GITHUB_ACTION_PATH + GITHUB_ACTION so that we can run scripts for Composite Run Steps (#615)

* Add environment variable for GITHUB_ACTION_PATH

* ah

* Remove debugging messages

* Set github action path at step level instead of global scope to avoid necessary removal

* Remove set context for github action

* Set github action path before and after composite action

* Copy GitHub Context, use this copied context for each composit step, and then set the action_path for each one (to avoid stamping over parent pointer GitHubContext

src/Runner.Worker/GitHubContext.cs

@@ -9,6 +9,7 @@ namespace GitHub.Runner.Worker
         private readonly HashSet<string> _contextEnvWhitelist = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
         {
             "action",
+            "action_path",
             "actor",
             "api_url",
             "base_ref",

src/Runner.Worker/Handlers/CompositeActionHandler.cs

@@ -56,6 +56,14 @@ namespace GitHub.Runner.Worker.Handlers
                 childScopeName = $"__{Guid.NewGuid()}";
             }
 
+            // Copy the github context so that we don't modify the original pointer
+            // We can't use PipelineContextData.Clone() since that creates a null pointer exception for copying a GitHubContext
+            var compositeGitHubContext = new GitHubContext();
+            foreach (var pair in githubContext)
+            {
+                compositeGitHubContext[pair.Key] = pair.Value;
+            }
+
             foreach (Pipelines.ActionStep actionStep in actionSteps)
             {
                 var actionRunner = HostContext.CreateService<IActionRunner>();
@@ -64,6 +72,11 @@ namespace GitHub.Runner.Worker.Handlers
                 actionRunner.Condition = actionStep.Condition;
 
                 var step = ExecutionContext.CreateCompositeStep(childScopeName, actionRunner, inputsData, Environment);
+
+                // Set GITHUB_ACTION_PATH
+                step.ExecutionContext.ExpressionValues["github"] = compositeGitHubContext;
+                step.ExecutionContext.SetGitHubContext("action_path", ActionDirectory);
+
                 compositeSteps.Add(step);
             }
 
@@ -176,9 +189,6 @@ namespace GitHub.Runner.Worker.Handlers
 
                 var actionStep = step as IActionRunner;
 
-                // Set GITHUB_ACTION
-                step.ExecutionContext.SetGitHubContext("action", step.ExecutionContext.GetFullyQualifiedContextName());
-
                 try
                 {
                     // Evaluate and merge action's env block to env context