var builder = new StringBuilder();
+            EscapeValue(value, builder);
+            item.SetMetadata(key, builder.ToString());
+        }
+
+        /// <summary>
+        /// Serialize metadata for use as a property value passed into an inner build.
+        /// </summary>
+        /// <param name="item">The item to serialize.</param>
+        /// <returns>A <see cref="string"/> containing the serialized metadata.</returns>
+        /// <remarks>Uses same hex-encoded format as MSBuild's EscapeUtilities.</remarks>
+        public static string SerializeMetadata(ITaskItem item)
+        {
+            var builder = new StringBuilder();
+            if (item is ITaskItem2 item2)
+            {
+                builder.Append($"Identity={item2.EvaluatedIncludeEscaped}");
+                var metadata = item2.CloneCustomMetadataEscaped();
+                foreach (var key in metadata.Keys)
+                {
+                    var value = metadata[key];
+                    builder.Append($"|{key.ToString()}={value.ToString()}");
+                }
+            }
+            else
+            {
+                builder.Append($"Identity=");
+                EscapeValue(item.ItemSpec, builder);
+
+                var metadata = item.CloneCustomMetadata();
+                foreach (var key in metadata.Keys)
+                {
+                    builder.Append($"|{key.ToString()}=");
+
+                    var value = metadata[key];
+                    EscapeValue(value.ToString(), builder);
+                }
+            }
+
+            return builder.ToString();
+        }
+
+        /// <summary>
+        /// Recreate an <see cref="ITaskItem"/> with metadata encoded in given <paramref name="value"/>.
+        /// </summary>
+        /// <param name="value">The serialized metadata.</param>
+        /// <returns>The deserialized <see cref="ITaskItem"/>.</returns>
+        public static ITaskItem DeserializeMetadata(string value)
+        {
+            var metadata = value.Split('|');
+            var item = new TaskItem();
+
+            // TaskItem implements ITaskITem2 explicitly and ITaskItem implicitly.
+            var item2 = (ITaskItem2)item;
+            foreach (var segment in metadata)
+            {
+                var keyAndValue = segment.Split(new[] { '=' }, count: 2);
+                if (string.Equals("Identity", keyAndValue[0]))
+                {
+                    item2.EvaluatedIncludeEscaped = keyAndValue[1];
+                    continue;
+                }
+
+                item2.SetMetadata(keyAndValue[0], keyAndValue[1]);
+            }
+
+            return item;
+        }
+
+        private static void EscapeValue(string value, StringBuilder builder)
+        {
+            if (string.IsNullOrEmpty(value))
+            {
+                builder.Append(value);
+                return;
+            }
+
+            if (value.IndexOfAny(CharsToEscape) == -1)
+            {
+                builder.Append(value);
+                return;
+            }
+
+            foreach (var @char in value)
+            {
+                if (CharsToEscapeHash.Contains(@char))
+                {
+                    builder.Append('%');
+                    builder.Append(HexDigitChar(@char / 0x10));
+                    builder.Append(HexDigitChar(@char & 0x0F));
+                    continue;
+                }
+
+                builder.Append(@char);
+            }
+        }
+
+        private static char HexDigitChar(int x)
+        {
+            return (char)(x + (x < 10 ? '0' : ('a' - 10)));
+        }
+    }
+}

src/Microsoft.Extensions.ApiDescription.Client/build/Microsoft.Extensions.ApiDescription.Client.props

@@ -6,49 +6,32 @@
     <_ApiDescriptionTasksAssemblyPath>$(MSBuildThisFileDirectory)/../tasks/$(_ApiDescriptionTasksAssemblyTarget)/Microsoft.Extensions.ApiDescription.Client.dll</_ApiDescriptionTasksAssemblyPath>
     <_ApiDescriptionTasksAssemblyTarget />
   </PropertyGroup>
+  <UsingTask TaskName="GetCurrentItems" AssemblyFile="$(_ApiDescriptionTasksAssemblyPath)" />
   <UsingTask TaskName="GetFileReferenceMetadata" AssemblyFile="$(_ApiDescriptionTasksAssemblyPath)" />
   <UsingTask TaskName="GetProjectReferenceMetadata" AssemblyFile="$(_ApiDescriptionTasksAssemblyPath)" />
   <UsingTask TaskName="GetUriReferenceMetadata" AssemblyFile="$(_ApiDescriptionTasksAssemblyPath)" />
   <UsingTask TaskName="Microsoft.Extensions.ApiDescription.Client.DownloadFile" AssemblyFile="$(_ApiDescriptionTasksAssemblyPath)" />
 
+  <!-- Settings users may update as they see fit. -->
   <PropertyGroup>
-    <ServiceProjectReferenceCheckIfNewer Condition="'$(ServiceProjectReferenceCheckIfNewer)' == ''">true</ServiceProjectReferenceCheckIfNewer>
+    <ServiceProjectReferenceCheckIfNewer
+        Condition="'$(ServiceProjectReferenceCheckIfNewer)' == ''">true</ServiceProjectReferenceCheckIfNewer>
     <ServiceProjectReferenceDirectory
-      Condition="'$(ServiceProjectReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceProjectReferenceDirectory)'))</ServiceProjectReferenceDirectory>
+        Condition="'$(ServiceProjectReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceProjectReferenceDirectory)'))</ServiceProjectReferenceDirectory>
 
-    <ServiceUriReferenceCheckIfNewer Condition="'$(ServiceUriReferenceCheckIfNewer)' == ''">true</ServiceUriReferenceCheckIfNewer>
+    <ServiceUriReferenceCheckIfNewer
+        Condition="'$(ServiceUriReferenceCheckIfNewer)' == ''">true</ServiceUriReferenceCheckIfNewer>
     <ServiceUriReferenceDirectory
-      Condition="'$(ServiceUriReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceUriReferenceDirectory)'))</ServiceUriReferenceDirectory>
+        Condition="'$(ServiceUriReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceUriReferenceDirectory)'))</ServiceUriReferenceDirectory>
 
-    <ServiceFileReferenceCheckIfNewer Condition="'$(ServiceFileReferenceCheckIfNewer)' == ''">true</ServiceFileReferenceCheckIfNewer>
+    <ServiceFileReferenceCheckIfNewer
+        Condition="'$(ServiceFileReferenceCheckIfNewer)' == ''">true</ServiceFileReferenceCheckIfNewer>
     <ServiceFileReferenceDirectory
-      Condition="'$(ServiceFileReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceFileReferenceDirectory)'))</ServiceFileReferenceDirectory>
+        Condition="'$(ServiceFileReferenceDirectory)' != ''">$([MSBuild]::EnsureTrailingSlash('$(ServiceFileReferenceDirectory)'))</ServiceFileReferenceDirectory>
-    <ServiceFileReferenceCSharpNamespace Condition="'$(ServiceFileReferenceCSharpNamespace)' == ''">$(RootNamespace)</ServiceFileReferenceCSharpNamespace>
+    <ServiceFileReferenceCSharpNamespace
-    <ServiceFileReferenceTypeScriptNamespace Condition="'$(ServiceFileReferenceTypeScriptNamespace)' == ''">$(RootNamespace)</ServiceFileReferenceTypeScriptNamespace>
+        Condition="'$(ServiceFileReferenceCSharpNamespace)' == ''">$(RootNamespace)</ServiceFileReferenceCSharpNamespace>
-
+    <ServiceFileReferenceTypeScriptNamespace
-    <DefaultDocumentGeneratorDependsOn>
+        Condition="'$(ServiceFileReferenceTypeScriptNamespace)' == ''">$(RootNamespace)</ServiceFileReferenceTypeScriptNamespace>
-      _DefaultDocumentGenerator_GetMetadata;
-      _DefaultDocumentGenerator_Core;
-      _DefaultDocumentGenerator_SetMetadata
-    </DefaultDocumentGeneratorDependsOn>
-    <ServiceProjectReferenceGeneratorDependsOn>
-      _ServiceProjectReferenceGenerator_GetTargetFramework;
-      _ServiceProjectReferenceGenerator_GetProjectTargetPath;
-      _ServiceProjectReferenceGenerator_Restore;
-      _ServiceProjectReferenceGenerator_Build;
-      _ServiceProjectReferenceGenerator_Core
-    </ServiceProjectReferenceGeneratorDependsOn>
-    <ServiceUriReferenceGeneratorDependsOn>
-      _ServiceUriReferenceGenerator_GetMetadata;
-      _ServiceUriReferenceGenerator_Core
-    </ServiceUriReferenceGeneratorDependsOn>
-    <ServiceFileReferenceGeneratorDependsOn>
-      _CheckServiceReferences;
-      ServiceProjectReferenceGenerator;
-      ServiceUriReferenceGenerator;
-      _ServiceFileReferenceGenerator_GetMetadata;
-      _ServiceFileReferenceGenerator_Core
-    </ServiceFileReferenceGeneratorDependsOn>
   </PropertyGroup>
 
   <!--
@@ -59,6 +42,33 @@
     <ServiceProjectReference>
       <!-- Name of the API description document generator. -->
       <DocumentGenerator>Default</DocumentGenerator>
+
+      <!-- Server project metadata which is likely applicable to all document generators. -->
+
+      <!--
+        Full path of the project's generated assembly. Corresponds to $(TargetPath). Because common code builds server
+        projects, file exists prior to document generator invocation.
+      -->
+      <ProjectAssemblyPath />
+      <!-- Server project's chosen configuration. Likely matches client project's configuration. -->
+      <ProjectConfiguration />
+      <!--
+        Server project's extensions path. Corresponds to $(MSBuildProjectExtensionsPath). User must set this if
+        server project's value is not 'obj/'.
+      -->
+      <ProjectExtensionsPath />
+      <!-- Runtime identifier to use when building the server project. -->
+      <ProjectRuntimeIdentifier />
+      <!-- Server project's target framework. Defaults to $(TargetFramewok) or first of $(TargetFrameworks). -->
+      <ProjectTargetFramework />
+
+      <!-- Metadata specific to the Default document generator (though other document generators are free to use it). -->
+
+      <!--
+        Options added to Default document generator tool's command line. Defaults to
+        $(DefaultDocumentGeneratorDefaultOptions) if that is set in the client project.
+      -->
+      <DefaultDocumentGeneratorOptions />
       <!--
         Name of the document to generate. Passed to the %(Method) when using Default document generator. Default is set
         in server project, falling back to "v1".
@@ -84,36 +94,19 @@
         the %(Service) fails. Default is set in server project and metadata has no further fallback.
       -->
       <Uri />
-
-      <!--
-        Full path of the project's generated assembly. Corresponds to $(TargetPath). Because common code builds server
-        projects, file exists prior to document generator invocation.
-      -->
-      <ProjectAssemblyPath />
-      <!-- Server project's chosen configuration. Likely matches client project's configuration. -->
-      <ProjectConfiguration />
-      <!--
-        Server project's extensions path. Corresponds to $(MSBuildProjectExtensionsPath). Must set this if project's
-        value is not 'obj/'.
-      -->
-      <ProjectExtensionsPath />
-      <!-- Runtime identifier to use when building the server project. -->
-      <ProjectRuntimeIdentifier />
-      <!-- Server project's target framework. Defaults to $(TargetFramewok) or first of $(TargetFrameworks). -->
-      <ProjectTargetFramework />
     </ServiceProjectReference>
 
     <ServiceUriReference>
       <!--
         Full path where the API description document is placed. Default filename is based on %(Identity).
-        Filenames and relative paths (if explicitly set) are combined with $(ServiceProjectReferenceDirectory).
+        Filenames and relative paths (if explicitly set) are combined with $(ServiceUriReferenceDirectory).
       -->
       <DocumentPath />
     </ServiceUriReference>
 
     <ServiceFileReference>
-      <!-- Name of the class to generate. -->
+      <!-- Name of the class to generate. Defaults to %(Filename)Client but with an uppercase first letter. -->
-      <ClassName>%(Filename)Client</ClassName>
+      <ClassName />
       <!-- Code generator to use. Required. -->
       <CodeGenerator />
       <!--
@@ -124,7 +117,7 @@
       <!--
         Path to place generated code. Code generator may interpret path as a filename or directory. Default filename or
         folder name is %(ClassName).[cs|ts]. Filenames and relative paths (if explicitly set) are combined with
-        $(ServiceProjectReferenceDirectory).
+        $(ServiceFileReferenceDirectory).
       -->
       <OutputPath />
     </ServiceFileReference>

src/Microsoft.Extensions.ApiDescription.Client/build/Microsoft.Extensions.ApiDescription.Client.targets

@@ -1,11 +1,34 @@
 <?xml version="1.0" encoding="utf-8" standalone="no"?>
 <Project>
+  <!-- Internal settings for Microsoft.Extensions.ApiDescription.Client.targets use. Not intended for customization. -->
+  <PropertyGroup>
+    <ServiceProjectReferenceGeneratorDependsOn>
+      _ServiceProjectReferenceGenerator_GetTargetFramework;
+      _ServiceProjectReferenceGenerator_GetProjectTargetPath;
+      _ServiceProjectReferenceGenerator_Build;
+      _ServiceProjectReferenceGenerator_Core;
+      _ServiceProjectReferenceGenerator_SetMetadata
+    </ServiceProjectReferenceGeneratorDependsOn>
+    <ServiceUriReferenceGeneratorDependsOn>
+      _ServiceUriReferenceGenerator_GetMetadata;
+      _ServiceUriReferenceGenerator_Core
+    </ServiceUriReferenceGeneratorDependsOn>
+    <ServiceFileReferenceGeneratorDependsOn>
+      _CheckServiceReferences;
+      ServiceProjectReferenceGenerator;
+      ServiceUriReferenceGenerator;
+      _ServiceFileReferenceGenerator_GetMetadata;
+      _ServiceFileReferenceGenerator_Core;
+      _ServiceFileReferenceGenerator_SetMetadata
+    </ServiceFileReferenceGeneratorDependsOn>
+  </PropertyGroup>
+
   <Target Name="_CheckServiceReferences">
-    <Error Condition="'@(ServiceProjectReference)' != '' AND '%(ServiceProjectReference.CodeGenerator)' == ''"
+    <Error Condition="'@(ServiceProjectReference)' != '' AND '%(CodeGenerator)' == ''"
         Text="ServiceProjectReference items '@(ServiceProjectReference)' lack CodeGenerator metadata." />
-    <Error Condition="'@(ServiceUriReference)' != '' AND '%(ServiceUriReference.CodeGenerator)' == ''"
+    <Error Condition="'@(ServiceUriReference)' != '' AND '%(CodeGenerator)' == ''"
         Text="ServiceUriReference items '@(ServiceUriReference)' lack CodeGenerator metadata." />
-    <Error Condition="'@(ServiceFileReference)' != '' AND '%(ServiceFileReference.CodeGenerator)' == ''"
+    <Error Condition="'@(ServiceFileReference)' != '' AND '%(CodeGenerator)' == ''"
         Text="ServiceFileReference items '@(ServiceFileReference)' lack CodeGenerator metadata." />
   </Target>
 
@@ -38,7 +61,7 @@
     </PropertyGroup>
     <ItemGroup>
       <ServiceProjectReference Update="@(ServiceProjectReference)" Condition="'%(FullPath)' == '$(_FullPath)'">
-        <TargetFramework Condition="'%(ServiceProjectReference.TargetFramework)' == ''">$(_TargetFramework)</TargetFramework>
+        <ProjectTargetFramework Condition="'%(ProjectTargetFramework)' == ''">$(_TargetFramework)</ProjectTargetFramework>
       </ServiceProjectReference>
       <_Temporary Remove="@(_Temporary)" />
     </ItemGroup>
@@ -53,17 +76,19 @@
   <!-- Metadata setup phase 2: Ensure items have ProjectTargetPath metadata. Call GetTargetPath in the target project. -->
   <!-- Inputs and outputs cause MSBuild to run target unconditionally and batch it (run once per TargetFramework x project combination). -->
   <Target Name="_ServiceProjectReferenceGenerator_GetProjectTargetPath"
-    Inputs="%(ServiceProjectReference.TargetFramework)%(FullPath)"
+      Inputs="%(ServiceProjectReference.TargetFramework)%(FullPath)')"
-    Outputs="&lt;not-a-file !&gt;">
+      Outputs="&lt;not-a-file !&gt;">
     <PropertyGroup>
       <_FullPath>%(ServiceProjectReference.FullPath)</_FullPath>
-      <_TargetFramework>%(ServiceProjectReference.TargetFramework)</_TargetFramework>
+      <_TargetFramework>%(ServiceProjectReference.ProjectTargetFramework)</_TargetFramework>
     </PropertyGroup>
     <ItemGroup>
       <_Temporary Remove="@(_Temporary)" />
     </ItemGroup>
 
-    <Message Importance="high" Text="%0A_ServiceProjectReferenceGenerator_GetProjectTargetPath: '$(_FullPath)' '$(_TargetFramework)'" />
+    <Message
+        Importance="high"
+        Text="%0A_ServiceProjectReferenceGenerator_GetProjectTargetPath: '$(_FullPath)' '$(_TargetFramework)'" />
     <MSBuild Projects="$(_FullPath)"
         Properties="TargetFramework=$(_TargetFramework)"
         RebaseOutputs="true"
@@ -78,7 +103,7 @@
     </PropertyGroup>
     <ItemGroup>
       <ServiceProjectReference Update="@(ServiceProjectReference)"
-          Condition="'%(FullPath)' == '$(_FullPath)' AND '%(ServiceProjectReference.TargetFramework)' == '$(_TargetFramework)'">
+          Condition="'%(ServiceProjectReference.FullPath)' == '$(_FullPath)' AND '%(ProjectTargetFramework)' == '$(_TargetFramework)'">
         <ProjectTargetPath>$(_ProjectTargetPath)</ProjectTargetPath>
       </ServiceProjectReference>
       <_Temporary Remove="@(_Temporary)" />
@@ -91,99 +116,85 @@
     </PropertyGroup>
   </Target>
 
-  <Target Name="_ServiceProjectReferenceGenerator_Restore"
-      Condition="'$(BuildProjectReferences)' == 'true'"
-      Inputs="@(ServiceProjectReference)"
-      Outputs="@(ServiceProjectReference -> '%(Directory)obj\project.assets.json')">
-    <MSBuild Projects="@(ServiceProjectReference -> '%(FullPath)')"
-        BuildInParallel="$(BuildInParallel)"
-        RemoveProperties="TargetFramework;TargetFrameworks;RuntimeIdentifier"
-        Targets="Restore" />
-  </Target>
-
   <Target Name="_ServiceProjectReferenceGenerator_Build"
       Condition="'$(BuildProjectReferences)' == 'true'"
       Inputs="@(ServiceProjectReference)"
-      Outputs="@(ServiceProjectReference -> '%(ProjectTargetPath)')">
+      Outputs="%(ProjectTargetPath)">
-    <MSBuild Projects="@(ServiceProjectReference)"
+    <MSBuild Projects="@(ServiceProjectReference -> Distinct())"
         BuildInParallel="$(BuildInParallel)"
-        RemoveProperties="TargetFrameworks;RuntimeIdentifier"
+        RemoveProperties="TargetFramework;TargetFrameworks;RuntimeIdentifier"
-        Targets="Build" />
+        Targets="Restore;Build" />
   </Target>
 
-  <Target Name="_ServiceProjectReferenceGenerator_Core"
+  <Target Name="_ServiceProjectReferenceGenerator_GetItems">
-      Condition="'@(ServiceProjectReference)' != ''"
+    <GetCurrentItems Input="$(GeneratorMetadata)">
-      DependsOnTargets="@(ServiceProjectReference -> '%(DocumentGenerator)DocumentGenerator')" />
+      <Output TaskParameter="Outputs" ItemName="CurrentServiceProjectReference" />
+    </GetCurrentItems>
+  </Target>
 
-  <Target Name="ServiceProjectReferenceGenerator"
+  <Target Name="_ServiceProjectReferenceGenerator_Inner" DependsOnTargets="_ServiceProjectReferenceGenerator_GetItems;$(GeneratorTarget)" />
-      Condition="'@(ServiceProjectReference)' != ''"
+
-      DependsOnTargets="$(ServiceProjectReferenceGeneratorDependsOn)" />
+  <Target Name="_ServiceProjectReferenceGenerator_Core" Inputs="@(ServiceProjectReference)" Outputs="%(DocumentPath)">
+    <Message Importance="high" Text="%0A_ServiceProjectReferenceGenerator_Core:" />
+    <Message Importance="high" Text="  @(ServiceProjectReference): %(DocumentPath)" />
+
+    <MSBuild BuildInParallel="$(BuildInParallel)"
+        Projects="$(MSBuildProjectFullPath)"
+        Properties="GeneratorTargetPath=%(ServiceProjectReference.DocumentPath);GeneratorTarget=%(DocumentGenerator)DocumentGenerator;GeneratorMetadata=%(SerializedMetadata);TargetFramework=%(ProjectTargetFramework)"
+        RemoveProperties="TargetFrameworks;RuntimeIdentifier"
+        Targets="_ServiceProjectReferenceGenerator_Inner" />
+  </Target>
+
+  <Target Name="_ServiceProjectReferenceGenerator_SetMetadata" Condition="'@(ServiceProjectReference)' != ''">
+    <!-- _ServiceProjectReferenceGenerator_GetMetadata guarantees %(DocumentPath) values are unique. -->
+    <ItemGroup>
+      <ServiceFileReference Remove="@(ServiceProjectReference -> '%(DocumentPath)')" />
+      <!-- Condition here is temporary. Useful while DefaultDocumentGenerator fails. -->
+      <ServiceFileReference Include="@(ServiceProjectReference -> '%(DocumentPath)')"
+          Condition="Exists('%(DocumentPath)')"
+          SourceProject="%(FullPath)" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="ServiceProjectReferenceGenerator" DependsOnTargets="$(ServiceProjectReferenceGeneratorDependsOn)" />
 
   <!-- DefaultDocumentGenerator -->
 
-  <Target Name="_DefaultDocumentGenerator_GetMetadata">
+  <Target Name="DefaultDocumentGenerator">
+    <Message Importance="high" Text="%0ADefaultDocumentGenerator:" />
+    <Message Importance="high" Text="  @(CurrentServiceProjectReference): %(DocumentPath)" />
+
     <ItemGroup>
-      <_Temporary Remove="@(_Temporary)" />
+      <!-- @(CurrentServiceProjectReference) item group will never contain more than one item. -->
-      <_Temporary Include="@(ServiceProjectReference -> WithMetadataValue('DocumentGenerator', 'Default'))" />
+      <CurrentServiceProjectReference Update="@(CurrentServiceProjectReference)">
+        <Command>dotnet getdocument --no-build --project %(FullPath) --output %(DocumentPath)</Command>
+        <DefaultDocumentGeneratorOptions
+            Condition="'%(DefaultDocumentGeneratorOptions)' == ''">$(DefaultDocumentGeneratorDefaultOptions)</DefaultDocumentGeneratorOptions>
+      </CurrentServiceProjectReference>
+      <CurrentServiceProjectReference Update="@(_Temporary)">
+        <Command>%(Command) --framework %(ProjectTargetFramework)</Command>
+        <Command Condition="'%(ProjectConfiguration)' == ''">%(Command) --configuration $(Configuration)</Command>
+        <Command Condition="'%(ProjectConfiguration)' != ''">%(Command) --configuration %(ProjectConfiguration)</Command>
+        <Command Condition="'%(Method)' != ''">%(Command) --method %(Method)</Command>
+        <Command Condition="'%(Service)' != ''">%(Command) --service %(Service)</Command>
+        <Command Condition="'%(Uri)' != ''">%(Command) --uri %(Uri)</Command>
+        <Command
+            Condition="'%(DefaultDocumentGeneratorOptions)' != ''">%(Command) %(DefaultDocumentGeneratorOptions)</Command>
+      </CurrentServiceProjectReference>
     </ItemGroup>
 
-    <Error Condition="'@(_Temporary)' != '' AND '%(_Temporary.Method)' != '' AND '%(_Temporary.Uri)' != ''"
+    <Message Importance="high" Text="%0A%(CurrentServiceProjectReference.Command)" />
-        Text="ServiceProjectReference items '@(_Temporary)' have both Method and Uri metadata." />
+    <Exec IgnoreExitCode="$([System.IO.File]::Exists('%(DocumentPath)'))" Command="%(CurrentServiceProjectReference.Command)" />
-    <Error Condition="'@(_Temporary)' != '' AND '%(_Temporary.Service)' != '' AND '%(_Temporary.Uri)' != ''"
-        Text="ServiceProjectReference items '@(_Temporary)' have both Service and Uri metadata." />
   </Target>
 
-  <Target Name="_DefaultDocumentGenerator_Core" Inputs="%(_Temporary.ProjectTargetPath)" Outputs="%(_Temporary.DocumentPath)">
-    <!-- aspnetcore2swagger -->
-    <PropertyGroup>
-      <_Command>dotnet getdocument --configuration $(Configuration) --no-build</_Command>
-    </PropertyGroup>
-    <ItemGroup>
-      <_Temporary Update="@(_Temporary)">
-        <Options
-          Condition="'%(_Temporary.Options)' == '' AND '$(DefaultDocumentGeneratorDefaultOptions)' != ''">$(DefaultDocumentGeneratorDefaultOptions)</Options>
-        <Command>$(_Command) --project %(FullPath) --output %(DocumentPath) --framework %(TargetFramework)</Command>
-      </_Temporary>
-      <_Temporary Update="@(_Temporary)">
-        <Command Condition="'%(_Temporary.Uri)' != ''">%(Command) --uri %(_Temporary.Uri)</Command>
-      </_Temporary>
-      <_Temporary Update="@(_Temporary)">
-        <Command Condition="'%(_Temporary.Service)' != ''">%(Command) --service %(_Temporary.Service) --method %(_Temporary.Method)</Command>
-      </_Temporary>
-      <_Temporary Update="@(_Temporary)">
-        <Command Condition="'%(_Temporary.Options)' != ''">%(Command) %(_Temporary.Options)</Command>
-      </_Temporary>
-    </ItemGroup>
-
-    <Message Importance="high" Text="%0A%(_Temporary.Command)" />
-    <Exec IgnoreExitCode="$([System.IO.File]::Exists('%(DocumentPath)'))" Command="%(_Temporary.Command)" />
-  </Target>
-
-  <!--
-    Separate from _DefaultDocumentGenerator_Core to ensure ServiceFileReference items are complete even if
-    ServiceProjectReference items are not built in any batch.
-  -->
-  <Target Name="_DefaultDocumentGenerator_SetMetadata" Condition="'@(_Temporary)' != ''">
-    <ItemGroup>
-      <ServiceFileReference Remove="@(_Temporary -> '%(DocumentPath)')" />
-      <!-- Condition here is temporary. Useful while DefaultDocumentGenerator fails. -->
-      <ServiceFileReference Include="@(_Temporary -> '%(DocumentPath)')"
-          Condition="Exists('%(_Temporary.DocumentPath)')"
-          SourceProject="%(_Temporary.FullPath)" />
-      <_Temporary Remove="@(_Temporary)" />
-    </ItemGroup>
-  </Target>
-
-  <Target Name="DefaultDocumentGenerator" DependsOnTargets="$(DefaultDocumentGeneratorDependsOn)" />
-
   <!-- ServiceUriReference support -->
 
-  <Target Name="_ServiceUriReferenceGenerator_GetMetadata">
+  <Target Name="_ServiceUriReferenceGenerator_GetMetadata" Condition="'@(ServiceUriReference)' != ''">
     <ItemGroup>
       <_Temporary Remove="@(_Temporary)" />
     </ItemGroup>
 
-    <GetUriReferenceMetadata DocumentDirectory="$(ServiceUriReferenceDirectory)" Inputs="@(ServiceUriReference)">
+    <GetUriReferenceMetadata Inputs="@(ServiceUriReference)" DocumentDirectory="$(ServiceUriReferenceDirectory)">
       <Output TaskParameter="Outputs" ItemName="_Temporary" />
     </GetUriReferenceMetadata>
 
@@ -199,9 +210,10 @@
         DestinationPath="%(DocumentPath)"
         Overwrite="$(ServiceUriReferenceCheckIfNewer)" />
 
+    <!-- _ServiceUriReferenceGenerator_GetMetadata guarantees %(DocumentPath) values are unique. -->
     <ItemGroup>
       <ServiceFileReference Remove="@(ServiceUriReference -> '%(DocumentPath)')" />
-      <ServiceFileReference Include="@(ServiceUriReference -> '%(DocumentPath)')" SourceUri="%(ServiceUriReference.Identity)" />
+      <ServiceFileReference Include="@(ServiceUriReference -> '%(DocumentPath)')" SourceUri="%(Identity)" />
     </ItemGroup>
   </Target>
 
@@ -209,12 +221,15 @@
 
   <!-- ServiceFileReference support -->
 
-  <Target Name="_ServiceFileReferenceGenerator_GetMetadata">
+  <Target Name="_ServiceFileReferenceGenerator_GetMetadata" Condition="'@(ServiceFileReference)' != ''">
     <ItemGroup>
       <_Temporary Remove="@(_Temporary)" />
     </ItemGroup>
 
-    <GetFileReferenceMetadata DocumentDirectory="$(ServiceFileReferenceDirectory)" Inputs="@(ServiceFileReference)">
+    <GetFileReferenceMetadata Inputs="@(ServiceFileReference)"
+        CSharpNamespace="$(ServiceFileReferenceCSharpNamespace)"
+        OutputDirectory="$(ServiceFileReferenceDirectory)"
+        TypeScriptNamespace="$(ServiceFileReferenceTypeScriptNamespace)">
       <Output TaskParameter="Outputs" ItemName="_Temporary" />
     </GetFileReferenceMetadata>
 
@@ -225,9 +240,38 @@
     </ItemGroup>
   </Target>
 
-  <Target Name="_ServiceFileReferenceGenerator_Core"
+  <Target Name="_ServiceFileReferenceGenerator_GetItems">
-      Condition="'@(ServiceFileReference)' != ''"
+    <GetCurrentItems Input="$(GeneratorMetadata)">
-      DependsOnTargets="@(ServiceFileReference -> '%(CodeGenerator)CodeGenerator')" />
+      <Output TaskParameter="Outputs" ItemName="CurrentServiceFileReference" />
+    </GetCurrentItems>
+  </Target>
 
-  <Target Name="ServiceFileReferenceGenerator" BeforeTargets="BeforeCompile" DependsOnTargets="$(ServiceFileReferenceGeneratorDependsOn)" />
+  <Target Name="_ServiceFileReferenceGenerator_Inner" DependsOnTargets="_ServiceFileReferenceGenerator_GetItems;$(GeneratorTarget)" />
+
+  <Target Name="_ServiceFileReferenceGenerator_Core" Inputs="@(ServiceFileReference)" Outputs="%(OutputPath)">
+    <Message Importance="high" Text="%0A_ServiceFileReferenceGenerator_Core:" />
+    <Message Importance="high" Text="  @(ServiceFileReference): %(DocumentPath)" />
+
+    <MSBuild BuildInParallel="$(BuildInParallel)"
+        Projects="$(MSBuildProjectFullPath)"
+        Properties="GeneratorTargetPath=%(ServiceProjectReference.OutputPath);GeneratorTarget=%(CodeGenerator)CodeGenerator;GeneratorMetadata=%(SerializedMetadata);TargetFramework=%(ProjectTargetFramework)"
+        RemoveProperties="TargetFrameworks;RuntimeIdentifier"
+        Targets="_ServiceFileReferenceGenerator_Inner" />
+  </Target>
+
+  <Target Name="_ServiceFileReferenceGenerator_SetMetadata" Condition="'@(ServiceFileReference)' != ''">
+    <!--
+      While %(DocumentPath) metadata may include duplicates (due to overlaps between ServiceUriReference and
+      ServiceProjectReference items), _ServiceFileReferenceGenerator_GetMetadata guarantees %(OutputPath) values are
+      unique.
+    -->
+    <ItemGroup>
+      <Compile Remove="@(ServiceFileReference -> '%(OutputPath)')" />
+      <Compile Include="@(ServiceFileReference -> '%(OutputPath)')" SourceDocument="%(FullPath)" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="ServiceFileReferenceGenerator"
+      BeforeTargets="BeforeCompile"
+      DependsOnTargets="$(ServiceFileReferenceGeneratorDependsOn)" />
 </Project>

src/Microsoft.Extensions.ApiDescription.Client/buildMultiTargeting/GenerationTasks.targets

@@ -1,29 +0,0 @@
-<?xml version="1.0" encoding="utf-8" standalone="no"?>
-<Project>
-  <!-- ServiceProjectReference support -->
-
-  <Target Name="ServiceProjectReferenceGenerator">
-    <MsBuild Projects="$(MSBuildProjectFile)"
-      Targets="ServiceProjectReferenceGenerator"
-      Properties="TargetFramework=$(TargetFrameworks.Split(';')[0])"
-      RemoveProperties="TargetFrameworks;RuntimeIdentifier" />
-  </Target>
-
-  <!-- ServiceUriReference support -->
-
-  <Target Name="ServiceUriReferenceGenerator">
-    <MsBuild Projects="$(MSBuildProjectFile)"
-      Targets="ServiceUriReferenceGenerator"
-      Properties="TargetFramework=$(TargetFrameworks.Split(';')[0])"
-      RemoveProperties="TargetFrameworks;RuntimeIdentifier" />
-  </Target>
-
-  <!-- ServiceFileReference support -->
-
-  <Target Name="ServiceFileReferenceGenerator" BeforeTargets="BeforeCompile">
-    <MsBuild Projects="$(MSBuildProjectFile)"
-      Targets="ServiceFileReferenceGenerator"
-      Properties="TargetFramework=$(TargetFrameworks.Split(';')[0])"
-      RemoveProperties="TargetFrameworks;RuntimeIdentifier" />
-  </Target>
-</Project>

src/Microsoft.Extensions.ApiDescription.Client/buildMultiTargeting/Microsoft.Extensions.ApiDescription.Client.targets

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8" standalone="no"?>
+<Project>
+  <Target Name="ServiceFileReferenceGenerator" BeforeTargets="BeforeCompile">
+    <MsBuild Projects="$(MSBuildProjectFile)"
+        Targets="ServiceFileReferenceGenerator"
+        Properties="TargetFramework=$(TargetFrameworks.Split(';')[0])"
+        RemoveProperties="TargetFrameworks;RuntimeIdentifier" />
+  </Target>
+</Project>