Minimalist error handling by exiting on error

generate/Cargo.toml

@@ -4,6 +4,3 @@ version = "0.0.0"
 authors = ["David Tolnay <dtolnay@gmail.com>"]
 edition = "2018"
 publish = false
-
-[dependencies]
-anyhow = "1"

generate/src/main.rs

@@ -11,6 +11,7 @@
 #![allow(
     clippy::cast_lossless,
     clippy::cast_possible_truncation, // https://github.com/rust-lang/rust-clippy/issues/9613
+    clippy::let_underscore_drop,
     clippy::match_wild_err_arm,
     clippy::module_name_repetitions,
     clippy::too_many_lines,
@@ -22,7 +23,6 @@ mod parse;
 mod write;
 
 use crate::parse::parse_xid_properties;
-use anyhow::Result;
 use std::collections::{BTreeMap as Map, VecDeque};
 use std::convert::TryFrom;
 use std::fs;
@@ -34,20 +34,11 @@ const CHUNK: usize = 64;
 const UCD: &str = "UCD";
 const TABLES: &str = "src/tables.rs";
 
-fn main() -> Result<()> {
+fn main() {
     let manifest_dir = Path::new(env!("CARGO_MANIFEST_DIR"));
     let unicode_ident_dir = manifest_dir.parent().unwrap();
     let ucd_dir = unicode_ident_dir.join(UCD);
-    if !ucd_dir.exists() {
-        writeln!(
-            io::stderr(),
-            "Not found: {}\nDownload from https://www.unicode.org/Public/zipped/l5.0.0/UCD.zip and unzip.",
-            ucd_dir.display(),
-        )?;
-        process::exit(1);
-    }
-
-    let properties = parse_xid_properties(&ucd_dir)?;
+    let properties = parse_xid_properties(&ucd_dir);
 
     let mut chunkmap = Map::<[u8; CHUNK], u8>::new();
     let mut dense = Vec::<[u8; CHUNK]>::new();
@@ -158,6 +149,8 @@ fn main() -> Result<()> {
 
     let out = write::output(&properties, &index_start, &index_continue, &halfdense);
     let path = unicode_ident_dir.join(TABLES);
-    fs::write(path, out)?;
-    Ok(())
+    if let Err(err) = fs::write(&path, out) {
+        let _ = writeln!(io::stderr(), "{}: {err}", path.display());
+        process::exit(1);
+    }
 }

generate/src/parse.rs

@@ -1,7 +1,8 @@
-use anyhow::{bail, Result};
 use std::collections::BTreeSet as Set;
 use std::fs;
+use std::io::{self, Write};
 use std::path::Path;
+use std::process;
 
 pub struct Properties {
     xid_start: Set<u32>,
@@ -18,7 +19,7 @@ impl Properties {
     }
 }
 
-pub fn parse_xid_properties(ucd_dir: &Path) -> Result<Properties> {
+pub fn parse_xid_properties(ucd_dir: &Path) -> Properties {
     let mut properties = Properties {
         xid_start: Set::new(),
         xid_continue: Set::new(),
@@ -26,15 +27,21 @@ pub fn parse_xid_properties(ucd_dir: &Path) -> Result<Properties> {
 
     let filename = "DerivedCoreProperties.txt";
     let path = ucd_dir.join(filename);
-    let contents = fs::read_to_string(path)?;
+    let contents = fs::read_to_string(path).unwrap_or_else(|err| {
+        let suggestion =
+            "Download from https://www.unicode.org/Public/zipped/l5.0.0/UCD.zip and unzip.";
+        let _ = writeln!(io::stderr(), "{}: {err}\n{suggestion}", ucd_dir.display());
+        process::exit(1);
+    });
+
     for (i, line) in contents.lines().enumerate() {
         if line.starts_with('#') || line.trim().is_empty() {
             continue;
         }
-        let (lo, hi, name) = match parse_line(line) {
-            Some(line) => line,
-            None => bail!("{} line {} is unexpected:\n{}", filename, i, line),
-        };
+        let (lo, hi, name) = parse_line(line).unwrap_or_else(|| {
+            let _ = writeln!(io::stderr(), "{filename} line {i} is unexpected:\n{line}");
+            process::exit(1);
+        });
         let set = match name {
             "XID_Start" => &mut properties.xid_start,
             "XID_Continue" => &mut properties.xid_continue,
@@ -43,7 +50,7 @@ pub fn parse_xid_properties(ucd_dir: &Path) -> Result<Properties> {
         set.extend(lo..=hi);
     }
 
-    Ok(properties)
+    properties
 }
 
 fn parse_line(line: &str) -> Option<(u32, u32, &str)> {