Thread through the original error when opening archives

This updates the management of opening archives to thread through the original
piece of error information from LLVM over to the end consumer, trans.

src/librustc_llvm/archive_ro.rs

@@ -39,14 +39,14 @@ impl ArchiveRO {
     ///
     /// If this archive is used with a mutable method, then an error will be
     /// raised.
-    pub fn open(dst: &Path) -> Option<ArchiveRO> {
+    pub fn open(dst: &Path) -> Result<ArchiveRO, String> {
         return unsafe {
             let s = path2cstr(dst);
             let ar = ::LLVMRustOpenArchive(s.as_ptr());
             if ar.is_null() {
-                None
+                Err(::last_error().unwrap_or("failed to open archive".to_string()))
             } else {
-                Some(ArchiveRO { ptr: ar })
+                Ok(ArchiveRO { ptr: ar })
             }
         };
 

src/librustc_trans/back/archive.rs

@@ -126,7 +126,7 @@ impl<'a> ArchiveBuilder<'a> {
             Some(ref src) => src,
             None => return None,
         };
-        self.src_archive = Some(ArchiveRO::open(src));
+        self.src_archive = Some(ArchiveRO::open(src).ok());
         self.src_archive.as_ref().unwrap().as_ref()
     }
 
@@ -186,9 +186,8 @@ impl<'a> ArchiveBuilder<'a> {
         where F: FnMut(&str) -> bool + 'static
     {
         let archive = match ArchiveRO::open(archive) {
-            Some(ar) => ar,
-            None => return Err(io::Error::new(io::ErrorKind::Other,
-                                              "failed to open archive")),
+            Ok(ar) => ar,
+            Err(e) => return Err(io::Error::new(io::ErrorKind::Other, e)),
         };
         self.additions.push(Addition::Archive {
             archive: archive,

src/librustc_trans/metadata.rs

@@ -31,10 +31,10 @@ impl MetadataLoader for LlvmMetadataLoader {
         // just keeping the archive along while the metadata is in use.
         let archive = ArchiveRO::open(filename)
             .map(|ar| OwningRef::new(box ar))
-            .ok_or_else(|| {
-                            debug!("llvm didn't like `{}`", filename.display());
-                            format!("failed to read rlib metadata: '{}'", filename.display())
-                        })?;
+            .map_err(|e| {
+                debug!("llvm didn't like `{}`: {}", filename.display(), e);
+                format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
+            })?;
         let buf: OwningRef<_, [u8]> = archive
             .try_map(|ar| {
                 ar.iter()
@@ -42,10 +42,10 @@ impl MetadataLoader for LlvmMetadataLoader {
                     .find(|sect| sect.name() == Some(METADATA_FILENAME))
                     .map(|s| s.data())
                     .ok_or_else(|| {
-                                    debug!("didn't find '{}' in the archive", METADATA_FILENAME);
-                                    format!("failed to read rlib metadata: '{}'",
-                                            filename.display())
-                                })
+                        debug!("didn't find '{}' in the archive", METADATA_FILENAME);
+                        format!("failed to read rlib metadata: '{}'",
+                                filename.display())
+                    })
             })?;
         Ok(buf.erase_owner())
     }