Merge pull request #255 from palfrey/use-error-source

Use Error::source not Error::cause in Rust versions that have it

Author: AndyGauge

.travis.yml

@@ -5,7 +5,8 @@ rust:
 - nightly
 # Oldest supported version for all features.
 # Use of https://github.com/rust-lang/rfcs/pull/16
-- 1.14.0
+# and Backtrace needs 1.25 (see https://github.com/alexcrichton/backtrace-rs/pull/137)
+- 1.25.0
 # Oldest supported version as dependency, with no features, tests, or examples.
 - 1.10.0
 

Cargo.toml

@@ -24,3 +24,6 @@ example_generated = []
 
 [dependencies]
 backtrace = { version = "0.3.3", optional = true }
+
+[build-dependencies]
+version_check = "0.1.5"

build.rs

@@ -0,0 +1,12 @@
+extern crate version_check;
+
+use version_check::is_min_version;
+
+fn main() {
+    // Switch on for versions that have Error::source
+    // As introduced by https://github.com/rust-lang/rust/pull/53533
+    if is_min_version("1.30").map(|(is_high_enough, _actual_version)| is_high_enough).unwrap_or(false)
+    {
+        println!("cargo:rustc-cfg=has_error_source");
+    }
+}

src/backtrace.rs

@@ -7,7 +7,7 @@ mod imp {
     use std::cell::UnsafeCell;
     use std::env;
     use std::fmt;
-    use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
+    use std::sync::atomic::{AtomicUsize, Ordering};
     use std::sync::{Arc, Mutex};
 
     /// Internal representation of a backtrace
@@ -33,7 +33,7 @@ mod imp {
         /// in the generated error implementations.
         #[doc(hidden)]
         pub fn new() -> InternalBacktrace {
-            static ENABLED: AtomicUsize = ATOMIC_USIZE_INIT;
+            static ENABLED: AtomicUsize = AtomicUsize::new(0);
 
             match ENABLED.load(Ordering::SeqCst) {
                 0 => {

src/error_chain.rs

@@ -1,3 +1,72 @@
+#[doc(hidden)]
+#[macro_export]
+#[cfg(not(has_error_source))]
+macro_rules! impl_error_chain_cause_or_source {
+    (
+        types {
+            $error_kind_name:ident
+        }
+
+        foreign_links {
+            $( $foreign_link_variant:ident ( $foreign_link_error_path:path )
+               $( #[$meta_foreign_links:meta] )*; )*
+        }
+    ) => {
+        #[allow(unknown_lints, renamed_and_removed_lints, unused_doc_comment, unused_doc_comments)]
+        fn cause(&self) -> Option<&::std::error::Error> {
+            match self.1.next_error {
+                Some(ref c) => Some(&**c),
+                None => {
+                    match self.0 {
+                        $(
+                            $(#[$meta_foreign_links])*
+                            $error_kind_name::$foreign_link_variant(ref foreign_err) => {
+                                foreign_err.cause()
+                            }
+                        ) *
+                        _ => None
+                    }
+                }
+            }
+        }
+    };
+}
+
+#[cfg(has_error_source)]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_error_chain_cause_or_source {
+    (
+        types {
+             $error_kind_name:ident
+        }
+
+        foreign_links {
+            $( $foreign_link_variant:ident ( $foreign_link_error_path:path )
+               $( #[$meta_foreign_links:meta] )*; )*
+        }
+    ) => {
+
+            #[allow(unknown_lints, renamed_and_removed_lints, unused_doc_comment, unused_doc_comments)]
+            fn source(&self) -> Option<&(std::error::Error + 'static)> {
+                match self.1.next_error {
+                    Some(ref c) => Some(&**c),
+                    None => {
+                        match self.0 {
+                        $(
+                            $(#[$meta_foreign_links])*
+                            $error_kind_name::$foreign_link_variant(ref foreign_err) => {
+                                foreign_err.source()
+                            }
+                        ) *
+                            _ => None
+                        }
+                    }
+                }
+            }
+        };
+}
+
 /// Prefer to use `error_chain` instead of this macro.
 #[doc(hidden)]
 #[macro_export]
@@ -179,21 +248,13 @@ macro_rules! impl_error_chain_processed {
                 self.description()
             }
 
-            #[allow(unknown_lints, renamed_and_removed_lints, unused_doc_comment, unused_doc_comments)]
-            fn cause(&self) -> Option<&::std::error::Error> {
-                match self.1.next_error {
-                    Some(ref c) => Some(&**c),
-                    None => {
-                        match self.0 {
-                            $(
-                                $(#[$meta_foreign_links])*
-                                $error_kind_name::$foreign_link_variant(ref foreign_err) => {
-                                    foreign_err.cause()
-                                }
-                            ) *
-                            _ => None
-                        }
-                    }
+            impl_error_chain_cause_or_source!{
+                types {
+                    $error_kind_name
+                }
+                foreign_links {
+                    $( $foreign_link_variant ( $foreign_link_error_path )
+                    $( #[$meta_foreign_links] )*; )*
                 }
             }
         }

src/lib.rs

@@ -570,7 +570,12 @@ impl<'a> Iterator for Iter<'a> {
     fn next<'b>(&'b mut self) -> Option<&'a error::Error> {
         match self.0.take() {
             Some(e) => {
-                self.0 = e.cause();
+                self.0 = match () {
+                    #[cfg(not(has_error_source))]
+                    () => e.cause(),
+                    #[cfg(has_error_source)]
+                    () => e.source(),
+                };
                 Some(e)
             }
             None => None,

tests/tests.rs

@@ -292,9 +292,15 @@ mod foreign_link_test {
             "Foreign error description"
         }
 
+        #[cfg(not(has_error_source))]
         fn cause(&self) -> Option<&::std::error::Error> {
             Some(&self.cause)
         }
+
+        #[cfg(has_error_source)]
+        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+            Some(&self.cause)
+        }
     }
 
     impl fmt::Display for ForeignError {
@@ -311,9 +317,15 @@ mod foreign_link_test {
             "Foreign error cause description"
         }
 
+        #[cfg(not(has_error_source))]
         fn cause(&self) -> Option<&::std::error::Error> {
             None
         }
+
+        #[cfg(has_error_source)]
+        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+            None
+        }
     }
 
     impl fmt::Display for ForeignErrorCause {
@@ -342,12 +354,21 @@ mod foreign_link_test {
     }
 
     #[test]
+    #[cfg(not(has_error_source))]
     fn finds_cause() {
         let chained_error = try_foreign_error().err().unwrap();
         assert_eq!(format!("{}", ForeignErrorCause {}),
                    format!("{}", ::std::error::Error::cause(&chained_error).unwrap()));
     }
 
+    #[test]
+    #[cfg(has_error_source)]
+    fn finds_source() {
+        let chained_error = try_foreign_error().err().unwrap();
+        assert_eq!(format!("{}", ForeignErrorCause {}),
+                   format!("{}", ::std::error::Error::source(&chained_error).unwrap()));
+    }
+
     #[test]
     fn iterates() {
         let chained_error = try_foreign_error().err().unwrap();