Wrap errors in a custom `OttolangyError` type

Give us a way to match on the type of error so we can return an
appropriate exit code.

3 files changed, 78 insertions, 3 deletions

diff --git a/Cargo.lock b/Cargo.lock
index a997dcb..047960a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -91,17 +91,73 @@ version = "0.0.1"
 dependencies = [
  "anyhow",
  "mailparse",
+ "thiserror",
  "whatlang",
  "xdg",
 ]
 
 [[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d0b9745dc2debf507c8422de05d7226cc1f0644216dfdfead988f9b1ab32a7"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
 name = "quoted_printable"
 version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "47b080c5db639b292ac79cbd34be0cfc5d36694768d8341109634d90b86930e2"
 
 [[package]]
+name = "syn"
+version = "1.0.63"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fd9bc7ccc2688b3344c2f48b9b546648b25ce0b20fc717ee7fa7981a8ca9717"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e0f4a65597094d4483ddaed134f409b2cb7c1beccf25201a9f73c719254fa98e"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7765189610d8241a44529806d6fd1f2e0a08734313a35d5b3a556f92b381f3c0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
 name = "whatlang"
 version = "0.11.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
index ad95cec..97e4592 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,5 +6,6 @@ edition = "2018"
 [dependencies]
 anyhow = "1.0.38"
 mailparse = "0.13.2"
+thiserror = "1.0.24"
 whatlang = "0.11.1"
 xdg = "2.2.0"
diff --git a/src/main.rs b/src/main.rs
index 44031b0..2775155 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,6 +15,7 @@
 
 use anyhow::{anyhow, Context, Error};
 use mailparse;
+use thiserror;
 use whatlang::{self, Lang};
 use xdg;
 
@@ -38,6 +39,23 @@ const ATTRIBUTION_EN: &'static str =
 "#;
 
 
+#[derive(thiserror::Error, Debug)]
+enum OttolangyError {
+    #[error("unable to parse email body: {0}")]
+    ParseMail(#[from] mailparse::MailParseError),
+
+    #[error("unable to parse email body")]
+    ParseMailUnknown,
+
+    #[error(transparent)]
+    Xdg(#[from] xdg::BaseDirectoriesError),
+
+    #[error(transparent)]
+    Io(#[from] std::io::Error),
+}
+
+
+// TODO: exit codes
 fn main() {
     match run() {
         Ok(_) => (),
@@ -76,7 +94,7 @@ fn run() -> Result<(), Error> {
 ///
 /// Given an email as input, parses it and extracts the body. For multipart
 /// emails, the body is extracted from the text part.
-fn get_email_body(email: &[u8]) -> Result<String, Error> {
+fn get_email_body(email: &[u8]) -> Result<String, OttolangyError> {
     let email = mailparse::parse_mail(&email)?;
 
     if email.subparts.is_empty() {
@@ -95,13 +113,13 @@ fn get_email_body(email: &[u8]) -> Result<String, Error> {
         }
     }
 
-    Err(anyhow!("unable to parse email body"))
+    Err(OttolangyError::ParseMailUnknown)
 }
 
 /// Write the attribution config to a file.
 ///
 /// Store the file in the XDG data directory.
-fn write_attribution(config: &str) -> Result<(), Error> {
+fn write_attribution(config: &str) -> Result<(), OttolangyError> {
     let xdg_dirs = xdg::BaseDirectories::with_prefix(PROGRAM_NAME)?;
 
     let muttrc_path = xdg_dirs.place_data_file(MUTTRC_FILENAME)?;