Handle sync fork failures with useful error messages

src/WingetCreateCLI/Commands/BaseCommand.cs

@@ -778,6 +778,24 @@ protected async Task<bool> GitHubSubmitManifests(Manifests manifests, string prT
                     Logger.ErrorLocalized(nameof(Resources.SyncForkWithUpstream_Message));
                     return false;
                 }
+                else if (e is BranchMergeConflictException)
+                {
+                    // While attempting to sync fork through the GitHub API, a branch merge conflict was detected.
+                    // The user will need to manually resolve the conflict.
+                    Logger.ErrorLocalized(nameof(Resources.BranchMergeConflict_Message));
+                    return false;
+                }
+                else if (e is GenericSyncFailureException)
+                {
+                    // While attempting to sync fork through the GitHub API, a generic sync failure occurred.
+                    Logger.ErrorLocalized(nameof(Resources.SyncForkFailed_Message));
+                    return false;
+                }
+                else if (e is HttpRequestException)
+                {
+                    Logger.ErrorLocalized(nameof(Resources.NetworkConnectionFailure_Message));
+                    return false;
+                }
                 else
                 {
                     throw;

src/WingetCreateCLI/Properties/Resources.resx

@@ -1400,4 +1400,10 @@ Warning: Using this argument may result in the token being logged. Consider an a
   <data name="ConfirmZippedBinary_Message" xml:space="preserve">
     <value>Does this executable depend on DLLs or any other files present in the zip archive?</value>
   </data>
+  <data name="SyncForkFailed_Message" xml:space="preserve">
+    <value>The forked repository could not be synced with the upstream commits. Sync your fork manually and try again.</value>
+  </data>
+  <data name="BranchMergeConflict_Message" xml:space="preserve">
+    <value>The forked repository could not be synced with the upstream commits due to a merge conflict. Resolve conflicts manually and try again.</value>
+  </data>
 </root>

src/WingetCreateCore/Common/Exceptions/BranchMergeConflictException.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license.
+
+namespace Microsoft.WingetCreateCore.Common.Exceptions
+{
+    using System;
+
+    /// <summary>
+    /// The exception that is thrown when the forked repo's branch has a merge conflict with the upstream branch.
+    /// </summary>
+    public class BranchMergeConflictException : Exception
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BranchMergeConflictException"/> class.
+        /// </summary>
+        public BranchMergeConflictException()
+        {
+        }
+    }
+}

src/WingetCreateCore/Common/Exceptions/GenericSyncFailureException.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license.
+
+namespace Microsoft.WingetCreateCore.Common.Exceptions
+{
+    using System;
+
+    /// <summary>
+    /// The exception that is thrown when a generic failure occurs while syncing the forked repo with upstream commits.
+    /// </summary>
+    public class GenericSyncFailureException : Exception
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GenericSyncFailureException"/> class.
+        /// </summary>
+        public GenericSyncFailureException()
+        {
+        }
+    }
+}

src/WingetCreateCore/Common/GitHub.cs

@@ -488,9 +488,11 @@ private async Task UpdateForkedRepoWithUpstreamCommits(Repository forkedRepo)
 
                 // Octokit .NET doesn't support sync fork endpoint, so we make a direct call to the GitHub API.
                 // Tracking issue for the request: https://github.com/octokit/octokit.net/issues/2989
-                // API reference: https://docs.github.com/en/rest/branches/branches?apiVersion=2022-11-28#sync-a-fork-branch-with-the-upstream-repository
                 HttpClient httpClient = new HttpClient();
 
+                // API reference: https://docs.github.com/en/rest/branches/branches?apiVersion=2022-11-28#sync-a-fork-branch-with-the-upstream-repository
+                var url = $"https://api.github.com/repos/{forkedRepo.Owner.Login}/{forkedRepo.Name}/merge-upstream";
+
                 // Headers
                 httpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", this.github.Credentials.Password);
                 httpClient.DefaultRequestHeaders.Add("Accept", "application/vnd.github+json");
@@ -501,8 +503,21 @@ private async Task UpdateForkedRepoWithUpstreamCommits(Repository forkedRepo)
                 JsonObject jsonObject = new JsonObject { { "branch", forkedRepo.DefaultBranch } };
                 var content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");
 
-                var url = $"https://api.github.com/repos/{forkedRepo.Owner.Login}/{forkedRepo.Name}/merge-upstream";
                 var response = await httpClient.PostAsync(url, content);
+
+                // 409 status code
+                if (response.StatusCode == System.Net.HttpStatusCode.Conflict)
+                {
+                    throw new BranchMergeConflictException();
+                }
+
+                // 422 status code
+                if (response.StatusCode == System.Net.HttpStatusCode.UnprocessableEntity)
+                {
+                    throw new GenericSyncFailureException();
+                }
+
+                // The API doesn't document another error code. If this fails, a generic HttpRequestException is thrown.
                 response.EnsureSuccessStatusCode();
             }
         }