Check for empty snippets (#5207)

Resolves #5206

tools/snippet-generator/Azure.Sdk.Tools.SnippetGenerator.Tests/Azure.Sdk.Tools.SnippetGenerator.Tests.csproj

@@ -6,12 +6,25 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.4" />
-      <PackageReference Include="NUnit" Version="3.13.1" />
+      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+      <PackageReference Include="NUnit" Version="3.13.2" />
+      <PackageReference Include="NUnit3TestAdapter" Version="4.3.1" />
     </ItemGroup>
 
     <ItemGroup>
       <ProjectReference Include="..\Azure.Sdk.Tools.SnippetGenerator\Azure.Sdk.Tools.SnippetGenerator.csproj" />
     </ItemGroup>
 
+    <ItemGroup>
+      <Compile Update="TestData\Snippets.cs">
+        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      </Compile>
+    </ItemGroup>
+
+    <ItemGroup>
+      <None Update="TestData\EmptySnippet.md">
+        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      </None>
+    </ItemGroup>
+
 </Project>

tools/snippet-generator/Azure.Sdk.Tools.SnippetGenerator.Tests/DirectoryProcessorTests.cs

@@ -0,0 +1,20 @@
+using System;
+using System.IO;
+using NUnit.Framework;
+
+namespace Azure.Sdk.Tools.SnippetGenerator.Tests
+{
+    public class DirectoryProcessorTests
+    {
+        [Test]
+        public void DirectoryProcessorValidatesEmptySnippets()
+        {
+            var path = Path.Join(TestContext.CurrentContext.TestDirectory, "TestData");
+            var files = new string[] { Path.Join(path, "EmptySnippet.md") };
+            var sut = new DirectoryProcessor(path);
+
+            InvalidOperationException ex = Assert.ThrowsAsync<InvalidOperationException>(async () => await sut.ProcessAsync(files));
+            StringAssert.Contains("Snippet 'Snippet:EmptySnippet' is empty", ex.Message);
+        }
+    }
+}

tools/snippet-generator/Azure.Sdk.Tools.SnippetGenerator.Tests/TestData/EmptySnippet.md

@@ -0,0 +1,2 @@
+```C# Snippet:EmptySnippet
+```

tools/snippet-generator/Azure.Sdk.Tools.SnippetGenerator.Tests/TestData/Snippets.cs

@@ -0,0 +1,17 @@
+using NUnit.Framework;
+
+namespace Azure.Sdk.Tools.SnippetGenerator.TestData
+{
+    public class Snippets
+    {
+        [Test]
+        public void EmptySnippet()
+        {
+#if SHOULD_NEVER_BE_DEFINED
+            #region Snippet:EmptySnippet
+            throw new NotImplementedException();
+            #endregion
+#endif
+        }
+    }
+}

tools/snippet-generator/Azure.Sdk.Tools.SnippetGenerator/DirectoryProcessor.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
 using System;
@@ -38,11 +38,16 @@ namespace Azure.Sdk.Tools.SnippetGenerator
             _snippets = new Lazy<Task<List<Snippet>>>(DiscoverSnippetsAsync);
         }
 
-        public async Task<IEnumerable<string>> ProcessAsync()
+        public async Task<IEnumerable<string>> ProcessAsync(IEnumerable<string> files = null)
         {
-            List<string> files = new List<string>();
-            files.AddRange(Directory.EnumerateFiles(_directory, "*.md", SearchOption.AllDirectories));
-            files.AddRange(Directory.EnumerateFiles(_directory, "*.cs", SearchOption.AllDirectories));
+            if (files is null)
+            {
+                List<string> discoveredFiles = new();
+                discoveredFiles.AddRange(Directory.EnumerateFiles(_directory, "*.md", SearchOption.AllDirectories));
+                discoveredFiles.AddRange(Directory.EnumerateFiles(_directory, "*.cs", SearchOption.AllDirectories));
+
+                files = discoveredFiles;
+            }
 
             foreach (var file in files)
             {
@@ -64,6 +69,11 @@ namespace Azure.Sdk.Tools.SnippetGenerator
                     selectedSnippet.IsUsed = true;
                     Console.WriteLine($"Replaced {selectedSnippet.Name} in {file}");
                     var result = FormatSnippet(selectedSnippet.Text);
+                    if (string.IsNullOrWhiteSpace(result))
+                    {
+                        throw new InvalidOperationException($"Snippet '{s}' is empty. Did you remember to implement the snippet code or are preprocessor conditions excluding it?");
+                    }
+
                     return result;
                 }
 
@@ -339,4 +349,4 @@ namespace Azure.Sdk.Tools.SnippetGenerator
             }
         }
     }
-}
+}