Don't use VPIO forcelist by default

This makes it so clients have to opt into the VPIO forcelist.
It is currently mainly needed by gecko, since sites may create multiple
streams to a builtin device with different prefs and processing params,
and HAL audio units to builtin device are not working properly when
there is a VPIO audio unit to the same builtin device on (anywhere) on
the system.

With the cfg flag vpio-forcelist a client can avoid VPIO altogether, by
not compiling with the flag, and by never creating input streams with
the VOICE pref.

Should a client need to mix VOICE and non-VOICE input streams to a
single device, it should enable vpio-forcelist.

Fixes #242.

Author: Pehrsons

Cargo.toml

@@ -26,6 +26,7 @@ itertools = "0.11"
 
 [features]
 audio-dump = []
+vpio-forcelist = []
 
 # Workaround for https://github.com/rust-lang/cargo/issues/6745 to allow this
 # Cargo.toml file to appear under a subdirectory of a workspace without being in

src/backend/mod.rs

@@ -3266,6 +3266,7 @@ impl<'ctx> CoreStreamData<'ctx> {
     }
 
     #[allow(non_upper_case_globals)]
+    #[cfg(feature = "vpio-forcelist")]
     fn should_force_vpio_for_input_device(id: AudioDeviceID) -> bool {
         assert!(id != kAudioObjectUnknown);
         debug_assert_running_serially();
@@ -3283,6 +3284,11 @@ impl<'ctx> CoreStreamData<'ctx> {
         }
     }
 
+    #[cfg(not(feature = "vpio-forcelist"))]
+    fn should_force_vpio_for_input_device(_id: AudioDeviceID) -> bool {
+        false
+    }
+
     fn should_block_vpio_for_device_pair(
         &self,
         in_device: &device_info,