fix: check stable API rust impl file exists at build time

When detecting Ruby versions like 3.5 (ruby-head), the build would fail
with a missing file error because is_stable() only checked version ranges
rather than verifying a corresponding ruby_X_Y.rs file exists.

Replace is_stable() with has_rust_impl() that checks for actual file
existence. This allows ruby-head or other versions without impls to
correctly fall back to compiled C when stable-api-compiled-fallback is
enabled, or error clearly when it's not.

Author: ianks

Gemfile

@@ -13,7 +13,7 @@ gem "racc"
 gem "base64"
 gem "yard"
 gem "mutex_m"
-gem "standard"
+gem "standard", "~> 1.52.0"
 gem "tsort"
 
 gem "ostruct", "~> 0.6.3"

crates/rb-sys/build/stable_api_config.rs

@@ -6,6 +6,23 @@ use crate::{
 };
 use std::{convert::TryFrom, error::Error, path::Path};
 
+/// Check if a Rust implementation file exists for the given Ruby version.
+fn has_rust_impl(version: Version) -> bool {
+    let crate_dir = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let path = crate_dir.join("src").join("stable_api").join(format!(
+        "ruby_{}_{}.rs",
+        version.major(),
+        version.minor()
+    ));
+
+    let exists = path.exists();
+
+    // Ensure we rebuild if the file is added or removed
+    println!("cargo:rerun-if-changed={}", path.display());
+
+    exists
+}
+
 pub fn setup(rb_config: &RbConfig) -> Result<(), Box<dyn Error>> {
     let ruby_version = Version::current(rb_config);
     let ruby_engine = rb_config.ruby_engine();
@@ -42,7 +59,7 @@ impl TryFrom<(RubyEngine, Version)> for Strategy {
             RubyEngine::Mri => {}
         }
 
-        if current_ruby_version.is_stable() {
+        if has_rust_impl(current_ruby_version) {
             strategy = Some(Strategy::RustOnly(current_ruby_version));
         } else {
             maybe_warn_old_ruby_version(current_ruby_version);
@@ -76,10 +93,10 @@ impl Strategy {
         println!("cargo:rustc-check-cfg=cfg(stable_api_has_rust_impl)");
         match self {
             Strategy::RustOnly(current_ruby_version) => {
-                if current_ruby_version.is_stable() {
+                if has_rust_impl(current_ruby_version) {
                     println!("cargo:rustc-cfg=stable_api_include_rust_impl");
                 } else {
-                    return Err(format!("A stable Ruby API is needed but could not find a candidate. If you are using a stable version of Ruby, try upgrading rb-sys. Otherwise if you are testing against ruby-head or Ruby < {}, enable the `stable-api-compiled-fallback` feature in rb-sys.", MIN_SUPPORTED_STABLE_VERSION).into());
+                    return Err(format!("No Rust stable API implementation found for Ruby {}. If you are using a stable version of Ruby, try upgrading rb-sys. Otherwise if you are testing against ruby-head or Ruby < {}, enable the `stable-api-compiled-fallback` feature in rb-sys.", current_ruby_version, MIN_SUPPORTED_STABLE_VERSION).into());
                 }
             }
             Strategy::CompiledOnly => {
@@ -88,7 +105,7 @@ impl Strategy {
                 println!("cargo:rustc-cfg=stable_api_export_compiled_as_api");
             }
             Strategy::RustThenCompiled(current_ruby_version) => {
-                if current_ruby_version.is_stable() {
+                if has_rust_impl(current_ruby_version) {
                     println!("cargo:rustc-cfg=stable_api_has_rust_impl");
                     println!("cargo:rustc-cfg=stable_api_include_rust_impl");
                 } else {
@@ -102,7 +119,7 @@ impl Strategy {
 
                 println!("cargo:rustc-cfg=stable_api_enable_compiled_mod");
 
-                if current_ruby_version.is_stable() {
+                if has_rust_impl(current_ruby_version) {
                     println!("cargo:rustc-cfg=stable_api_include_rust_impl");
                 } else {
                     println!("cargo:rustc-cfg=stable_api_export_compiled_as_api");

crates/rb-sys/build/version.rs

@@ -36,11 +36,6 @@ impl Version {
             }
         }
     }
-
-    #[allow(dead_code)]
-    pub fn is_stable(&self) -> bool {
-        *self >= MIN_SUPPORTED_STABLE_VERSION && *self <= LATEST_STABLE_VERSION
-    }
 }
 
 impl std::fmt::Display for Version {

script/show-asm

@@ -585,9 +585,9 @@ class ShowAsm
         archhdrdir = ruby_config["rubyarchhdrdir"]
 
         cmd = [cc, src_file.path,
-          "-S",                     # Output assembly
-          "-O3",                    # Optimize
-          "-fno-stack-protector",   # Disable stack canary for fair comparison
+          "-S", # Output assembly
+          "-O3", # Optimize
+          "-fno-stack-protector", # Disable stack canary for fair comparison
           "-I#{hdrdir}",
           "-I#{archhdrdir}",
           "-o", asm_file.path]