Improve error handling with anyhow

Cargo.lock

@@ -63,6 +63,12 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "anyhow"
+version = "1.0.41"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15af2628f6890fe2609a3b91bef4c83450512802e59489f9c1cb1fa5df064a61"
+
 [[package]]
 name = "assign"
 version = "1.1.1"
@@ -1218,6 +1224,7 @@ dependencies = [
 name = "mxadm"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "clap",
  "directories",
  "lazy_static",

Cargo.toml

@@ -15,3 +15,4 @@ serde = "1.0"
 serde-lexpr = "0.1.0"
 directories = "3.0"
 lazy_static = "1.4.0"
+anyhow = "1.0.41"

src/commands.rs

@@ -1,3 +1,4 @@
+use anyhow::{Context, Result};
 use matrix_sdk::{
     ruma::{api::client::r0::alias, RoomAliasId, RoomId, UserId},
     Client, Session, SyncSettings,
@@ -8,7 +9,7 @@ use std::io::{self, Write};
 
 use crate::session::{build_client_config, restore_session, save_session};
 
-type CommandResult = Result<(), Box<dyn std::error::Error>>;
+type CommandResult = Result<()>;
 
 macro_rules! room_fmt {
     () => {
@@ -18,7 +19,8 @@ macro_rules! room_fmt {
 
 pub async fn login(username: Option<&str>) -> CommandResult {
     let user_id = match username {
-        Some(s) => UserId::try_from(s)?,
+        Some(s) => UserId::try_from(s)
+            .with_context(|| format!("Failed to parse '{}' as User ID", username))?,
         None => {
             let mut s = String::new();
 
@@ -27,17 +29,20 @@ pub async fn login(username: Option<&str>) -> CommandResult {
 
             let stdin = io::stdin();
             stdin.read_line(&mut s)?;
-            UserId::try_from(s.trim_end())?
+            UserId::try_from(s.trim_end())
+                .with_context(|| format!("Failed to parse '{}' as User ID", s))?
         }
     };
 
     let password = prompt_password_stderr("Password: ")?;
 
-    let client =
-        Client::new_from_user_id_with_config(user_id.clone(), build_client_config()).await?;
+    let client = Client::new_from_user_id_with_config(user_id.clone(), build_client_config())
+        .await
+        .context("Unable to initialise client")?;
     let response = client
         .login(user_id.localpart(), &password, None, Some("mxadm"))
-        .await?;
+        .await
+        .context("Login failed")?;
     println!(
         "{} logged in? {}",
         client.homeserver().await,
@@ -81,7 +86,10 @@ pub async fn list_rooms() -> CommandResult {
 
     print!("Syncing...");
     io::stderr().flush().unwrap();
-    client.sync_once(sync_settings).await?;
+    client
+        .sync_once(sync_settings)
+        .await
+        .context("Sync failed")?;
     println!(" done");
 
     println!("Joined rooms:");
@@ -100,8 +108,10 @@ pub async fn list_rooms() -> CommandResult {
 }
 
 pub async fn add_alias(room_id: &str, alias: &str) -> CommandResult {
-    let room_id = RoomId::try_from(room_id)?;
-    let alias_id = RoomAliasId::try_from(alias)?;
+    let room_id = RoomId::try_from(room_id)
+        .with_context(|| format!("Failed to parse '{}' as room ID", room_id))?;
+    let alias_id = RoomAliasId::try_from(alias)
+        .with_context(|| format!("Failed to parse '{}' as room alias", alias))?;
     let client = restore_session().await?;
 
     let request = alias::create_alias::Request::new(&alias_id, &room_id);
@@ -111,11 +121,15 @@ pub async fn add_alias(room_id: &str, alias: &str) -> CommandResult {
 }
 
 pub async fn del_alias(alias: &str) -> CommandResult {
-    let alias_id = RoomAliasId::try_from(alias)?;
+    let alias_id = RoomAliasId::try_from(alias)
+        .with_context(|| format!("Failed to parse '{}' as room alias", alias))?;
     let client = restore_session().await?;
 
     let request = alias::delete_alias::Request::new(&alias_id);
-    client.send(request, None).await?;
+    client
+        .send(request, None)
+        .await
+        .with_context(|| format!("Failed to delete alias '{}'", alias))?;
 
     Ok(())
 }

src/main.rs

@@ -2,14 +2,17 @@
 extern crate clap;
 #[macro_use]
 extern crate lazy_static;
+#[macro_use]
+extern crate anyhow;
 
 mod commands;
 mod session;
 
+use anyhow::Result;
 use clap::{App, SubCommand};
 
 #[tokio::main]
-async fn main() -> Result<(), Box<dyn std::error::Error>> {
+async fn main() -> Result<()> {
     let matches = App::new(crate_name!())
         .version(crate_version!())
         .about(crate_description!())
@@ -55,7 +58,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         ("del-alias", Some(submatches)) => {
             commands::del_alias(submatches.value_of("alias").unwrap()).await?
         }
-        ("", None) => eprintln!("No subcommand given"),
+        ("", None) => bail!("No subcommand given"),
         (c, _) => {
             todo!("Subcommand '{}' not implemented yet!", c);
         }

src/session.rs

@@ -1,7 +1,9 @@
+use anyhow::{Context, Result};
 use directories::ProjectDirs;
 use matrix_sdk::{Client, ClientConfig, Session};
 use serde_lexpr;
 use std::fs::{create_dir_all, File};
+use std::io::ErrorKind;
 
 lazy_static! {
     static ref PROJECT_DIRS: ProjectDirs = ProjectDirs::from("me", "petrichor", "mxadm")
@@ -13,18 +15,25 @@ pub fn build_client_config() -> ClientConfig {
     ClientConfig::new().store_path(PROJECT_DIRS.cache_dir().join("store"))
 }
 
-pub fn save_session(session: Session) -> Result<(), Box<dyn std::error::Error>> {
+pub fn save_session(session: Session) -> Result<()> {
     let cache_dir = PROJECT_DIRS.cache_dir();
     if !cache_dir.exists() {
-        create_dir_all(cache_dir)?;
+        create_dir_all(cache_dir)
+            .with_context(|| format!("Failed to create cache directory {}", cache_dir.display()))?;
     }
     let mut session_file = File::create(cache_dir.join(SESSION_FILE))?;
     serde_lexpr::to_writer(&mut session_file, &session)?;
     Ok(())
 }
 
-pub async fn restore_session() -> Result<Client, Box<dyn std::error::Error>> {
-    let session_file = File::open(PROJECT_DIRS.cache_dir().join(SESSION_FILE))?;
+pub async fn restore_session() -> Result<Client> {
+    let session_file = match File::open(PROJECT_DIRS.cache_dir().join(SESSION_FILE)) {
+        Err(e) => match e.kind() {
+            ErrorKind::NotFound => bail!("Session file not found: try `mxadm login` first"),
+            _ => return Err(e).context("Unable to open session file"),
+        },
+        Ok(f) => f,
+    };
     let session_info: Session = serde_lexpr::from_reader(session_file)?;
 
     let client =