On Windows, there is an IsWhitespaceOrNull() overload with TCHAR, and
the compiler doesn't know which one to pass to std::find_if().

Don't copy the input StringView.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/974

cue_next_word() can return a pointer one past the end of the string if
the word is followed by the terminating null byte.

The ones in std have overloads for const char/char.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This makes ccache more efficient when recompiling with different
plugins.

Found with modernize-use-default-member-init
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-redundant-access-specifiers
Signed-off-by: Rosen Penev <rosenp@gmail.com>

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Similar to c45f1138

Closes https://github.com/MusicPlayerDaemon/MPD/issues/781

Found with modernize-use-bool-literals
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-override
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This is needed to correctly load playlist entries that reference a song in a cuesheet that is treated as a folder.

This commit adds a PlaylistPlugin attribute "as_folder" which for now
is only enabled in the "CUE" playlist plugin (which handles separate
"*.cue" files).  If a playlist with this flag set is being scanned
during database update, it will be parsed and its contents will be
added to the database.  This allows clients to inspect them like
directories and its contents will be searchable.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/39

Simplify the plugin by using a trivial relative URI; later,
playlist_check_translate_song() will set the correct full URI.