Use autocfg crate to detect Rust features.

Issue #135

Author: azriel91

Cargo.toml

@@ -32,6 +32,9 @@ gimli = { version = "0.16.0", optional = true }
 memmap = { version = "0.7.0", optional = true }
 object = { version = "0.9.0", optional = true }
 
+[build-dependencies]
+autocfg = "0.1"
+
 [target.'cfg(unix)'.dependencies]
 libc = { version = "0.2", default-features = false }
 

build.rs

@@ -0,0 +1,10 @@
+extern crate autocfg;
+
+fn main() {
+    let ac = autocfg::new();
+
+    // `repr_align` was stabilized in Rust 1.25:
+    //
+    // https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1250-2018-03-29
+    ac.emit_rustc_version(1, 25);
+}

src/backtrace/dbghelp.rs

@@ -37,7 +37,7 @@ impl Frame {
 
 // This beast is to maintain Rust 1.18 Compatibility
 cfg_if! {
-    if #[cfg(feature = "repr_align")] {
+    if #[cfg(rustc_1_25)] {
         #[repr(C, align(16))] // required by `CONTEXT`, is a FIXME in winapi right now
         struct MyContext(CONTEXT);
 
@@ -122,7 +122,7 @@ cfg_if! {
             }
         }
     } else {
-        compile_error!("`no_std` is not supported for versions of Rust prior to 1.24.");
+        compile_error!("`no_std` is not supported for versions of Rust prior to 1.25.");
     }
 }
 

src/symbolize/dbghelp.rs

@@ -68,18 +68,18 @@ impl Symbol {
 }
 
 // Maintain Rust 1.18 Compatibility
-#[cfg(feature = "repr_align")]
+#[cfg(rustc_1_25)]
 #[repr(C, align(8))]
 struct Aligned8<T>(T);
 
 pub unsafe fn resolve(addr: *mut c_void, cb: &mut FnMut(&super::Symbol)) {
     let size: usize = 2 * MAX_SYM_NAME + mem::size_of::<SYMBOL_INFOW>();
-    #[cfg(feature = "repr_align")]
+    #[cfg(rustc_1_25)]
     let mut data = Aligned8([0u8; size]);
-    #[cfg(not(feature = "repr_align"))]
+    #[cfg(not(rustc_1_25))]
     let mut data = vec![0u8; size];
 
-    #[cfg(feature = "repr_align")]
+    #[cfg(rustc_1_25)]
     let data = &mut data.0;
 
     let info = &mut *(data.as_mut_ptr() as *mut SYMBOL_INFOW);