Emit build-graph.json for editor tooling

src/Fallout.Build/Execution/Extensions/SerializeBuildGraphAttribute.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Fallout.Common.Execution;
+using Fallout.Common.IO;
+using Fallout.Common.Utilities;
+
+namespace Fallout.Build.Execution.Extensions;
+
+/// <summary>
+/// Emits <c>build-graph.json</c> into the temporary directory on every build initialization,
+/// giving editor tooling (the VS Code extension) a machine-readable projection of the target
+/// graph: names, descriptions, the default/listed flags, the declaring type, and the four
+/// relation kinds. Best-effort — a serialization failure never fails the build.
+/// </summary>
+internal class SerializeBuildGraphAttribute : BuildExtensionAttributeBase, IOnBuildInitialized
+{
+    private const string GraphFileName = "build-graph.json";
+
+    /// <summary>Schema version consumers gate on; bump only on a breaking shape change.</summary>
+    private const int SchemaVersion = 1;
+
+    private static readonly JsonSerializerOptions serializerOptions =
+        new()
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            WriteIndented = true,
+        };
+
+    private AbsolutePath GraphFile => Build.TemporaryDirectory / GraphFileName;
+
+    public void OnBuildInitialized(
+        IReadOnlyCollection<ExecutableTarget> executableTargets,
+        IReadOnlyCollection<ExecutableTarget> executionPlan)
+    {
+        try
+        {
+            var model = new BuildGraphModel(
+                SchemaVersion,
+                ResolveFalloutVersion(),
+                executableTargets
+                    .OrderBy(x => x.Name, StringComparer.Ordinal)
+                    .Select(ToModel)
+                    .ToList());
+
+            GraphFile.WriteJson(model, serializerOptions );
+        }
+        catch (Exception exception)
+        {
+            // Emission is a convenience for editor tooling — never let it break a build.
+            Serilog.Log.Verbose(exception, "Failed to emit {GraphFileName}", GraphFileName);
+        }
+    }
+
+    private static TargetModel ToModel(ExecutableTarget target)
+        => new(
+            target.Name,
+            target.Description,
+            target.Member?.DeclaringType?.Name,
+            target.IsDefault,
+            target.Listed,
+            SortedNames(target.ExecutionDependencies),
+            SortedNames(target.OrderDependencies),
+            SortedNames(target.TriggerDependencies),
+            SortedNames(target.Triggers));
+
+    // Sorted for deterministic output — the graph carries no execution order, so the display
+    // order is irrelevant to consumers and a stable ordering avoids spurious file churn.
+    private static IReadOnlyList<string> SortedNames(IEnumerable<ExecutableTarget> targets)
+        => targets.Select(x => x.Name).OrderBy(x => x, StringComparer.Ordinal).ToList();
+
+    // Mirrors Fallout.Migrate: the informational version up to the build-metadata separator,
+    // so the pin aligns with the running tool. Null for local/dev builds without a `+` suffix.
+    private static string ResolveFalloutVersion()
+    {
+        var informational = typeof(SerializeBuildGraphAttribute).Assembly
+            .GetCustomAttribute<AssemblyInformationalVersionAttribute>()
+            ?.InformationalVersion;
+        if (string.IsNullOrEmpty(informational))
+            return null;
+
+        var plusIndex = informational.IndexOf('+');
+        return plusIndex == -1 ? informational : informational[..plusIndex];
+    }
+
+    private sealed record BuildGraphModel(
+        int Version,
+        string FalloutVersion,
+        IReadOnlyList<TargetModel> Targets);
+
+    private sealed record TargetModel(
+        string Name,
+        string Description,
+        string DeclaredIn,
+        bool Default,
+        bool Listed,
+        IReadOnlyList<string> DependsOn,
+        IReadOnlyList<string> After,
+        IReadOnlyList<string> TriggeredBy,
+        IReadOnlyList<string> Triggers);
+}

src/Fallout.Build/FalloutBuild.cs

@@ -52,6 +52,7 @@ namespace Fallout.Common;
 // [SaveBuildProfile(Priority = 30)]
 // [LoadBuildProfiles(Priority = 25)]
 // After logo
+[SerializeBuildGraph(Priority = 20)]
 [HandlePlanRequests(Priority = 10)]
 [HandleHelpRequests(Priority = 5)]
 [Telemetry]