Change revwalk to iterate over Result<Oid>

Turns out iteration can fail! Probably shouldn't be swallowing errors...

Closes rust-lang#112

examples/log.rs

@@ -98,6 +98,7 @@ fn run(args: &Args) -> Result<(), Error> {
         ($e:expr) => (match $e { Ok(t) => t, Err(e) => return Some(Err(e)) })
     }
     let revwalk = revwalk.filter_map(|id| {
+        let id = filter_try!(id);
         let commit = filter_try!(repo.find_commit(id));
         let parents = commit.parents().len();
         if parents < args.min_parents() { return None }

examples/rev-list.rs

@@ -64,6 +64,7 @@ fn run(args: &Args) -> Result<(), git2::Error> {
     }
 
     for id in revwalk {
+        let id = try!(id);
         println!("{}", id);
     }
     Ok(())

src/call.rs

@@ -32,7 +32,7 @@ pub fn try(ret: libc::c_int) -> Result<libc::c_int, Error> {
     }
 }
 
-fn last_error(code: libc::c_int) -> Error {
+pub fn last_error(code: libc::c_int) -> Error {
     // Apparently libgit2 isn't necessarily guaranteed to set the last error
     // whenever a function returns a negative value!
     Error::last_error(code).unwrap_or_else(|| {

src/revwalk.rs

@@ -164,25 +164,23 @@ impl<'repo> Drop for Revwalk<'repo> {
 }
 
 impl<'repo> Iterator for Revwalk<'repo> {
-    type Item = Oid;
-    fn next(&mut self) -> Option<Oid> {
+    type Item = Result<Oid, Error>;
+    fn next(&mut self) -> Option<Result<Oid, Error>> {
         let mut out: raw::git_oid = raw::git_oid{ id: [0; raw::GIT_OID_RAWSZ] };
         unsafe {
             match raw::git_revwalk_next(&mut out, self.raw()) {
                 0 => (),
-                _ => return None,
+                raw::GIT_ITEROVER => return None,
+                err => return Some(Err(::call::last_error(err))),
             }
 
-            Some(Binding::from_raw(&out as *const _))
+            Some(Ok(Binding::from_raw(&out as *const _)))
         }
     }
 }
 
 #[cfg(test)]
 mod tests {
-    extern crate std;
-    use std::vec::{Vec};
-
     #[test]
     fn smoke() {
         let (_td, repo) = ::test::repo_init();
@@ -192,7 +190,8 @@ mod tests {
         let mut walk = repo.revwalk().unwrap();
         walk.push(target).unwrap();
 
-        let oids: Vec<::Oid> = walk.by_ref().collect();
+        let oids: Vec<::Oid> = walk.by_ref().collect::<Result<Vec<_>, _>>()
+                                            .unwrap();
 
         assert_eq!(oids.len(), 1);
         assert_eq!(oids[0], target);