Use anyhow for idiomatic error handling

Good for CLI applications, it provides some nicer ergonomics, features
to inject context if needed, as well as non-trivial optimizations
compared to using `Box<dyn Error>`.

For the xtasks use case, I'm going with the simpler `anyhow` over
something like `color-eyre`, which supports more complicated output
formatting (but has other trade-offs).

See:
- dtolnay/anyhow#96

xtask/Cargo.toml

@@ -9,4 +9,5 @@ publish = false
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.71"
 xshell = "0.2.2"

xtask/src/fixup.rs

@@ -1,20 +1,18 @@
-use std::{
-    fs,
-    path::{Path, PathBuf},
-};
-
+use anyhow::Result;
+use std::fs;
+use std::path::{Path, PathBuf};
 use xshell::{cmd, Shell};
 
-use crate::{project_root, verbose_cd, DynError};
+use crate::{project_root, verbose_cd};
 
-pub fn format_cue() -> Result<(), DynError> {
+pub fn format_cue() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, cue_dir());
     cmd!(sh, "cue fmt --simplify").run()?;
     Ok(())
 }
 
-pub fn format_markdown() -> Result<(), DynError> {
+pub fn format_markdown() -> Result<()> {
     let sh = Shell::new()?;
     let root = project_root();
     verbose_cd(&sh, &root);
@@ -32,21 +30,21 @@ pub fn format_markdown() -> Result<(), DynError> {
     Ok(())
 }
 
-pub fn format_rust() -> Result<(), DynError> {
+pub fn format_rust() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, project_root());
     cmd!(sh, "cargo fmt").run()?;
     Ok(())
 }
 
-pub fn lint_cue() -> Result<(), DynError> {
+pub fn lint_cue() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, cue_dir());
     cmd!(sh, "cue vet --concrete").run()?;
     Ok(())
 }
 
-pub fn lint_rust() -> Result<(), DynError> {
+pub fn lint_rust() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, project_root());
     cmd!(
@@ -67,14 +65,14 @@ pub fn lint_rust() -> Result<(), DynError> {
     Ok(())
 }
 
-pub fn regenerate_ci_yaml() -> Result<(), DynError> {
+pub fn regenerate_ci_yaml() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, cue_dir());
     cmd!(sh, "cue cmd regen-ci-yaml").run()?;
     Ok(())
 }
 
-pub fn spellcheck() -> Result<(), DynError> {
+pub fn spellcheck() -> Result<()> {
     let sh = Shell::new()?;
     verbose_cd(&sh, project_root());
     cmd!(sh, "codespell --write-changes").run()?;
@@ -85,7 +83,7 @@ fn cue_dir() -> PathBuf {
     project_root().join(".github/cue")
 }
 
-fn find_markdown_files<P: AsRef<Path>>(dir: P) -> Result<Vec<PathBuf>, DynError> {
+fn find_markdown_files<P: AsRef<Path>>(dir: P) -> Result<Vec<PathBuf>> {
     let mut result = Vec::new();
     for entry in fs::read_dir(dir)? {
         let path = entry?.path();

xtask/src/main.rs

@@ -1,15 +1,11 @@
-use std::{
-    env,
-    error::Error,
-    path::{Path, PathBuf},
-};
+use anyhow::Result;
+use std::env;
+use std::path::{Path, PathBuf};
 use xshell::Shell;
 
 mod fixup;
 
-type DynError = Box<dyn Error>;
-
-fn main() -> Result<(), DynError> {
+fn main() -> Result<()> {
     let task = env::args().nth(1);
     match task {
         None => tasks::print_help()?,
@@ -20,7 +16,7 @@ fn main() -> Result<(), DynError> {
             "fixup.markdown" => tasks::fixup_markdown()?,
             "fixup.rust" => tasks::fixup_rust()?,
             "fixup.spelling" => tasks::fixup_spelling()?,
-            invalid => return Err(format!("Invalid task name: {}", invalid).into()),
+            invalid => return Err(anyhow::anyhow!("Invalid task name: {}", invalid)),
         },
     };
     Ok(())
@@ -30,7 +26,7 @@ pub mod tasks {
     use crate::fixup::{format_cue, format_markdown, format_rust};
     use crate::fixup::{lint_cue, lint_rust};
     use crate::fixup::{regenerate_ci_yaml, spellcheck};
-    use crate::DynError;
+    use anyhow::Result;
 
     const HELP: &str = "\
 NAME
@@ -48,33 +44,33 @@ COMMANDS
     fixup.rust             Fix lints and format Rust files in-place.
 ";
 
-    pub fn fixup() -> Result<(), DynError> {
+    pub fn fixup() -> Result<()> {
         fixup_spelling()?; // affects all file types; run this first
         fixup_github_actions()?;
         fixup_markdown()?;
         fixup_rust()
     }
 
-    pub fn fixup_github_actions() -> Result<(), DynError> {
+    pub fn fixup_github_actions() -> Result<()> {
         lint_cue()?;
         format_cue()?;
         regenerate_ci_yaml()
     }
 
-    pub fn fixup_markdown() -> Result<(), DynError> {
+    pub fn fixup_markdown() -> Result<()> {
         format_markdown()
     }
 
-    pub fn fixup_rust() -> Result<(), DynError> {
+    pub fn fixup_rust() -> Result<()> {
         lint_rust()?;
         format_rust()
     }
 
-    pub fn fixup_spelling() -> Result<(), DynError> {
+    pub fn fixup_spelling() -> Result<()> {
         spellcheck()
     }
 
-    pub fn print_help() -> Result<(), DynError> {
+    pub fn print_help() -> Result<()> {
         print!("{}", HELP);
         Ok(())
     }