Add a way to completely exclude the vst3-sys dep

Because technically you might still include GPL'd symbols even if you
wouldn't use the `nih_export_vst3!()` macro.

Cargo.toml

@@ -34,10 +34,15 @@ members = [
 ]
 
 [features]
-default = []
+default = ["vst3"]
 # Enabling this feature will cause the plugin to terminate when allocations
 # occur in the processing function while compiling in debug mode.
-assert_process_allocs = ["assert_no_alloc"]
+assert_process_allocs = ["dep:assert_no_alloc"]
+# Enables the `nih_export_vst3()` macro. Enabled by default. This feature exists
+# mostly for GPL-compliance reasons, since even if you don't use the VST3
+# wrapper you might otherwise still include a couple (unused) symbols from the
+# `vst3-sys` create.
+vst3 = ["dep:vst3-sys"]
 # Add adapters to the Buffer object for reading the channel data to and from
 # `std::simd` vectors. Requires a nightly compiler.
 simd = []
@@ -60,7 +65,7 @@ parking_lot = "0.12"
 raw-window-handle = "0.4"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-vst3-sys = { git = "https://github.com/robbert-vdh/vst3-sys.git", branch = "fix/note-off-event" }
+vst3-sys = { git = "https://github.com/robbert-vdh/vst3-sys.git", branch = "fix/note-off-event", optional = true }
 widestring = "1.0.0-beta.1"
 
 assert_no_alloc = { version = "1.1", optional = true }

src/prelude.rs

@@ -4,9 +4,11 @@ pub use crate::nih_debug_assert_eq;
 pub use crate::nih_debug_assert_failure;
 pub use crate::nih_debug_assert_ne;
 pub use crate::nih_export_clap;
-pub use crate::nih_export_vst3;
 pub use crate::nih_log;
 
+#[cfg(feature = "vst3")]
+pub use crate::nih_export_vst3;
+
 pub use crate::formatters;
 pub use crate::util;
 

src/wrapper.rs

@@ -4,4 +4,6 @@
 pub mod clap;
 pub mod state;
 pub(crate) mod util;
+
+#[cfg(feature = "vst3")]
 pub mod vst3;