Merge pull request #130 from dtolnay/ensure

Use concat/stringify macros by absolute path

build.rs

@@ -2,6 +2,7 @@ use std::env;
 use std::fs;
 use std::path::Path;
 use std::process::{Command, ExitStatus, Stdio};
+use std::str;
 
 // This code exercises the surface area that we expect of the std Backtrace
 // type. If the current toolchain is able to compile it, we go ahead and use
@@ -35,12 +36,20 @@ const PROBE: &str = r#"
 "#;
 
 fn main() {
-    if !cfg!(feature = "std") {
-        return;
+    if cfg!(feature = "std") {
+        match compile_probe() {
+            Some(status) if status.success() => println!("cargo:rustc-cfg=backtrace"),
+            _ => {}
+        }
     }
-    match compile_probe() {
-        Some(status) if status.success() => println!("cargo:rustc-cfg=backtrace"),
-        _ => {}
+
+    let rustc = match rustc_minor_version() {
+        Some(rustc) => rustc,
+        None => return,
+    };
+
+    if rustc < 38 {
+        println!("cargo:rustc-cfg=anyhow_no_macro_reexport");
     }
 }
 
@@ -61,3 +70,14 @@ fn compile_probe() -> Option<ExitStatus> {
         .status()
         .ok()
 }
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    pieces.next()?.parse().ok()
+}

src/lib.rs

@@ -622,4 +622,27 @@ pub mod private {
     {
         Error::from_adhoc(message, backtrace!())
     }
+
+    #[cfg(anyhow_no_macro_reexport)]
+    pub use crate::{__anyhow_concat as concat, __anyhow_stringify as stringify};
+    #[cfg(not(anyhow_no_macro_reexport))]
+    pub use core::{concat, stringify};
+
+    #[cfg(anyhow_no_macro_reexport)]
+    #[doc(hidden)]
+    #[macro_export]
+    macro_rules! __anyhow_concat {
+        ($($tt:tt)*) => {
+            concat!($($tt)*)
+        };
+    }
+
+    #[cfg(anyhow_no_macro_reexport)]
+    #[doc(hidden)]
+    #[macro_export]
+    macro_rules! __anyhow_stringify {
+        ($($tt:tt)*) => {
+            stringify!($($tt)*)
+        };
+    }
 }

src/macros.rs

@@ -114,7 +114,10 @@ macro_rules! bail {
 #[macro_export]
 macro_rules! ensure {
     ($cond:expr $(,)?) => {
-        $crate::ensure!($cond, concat!("Condition failed: `", stringify!($cond), "`"))
+        $crate::ensure!(
+            $cond,
+            $crate::private::concat!("Condition failed: `", $crate::private::stringify!($cond), "`"),
+        )
     };
     ($cond:expr, $msg:literal $(,)?) => {
         if !$cond {