use attribute after check the rustc version

bitflags · May 3, 2020 · 43da098 · 43da098
1 parent a218659
commit 43da098
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Showing 2 changed files with 48 additions and 11 deletions.
diff --git a/build.rs b/build.rs
@@ -2,12 +2,17 @@ use std::env;
 use std::process::Command;
 use std::str::{self, FromStr};
 
-fn main(){
+fn main() {
     let minor = match rustc_minor_version() {
         Some(minor) => minor,
         None => return,
     };
 
+    // #[repr(transparent)] stabilized in Rust 1.28:
+    if minor >= 28 {
+        println!("cargo:rustc-cfg=bitflags_repr_transparent");
+    }
+
     // const fn stabilized in Rust 1.31:
     if minor >= 31 {
         println!("cargo:rustc-cfg=bitflags_const_fn");
@@ -41,4 +46,4 @@ fn rustc_minor_version() -> Option<u32> {
     };
 
     u32::from_str(next).ok()
-}
+}
diff --git a/src/lib.rs b/src/lib.rs
@@ -390,6 +390,25 @@ macro_rules! bitflags {
     };
 }
 
+#[macro_export(local_inner_macros)]
+#[doc(hidden)]
+#[cfg(bitflags_repr_transparent)]
+macro_rules! __repr_transparent {
+    ($($inner:tt)*) => {
+        #[repr(transparent)]
+        $($inner)*
+    }
+}
+
+#[macro_export(local_inner_macros)]
+#[doc(hidden)]
+#[cfg(not(bitflags_repr_transparent))]
+macro_rules! __repr_transparent {
+    ($($inner:tt)*) => {
+        $($inner)*
+    }
+}
+
 #[macro_export(local_inner_macros)]
 #[doc(hidden)]
 macro_rules! __bitflags {
@@ -402,11 +421,12 @@ macro_rules! __bitflags {
             )+
         }
     ) => {
-        $(#[$outer])*
-        #[repr(transparent)]
-        #[derive(Copy, PartialEq, Eq, Clone, PartialOrd, Ord, Hash)]
-        $($vis)* struct $BitFlags {
-            bits: $T,
+        __repr_transparent! {
+            $(#[$outer])*
+            #[derive(Copy, PartialEq, Eq, Clone, PartialOrd, Ord, Hash)]
+            $($vis)* struct $BitFlags {
+                bits: $T,
+            }
         }
 
         __impl_bitflags! {
@@ -1029,9 +1049,18 @@ mod tests {
         assert_eq!(unsafe { Flags::from_bits_unchecked(0) }, Flags::empty());
         assert_eq!(unsafe { Flags::from_bits_unchecked(0b1) }, Flags::A);
         assert_eq!(unsafe { Flags::from_bits_unchecked(0b10) }, Flags::B);
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b11) }, (Flags::A | Flags::B));
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b1000) }, (extra | Flags::empty()));
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b1001) }, (extra | Flags::A));
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b11) },
+            (Flags::A | Flags::B)
+        );
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b1000) },
+            (extra | Flags::empty())
+        );
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b1001) },
+            (extra | Flags::A)
+        );
     }
 
     #[test]
@@ -1276,7 +1305,10 @@ mod tests {
         let extra = unsafe { Flags::from_bits_unchecked(0xb8) };
         assert_eq!(format!("{:?}", extra), "0xb8");
         assert_eq!(format!("{:?}", Flags::A | extra), "A | 0xb8");
-        assert_eq!(format!("{:?}", Flags::ABC | extra), "A | B | C | ABC | 0xb8");
+        assert_eq!(
+            format!("{:?}", Flags::ABC | extra),
+            "A | B | C | ABC | 0xb8"
+        );
     }
 
     #[test]