Add extension traits for handling Result<Option<T>, E> conversion

This extension traits help transforming Result<Option<T>, E> to
Result<T, E> or transforming an iterator over the former type to an
iterator over the latter type.

Should be moved to resiter of course, but we need to implement this
first.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

lib/core/libimagerror/src/iter.rs

@@ -128,3 +128,49 @@ impl<I, T> TraceIterator<T> for I where
     I: Iterator<Item = Result<T, Error>>
 {}
 
+
+/// Extension trait for doing
+///
+/// ```ignore
+///     Iterator<Item = Result<Option<T>, E>>  ->  Iterator<Item = Result<T, E>>
+/// ```
+///
+pub trait IterInnerOkOrElse<T, E, F>
+    where T: Sized,
+          E: Sized,
+          Self: Iterator<Item = Result<Option<T>, E>> + Sized,
+          F: Fn() -> E,
+{
+    fn map_inner_ok_or_else(self, f: F) -> IterInnerOkOrElseImpl<Self, T, E, F>;
+}
+
+pub struct IterInnerOkOrElseImpl<I, T, E, F>(I, F)
+    where I: Iterator<Item = Result<Option<T>, E>> + Sized,
+          T: Sized,
+          E: Sized,
+          F: Fn() -> E;
+
+impl<I, T, E, F> IterInnerOkOrElse<T, E, F> for I
+    where I: Iterator<Item = Result<Option<T>, E>> + Sized,
+          T: Sized,
+          E: Sized,
+          F: Fn() -> E,
+{
+    fn map_inner_ok_or_else(self, f: F) -> IterInnerOkOrElseImpl<I, T, E, F> {
+        IterInnerOkOrElseImpl(self, f)
+    }
+}
+
+impl<I, T, E, F> Iterator for IterInnerOkOrElseImpl<I, T, E, F>
+    where I: Iterator<Item = Result<Option<T>, E>> + Sized,
+          T: Sized,
+          E: Sized,
+          F: Fn() -> E,
+{
+    type Item = Result<T, E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().map(|e| e.and_then(|opt| opt.ok_or_else(|| (self.1)())))
+    }
+}
+

lib/core/libimagerror/src/lib.rs

@@ -44,6 +44,7 @@ pub mod errors;
 pub mod exit;
 pub mod io;
 pub mod iter;
+pub mod result;
 pub mod str;
 pub mod trace;
 

lib/core/libimagerror/src/result.rs

@@ -0,0 +1,38 @@
+//
+// imag - the personal information management suite for the commandline
+// Copyright (C) 2015-2019 the imag contributors
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; version
+// 2.1 of the License.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+//
+
+/// Extension trait for doing `Result<Option<T>, E>  ->  Result<T, E>`
+pub trait ResultOptionExt<T, E, F>
+    where T: Sized,
+          E: Sized,
+          F: FnOnce() -> E
+{
+    fn inner_ok_or_else(self, f: F) -> Result<T, E>;
+}
+
+impl<T, E, F> ResultOptionExt<T, E, F> for Result<Option<T>, E>
+    where T: Sized,
+          E: Sized,
+          F: FnOnce() -> E
+{
+    fn inner_ok_or_else(self, f: F) -> Result<T, E> {
+        self.and_then(|opt| opt.ok_or_else(f))
+    }
+}
+