add support for using environment variables instead of command-line arguments (#665)

docs/release-notes.md

@@ -48,6 +48,7 @@ For modders:
     * Now detects XNB mods more accurately, and consolidates multi-folder XNB mods in logged messages.
   * SMAPI now automatically removes invalid content when loading a save to prevent crashes. A warning is shown in-game when this happens. This applies for locations and NPCs.
   * Added support for configuring console colors via `smapi-internal/config.json` (intended for players with unusual consoles).
+  * Added support for specifying SMAPI command-line arguments as environment variables for Linux/Mac compatibility.
   * Improved launch script compatibility on Linux (thanks to kurumushi and toastal!).
   * Save Backup now works in the background, to avoid affecting startup time for players with a large number of saves.
   * The installer now recognises custom game paths stored in `stardewvalley.targets`.

docs/technical/smapi.md

@@ -40,14 +40,25 @@ argument | purpose
 `--uninstall` | Preselects the uninstall action, skipping the prompt asking what the user wants to do.
 `--game-path "path"` | Specifies the full path to the folder containing the Stardew Valley executable, skipping automatic detection and any prompt to choose a path. If the path is not valid, the installer displays an error.
 
-SMAPI itself recognises two arguments, but these are intended for internal use or testing and may
-change without warning.
+SMAPI itself recognises two arguments **on Windows only**, but these are intended for internal use
+or testing and may change without warning. On Linux/Mac, see _environment variables_ below.
 
 argument | purpose
 -------- | -------
 `--no-terminal` | SMAPI won't write anything to the console window. (Messages will still be written to the log file.)
 `--mods-path` | The path to search for mods, if not the standard `Mods` folder. This can be a path relative to the game folder (like `--mods-path "Mods (test)"`) or an absolute path.
 
+### Environment variables
+The above SMAPI arguments don't work on Linux/Mac due to the way the game launcher works. You can
+set temporary environment variables instead. For example:
+> SMAPI_MODS_PATH="Mods (multiplayer)" /path/to/StardewValley
+
+environment variable | purpose
+-------------------- | -------
+`SMAPI_NO_TERMINAL` | Equivalent to `--no-terminal` above.
+`SMAPI_MODS_PATH` | Equivalent to `--mods-path` above.
+
+
 ### Compile flags
 SMAPI uses a small number of conditional compilation constants, which you can set by editing the
 `<DefineConstants>` element in `SMAPI.csproj`. Supported constants:

src/SMAPI/Program.cs

@@ -116,21 +116,27 @@ namespace StardewModdingAPI
         /// <remarks>This method is separate from <see cref="Main"/> because that can't contain any references to assemblies loaded by <see cref="CurrentDomain_AssemblyResolve"/> (e.g. via <see cref="Constants"/>), or Mono will incorrectly show an assembly resolution error before assembly resolution is set up.</remarks>
         private static void Start(string[] args)
         {
-            // get flags from arguments
-            bool writeToConsole = !args.Contains("--no-terminal");
+            // get flags
+            bool writeToConsole = !args.Contains("--no-terminal") && Environment.GetEnvironmentVariable("SMAPI_NO_TERMINAL") == null;
 
-            // get mods path from arguments
-            string modsPath = null;
+            // get mods path
+            string modsPath;
             {
+                string rawModsPath = null;
+
+                // get from command line args
                 int pathIndex = Array.LastIndexOf(args, "--mods-path") + 1;
                 if (pathIndex >= 1 && args.Length >= pathIndex)
-                {
-                    modsPath = args[pathIndex];
-                    if (!string.IsNullOrWhiteSpace(modsPath) && !Path.IsPathRooted(modsPath))
-                        modsPath = Path.Combine(Constants.ExecutionPath, modsPath);
-                }
-                if (string.IsNullOrWhiteSpace(modsPath))
-                    modsPath = Constants.DefaultModsPath;
+                    rawModsPath = args[pathIndex];
+
+                // get from environment variables
+                if (string.IsNullOrWhiteSpace(rawModsPath))
+                    rawModsPath = Environment.GetEnvironmentVariable("SMAPI_MODS_PATH");
+
+                // normalise
+                modsPath = !string.IsNullOrWhiteSpace(rawModsPath)
+                    ? Path.Combine(Constants.ExecutionPath, rawModsPath)
+                    : Constants.DefaultModsPath;
             }
 
             // load SMAPI