aspnetcore/build/tasks/BuildGraph/GraphBuilder.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace RepoTools.BuildGraph
{
    public static class GraphBuilder
    {
        public static IList<GraphNode> Generate(IList<Repository> repositories, string root)
        {
            // Build global list of primary projects
            var primaryProjects = repositories.SelectMany(c => c.Projects)
                .ToDictionary(p => p.Name, StringComparer.OrdinalIgnoreCase);
            var graphNodes = repositories.Select(r => new GraphNode { Repository = r })
                .ToDictionary(r => r.Repository);

            GraphNode searchRoot = null;

            foreach (var project in repositories.SelectMany(r => r.AllProjects))
            {
                var thisProjectRepositoryNode = graphNodes[project.Repository];
                if (!string.IsNullOrEmpty(root) && string.Equals(root, project.Repository.Name, StringComparison.OrdinalIgnoreCase))
                {
                    searchRoot = thisProjectRepositoryNode;
                }

                foreach (var packageDependency in project.PackageReferences)
                {
                    if (primaryProjects.TryGetValue(packageDependency, out var dependencyProject))
                    {
                        var dependencyRepository = dependencyProject.Repository;
                        var dependencyNode = graphNodes[dependencyRepository];

                        thisProjectRepositoryNode.Incoming.Add(dependencyNode);
                        dependencyNode.Outgoing.Add(thisProjectRepositoryNode);
                    }
                }
            }

            var results = new HashSet<GraphNode>();
            if (searchRoot != null)
            {
                Visit(results, searchRoot);
                return results.ToList();
            }

            return graphNodes.Values.ToList();
        }

        private static void Visit(HashSet<GraphNode> results, GraphNode searchRoot)
        {
            if (results.Add(searchRoot))
            {
                foreach (var node in searchRoot.Outgoing)
                {
                    Visit(results, node);
                }
            }
        }
    }
}