Change interface of Viewer to propagate io errors

Because we need to catch errors that are caused by a borken pipe when
writing to stdout (for example), this patch changes the interface of the
Viewer trait to return an error enum that can be used to check whether
an IO error happened.

The calling code can then decide whether to ignore a broken pipe error
or whether to handle it properly.

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

lib/entry/libimagentryview/src/builtin/editor.rs

@@ -24,9 +24,9 @@ use libimagrt::runtime::Runtime;
 use libimagentryedit::edit::edit_in_tmpfile;
 
 use crate::viewer::Viewer;
-use failure::Fallible as Result;
+use crate::error::Result;
+use crate::error::Error;
 use failure::ResultExt;
-use failure::Error;
 
 pub struct EditorView<'a>(&'a Runtime<'a>);
 

lib/entry/libimagentryview/src/builtin/md.rs

@@ -27,8 +27,8 @@ use pulldown_cmark::Parser;
 use syntect::parsing::SyntaxSet;
 
 use crate::viewer::Viewer;
-use failure::Fallible as Result;
-use failure::Error;
+use crate::error::Result;
+use crate::error::Error;
 
 pub struct MarkdownViewer<'a> {
     rt:                 &'a Runtime<'a>,
@@ -66,6 +66,7 @@ impl<'a> Viewer for MarkdownViewer<'a> {
                           self.resource_access.clone(),
                           syntax_set)
         .map_err(|e| e.compat())
+        .map_err(::failure::Error::from)
         .map_err(Error::from)
     }
 }

lib/entry/libimagentryview/src/builtin/plain.rs

@@ -22,7 +22,7 @@ use std::io::Write;
 use libimagstore::store::Entry;
 
 use crate::viewer::Viewer;
-use failure::Fallible as Result;
+use crate::error::Result;
 
 pub struct PlainViewer {
     show_header: bool

lib/entry/libimagentryview/src/builtin/stdout.rs

@@ -24,7 +24,7 @@ use libimagstore::store::Entry;
 use toml::ser::to_string;
 
 use crate::viewer::Viewer;
-use failure::Fallible as Result;
+use crate::error::Result;
 
 pub struct StdoutViewer {
     view_header: bool,

lib/entry/libimagentryview/src/error.rs

@@ -0,0 +1,66 @@
+//
+// imag - the personal information management suite for the commandline
+// Copyright (C) 2015-2019 Matthias Beyer <mail@beyermatthias.de> and 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
+//
+
+use std::fmt::Display;
+use std::fmt::Debug;
+
+use failure::Fail;
+
+#[derive(Debug)]
+pub enum Error {
+    Io(::std::io::Error),
+    Other(::failure::Error),
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
+        match self {
+            Error::Io(e)    => write!(f, "{}", e),
+            Error::Other(e) => write!(f, "{}", e),
+        }
+    }
+}
+
+impl Fail for Error {
+    /* empty */
+}
+
+impl From<::std::io::Error> for Error {
+    fn from(ioe: ::std::io::Error) -> Self {
+        Error::Io(ioe)
+    }
+}
+
+impl From<::failure::Error> for Error {
+    fn from(fe: ::failure::Error) -> Self {
+        Error::Other(fe)
+    }
+}
+
+impl<D> From<::failure::Context<D>> for Error
+    where D: Debug + Display + Send + Sync
+{
+    fn from(ctx: ::failure::Context<D>) -> Self {
+        Error::Other(ctx.into())
+    }
+}
+
+/// Convenient helper type
+pub type Result<T> = ::std::result::Result<T, Error>;
+

lib/entry/libimagentryview/src/lib.rs

@@ -56,5 +56,6 @@ extern crate libimagerror;
 extern crate libimagentryedit;
 
 pub mod builtin;
+pub mod error;
 pub mod viewer;
 

lib/entry/libimagentryview/src/viewer.rs

@@ -22,7 +22,7 @@ use std::ops::Deref;
 
 use libimagstore::store::Entry;
 
-use failure::Fallible as Result;
+use crate::error::Result;
 
 pub trait Viewer {