Allow mapping a runtime feature to a set of target_features (#1311)

Author: adamgemmell

crates/std_detect/src/detect/arch/aarch64.rs

@@ -72,7 +72,8 @@ features! {
     @FEATURE: #[stable(feature = "simd_aarch64", since = "1.60.0")] pmull: "pmull";
     /// FEAT_PMULL (Polynomial Multiply)
     @FEATURE: #[stable(feature = "simd_aarch64", since = "1.60.0")] fp: "fp";
-    /// FEAT_FP (Floating point support)
+    implied by target_features: ["neon"];
+    /// FEAT_FP (Floating point support) - Implied by `neon` target_feature
     @FEATURE: #[stable(feature = "simd_aarch64", since = "1.60.0")] fp16: "fp16";
     /// FEAT_FP16 (Half-float support)
     @FEATURE: #[stable(feature = "simd_aarch64", since = "1.60.0")] sve: "sve";

crates/std_detect/src/detect/macros.rs

@@ -1,3 +1,14 @@
+#[macro_export]
+macro_rules! detect_feature {
+    ($feature:tt, $feature_lit:tt) => {
+        $crate::detect_feature!($feature, $feature_lit : $feature_lit)
+    };
+    ($feature:tt, $feature_lit:tt : $($target_feature_lit:tt),*) => {
+        $(cfg!(target_feature = $target_feature_lit) ||)*
+            $crate::detect::__is_feature_detected::$feature()
+    };
+}
+
 #[allow(unused)]
 macro_rules! features {
     (
@@ -7,7 +18,9 @@ macro_rules! features {
       @MACRO_ATTRS: $(#[$macro_attrs:meta])*
       $(@BIND_FEATURE_NAME: $bind_feature:tt; $feature_impl:tt; )*
       $(@NO_RUNTIME_DETECTION: $nort_feature:tt; )*
-      $(@FEATURE: #[$stability_attr:meta] $feature:ident: $feature_lit:tt; $(#[$feature_comment:meta])*)*
+      $(@FEATURE: #[$stability_attr:meta] $feature:ident: $feature_lit:tt;
+          $(implied by target_features: [$($target_feature_lit:tt),*];)?
+          $(#[$feature_comment:meta])*)*
     ) => {
         #[macro_export]
         $(#[$macro_attrs])*
@@ -17,8 +30,7 @@ macro_rules! features {
         macro_rules! $macro_name {
             $(
                 ($feature_lit) => {
-                    cfg!(target_feature = $feature_lit) ||
-                        $crate::detect::__is_feature_detected::$feature()
+                    $crate::detect_feature!($feature, $feature_lit $(: $($target_feature_lit),*)?)
                 };
             )*
             $(