add descriptive error for PathTooLongException which crashes SMAPI or the installer

docs/release-notes.md

@@ -9,8 +9,9 @@
 
 ## Upcoming release
 * For players:
-  * Fixed console showing _found 1 mod with warnings_ with no mods listed.
   * If the installer crashes, the window now stays open if possible so you can read the error and ask for help.
+  * Added descriptive error if possible when a `PathTooLongException` crashes SMAPI or the installer.
+  * Fixed console showing _found 1 mod with warnings_ with no mods listed.
 
 * For mod authors:
   * Added three stages to the `LoadStageChanged` event: `CreatedInitialLocations`/`SaveAddedLocations` (raised immediately after the game adds locations but before they're initialized), and `ReturningToTitle` (raised before exiting to the title screen).

src/SMAPI.Installer/InteractiveInstaller.cs

@@ -279,6 +279,7 @@ namespace StardewModdingApi.Installer
             /*********
             ** Step 4: validate assumptions
             *********/
+            // executable exists
             if (!File.Exists(paths.ExecutablePath))
             {
                 this.PrintError("The detected game install path doesn't contain a Stardew Valley executable.");
@@ -286,6 +287,17 @@ namespace StardewModdingApi.Installer
                 return;
             }
 
+            // game folder doesn't contain paths beyond the max limit
+            {
+                string[] tooLongPaths = PathUtilities.GetTooLongPaths(Path.Combine(paths.GamePath, "Mods")).ToArray();
+                if (tooLongPaths.Any())
+                {
+                    this.PrintError($"SMAPI can't install to the detected game folder, because some of its files exceed the maximum {context.Platform} path length.\nIf you need help fixing this error, see https://smapi.io/help\n\nAffected paths:\n   {string.Join("\n   ", tooLongPaths)}");
+                    Console.ReadLine();
+                    return;
+                }
+            }
+
 
             /*********
             ** Step 5: ask what to do

src/SMAPI.Toolkit/Properties/AssemblyInfo.cs

@@ -1,4 +1,5 @@
 using System.Runtime.CompilerServices;
 
 [assembly: InternalsVisibleTo("StardewModdingAPI")]
+[assembly: InternalsVisibleTo("SMAPI.Installer")]
 [assembly: InternalsVisibleTo("SMAPI.Web")]

src/SMAPI.Toolkit/Utilities/PathUtilities.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Diagnostics.Contracts;
 using System.IO;
 using System.Linq;
@@ -133,5 +134,29 @@ namespace StardewModdingAPI.Toolkit.Utilities
         {
             return !Regex.IsMatch(str, "[^a-z0-9_.-]", RegexOptions.IgnoreCase);
         }
+
+        /// <summary>Get the paths which exceed the OS length limit.</summary>
+        /// <param name="rootPath">The root path to search.</param>
+        internal static IEnumerable<string> GetTooLongPaths(string rootPath)
+        {
+            return Directory
+                .EnumerateFileSystemEntries(rootPath, "*.*", SearchOption.AllDirectories)
+                .Where(PathUtilities.IsPathTooLong);
+        }
+
+        /// <summary>Get whether a file or directory path exceeds the OS path length limit.</summary>
+        /// <param name="path">The path to test.</param>
+        internal static bool IsPathTooLong(string path)
+        {
+            try
+            {
+                _ = Path.GetFullPath(path);
+                return false;
+            }
+            catch (PathTooLongException)
+            {
+                return true;
+            }
+        }
     }
 }

src/SMAPI/Framework/Logging/LogManager.cs

@@ -252,11 +252,22 @@ namespace StardewModdingAPI.Framework.Logging
                     break;
 
                 // missing content folder exception
-                case FileNotFoundException ex when ex.Message == "Could not find file 'C:\\Program Files (x86)\\Steam\\SteamApps\\common\\Stardew Valley\\Content\\XACT\\FarmerSounds.xgs'.": // path in error is hardcoded regardless of install path
+                case FileNotFoundException ex when ex.Message == "Couldn't find file 'C:\\Program Files (x86)\\Steam\\SteamApps\\common\\Stardew Valley\\Content\\XACT\\FarmerSounds.xgs'.": // path in error is hardcoded regardless of install path
                     this.Monitor.Log("The game can't find its Content\\XACT\\FarmerSounds.xgs file. You can usually fix this by resetting your content files (see https://smapi.io/troubleshoot#reset-content ), or by uninstalling and reinstalling the game.", LogLevel.Error);
                     this.Monitor.Log($"Technical details: {ex.GetLogSummary()}");
                     break;
 
+                // path too long exception
+                case PathTooLongException:
+                    {
+                        string[] affectedPaths = PathUtilities.GetTooLongPaths(Constants.ModsPath).ToArray();
+                        string message = affectedPaths.Any()
+                            ? $"SMAPI can't launch because some of your mod files exceed the maximum path length on {Constants.Platform}.\nIf you need help fixing this error, see https://smapi.io/help\n\nAffected paths:\n   {string.Join("\n   ", affectedPaths)}"
+                            : $"The game failed to launch: {exception.GetLogSummary()}";
+                        this.MonitorForGame.Log(message, LogLevel.Error);
+                    }
+                    break;
+
                 // generic exception
                 default:
                     this.MonitorForGame.Log($"The game failed to launch: {exception.GetLogSummary()}", LogLevel.Error);