Merge pull request #4446 from livarcocc/fix_projectmodel_perf

Applying @brthor perf improvement to GetTypeBuildExclusionList.

Author: Livar

src/Microsoft.DotNet.ProjectModel/ProjectModelPlatformExtensions.cs

@@ -38,33 +38,65 @@ private static void CollectDependencies(IDictionary<string, LibraryExport> expor
 
         public static HashSet<string> GetTypeBuildExclusionList(this ProjectContext context, IDictionary<string, LibraryExport> exports)
         {
-            var acceptedExports = new HashSet<string>();
+            var rootProject = context.RootProject;
+            var buildExports = new HashSet<string>();
+            var nonBuildExports = new HashSet<string>();
 
-            // Accept the root project, obviously :)
-            acceptedExports.Add(context.RootProject.Identity.Name);
+            var nonBuildExportsToSearch = new Stack<string>();
+            var buildExportsToSearch = new Stack<string>();
 
-            // Walk all dependencies, tagging exports. But don't walk through Build dependencies.
-            CollectNonBuildDependencies(exports, context.RootProject.Dependencies, acceptedExports);
+            LibraryExport export;
+            string exportName;
 
-            // Whatever is left in exports was brought in ONLY by a build dependency
-            var exclusionList = new HashSet<string>(exports.Keys);
-            exclusionList.ExceptWith(acceptedExports);
-            return exclusionList;
-        }
+            // Root project is non-build
+            nonBuildExportsToSearch.Push(rootProject.Identity.Name);
+            nonBuildExports.Add(rootProject.Identity.Name);
 
-        private static void CollectNonBuildDependencies(IDictionary<string, LibraryExport> exports, IEnumerable<LibraryRange> dependencies, HashSet<string> acceptedExports)
-        {
-            foreach (var dependency in dependencies)
+            // Mark down all nonbuild exports and all of their dependencies
+            // Mark down build exports to come back to them later
+            while (nonBuildExportsToSearch.Count > 0)
             {
-                var export = exports[dependency.Name];
-                if (!dependency.Type.Equals(LibraryDependencyType.Build))
+                exportName = nonBuildExportsToSearch.Pop();
+                export = exports[exportName];
+
+                foreach (var dependency in export.Library.Dependencies)
                 {
-                    acceptedExports.Add(export.Library.Identity.Name);
-                    CollectNonBuildDependencies(exports, export.Library.Dependencies, acceptedExports);
+                    if (!dependency.Type.Equals(LibraryDependencyType.Build))
+                    {
+                        if (!nonBuildExports.Contains(dependency.Name))
+                        {
+                            nonBuildExportsToSearch.Push(dependency.Name);
+                            nonBuildExports.Add(dependency.Name);
+                        }
+                    }
+                    else
+                    {
+                        buildExportsToSearch.Push(dependency.Name);
+                    }
                 }
             }
-        }
 
+            // Go through exports marked build and their dependencies
+            // For Exports not marked as non-build, mark them down as build
+            while (buildExportsToSearch.Count > 0)
+            {
+                exportName = buildExportsToSearch.Pop();
+                export = exports[exportName];
+
+                buildExports.Add(exportName);
+
+                foreach (var dependency in export.Library.Dependencies)
+                {
+                    if (!nonBuildExports.Contains(dependency.Name))
+                    {
+                        buildExportsToSearch.Push(dependency.Name);
+                    }
+                }
+            }
+
+            return buildExports;
+        }
+        
         public static IEnumerable<LibraryExport> FilterExports(this IEnumerable<LibraryExport> exports, HashSet<string> exclusionList)
         {
             return exports.Where(e => !exclusionList.Contains(e.Library.Identity.Name));