Launcher: GET MODS installs plugin mods and mod packs instead of refusing them

A Thunderstore install was refused unless the package held layout.toc, reskate-levels.json or a
parks folder, so a package with only a plugin, or a pack whose manifest only lists dependencies,
could not be installed from GET MODS. reskate-plugin.json now counts as content (and finds the mod
inside a package like the other markers), and a manifest with dependencies is a mod pack, as
InstallOptions::require_content always said.

Launcher/Test/mod_manager_tests.cpp

@@ -403,6 +403,45 @@ int main() {
                   !fs::exists(store / L"Team-Empty"),
               "Thunderstore installs refuse a package with nothing to load");
         check(install(store, sources / L"empty.zip") == "empty", "A plain install still takes a description-only mod");
+        make_zip(sources / L"empty-list.zip", {{"manifest.json", R"({"name":"Nothing","dependencies":[]})"}});
+        options.folder = "Team-Empty_List";
+        check(error_of([&] { launcher_mods::install(store, sources / L"empty-list.zip", true, {}, cancel, options); })
+                      .find("plugins and mod packs") != std::string::npos &&
+                  !fs::exists(store / L"Team-Empty_List"),
+              "An empty dependencies list is not a mod pack, and the refusal names plugins and packs");
+
+        // A plugin-only package: reskate-plugin.json is something to load, at the top or one folder down.
+        make_zip(sources / L"plugin.zip", {{"manifest.json", manifest}, {"icon.png", "png"}, {"README.md", "readme"},
+            {"reskate-plugin.json", R"({"api":1})"}, {"main.luau", "-- plugin"}});
+        options.folder = "Team-Plugin";
+        check(launcher_mods::install(store, sources / L"plugin.zip", true, {}, cancel, options) == "Team-Plugin" &&
+                  read(store / L"Team-Plugin" / L"main.luau") == "-- plugin" &&
+                  read(store / L"Team-Plugin" / L"icon.png") == "png",
+              "Thunderstore installs take a plugin-only package");
+        make_zip(sources / L"nested-plugin.zip", {{"manifest.json", manifest}, {"icon.png", "png"}, {"README.md", "readme"},
+            {"Plugin/reskate-plugin.json", R"({"api":1})"}, {"Plugin/main.luau", "-- nested"}});
+        options.folder = "Team-Nested_Plugin";
+        check(launcher_mods::install(store, sources / L"nested-plugin.zip", true, {}, cancel, options) == "Team-Nested_Plugin" &&
+                  read(store / L"Team-Nested_Plugin" / L"reskate-plugin.json") == R"({"api":1})" &&
+                  read(store / L"Team-Nested_Plugin" / L"main.luau") == "-- nested" &&
+                  read(store / L"Team-Nested_Plugin" / L"icon.png") == "png" &&
+                  read(store / L"Team-Nested_Plugin" / L"README.md") == "readme" &&
+                  !fs::exists(store / L"Team-Nested_Plugin" / L"Plugin"),
+              "A plugin one folder down is the mod, and the package files follow it in");
+        const auto plugin_manifest = read(store / L"Team-Nested_Plugin" / L"manifest.json");
+        check(plugin_manifest.find("Desert_Springs") != std::string::npos && plugin_manifest.find(R"("Zee")") != std::string::npos,
+              "The carried manifest.json gets the team as author");
+
+        // A mod pack: nothing of its own to load, only dependencies the launcher installs first.
+        make_zip(sources / L"modpack.zip", {
+            {"manifest.json", R"({"name":"Pack","version_number":"1.0.0","dependencies":["Zee-Desert_Springs-1.2.3"]})"},
+            {"icon.png", "png"}, {"README.md", "readme"}});
+        options.folder = "Team-Pack";
+        check(launcher_mods::install(store, sources / L"modpack.zip", true, {}, cancel, options) == "Team-Pack" &&
+                  read(store / L"Team-Pack" / L"icon.png") == "png",
+              "Thunderstore installs take a mod pack that only lists dependencies");
+        const auto pack = installed("Team-Pack");
+        check(pack && pack->author == "Zee" && pack->version == "1.0.0", "A mod pack is listed with its team as author");
     }
 
     // A built-in pack in ReSkate's own format unpacks to exactly its files (a name with spaces

Launcher/mod_manager.cpp

@@ -23,13 +23,15 @@ namespace fs = std::filesystem;
 namespace dingosdk::launcher_mods {
 namespace {
 
-// What the game loads from a mod, and the files that only describe one.
-constexpr std::array<std::string_view, 2> content_markers{"layout.toc", "reskate-levels.json"};
+// What the game loads from a mod (a plugin's reskate-plugin.json sits at its
+// mod's top), and the files that only describe one.
+constexpr std::array<std::string_view, 3> content_markers{"layout.toc", "reskate-levels.json", "reskate-plugin.json"};
 constexpr std::array<std::string_view, 2> info_markers{"manifest.json", "reskate-mod.json"};
 // Thunderstore requires these at the top of a package (lower case here); they
 // follow the mod in when it is packed one folder deeper.
 constexpr std::array<std::string_view, 4> package_files{"manifest.json", "icon.png", "readme.md", "changelog.md"};
-constexpr char no_mod[] = " does not contain a ReSkate mod (no layout.toc, reskate-levels.json or manifest.json).";
+constexpr char no_mod[] =
+    " does not contain a ReSkate mod (no layout.toc, reskate-levels.json, reskate-plugin.json or manifest.json).";
 // Staging lives inside Mods so the final move is a rename on one volume; the
 // leading dot keeps the runtime from ever treating it as a mod.
 constexpr wchar_t staging_folder[] = L".reskate-install";
@@ -84,8 +86,9 @@ struct Root {
     bool content{};       // holds something the game loads
 };
 
-// The shallowest folder holding game content (layout.toc, reskate-levels.json
-// or parks/<map>.park.json), else the shallowest holding only a description.
+// The shallowest folder holding game content (layout.toc, reskate-levels.json,
+// reskate-plugin.json or parks/<map>.park.json), else the shallowest holding
+// only a description.
 // Content wins so a package's own manifest.json at the top cannot hide a mod
 // packed one folder down.
 std::optional<Root> mod_root(const std::vector<std::string>& files) {
@@ -146,15 +149,11 @@ std::string mod_name(const Root& root, const std::string& source_name, const Ins
     return folder_name(root.folder.empty() ? without_version(source_name) : last_folder(root.folder));
 }
 
-// Last steps in staging: a source that gives the game nothing to load is
-// refused when asked, and the author goes into manifest.json.
-void finish(const fs::path& staging, const Root& root, const std::string& source_name, const InstallOptions& options) {
-    if (options.require_content && !root.content)
-        fail(source_name + " has nothing for ReSkate to load: no layout.toc, reskate-levels.json or parks folder. "
-             "Only mods built with ReSkate Studio, and park mods, can be installed.");
-    const auto manifest = staging / mods::manifest_file;
+// The mod's manifest.json as an object, if it has a readable one. An unreadable
+// manifest is the mod's own business; the game reports it.
+std::optional<Json> read_manifest(const fs::path& manifest) {
     std::error_code error;
-    if (options.author.empty() || !fs::is_regular_file(manifest, error)) return;
+    if (!fs::is_regular_file(manifest, error)) return std::nullopt;
     try {
         std::string text;
         {
@@ -163,13 +162,28 @@ void finish(const fs::path& staging, const Root& root, const std::string& source
         }
         if (text.starts_with("\xef\xbb\xbf")) text.erase(0, 3);
         auto json = Json::parse(text, JsonLimits{1024 * 1024, 16, 65536});
-        if (!json.is_object()) return;
-        if (json.contains("author") && json.at("author").is_string() && !json.at("author").string().empty()) return;
-        json.items()["author"] = Json(options.author);
-        std::ofstream(manifest, std::ios::binary | std::ios::trunc) << json.dump(4) << '\n';
+        if (json.is_object()) return json;
     } catch (...) {
-        // An unreadable manifest is the mod's own business; the game reports it.
     }
+    return std::nullopt;
+}
+
+// Last steps in staging: a source that gives the game nothing to load is
+// refused when asked, unless its manifest.json lists dependencies (a mod pack:
+// what it brings is those), and the author goes into manifest.json.
+void finish(const fs::path& staging, const Root& root, const std::string& source_name, const InstallOptions& options) {
+    const auto manifest = staging / mods::manifest_file;
+    auto json = read_manifest(manifest);
+    const bool pack = json && json->contains("dependencies") && json->at("dependencies").is_array() &&
+        !json->at("dependencies").empty();
+    if (options.require_content && !root.content && !pack)
+        fail(source_name + " has nothing for ReSkate to load: no layout.toc, reskate-levels.json, reskate-plugin.json "
+             "or parks folder, and no dependencies. Only mods built with ReSkate Studio, park mods, plugins and mod "
+             "packs can be installed.");
+    if (options.author.empty() || !json) return;
+    if (json->contains("author") && json->at("author").is_string() && !json->at("author").string().empty()) return;
+    json->items()["author"] = Json(options.author);
+    std::ofstream(manifest, std::ios::binary | std::ios::trunc) << json->dump(4) << '\n';
 }
 
 // Entry names from an archive are untrusted: no absolute paths, drive

Launcher/mod_manager.h

@@ -40,8 +40,8 @@ struct InstallOptions {
 };
 
 // Installs `source` (a .zip, or a folder) as Mods/<name> and returns <name>.
-// The mod is the shallowest folder holding layout.toc, reskate-levels.json or
-// parks/<map>.park.json, else the shallowest holding manifest.json or
+// The mod is the shallowest folder holding layout.toc, reskate-levels.json,
+// reskate-plugin.json or parks/<map>.park.json, else the shallowest holding manifest.json or
 // reskate-mod.json. Thunderstore's manifest.json, icon.png, README.md and
 // CHANGELOG.md at the top of a package are copied in when the mod sits one
 // folder deeper. A top-level mod takes the archive's name without a trailing