Make the feature opt-in

bench/Cargo.toml

@@ -13,7 +13,7 @@ test = false
 criterion = "0.5.1"
 rb-sys-test-helpers = { path = "../crates/rb-sys-test-helpers" }
 rb-sys = { path = "../crates/rb-sys", features = [
-  "stable-api-compiled",
+  "stable-api-compiled-testing",
   "link-ruby",
   "fuzz",
 ] }

crates/rb-sys-test-helpers-macros/Cargo.toml

@@ -20,4 +20,7 @@ quote = "1.0"
 
 [dev-dependencies]
 rb-sys-test-helpers = { path = "../rb-sys-test-helpers" }
-rb-sys = { path = "../rb-sys", features = ["link-ruby", "stable-api-compiled"] }
+rb-sys = { path = "../rb-sys", features = [
+  "link-ruby",
+  "stable-api-compiled-testing",
+] }

crates/rb-sys-test-helpers/Cargo.toml

@@ -14,7 +14,10 @@ bench = false
 doctest = true
 
 [dependencies]
-rb-sys = { path = "../rb-sys", features = ["link-ruby", "stable-api-compiled"] }
+rb-sys = { path = "../rb-sys", features = [
+  "link-ruby",
+  "stable-api-compiled-testing",
+] }
 rb-sys-test-helpers-macros = { version = "0.1.0", path = "../rb-sys-test-helpers-macros" }
 
 [build-dependencies]

crates/rb-sys-tests/Cargo.toml

@@ -12,7 +12,10 @@ doctest = false
 doc = false
 
 [dependencies]
-rb-sys = { path = "../rb-sys", features = ["link-ruby", "stable-api-compiled"] }
+rb-sys = { path = "../rb-sys", features = [
+  "link-ruby",
+  "stable-api-compiled-testing",
+] }
 rb-sys-env = { path = "../rb-sys-env" }
 rb-sys-test-helpers = { path = "../rb-sys-test-helpers" }
 rusty-fork = "0.3.0"

crates/rb-sys-tests/src/stable_api_test.rs

@@ -11,7 +11,7 @@ macro_rules! parity_test {
           #[allow(unused)]
           let rust_result = unsafe { stable_api::get_default().$func(data) };
           #[allow(unused_unsafe)]
-          let compiled_c_result = unsafe { stable_api::get_fallback().$func(data) };
+          let compiled_c_result = unsafe { stable_api::get_compiled().$func(data) };
 
           assert_eq!(
               compiled_c_result, rust_result,

crates/rb-sys/Cargo.toml

@@ -18,7 +18,10 @@ rb-sys-build = { version = "0.9.79", path = "../rb-sys-build" }
 
 [dev-dependencies]
 rb-sys-test-helpers = { path = "../rb-sys-test-helpers" }
-rb-sys = { path = ".", features = ["link-ruby", "stable-api-compiled"] }
+rb-sys = { path = ".", features = [
+  "link-ruby",
+  "stable-api-compiled-fallback",
+] }
 rusty-fork = "0.3.0"
 
 [features]
@@ -28,7 +31,10 @@ fuzz = []
 no-link-ruby = []
 ruby-static = []
 global-allocator = []
-stable-api-compiled = []
+stable-api-compiled-fallback = [] # Fallback to compiled C API
+stable-api-compiled-testing = [
+  "stable-api-compiled-fallback",
+] # For testing the fallback in rb-sys (internal)
 ruby-macros = [] # deprecated
 bindgen-rbimpls = ["rb-sys-build/bindgen-rbimpls"]
 bindgen-deprecated-types = ["rb-sys-build/bindgen-deprecated-types"]

crates/rb-sys/build/features.rs

@@ -19,10 +19,19 @@ pub fn is_global_allocator_enabled(rb_config: &RbConfig) -> bool {
 }
 
 pub fn is_compiled_stable_api_needed(ver: &Version) -> bool {
-    let needs_rust_impls = MIN_SUPPORTED_STABLE_VERSION > *ver || *ver > LATEST_STABLE_VERSION;
-    let is_feature_enabled = is_env_variable_defined("CARGO_FEATURE_STABLE_API_COMPILED");
+    let needs_c_fallback = MIN_SUPPORTED_STABLE_VERSION > *ver || *ver > LATEST_STABLE_VERSION;
+    let wants_c_fallback = explicitly_enabled_stable_api_compiled_fallback();
 
-    needs_rust_impls || is_feature_enabled
+    (needs_c_fallback && wants_c_fallback) || testing_stable_api_compiled_fallback()
+}
+
+pub fn explicitly_enabled_stable_api_compiled_fallback() -> bool {
+    cfg!(rb_sys_use_stable_api_compiled_fallback)
+        || is_env_variable_defined("CARGO_FEATURE_STABLE_API_COMPILED_FALLBACK")
+}
+
+pub fn testing_stable_api_compiled_fallback() -> bool {
+    is_env_variable_defined("CARGO_FEATURE_STABLE_API_COMPILED_TESTING")
 }
 
 pub fn is_gem_enabled() -> bool {

crates/rb-sys/build/main.rs

@@ -79,8 +79,13 @@ fn main() {
     );
     export_cargo_cfg(&mut rbconfig, &mut cfg_capture_file);
 
+    if explicitly_enabled_stable_api_compiled_fallback() {
+        println!("cargo:rustc-cfg=explicitly_enabled_stable_api_compiled_fallback");
+    }
+
     if is_compiled_stable_api_needed(&current_ruby_version) {
         c_glue::compile().expect("stable API C glue to compile");
+        println!("cargo:rustc-cfg=has_stable_api_compiled");
     }
 
     if is_link_ruby_enabled() {
@@ -143,7 +148,7 @@ fn export_cargo_cfg(rbconfig: &mut RbConfig, cap: &mut File) {
     rustc_cfg(rbconfig, "ruby_api_version", "RUBY_API_VERSION");
 
     if Version::current(rbconfig) <= LATEST_STABLE_VERSION {
-        println!("cargo:rustc-cfg=ruby_api_stable");
+        println!("cargo:rustc-cfg=current_ruby_is_stable");
     }
 
     if is_global_allocator_enabled(rbconfig) {

crates/rb-sys/src/stable_api.rs

@@ -127,42 +127,58 @@ pub trait StableApiDefinition {
     unsafe fn rb_type(&self, obj: VALUE) -> crate::ruby_value_type;
 }
 
-#[cfg(any(not(ruby_api_stable), ruby_lt_2_6))]
-use compiled as abi;
-
-#[cfg(any(not(ruby_api_stable), ruby_lt_2_6, feature = "stable-api-compiled"))]
+#[cfg(all(
+    explicitly_enabled_stable_api_compiled_fallback,
+    has_stable_api_compiled,
+    any(not(current_ruby_is_stable), ruby_lt_2_6,)
+))]
+use compiled as api;
+
+#[cfg(all(
+    explicitly_enabled_stable_api_compiled_fallback,
+    has_stable_api_compiled,
+))]
 mod compiled;
 
+#[cfg(all(
+    not(has_stable_api_compiled),
+    any(not(current_ruby_is_stable), ruby_lt_2_6)
+))]
+compile_error!("Compiled stable API is needed but could not find it.");
+
 #[cfg(ruby_eq_2_6)]
 #[path = "stable_api/ruby_2_6.rs"]
-mod abi;
+mod api;
 
 #[cfg(ruby_eq_2_7)]
 #[path = "stable_api/ruby_2_7.rs"]
-mod abi;
+mod api;
 
 #[cfg(ruby_eq_3_0)]
 #[path = "stable_api/ruby_3_0.rs"]
-mod abi;
+mod api;
 
 #[cfg(ruby_eq_3_1)]
 #[path = "stable_api/ruby_3_1.rs"]
-mod abi;
+mod api;
 
 #[cfg(ruby_eq_3_2)]
 #[path = "stable_api/ruby_3_2.rs"]
-mod abi;
+mod api;
 
 /// Get the default stable API definition for the current Ruby version.
-pub const fn get_default() -> &'static abi::Definition {
-    const API: abi::Definition = abi::Definition {};
+pub const fn get_default() -> &'static api::Definition {
+    const API: api::Definition = api::Definition {};
     &API
 }
 
 /// Get the fallback stable API definition for the current Ruby version, which
 /// is compiled C code that is linked into to this crate.
-#[cfg(feature = "stable-api-compiled")]
-pub const fn get_fallback() -> &'static compiled::Definition {
+#[cfg(all(
+    explicitly_enabled_stable_api_compiled_fallback,
+    has_stable_api_compiled,
+))]
+pub const fn get_compiled() -> &'static compiled::Definition {
     const COMPILED_API: compiled::Definition = compiled::Definition {};
     &COMPILED_API
 }

examples/rust_reverse/ext/rust_reverse/Cargo.toml

@@ -1,11 +1,13 @@
 [package]
 name = "rust_reverse"
 version = "0.9.79"
-autotests = true # set true if you want to use "cargo test"
+autotests = true      # set true if you want to use "cargo test"
 edition = "2018"
 
 [dependencies]
-rb-sys = { version = "0.9.79", path = "./../../../../crates/rb-sys", features = ["global-allocator"] }
+rb-sys = { version = "0.9.79", path = "./../../../../crates/rb-sys", features = [
+  "global-allocator",
+] }
 
 [lib]
 crate-type = ["cdylib"]

examples/rust_reverse/ext/rust_reverse/extconf.rb

@@ -20,7 +20,7 @@
   r.ext_dir = "."
 
   # Extra flags to pass to the $RUSTFLAGS environment variable (optional)
-  r.extra_rustflags << "--cfg=some_nested_config_var_for_crate"
+  r.extra_rustflags << "--cfg=rb_sys_use_stable_api_compiled_fallback"
 
   # Force a rust toolchain to be installed via rustup (optional)
   # You can also set the env var `RB_SYS_FORCE_INSTALL_RUST_TOOLCHAIN=true`

examples/rust_reverse/ext/rust_reverse/extconf_bare.rb

@@ -5,4 +5,6 @@
 require "mkmf"
 require "rb_sys/mkmf"
 
-create_rust_makefile("rust_reverse")
+create_rust_makefile("rust_reverse") do |r|
+  r.extra_rustflags << "--cfg=rb_sys_use_stable_api_compiled_fallback"
+end

fuzz/Cargo.toml

@@ -11,7 +11,7 @@ cargo-fuzz = true
 libfuzzer-sys = "0.4"
 rb-sys-test-helpers = { path = "../crates/rb-sys-test-helpers" }
 rb-sys = { path = "../crates/rb-sys", features = [
-  "stable-api-compiled",
+  "stable-api-compiled-testing",
   "link-ruby",
   "fuzz",
 ] }