Include compiler error details (file, line, column) in Build action structured response

.config/dotnet-tools.json

@@ -2,4 +2,4 @@
   "version": 1,
   "isRoot": true,
   "tools": {}
-}
+}

DotNetMcp.Tests/Errors/ErrorResultFactoryTests.cs

@@ -1347,5 +1347,170 @@ public void CreateResult_WithExitCode106_SerializesToValidJson()
     }
 
     #endregion
+
+    #region ParseBuildOutput Tests
+
+    [Fact]
+    public void ParseBuildOutput_WithCompilerError_ReturnsFailureWithDiagnostic()
+    {
+        // Arrange - simulate what DotNetCommandExecutor.ExecuteCommandAsync returns for a failed build
+        var rawOutput = """
+            Command: dotnet build "MyProject.csproj"
+            Build FAILED.
+
+            Build FAILED.
+
+            Error(s)
+            Program.cs(9,51): error CS0246: The type or namespace name 'IRenderable' could not be found (are you missing a using directive or an assembly reference?) [MyProject.csproj]
+               0 Warning(s)
+               1 Error(s)
+
+            Exit Code: 1
+            """;
+
+        // Act
+        var result = ErrorResultFactory.ParseBuildOutput(rawOutput, project: "MyProject.csproj", configuration: "Debug");
+
+        // Assert
+        Assert.False(result.Success);
+        Assert.Equal("MyProject.csproj", result.Project);
+        Assert.Equal("Debug", result.Configuration);
+        Assert.Equal(1, result.ErrorCount);
+        Assert.Equal(0, result.WarningCount);
+        Assert.Contains("FAILED", result.Summary, StringComparison.OrdinalIgnoreCase);
+
+        Assert.NotNull(result.Errors);
+        var diag = Assert.Single(result.Errors);
+        Assert.Equal("CS0246", diag.Code);
+        Assert.Contains("IRenderable", diag.Message);
+        Assert.Equal("error", diag.Severity);
+        Assert.Equal(9, diag.Line);
+        Assert.Equal(51, diag.Column);
+        Assert.False(string.IsNullOrWhiteSpace(diag.File));
+        Assert.Contains("Program.cs", diag.File);
+
+        Assert.Null(result.Warnings);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithWarning_ReturnsSuccessWithWarningDiagnostic()
+    {
+        // Arrange
+        var rawOutput = """
+            Command: dotnet build "MyProject.csproj"
+            Program.cs(3,1): warning CS0219: The variable 'x' is assigned but its value is never used [MyProject.csproj]
+            Build succeeded.
+               1 Warning(s)
+               0 Error(s)
+
+            Exit Code: 0
+            """;
+
+        // Act
+        var result = ErrorResultFactory.ParseBuildOutput(rawOutput, project: "MyProject.csproj");
+
+        // Assert
+        Assert.True(result.Success);
+        Assert.Equal(0, result.ErrorCount);
+        Assert.Equal(1, result.WarningCount);
+        Assert.Contains("succeeded", result.Summary, StringComparison.OrdinalIgnoreCase);
+
+        Assert.Null(result.Errors);
+        Assert.NotNull(result.Warnings);
+        var diag = Assert.Single(result.Warnings);
+        Assert.Equal("CS0219", diag.Code);
+        Assert.Equal("warning", diag.Severity);
+        Assert.Equal(3, diag.Line);
+        Assert.Equal(1, diag.Column);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithSuccessNoWarnings_ReturnsCleanSuccess()
+    {
+        // Arrange
+        var rawOutput = """
+            Command: dotnet build "MyProject.csproj"
+            Build succeeded.
+               0 Warning(s)
+               0 Error(s)
+
+            Exit Code: 0
+            """;
+
+        // Act
+        var result = ErrorResultFactory.ParseBuildOutput(rawOutput, project: "MyProject.csproj");
+
+        // Assert
+        Assert.True(result.Success);
+        Assert.Equal(0, result.ErrorCount);
+        Assert.Equal(0, result.WarningCount);
+        Assert.Equal("Build succeeded", result.Summary);
+        Assert.Null(result.Errors);
+        Assert.Null(result.Warnings);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithNullInput_ReturnsSafeSuccess()
+    {
+        var result = ErrorResultFactory.ParseBuildOutput(null!);
+        Assert.True(result.Success);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithEmptyInput_ReturnsSafeSuccess()
+    {
+        var result = ErrorResultFactory.ParseBuildOutput(string.Empty);
+        Assert.True(result.Success);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithAbsoluteProjectPath_SanitizesToFilename()
+    {
+        // Absolute project paths should be reduced to just the filename to avoid leaking machine paths.
+        // Path.GetFullPath ensures this is a rooted/absolute path on any platform.
+        var absolutePath = Path.GetFullPath(Path.Join("my-project", "MyApp.csproj"));
+        var rawOutput = "Command: dotnet build\nBuild succeeded.\n   0 Warning(s)\n   0 Error(s)\nExit Code: 0";
+
+        var result = ErrorResultFactory.ParseBuildOutput(rawOutput, project: absolutePath);
+
+        Assert.True(result.Success);
+        Assert.Equal("MyApp.csproj", result.Project);
+    }
+
+    [Fact]
+    public void ParseBuildOutput_WithRelativeProjectPath_PreservesAsIs()
+    {
+        var result = ErrorResultFactory.ParseBuildOutput(
+            "Command: dotnet build\nBuild succeeded.\nExit Code: 0",
+            project: "src/MyApp.csproj");
+
+        Assert.Equal("src/MyApp.csproj", result.Project);
+    }
+
+    #endregion
+
+    #region ErrorResult File/Line/Column Tests
+
+    [Fact]
+    public void CreateResult_WithCompilerError_PopulatesFileLineColumn()
+    {
+        // Arrange
+        var output = "Program.cs(9,51): error CS0246: The type or namespace name 'IRenderable' could not be found";
+        var error = "";
+        var exitCode = 1;
+
+        // Act
+        var result = ErrorResultFactory.CreateResult(output, error, exitCode);
+
+        // Assert
+        var errorResponse = Assert.IsType<ErrorResponse>(result);
+        var parsedError = Assert.Single(errorResponse.Errors);
+        Assert.Equal("CS0246", parsedError.Code);
+        Assert.Contains("Program.cs", parsedError.File);
+        Assert.Equal(9, parsedError.Line);
+        Assert.Equal(51, parsedError.Column);
+    }
+
+    #endregion
 }
 

DotNetMcp.Tests/Scenarios/BuildErrorScenarioTests.cs

@@ -1,3 +1,4 @@
+using System.Text.Json;
 using DotNetMcp;
 using Xunit;
 
@@ -26,14 +27,14 @@ public async Task Scenario_DotnetProject_Build_WithCompileError_ReturnsMachineRe
         var projectDir = Path.GetDirectoryName(projectPath);
         Assert.False(string.IsNullOrWhiteSpace(projectDir));
 
-        // Introduce a compile error.
+        // Introduce a compile error: reference an unresolved type so we get a CS0246 diagnostic.
         var programPath = Path.Join(projectDir!, "Program.cs");
         Assert.True(File.Exists(programPath), "Expected Program.cs to exist");
-        await File.AppendAllTextAsync(programPath, "\nthis_will_not_compile\n", cancellationToken);
+        await File.WriteAllTextAsync(programPath, "IAmABogusType bogus = new IAmABogusType();\n", cancellationToken);
 
         await using var client = await McpScenarioClient.CreateAsync(cancellationToken);
 
-        var text = await client.CallToolTextAsync(
+        var result = await client.CallToolAsync(
             toolName: "dotnet_project",
             args: new Dictionary<string, object?>
             {
@@ -43,7 +44,49 @@ public async Task Scenario_DotnetProject_Build_WithCompileError_ReturnsMachineRe
             },
             cancellationToken);
 
-        // Contract sanity: output should mention a build/compile failure.
+        // Text content sanity: output should mention a build/compile failure.
+        var text = result.GetText();
         Assert.Contains("error", text, StringComparison.OrdinalIgnoreCase);
+
+        // Structured content: verify BuildResult is present and includes compiler error details.
+        Assert.True(result.StructuredContent.HasValue, "Expected structured content in Build response");
+        var structuredJson = result.StructuredContent!.Value.GetRawText();
+        Assert.False(string.IsNullOrWhiteSpace(structuredJson));
+
+        using var doc = JsonDocument.Parse(structuredJson);
+        var root = doc.RootElement;
+
+        // success should be false
+        Assert.True(root.TryGetProperty("success", out var successProp));
+        Assert.False(successProp.GetBoolean());
+
+        // errorCount should be > 0
+        Assert.True(root.TryGetProperty("errorCount", out var errorCountProp));
+        Assert.True(errorCountProp.GetInt32() > 0, "Expected at least one error in errorCount");
+
+        // errors array should be present and non-empty
+        Assert.True(root.TryGetProperty("errors", out var errorsProp), "Expected 'errors' array in BuildResult");
+        Assert.Equal(JsonValueKind.Array, errorsProp.ValueKind);
+        Assert.True(errorsProp.GetArrayLength() > 0, "Expected at least one entry in 'errors' array");
+
+        // Each diagnostic should have file, line, column, code, message
+        foreach (var diagnostic in errorsProp.EnumerateArray())
+        {
+            Assert.True(diagnostic.TryGetProperty("code", out var codeProp), "Diagnostic missing 'code'");
+            Assert.False(string.IsNullOrWhiteSpace(codeProp.GetString()), "Diagnostic 'code' should not be empty");
+
+            Assert.True(diagnostic.TryGetProperty("message", out var msgProp), "Diagnostic missing 'message'");
+            Assert.False(string.IsNullOrWhiteSpace(msgProp.GetString()), "Diagnostic 'message' should not be empty");
+
+            // file/line/column should be present for Roslyn compiler errors
+            Assert.True(diagnostic.TryGetProperty("file", out var fileProp), "Diagnostic missing 'file'");
+            Assert.False(string.IsNullOrWhiteSpace(fileProp.GetString()), "Diagnostic 'file' should not be empty");
+
+            Assert.True(diagnostic.TryGetProperty("line", out var lineProp), "Diagnostic missing 'line'");
+            Assert.True(lineProp.GetInt32() > 0, "Diagnostic 'line' should be > 0");
+
+            Assert.True(diagnostic.TryGetProperty("column", out var colProp), "Diagnostic missing 'column'");
+            Assert.True(colProp.GetInt32() > 0, "Diagnostic 'column' should be > 0");
+        }
     }
 }

DotNetMcp.Tests/Scenarios/McpScenarioClient.cs

@@ -85,6 +85,23 @@ public async Task<string> CallToolTextAsync(string toolName, Dictionary<string,
         return text ?? string.Empty;
     }
 
+    /// <summary>
+    /// Calls an MCP tool and returns the full <see cref="CallToolResult"/>, including any structured content.
+    /// </summary>
+    /// <param name="toolName">The name of the tool to call.</param>
+    /// <param name="args">The arguments to pass to the tool.</param>
+    /// <param name="cancellationToken">A cancellation token to cancel the operation.</param>
+    /// <returns>The full <see cref="CallToolResult"/> from the tool response.</returns>
+    public async Task<CallToolResult> CallToolAsync(string toolName, Dictionary<string, object?> args, CancellationToken cancellationToken)
+    {
+        if (_client is null)
+        {
+            throw new InvalidOperationException("MCP client not initialized.");
+        }
+
+        return await _client.CallToolAsync(toolName, args, cancellationToken: cancellationToken);
+    }
+
     /// <summary>
     /// Disposes the MCP client and releases all associated resources.
     /// </summary>

DotNetMcp.Tests/Tools/ConsolidatedProjectToolTests.cs

@@ -1807,6 +1807,32 @@ public async Task DotnetProject_Build_WithAllNewFlags_WiresAll()
         MachineReadableCommandAssertions.AssertExecutedDotnetCommand(result, "dotnet build \"MyProject.csproj\" -c Release -f net8.0 --no-restore -v minimal -o \"out\"");
     }
 
+    [Fact]
+    public async Task DotnetProject_Build_ReturnsStructuredContent()
+    {
+        // Build action should always return structured content (BuildResult) regardless of success/failure.
+        var callResult = await _tools.DotnetProject(
+            action: DotnetProjectAction.Build,
+            project: "MyProject.csproj",
+            configuration: "Release");
+
+        // Text content should still be present
+        var text = callResult.GetText();
+        Assert.NotNull(text);
+
+        // Structured content must be populated
+        Assert.True(callResult.StructuredContent.HasValue, "Build action should always return structured content");
+        var structuredJson = callResult.StructuredContent!.Value.GetRawText();
+        Assert.False(string.IsNullOrWhiteSpace(structuredJson));
+
+        // The structured content should be a valid BuildResult with success/errorCount/summary
+        using var doc = System.Text.Json.JsonDocument.Parse(structuredJson);
+        var root = doc.RootElement;
+        Assert.True(root.TryGetProperty("success", out _), "BuildResult should have 'success' field");
+        Assert.True(root.TryGetProperty("errorCount", out _), "BuildResult should have 'errorCount' field");
+        Assert.True(root.TryGetProperty("summary", out _), "BuildResult should have 'summary' field");
+    }
+
     [Fact]
     public async Task DotnetProject_Restore_WithVerbosity_WiresFlag()
     {