Detect retpolines in build.rs as cfg is never set for them. Fixes #46

Author: calebzulawski

multiversion-macros/build.rs

@@ -0,0 +1,24 @@
+fn main() {
+    // retpolines are not yet recognized by rust as a regular target feature.
+    // We can't detect them with `cfg(target_feature = "retpoline")`, but we can detect them in
+    // rustflags, since they shouldn't be the default for any target.
+    let rustflags = std::env::var("CARGO_ENCODED_RUSTFLAGS").unwrap();
+    let retpolines_enabled = rustflags.split('\x1f').any(|flag| {
+        let features = flag
+            .strip_prefix("target-feature=")
+            .or(flag.strip_prefix("-Ctarget-feature="));
+        if let Some(features) = features {
+            features
+                .split(',')
+                .any(|feature| feature.starts_with("+retpoline"))
+        } else {
+            false
+        }
+    });
+
+    if retpolines_enabled {
+        println!("cargo::rustc-cfg=retpoline")
+    }
+    println!("cargo::rustc-check-cfg=cfg(retpoline)");
+    println!("cargo::rerun-if-changed=build.rs");
+}

multiversion-macros/src/dispatcher.rs

@@ -381,27 +381,11 @@ impl Dispatcher {
                     if !crate::util::fn_params(&self.func.sig).is_empty()
                         || self.func.sig.asyncness.is_some()
                         || util::impl_trait_present(&self.func.sig)
+                        || cfg!(retpoline)
                     {
                         self.direct_dispatcher_fn()?
                     } else {
-                        let indirect = self.indirect_dispatcher_fn()?;
-                        let direct = self.direct_dispatcher_fn()?;
-                        parse_quote! {
-                            {
-                                #[cfg(not(any(
-                                    target_feature = "retpoline",
-                                    target_feature = "retpoline-indirect-branches",
-                                    target_feature = "retpoline-indirect-calls",
-                                )))]
-                                #indirect
-                                #[cfg(any(
-                                    target_feature = "retpoline",
-                                    target_feature = "retpoline-indirect-branches",
-                                    target_feature = "retpoline-indirect-calls",
-                                ))]
-                                #direct
-                            }
-                        }
+                        self.indirect_dispatcher_fn()?
                     }
                 } else {
                     self.static_dispatcher_fn()