add public file watching api

loader/include/Geode/utils/file.hpp

@@ -252,4 +252,40 @@ namespace geode::utils::file {
      * @param options Picker options
      */
     GEODE_DLL Result<std::vector<ghc::filesystem::path>> pickFiles(FilePickOptions const& options);
+
+    class GEODE_DLL FileWatchEvent : public Event {
+    protected:
+        ghc::filesystem::path m_path;
+    
+    public:
+        FileWatchEvent(ghc::filesystem::path const& path);
+        ghc::filesystem::path getPath() const;
+    };
+
+    class GEODE_DLL FileWatchFilter : public EventFilter<FileWatchEvent> {
+    protected:
+        ghc::filesystem::path m_path;
+    
+    public:
+        using Callback = void(FileWatchEvent*);
+
+        ListenerResult handle(utils::MiniFunction<Callback> callback, FileWatchEvent* event);
+        FileWatchFilter(ghc::filesystem::path const& path);
+    };
+
+    /**
+     * Watch a file for changes. Whenever the file is modified on disk, a 
+     * FileWatchEvent is emitted. Add an EventListener with FileWatchFilter 
+     * to catch these events
+     * @param file The file to watch
+     * @note Watching uses file system equivalence instead of path equivalence, 
+     * so different paths that point to the same file will be considered the 
+     * same
+     */
+    GEODE_DLL Result<> watchFile(ghc::filesystem::path const& file);
+    /**
+     * Stop watching a file for changes
+     * @param file The file to unwatch
+     */
+    GEODE_DLL void unwatchFile(ghc::filesystem::path const& file);
 }

loader/src/internal/FileWatcher.hpp

@@ -25,12 +25,28 @@ protected:
 public:
     bool watching() const;
 
-    ghc::filesystem::path path() {
+    ghc::filesystem::path path() const {
         return m_file;
     }
 
     FileWatcher(
-        ghc::filesystem::path const& file, FileWatchCallback callback, ErrorCallback error = nullptr
+        ghc::filesystem::path const& file,
+        FileWatchCallback callback,
+        ErrorCallback error = nullptr
     );
+    FileWatcher(FileWatcher const&) = delete;
+    inline FileWatcher(FileWatcher&& other)
+      : m_file(std::move(other.m_file)),
+        m_callback(std::move(other.m_callback)),
+        m_error(std::move(other.m_error)),
+        m_filemode(other.m_filemode),
+        m_platformHandle(other.m_platformHandle),
+        m_exiting(other.m_exiting)
+    {
+        other.m_callback = nullptr;
+        other.m_error = nullptr;
+        other.m_platformHandle = nullptr;
+        other.m_exiting = true;
+    }
     ~FileWatcher();
 };

loader/src/utils/file.cpp

@@ -11,6 +11,7 @@
 #include <mz_strm_os.h>
 #include <mz_strm_mem.h>
 #include <mz_zip.h>
+#include <internal/FileWatcher.hpp>
 
 using namespace geode::prelude;
 using namespace geode::utils::file;
@@ -551,3 +552,54 @@ Result<> Zip::addAllFrom(Path const& dir) {
 Result<> Zip::addFolder(Path const& entry) {
     return m_impl->addFolder(entry);
 }
+
+FileWatchEvent::FileWatchEvent(ghc::filesystem::path const& path)
+  : m_path(path) {}
+
+ghc::filesystem::path FileWatchEvent::getPath() const {
+    return m_path;
+}
+
+ListenerResult FileWatchFilter::handle(
+    MiniFunction<Callback> callback,
+    FileWatchEvent* event
+) {
+    std::error_code ec;
+    if (ghc::filesystem::equivalent(event->getPath(), m_path, ec)) {
+        callback(event);
+    }
+    return ListenerResult::Propagate;
+}
+
+FileWatchFilter::FileWatchFilter(ghc::filesystem::path const& path) 
+  : m_path(path) {}
+
+// This is a vector because need to use ghc::filesystem::equivalent for 
+// comparisons and removal is not exactly performance-critical here
+// (who's going to add and remove 500 file watchers every frame)
+static std::vector<std::unique_ptr<FileWatcher>> FILE_WATCHERS {};
+
+Result<> file::watchFile(ghc::filesystem::path const& file) {
+    if (!ghc::filesystem::exists(file)) {
+        return Err("File does not exist");
+    }
+    auto watcher = std::make_unique<FileWatcher>(
+        file,
+        [](auto const& path) {
+            Loader::get()->queueInGDThread([=] {
+                FileWatchEvent(path).post();
+            });
+        }
+    );
+    if (!watcher->watching()) {
+        return Err("Unknown error watching file");
+    }
+    FILE_WATCHERS.emplace_back(std::move(watcher));
+    return Ok();
+}
+
+void file::unwatchFile(ghc::filesystem::path const& file) {
+    ranges::remove(FILE_WATCHERS, [=](std::unique_ptr<FileWatcher> const& watcher) {
+        return ghc::filesystem::equivalent(file, watcher->path());
+    });
+}