Amend Build project to target netstandard2.1

Author: gunndabad

src/GovUk.Frontend.AspNetCore.Build/DownloadNpmPackage.cs

@@ -34,7 +34,7 @@ public override bool Execute()
 
         async Task ExecuteAsync()
         {
-            var includePatterns = Include?.Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries) ?? ["**"];
+            var includePatterns = Include?.Split('\n', StringSplitOptions.RemoveEmptyEntries)?.Select(s => s.Trim()) ?? ["**"];
 
             var downloader = new NpmPackageDownloader();
             await downloader.DownloadPackage(Package, Version, PackageBaseDirectory ?? "", DestinationDirectory, includePatterns);

src/GovUk.Frontend.AspNetCore.Build/GovUk.Frontend.AspNetCore.Build.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>netstandard2.1</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <PackDependencies>false</PackDependencies>
     <PackFolder>tools</PackFolder>
@@ -16,6 +16,7 @@
     <PackageReference Include="Microsoft.Build.Utilities.Core" Version="17.8.27"  />
     <!-- TODO Figure out how to get this out of the generated NuGet package's dependency list -->
     <PackageReference Include="Microsoft.Extensions.FileSystemGlobbing" Version="8.0.0" Pack="true" PrivateAssets="all" />
+    <PackageReference Include="System.Text.Json" Version="8.0.5" Pack="true" PrivateAssets="all" />
     <PackageReference Include="MinVer" Version="2.3.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

src/GovUk.Frontend.AspNetCore.Build/NpmPackageDownloader.cs

@@ -27,9 +27,18 @@ public async Task DownloadPackage(
         string destinationDirectory,
         IEnumerable<string> includePatterns)
     {
-        ArgumentNullException.ThrowIfNull(package);
-        ArgumentNullException.ThrowIfNull(version);
-        ArgumentNullException.ThrowIfNull(destinationDirectory);
+        if (package is null)
+        {
+            throw new ArgumentNullException(nameof(package));
+        }
+        if (version is null)
+        {
+            throw new ArgumentNullException(nameof(version));
+        }
+        if (destinationDirectory is null)
+        {
+            throw new ArgumentNullException(nameof(destinationDirectory));
+        }
 
         Directory.CreateDirectory(destinationDirectory);
 
@@ -60,13 +69,13 @@ public async Task DownloadPackage(
 
         var results = matcher.Execute(contents);
 
-        await Parallel.ForEachAsync(
-            results.Files,
-            async (r, ct) =>
-            {
-                var hash = ((NpmPackageFileInfo)contents.GetFile(r.Path)!).Hash;
-                await DownloadFileAsync(package, version, r.Path, hash, packageBaseDirectory, destinationDirectory, ct);
-            });
+        var tasks = results.Files.Select(r =>
+        {
+            var hash = ((NpmPackageFileInfo)contents.GetFile(r.Path)!).Hash;
+            return DownloadFileAsync(package, version, r.Path, hash, packageBaseDirectory, destinationDirectory, CancellationToken.None);
+        });
+
+        await Task.WhenAll(tasks);
     }
 
     private async Task DownloadFileAsync(
@@ -85,7 +94,7 @@ private async Task DownloadFileAsync(
         {
             await using var efs = File.OpenRead(destinationPath);
             using var sha = SHA256.Create();
-            var currentFileHash = Convert.ToBase64String(await sha.ComputeHashAsync(efs, cancellationToken));
+            var currentFileHash = Convert.ToBase64String(sha.ComputeHash(efs));
 
             if (currentFileHash == hash)
             {
@@ -102,7 +111,7 @@ private async Task DownloadFileAsync(
         Directory.CreateDirectory(destinationDirectory);
 
         await using var fs = File.Create(destinationPath);
-        await response.Content.CopyToAsync(fs, cancellationToken);
+        await response.Content.CopyToAsync(fs);
     }
 
     private async Task<DirectoryInfoBase> GetPackageContentsAsync(string package, string version)