feat: make VST3 an opt-in cargo feature

Cargo.toml declared Apache-2.0 while the default build linked vst3-sys,
whose bindings are GPLv3 — so the artifact a fresh clone produced could
not legally be distributed under the licence the repo claimed. A template
should not hand that trap to every project cloned from it.

NIH-plug already anticipates this: its `vst3` feature exists, in upstream's
own words, "mostly for GPL-compliance reasons". Taking `default-features =
false` and re-exporting `vst3` as a local opt-in makes the default build
CLAP-only and genuinely Apache-2.0 clean, while `--features vst3` remains
one flag away for anyone who accepts GPLv3.

Gating the feature rather than relicensing keeps the decision with whoever
uses the template. Reversing it is a one-line default plus removing two
cfg attributes, where relicensing to GPLv3 now would commit every
downstream plugin to that choice.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHt4DykxXaQnyaJfyS8KCn

Cargo.toml

@@ -10,6 +10,14 @@ license = "Apache-2.0"
 [workspace]
 members = ["xtask"]
 
+[features]
+# CLAP only by default. NIH-plug's VST3 bindings (vst3-sys) are GPLv3, so linking
+# them makes the resulting binary GPLv3 regardless of what this package declares.
+# Opt in explicitly — and relicense this crate — if you intend to ship a VST3:
+#   cargo xtask bundle nih_plug_template --release --features vst3
+default = []
+vst3 = ["nih_plug/vst3"]
+
 [lib]
 # `cdylib` is the plugin binary; `lib` (rlib) lets `cargo test` link the unit tests.
 crate-type = ["cdylib", "lib"]
@@ -17,7 +25,8 @@ crate-type = ["cdylib", "lib"]
 [dependencies]
 # Pinned to the same commit as musiikki/codename-206.
 # Update the `rev` when you want to update NIH-plug.
-nih_plug = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23", features = ["assert_process_allocs"] }
+# `default-features = false` drops nih_plug's default `vst3` feature; see [features] above.
+nih_plug = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23", default-features = false, features = ["assert_process_allocs"] }
 nih_plug_egui = { git = "https://github.com/robbert-vdh/nih-plug.git", rev = "f36931f7af4646065488a9845d8f8c2f95252c23" }
 
 [profile.release]

README.md

@@ -21,13 +21,16 @@ cd my-plugin
 # Install Rust via rustup: https://rustup.rs
 # No VST3 SDK needed — NIH-plug bundles its own bindings.
 
-# Build + bundle the VST3 and CLAP
+# Build + bundle the CLAP (default)
 cargo xtask bundle nih_plug_template --release
+
+# Add the VST3 as well — see the licensing note below before you do this
+cargo xtask bundle nih_plug_template --release --features vst3
 ```
 
-**Output:** `target/bundled/<name>.vst3` and `<name>.clap`, where `<name>` is the `name` set
-in `bundler.toml` — **not** the crate name. Out of the box that means
-`target/bundled/Plugin Name.vst3`.
+**Output:** `target/bundled/<name>.clap` (and `<name>.vst3` with `--features vst3`), where
+`<name>` is the `name` set in `bundler.toml` — **not** the crate name. Out of the box that
+means `target/bundled/Plugin Name.clap`.
 
 On Linux the egui editor needs the GUI development headers:
 
@@ -40,6 +43,8 @@ sudo apt install pkg-config libgl-dev libx11-dev libxcursor-dev libxcb1-dev \
 
 ### FL Studio
 
+Build with `--features vst3` first if you want the VST3 (see the licensing note below).
+
 FL Studio scans `C:\Program Files\Common Files\VST3` by default, **ignores directory junctions**
 (so a symlinked bundle is invisible to its scanner), and caches failed scans.
 
@@ -50,23 +55,23 @@ FL Studio scans `C:\Program Files\Common Files\VST3` by default, **ignores direc
 ### Linux
 
 ```bash
-# VST3
-cp -r "target/bundled/Plugin Name.vst3" ~/.vst3/
-
 # CLAP
 cp -r "target/bundled/Plugin Name.clap" ~/.clap/
 
+# VST3 (only exists if you built with --features vst3)
+cp -r "target/bundled/Plugin Name.vst3" ~/.vst3/
+
 # Or globally:
-# sudo cp -r "target/bundled/Plugin Name.vst3" /usr/lib/vst3/
 # sudo cp -r "target/bundled/Plugin Name.clap" /usr/lib/clap/
+# sudo cp -r "target/bundled/Plugin Name.vst3" /usr/lib/vst3/
 ```
 
 ## Project Structure
 
 ```
-Cargo.toml          # Package deps — NIH-plug pinned to codename-206's rev
+Cargo.toml          # Package deps + the opt-in `vst3` feature — NIH-plug pinned to codename-206's rev
 bundler.toml        # Bundle name for `cargo xtask bundle`
-src/lib.rs          # Plugin skeleton — fill in params, DSP, editor
+src/lib.rs          # Plugin skeleton — params, DSP, and egui editor, with one example gain param
 xtask/              # Bundler xtask (cargo xtask bundle)
 .cargo/config.toml  # xtask alias
 ```
@@ -77,6 +82,16 @@ Apache-2.0
 
 ## VST3 Licensing Note
 
-You must accept Steinberg's VST3 SDK licence before distributing VST3 binaries.
-NIH-plug's VST3 bindings are GPLv3; if you distribute, the plugin must also be GPLv3
-(or you need a commercial Steinberg licence). CLAP has no such restriction.
+NIH-plug's VST3 bindings (`vst3-sys`) are GPLv3. Linking them makes the resulting binary
+GPLv3 regardless of what `Cargo.toml` declares, so **VST3 is behind an opt-in `vst3` feature
+and this template builds CLAP only by default.** That keeps the default build consistent with
+the Apache-2.0 licence in `Cargo.toml`/`LICENSE`.
+
+If you want to ship a VST3:
+
+1. Build with `--features vst3`.
+2. Relicense your plugin as GPLv3 (or obtain a commercial Steinberg licence) and update
+   `Cargo.toml`, `LICENSE`, and the SPDX headers in `src/`.
+3. Accept Steinberg's VST3 SDK licence.
+
+CLAP has no such restriction.

src/lib.rs

@@ -133,6 +133,7 @@ impl ClapPlugin for MyPlugin {
     const CLAP_FEATURES: &'static [ClapFeature] = &[ClapFeature::AudioEffect];
 }
 
+#[cfg(feature = "vst3")]
 impl Vst3Plugin for MyPlugin {
     // TODO: Replace with a unique 16-byte Class ID.
     // Must be exactly 16 bytes — padded with '!' if shorter.
@@ -141,4 +142,5 @@ impl Vst3Plugin for MyPlugin {
 }
 
 nih_export_clap!(MyPlugin);
+#[cfg(feature = "vst3")]
 nih_export_vst3!(MyPlugin);