Merge pull request #211 from dtolnay/causedby

Print causes with error

src/error.rs

@@ -1,6 +1,8 @@
+use std::error::Error as StdError;
 use std::fmt::{self, Display};
 use std::io;
 
+#[derive(Debug)]
 pub enum Error {
     Io(io::Error),
     TomlSer(toml::ser::Error),
@@ -29,12 +31,20 @@ impl From<toml::de::Error> for Error {
 
 impl Display for Error {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        use self::Error::*;
-
         match self {
-            Io(e) => e.fmt(formatter),
-            TomlSer(e) => e.fmt(formatter),
-            TomlDe(e) => e.fmt(formatter),
+            Error::Io(e) => e.fmt(formatter),
+            Error::TomlSer(e) => e.fmt(formatter),
+            Error::TomlDe(e) => e.fmt(formatter),
+        }
+    }
+}
+
+impl StdError for Error {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        match self {
+            Error::Io(e) => e.source(),
+            Error::TomlSer(e) => e.source(),
+            Error::TomlDe(e) => e.source(),
         }
     }
 }

src/main.rs

@@ -36,6 +36,7 @@ use bat::{PagingMode, PrettyPrinter};
 use clap::{Parser, ValueEnum};
 use quote::quote;
 use std::env;
+use std::error::Error as StdError;
 use std::ffi::OsString;
 use std::fs;
 use std::io::{self, BufRead, IsTerminal, Write};
@@ -54,7 +55,13 @@ fn main() {
     process::exit(match result {
         Ok(code) => code,
         Err(err) => {
-            let _ = writeln!(io::stderr(), "{}", err);
+            let mut stderr = io::stderr().lock();
+            let _ = writeln!(stderr, "{}", err);
+            let mut err = &err as &dyn StdError;
+            while let Some(source) = err.source() {
+                let _ = writeln!(stderr, "\nCaused by:\n  {}", source);
+                err = source;
+            }
             1
         }
     });