Use anyhow for error handling

Summary:
This is a nice solution if you don't want to spend
too much time thinking about error handling.
You have one common return type and can basically use `?`
everywhere while still maintaining the flexibility to
create custom error types where needed.

Reviewed By: jknoxville

Differential Revision: D21349046

fbshipit-source-id: 073539ce8422cdb3e0141886e95321052bc0c7a3

packer/src/error.rs

@@ -7,27 +7,19 @@
 
 use crate::types::{PackType, Platform};
 use std::fmt;
-use std::io;
 use std::path::PathBuf;
 
 #[derive(Debug)]
 pub enum Error {
-    IOError(io::Error),
     MissingPackFile(Platform, PackType, PathBuf),
+    MissingPackDefinition(Platform, PackType),
 }
 
-impl From<io::Error> for Error {
-    fn from(e: io::Error) -> Self {
-        Error::IOError(e)
-    }
-}
+impl std::error::Error for Error {}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        use Error::*;
-
         match self {
-            IOError(e) => write!(f, "IO Error: {}", e),
             Error::MissingPackFile(platform, pack_type, path) => write!(
                 f,
                 "Couldn't open file to pack for platform {:?} and type {:?}: {}",
@@ -35,6 +27,11 @@ impl fmt::Display for Error {
                 pack_type,
                 path.to_string_lossy()
             ),
+            Error::MissingPackDefinition(platform, pack_type) => write!(
+                f,
+                "Missing packlist definition for platform {:?} and pack type {:?}.",
+                platform, pack_type,
+            ),
         }
     }
 }