Update source-build-externals and package source mapping logic

Author: MichaelSimons

eng/Version.Details.xml

@@ -186,7 +186,7 @@
     </Dependency>
     <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="7.0.0-alpha.1.22402.1">
       <Uri>https://github.com/MichaelSimons/source-build-externals</Uri>
-      <Sha>97d5463ffc198019d4b68f18d3c0a4e0976782bb</Sha>
+      <Sha>85d7e996e497861648ffbfd0e929b2b627ce7f46</Sha>
       <SourceBuild RepoName="source-build-externals" ManagedOnly="true" />
     </Dependency>
     <Dependency Name="Microsoft.SourceBuild.Intermediate.symreader" Version="1.4.0-beta2-21475-02">

src/SourceBuild/tarball/content/tools-local/tasks/Microsoft.DotNet.SourceBuild.Tasks.XPlat/UpdateNuGetConfigPackageSourcesMappings.cs

@@ -47,11 +47,12 @@ public override bool Execute()
             }
 
             // Union all package sources to get the distinct list.  These will get added to the source-build sources.
-            IEnumerable<string> packagePatterns = pkgSrcMappingElement.Descendants()
+            string[] packagePatterns = pkgSrcMappingElement.Descendants()
                 .Where(e => e.Name == "packageSource")
                 .SelectMany(e => e.Descendants().Where(e => e.Name == "package"))
                 .Select(e => e.Attribute("pattern").Value)
-                .Distinct();
+                .Distinct()
+                .ToArray();
 
             if (!BuildWithOnlineSources)
             {
@@ -60,6 +61,11 @@ public override bool Execute()
             }
 
             XElement pkgSrcMappingClearElement = pkgSrcMappingElement.Descendants().FirstOrDefault(e => e.Name == "clear");
+            if (pkgSrcMappingClearElement == null)
+            {
+                pkgSrcMappingClearElement = new XElement("clear");
+                pkgSrcMappingElement.AddFirst(pkgSrcMappingClearElement);
+            }
 
             foreach (string packageSource in SourceBuildSources)
             {
@@ -69,15 +75,7 @@ public override bool Execute()
                     pkgSrc.Add(new XElement("package", new XAttribute("pattern", packagePattern)));
                 }
 
-                if (pkgSrcMappingClearElement != null)
-                {
-                    pkgSrcMappingClearElement.AddAfterSelf(pkgSrc);
-                }
-                else
-                {
-                    pkgSrcMappingElement.AddFirst(pkgSrc);
-                    pkgSrcMappingElement.AddFirst(new XElement("clear"));
-                }
+                pkgSrcMappingElement.AddAfterSelf(pkgSrc);
             }
 
             using (var writer = XmlWriter.Create(NuGetConfigFile, new XmlWriterSettings { NewLineChars = newLineChars, Indent = true }))