Add Rust AppHost scaffold regression coverage (#17283)

* Add Rust AppHost scaffold regression coverage

Centralize the Rust AppHost marker filename and add language support tests that assert Rust scaffolding emits apphost.rs without apphost.ts, detection requires the Rust marker plus Cargo.toml, and the runtime spec remains cargo run.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Test Rust detection requires Cargo manifest

Add a negative Rust language-support test covering apphost.rs without Cargo.toml so detection keeps requiring the Cargo manifest.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Use collection assertion for Rust scaffold files

Replace individual scaffold file key assertions with Assert.Collection so the test verifies the exact Rust scaffold file set.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: sebastienros

src/Aspire.Hosting.CodeGeneration.Rust/RustLanguageSupport.cs

@@ -15,14 +15,15 @@ internal sealed class RustLanguageSupport : ILanguageSupport
     /// The language/runtime identifier for Rust.
     /// </summary>
     private const string LanguageId = "rust";
+    private const string AppHostFileName = "apphost.rs";
 
     /// <summary>
     /// The code generation target language. This maps to the ICodeGenerator.Language property.
     /// </summary>
     private const string CodeGenTarget = "Rust";
 
     private const string LanguageDisplayName = "Rust";
-    private static readonly string[] s_detectionPatterns = ["apphost.rs"];
+    private static readonly string[] s_detectionPatterns = [AppHostFileName];
 
     /// <inheritdoc />
     public string Language => LanguageId;
@@ -68,8 +69,8 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             lazy_static = "1.4"
             """;
 
-        // Create apphost.rs marker file for detection
-        files["apphost.rs"] = """
+        // Create the marker file the CLI uses to recognize Rust AppHosts.
+        files[AppHostFileName] = """
             // Aspire Rust AppHost marker file
             // This file is used to detect the project type.
             // The actual entry point is in src/main.rs.
@@ -105,7 +106,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// <inheritdoc />
     public DetectionResult Detect(string directoryPath)
     {
-        var appHostPath = Path.Combine(directoryPath, "apphost.rs");
+        var appHostPath = Path.Combine(directoryPath, AppHostFileName);
         if (!File.Exists(appHostPath))
         {
             return DetectionResult.NotFound;
@@ -117,7 +118,7 @@ public DetectionResult Detect(string directoryPath)
             return DetectionResult.NotFound;
         }
 
-        return DetectionResult.Found(LanguageId, "apphost.rs");
+        return DetectionResult.Found(LanguageId, AppHostFileName);
     }
 
     /// <inheritdoc />

tests/Aspire.Hosting.CodeGeneration.Rust.Tests/Aspire.Hosting.CodeGeneration.Rust.Tests.csproj

@@ -17,6 +17,7 @@
 
   <ItemGroup>
     <Compile Include="$(TestsSharedDir)TestModuleInitializer.cs" Link="shared/TestModuleInitializer.cs" />
+    <Compile Include="$(TestsSharedDir)TempDirectory.cs" Link="shared/TempDirectory.cs" />
     <!-- Share test types with TypeScript tests -->
     <Compile Include="..\Aspire.Hosting.CodeGeneration.TypeScript.Tests\TestTypes\*.cs" Link="TestTypes\%(Filename)%(Extension)" />
   </ItemGroup>

tests/Aspire.Hosting.CodeGeneration.Rust.Tests/RustLanguageSupportTests.cs

@@ -0,0 +1,83 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.TypeSystem;
+
+namespace Aspire.Hosting.CodeGeneration.Rust.Tests;
+
+public class RustLanguageSupportTests
+{
+    private readonly RustLanguageSupport _languageSupport = new();
+
+    [Fact]
+    public void Scaffold_CreatesRustAppHostFilesOnly()
+    {
+        using var testDir = new TestTempDirectory();
+
+        var files = _languageSupport.Scaffold(new ScaffoldRequest
+        {
+            TargetPath = testDir.Path,
+            ProjectName = "RustApp"
+        });
+
+        Assert.Collection(
+            files.Keys.Order(StringComparer.Ordinal),
+            key => Assert.Equal("Cargo.toml", key),
+            key => Assert.Equal("apphost.rs", key),
+            key => Assert.Equal("apphost.run.json", key),
+            key => Assert.Equal("src/main.rs", key));
+    }
+
+    [Fact]
+    public void Detect_ReturnsRustAppHostWhenMarkerAndCargoExist()
+    {
+        using var testDir = new TestTempDirectory();
+
+        File.WriteAllText(Path.Combine(testDir.Path, "apphost.rs"), "// marker");
+        File.WriteAllText(Path.Combine(testDir.Path, "Cargo.toml"), "[package]");
+
+        var result = _languageSupport.Detect(testDir.Path);
+
+        Assert.True(result.IsValid);
+        Assert.Equal("rust", result.Language);
+        Assert.Equal("apphost.rs", result.AppHostFile);
+    }
+
+    [Fact]
+    public void Detect_DoesNotTreatTypeScriptAppHostAsRust()
+    {
+        using var testDir = new TestTempDirectory();
+
+        File.WriteAllText(Path.Combine(testDir.Path, "apphost.ts"), "// typescript");
+        File.WriteAllText(Path.Combine(testDir.Path, "Cargo.toml"), "[package]");
+
+        var result = _languageSupport.Detect(testDir.Path);
+
+        Assert.False(result.IsValid);
+    }
+
+    [Fact]
+    public void Detect_RequiresCargoManifest()
+    {
+        using var testDir = new TestTempDirectory();
+
+        File.WriteAllText(Path.Combine(testDir.Path, "apphost.rs"), "// marker");
+
+        var result = _languageSupport.Detect(testDir.Path);
+
+        Assert.False(result.IsValid);
+    }
+
+    [Fact]
+    public void GetRuntimeSpec_UsesCargoRun()
+    {
+        var runtimeSpec = _languageSupport.GetRuntimeSpec();
+
+        Assert.Equal("rust", runtimeSpec.Language);
+        Assert.Equal("Rust", runtimeSpec.DisplayName);
+        Assert.Equal("Rust", runtimeSpec.CodeGenLanguage);
+        Assert.Equal(["apphost.rs"], runtimeSpec.DetectionPatterns);
+        Assert.Equal("cargo", runtimeSpec.Execute.Command);
+        Assert.Equal(["run"], runtimeSpec.Execute.Args);
+    }
+}