Make this idle event per-partition.

Eliminate global variables, convert them to MixerMemento fields.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1583

This reveals more about the nature of an error instead of just
returning "problems setting volume".

- supporting bmp and tiff seems outdated
- webp is more widely used for coverimages

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1337

SonarLint reports the latter to be better:

std::scoped_lock basically provides the same feature as std::lock_guard,
but is more generic: It can lock several mutexes at the same time, with a
deadlock prevention mechanism (see {rule:cpp:S5524}). The equivalent code
to perform simultaneous locking with std::lock_guard is significantly more
complex. Therefore, it is simpler to use std::scoped_lock all the time,
even when locking only one mutex (there will be no performance impact).
Signed-off-by: Rosen Penev <rosenp@gmail.com>

C arrays can be used with make_unique in C++17.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1328

Unlike GetFilenameSuffix(), uri_get_suffix() removes the query string
first, which breaks file names with question marks in the name.
Therefore, uri_get_suffix() shall only be applied to remote URIs.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1316

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1106

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1285

This commit also increases the PROTOCOL_VERSION so clients can detect
the availability of the feature.

During the libfmt migration, I converted "%1.3f" to just "{:1.3}"
without the "f" suffix, but libfmt defaults to scientific notation,
which can break some MPD clients.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1291

This replaces the output parameter (which is bad API design).  As a
side effect, it fixes the bad [[gnu::pure]] attribute added by commit
a636d212 which caused optimizing compilers to miscompile calls to
that function.  "Pure" functions can be assumed to have no output
arguments, so the compiler can assume the function doesn't modify
them.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1282

Another one from https://github.com/MusicPlayerDaemon/MPD/issues/888

Closes https://github.com/MusicPlayerDaemon/MPD/issues/888

Some users want certain clients to fully control playback, but do not
want them to be able to trigger database update.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1124

This was a no-op previously, but this operation makes no sense.

The existing implementation has been utterly broken forever; I cannot
explain what it actually does, but it doesn't do what the
documentation says.

Use MoveRange() instead of MoveId().

Now, "+0" means "right after the current song" and "-0" means "right
before the current song".  Mnemonic: there are zero songs between the
current song and the newly added song.

A similar feature was present long ago in MPD, but was deprecated in
version 0.16 because the implementation was broken.  This commit
re-adds the feature in a way that's well-defined and not broken.

Close https://github.com/MusicPlayerDaemon/MPD/issues/1221

Validate early, so we avoid the rollback if an error occurs.

Skip the LookupRemoteTag() call if the MoveId() call fails.

Prevent a segfault when accessing album art.

Fix #1224 #1225

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Instead of checking for "cover.jpg" in the virtual directory
representing the CUE sheet, check its enclosing directory.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1206