src: Reload buffers when their contents' hash changes

Instead of triggering a reload event when the timestamp of a buffer's
underlying file changes, do so when its contents are actually modified.

src/buffer.cc

@@ -78,7 +78,7 @@ Buffer::Buffer(String name, Flags flags, StringView data,
       m_history{{HistoryId::Invalid}},
       m_history_id{HistoryId::First},
       m_last_save_history_id{HistoryId::First},
-      m_fs_timestamp{fs_timestamp.tv_sec, fs_timestamp.tv_nsec}
+      m_fs_status{fs_timestamp, data.length(), hash_value(data)}
 {
     ParsedLines parsed_lines = parse_lines(data);
 
@@ -122,7 +122,7 @@ void Buffer::on_registered()
             run_hook_in_own_context(Hook::BufNewFile, m_name);
         else
         {
-            kak_assert(m_fs_timestamp != InvalidTime);
+            kak_assert(m_fs_status.timestamp != InvalidTime);
             run_hook_in_own_context(Hook::BufOpenFile, m_name);
         }
     }
@@ -305,7 +305,7 @@ void Buffer::reload(StringView data, timespec fs_timestamp)
     apply_options(options(), parsed_lines);
 
     m_last_save_history_id = m_history_id;
-    m_fs_timestamp = fs_timestamp;
+    m_fs_status = {fs_timestamp, data.length(), hash_value(data)};
 }
 
 void Buffer::commit_undo_group()
@@ -607,7 +607,7 @@ void Buffer::notify_saved()
 
     m_flags &= ~Flags::New;
     m_last_save_history_id = m_history_id;
-    m_fs_timestamp = get_fs_timestamp(m_name);
+    m_fs_status.timestamp = get_fs_timestamp(m_name);
 }
 
 BufferCoord Buffer::advance(BufferCoord coord, ByteCount count) const
@@ -663,16 +663,16 @@ BufferCoord Buffer::char_prev(BufferCoord coord) const
     return { coord.line, column };
 }
 
-timespec Buffer::fs_timestamp() const
+void Buffer::set_fs_status(FsStatus status)
 {
     kak_assert(m_flags & Flags::File);
-    return m_fs_timestamp;
+    m_fs_status = std::move(status);
 }
 
-void Buffer::set_fs_timestamp(timespec ts)
+const FsStatus& Buffer::fs_status() const
 {
     kak_assert(m_flags & Flags::File);
-    m_fs_timestamp = ts;
+    return m_fs_status;
 }
 
 void Buffer::on_option_changed(const Option& option)

src/buffer.hh

@@ -5,6 +5,7 @@
 #include "coord.hh"
 #include "constexpr_utils.hh"
 #include "enum.hh"
+#include "file.hh"
 #include "optional.hh"
 #include "safe_ptr.hh"
 #include "scope.hh"
@@ -142,8 +143,8 @@ public:
     BufferCoord replace(BufferCoord begin, BufferCoord end, StringView content);
 
     size_t          timestamp() const;
-    timespec       fs_timestamp() const;
-    void           set_fs_timestamp(timespec ts);
+    void            set_fs_status(FsStatus);
+    const FsStatus& fs_status() const;
 
     void           commit_undo_group();
     bool           undo(size_t count = 1);
@@ -284,7 +285,7 @@ private:
 
     Vector<Change, MemoryDomain::BufferMeta> m_changes;
 
-    timespec m_fs_timestamp;
+    FsStatus m_fs_status;
 
     // Values are just data holding by the buffer, they are not part of its
     // observable state

src/client.cc

@@ -287,7 +287,7 @@ void Client::reload_buffer()
     {
         context().print_status({ format("error while reloading buffer: '{}'", error.what()),
                                  context().faces()["Error"] });
-        buffer.set_fs_timestamp(get_fs_timestamp(buffer.name()));
+        buffer.set_fs_status(get_fs_status(buffer.name()));
     }
 }
 
@@ -312,7 +312,7 @@ void Client::on_buffer_reload_key(Key key)
     else if (key == 'n' or key == 'N' or key == Key::Escape)
     {
         // reread timestamp in case the file was modified again
-        buffer.set_fs_timestamp(get_fs_timestamp(buffer.name()));
+        buffer.set_fs_status(get_fs_status(buffer.name()));
         print_status({ format("'{}' kept", buffer.display_name()),
                        context().faces()["Information"] });
         if (key == 'N')
@@ -354,9 +354,16 @@ void Client::check_if_buffer_needs_reloading()
         return;
 
     const String& filename = buffer.name();
-    timespec ts = get_fs_timestamp(filename);
-    if (ts == InvalidTime or ts == buffer.fs_timestamp())
+    const timespec ts = get_fs_timestamp(filename);
+    const auto status = buffer.fs_status();
+
+    if (ts == InvalidTime or ts == status.timestamp)
         return;
+
+    if (MappedFile fd{filename};
+        fd.st.st_size == status.file_size and hash_data(fd.data, fd.st.st_size) == status.hash)
+        return;
+
     if (reload == Autoreload::Ask)
     {
         StringView bufname = buffer.display_name();

src/file.cc

@@ -610,6 +610,13 @@ timespec get_fs_timestamp(StringView filename)
     return st.st_mtim;
 }
 
+FsStatus get_fs_status(StringView filename)
+{
+    MappedFile fd{filename};
+
+    return {fd.st.st_mtim, fd.st.st_size, hash_data(fd.data, fd.st.st_size)};
+}
+
 String get_kak_binary_path()
 {
     char buffer[2048];

src/file.hh

@@ -86,7 +86,15 @@ Vector<String> list_files(StringView directory);
 
 void make_directory(StringView dir, mode_t mode);
 
+struct FsStatus
+{
+    timespec timestamp;
+    ByteCount file_size;
+    size_t hash;
+};
+
 timespec get_fs_timestamp(StringView filename);
+FsStatus get_fs_status(StringView filename);
 
 constexpr bool operator==(const timespec& lhs, const timespec& rhs)
 {