fix: Evaluate RootLayout.ForCurrentDirectory lazily

This prevents start-up failures in the container environment (and
any other time we're not in a repo).

Fixes #14005

tools/Google.Cloud.Tools.ReleaseManager/CommandBase.cs

@@ -14,8 +14,10 @@
 
 using Google.Cloud.Tools.Common;
 using LibGit2Sharp;
+using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 
 namespace Google.Cloud.Tools.ReleaseManager
 {
@@ -28,6 +30,10 @@ public abstract class CommandBase : ICommand
         // releases, but fundamentally it's "the current source of truth we're basing this release on".
         internal const string PrimaryBranch = "main";
 
+        // This is lazy so that we can construct instances of CommandBase even when the current directory isn't
+        // in a repo, but we don't go hunting for the root multiple times.
+        private readonly Lazy<RootLayout> _lazyLayout = new(RootLayout.ForCurrentDirectory, LazyThreadSafetyMode.ExecutionAndPublication);
+
         private readonly int _minArgs;
         private readonly int _maxArgs;
 
@@ -43,7 +49,7 @@ public abstract class CommandBase : ICommand
         /// <remarks>
         /// Currently this is always derived from the current directory, but we may later have a way of specifying it separately.
         /// </remarks>
-        protected RootLayout RootLayout { get; }
+        protected RootLayout RootLayout => _lazyLayout.Value;
 
         protected CommandBase(string command, string description, int minArgs, int maxArgs, string expectedArguments)
         {
@@ -52,7 +58,6 @@ protected CommandBase(string command, string description, int minArgs, int maxAr
             _minArgs = minArgs;
             _maxArgs = maxArgs;
             ExpectedArguments = expectedArguments;
-            RootLayout = RootLayout.ForCurrentDirectory();
         }
 
         protected CommandBase(string command, string description, params string[] argNames)

tools/Google.Cloud.Tools.ReleaseManager/DetectPrChangesCommand.cs

@@ -35,18 +35,13 @@ public class DetectPrChangesCommand : ICommand
 
     public string ExpectedArguments => "<pre-PR git directory> <[id [id...]]";
 
-    private readonly RootLayout _rootLayout;
-
-    public DetectPrChangesCommand()
-    {
-        _rootLayout = RootLayout.ForCurrentDirectory();
-    }
-
     public int Execute(string[] args)
     {
+        var rootLayout = RootLayout.ForCurrentDirectory();
+
         string oldCommitDirectory = args[0];
         bool anyFailures = false;
-        var catalog = ApiCatalog.Load(_rootLayout);
+        var catalog = ApiCatalog.Load(rootLayout);
         var tags = LoadRepositoryTags();
 
         var apiIds = args.Skip(1).ToList();
@@ -57,14 +52,14 @@ public int Execute(string[] args)
                 LogHeader($"{id} has been deleted");
                 continue;
             }
-            anyFailures |= CompareApi(oldCommitDirectory, tags, api);
+            anyFailures |= CompareApi(rootLayout, oldCommitDirectory, tags, api);
         }
 
         return anyFailures ? 1 : 0;
 
         HashSet<string> LoadRepositoryTags()
         {
-            using var repo = new Repository(_rootLayout.RepositoryRoot);
+            using var repo = new Repository(rootLayout.RepositoryRoot);
             return new HashSet<string>(repo.Tags.Select(tag => tag.FriendlyName));
         }
     }
@@ -76,7 +71,7 @@ HashSet<string> LoadRepositoryTags()
     /// along the way (TFMs, output locations etc). We could potentially refactor much of it into a class,
     /// but it's simpler to keep it like this for now.</remarks>
     /// <returns>Whether the comparison has failed in some way.</returns>
-    private bool CompareApi(string oldCommitDirectory, HashSet<string> tags, ApiMetadata api)
+    private bool CompareApi(RootLayout rootLayout, string oldCommitDirectory, HashSet<string> tags, ApiMetadata api)
     {
         string id = api.Id;
         LogHeader($"Finding changes in {id}...");
@@ -129,7 +124,7 @@ private bool CompareApi(string oldCommitDirectory, HashSet<string> tags, ApiMeta
         LogHeader($"Comparing with previous NuGet package");
         try
         {
-            CheckVersionCompatibilityCommand.CheckCompatibilityWithPreviousRelease(_rootLayout, tags, api);
+            CheckVersionCompatibilityCommand.CheckCompatibilityWithPreviousRelease(rootLayout, tags, api);
         }
         catch (UserErrorException ex)
         {