Replace deprecated 'error-chain' with 'thiserror' (#1820)

We can't use #[from] on Error::Msg(String) because String does not implement Error.
(Which it shouldn't; see e.g. https://internals.rust-lang.org/t/impl-error-for-string/8881.)
So we implement From manually for Error::Msg, since our current code was written
in that way for error-chain.

src/assets.rs

@@ -163,7 +163,7 @@ impl HighlightingAssets {
             syntax_set
                 .find_syntax_by_token(language)
                 .map(|syntax| SyntaxReferenceInSet { syntax, syntax_set })
-                .ok_or_else(|| ErrorKind::UnknownSyntax(language.to_owned()).into())
+                .ok_or_else(|| Error::UnknownSyntax(language.to_owned()))
         } else {
             let line_syntax = self.get_first_line_syntax(&mut input.reader)?;
 
@@ -189,30 +189,27 @@ impl HighlightingAssets {
                     .unwrap_or_else(|| path.to_owned());
 
                 match mapping.get_syntax_for(absolute_path) {
-                    Some(MappingTarget::MapToUnknown) => line_syntax.ok_or_else(|| {
-                        ErrorKind::UndetectedSyntax(path.to_string_lossy().into()).into()
-                    }),
+                    Some(MappingTarget::MapToUnknown) => line_syntax
+                        .ok_or_else(|| Error::UndetectedSyntax(path.to_string_lossy().into())),
 
                     Some(MappingTarget::MapTo(syntax_name)) => {
                         let syntax_set = self.get_syntax_set()?;
                         syntax_set
                             .find_syntax_by_name(syntax_name)
                             .map(|syntax| SyntaxReferenceInSet { syntax, syntax_set })
-                            .ok_or_else(|| ErrorKind::UnknownSyntax(syntax_name.to_owned()).into())
+                            .ok_or_else(|| Error::UnknownSyntax(syntax_name.to_owned()))
                     }
 
                     None => {
                         let file_name = path.file_name().unwrap_or_default();
                         self.get_extension_syntax(file_name)?
                             .or(line_syntax)
-                            .ok_or_else(|| {
-                                ErrorKind::UndetectedSyntax(path.to_string_lossy().into()).into()
-                            })
+                            .ok_or_else(|| Error::UndetectedSyntax(path.to_string_lossy().into()))
                     }
                 }
             } else {
                 // If a path wasn't provided, we fall back to the detect first-line syntax.
-                line_syntax.ok_or_else(|| ErrorKind::UndetectedSyntax("[unknown]".into()).into())
+                line_syntax.ok_or_else(|| Error::UndetectedSyntax("[unknown]".into()))
             }
         }
     }
@@ -314,14 +311,14 @@ pub(crate) fn get_integrated_themeset() -> ThemeSet {
 }
 
 fn asset_from_cache<T: serde::de::DeserializeOwned>(path: &Path, description: &str) -> Result<T> {
-    let contents = fs::read(path).chain_err(|| {
+    let contents = fs::read(path).map_err(|_| {
         format!(
             "Could not load cached {} '{}'",
             description,
             path.to_string_lossy()
         )
     })?;
-    from_reader(&contents[..]).chain_err(|| format!("Could not parse cached {}", description))
+    from_reader(&contents[..]).map_err(|_| format!("Could not parse cached {}", description).into())
 }
 
 #[cfg(test)]

src/assets_metadata.rs

@@ -52,16 +52,15 @@ impl AssetsMetadata {
     pub fn load_from_folder(path: &Path) -> Result<Option<Self>> {
         match Self::try_load_from_folder(path) {
             Ok(metadata) => Ok(Some(metadata)),
-            Err(e) => match e.kind() {
-                ErrorKind::SerdeYamlError(_) => Err(e),
-                _ => {
-                    if path.join("syntaxes.bin").exists() || path.join("themes.bin").exists() {
-                        Ok(Some(Self::default()))
-                    } else {
-                        Ok(None)
-                    }
+            Err(e) => {
+                if let Error::SerdeYamlError(_) = e {
+                    Err(e)
+                } else if path.join("syntaxes.bin").exists() || path.join("themes.bin").exists() {
+                    Ok(Some(Self::default()))
+                } else {
+                    Ok(None)
                 }
-            },
+            }
         }
     }
 

src/bin/bat/app.rs

@@ -62,7 +62,7 @@ impl App {
             // Read arguments from bats config file
             let mut args = get_args_from_env_var()
                 .unwrap_or_else(get_args_from_config_file)
-                .chain_err(|| "Could not parse configuration file")?;
+                .map_err(|_| "Could not parse configuration file")?;
 
             // Put the zero-th CLI argument (program name) first
             args.insert(0, cli_args.next().unwrap());

src/bin/bat/main.rs

@@ -1,6 +1,3 @@
-// `error_chain!` can recurse deeply
-#![recursion_limit = "1024"]
-
 mod app;
 mod assets;
 mod clap_app;

src/build_assets.rs

@@ -267,7 +267,7 @@ impl SyntaxSetDependencyBuilder {
 
 fn asset_to_cache<T: serde::Serialize>(asset: &T, path: &Path, description: &str) -> Result<()> {
     print!("Writing {} to {} ... ", description, path.to_string_lossy());
-    syntect::dumps::dump_to_file(asset, &path).chain_err(|| {
+    syntect::dumps::dump_to_file(asset, &path).map_err(|_| {
         format!(
             "Could not save {} to {}",
             description,

src/error.rs

@@ -1,42 +1,52 @@
-use error_chain::error_chain;
 use std::io::Write;
+use thiserror::Error;
 
-error_chain! {
-    foreign_links {
-        Clap(::clap::Error) #[cfg(feature = "minimal-application")];
-        Io(::std::io::Error);
-        SyntectError(::syntect::LoadingError);
-        ParseIntError(::std::num::ParseIntError);
-        GlobParsingError(::globset::Error);
-        SerdeYamlError(::serde_yaml::Error);
-    }
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error(transparent)]
+    Io(#[from] ::std::io::Error),
+    #[error(transparent)]
+    SyntectError(#[from] ::syntect::LoadingError),
+    #[error(transparent)]
+    ParseIntError(#[from] ::std::num::ParseIntError),
+    #[error(transparent)]
+    GlobParsingError(#[from] ::globset::Error),
+    #[error(transparent)]
+    SerdeYamlError(#[from] ::serde_yaml::Error),
+    #[error("unable to detect syntax for {0}")]
+    UndetectedSyntax(String),
+    #[error("unknown syntax: '{0}'")]
+    UnknownSyntax(String),
+    #[error("Unknown style '{0}'")]
+    UnknownStyle(String),
+    #[error("Use of bat as a pager is disallowed in order to avoid infinite recursion problems")]
+    InvalidPagerValueBat,
+    #[error("{0}")]
+    Msg(String),
+}
 
-    errors {
-        UndetectedSyntax(input: String) {
-            description("unable to detect syntax"),
-            display("unable to detect syntax for {}", input)
-        }
-        UnknownSyntax(name: String) {
-            description("unknown syntax"),
-            display("unknown syntax: '{}'", name)
-        }
-        InvalidPagerValueBat {
-            description("invalid value `bat` for pager property"),
-            display("Use of bat as a pager is disallowed in order to avoid infinite recursion problems")
-        }
+impl From<&'static str> for Error {
+    fn from(s: &'static str) -> Self {
+        Error::Msg(s.to_owned())
     }
 }
 
+impl From<String> for Error {
+    fn from(s: String) -> Self {
+        Error::Msg(s)
+    }
+}
+
+pub type Result<T> = std::result::Result<T, Error>;
+
 pub fn default_error_handler(error: &Error, output: &mut dyn Write) {
     use ansi_term::Colour::Red;
 
     match error {
-        Error(ErrorKind::Io(ref io_error), _)
-            if io_error.kind() == ::std::io::ErrorKind::BrokenPipe =>
-        {
+        Error::Io(ref io_error) if io_error.kind() == ::std::io::ErrorKind::BrokenPipe => {
             ::std::process::exit(0);
         }
-        Error(ErrorKind::SerdeYamlError(_), _) => {
+        Error::SerdeYamlError(_) => {
             writeln!(
                 output,
                 "{}: Error while parsing metadata.yaml file: {}",

src/output.rs

@@ -52,7 +52,7 @@ impl OutputType {
         use std::process::{Command, Stdio};
 
         let pager_opt =
-            pager::get_pager(pager_from_config).chain_err(|| "Could not parse pager command.")?;
+            pager::get_pager(pager_from_config).map_err(|_| "Could not parse pager command.")?;
 
         let pager = match pager_opt {
             Some(pager) => pager,
@@ -60,7 +60,7 @@ impl OutputType {
         };
 
         if pager.kind == PagerKind::Bat {
-            return Err(ErrorKind::InvalidPagerValueBat.into());
+            return Err(Error::InvalidPagerValueBat);
         }
 
         let resolved_path = match grep_cli::resolve_binary(&pager.bin) {
@@ -142,7 +142,7 @@ impl OutputType {
             OutputType::Pager(ref mut command) => command
                 .stdin
                 .as_mut()
-                .chain_err(|| "Could not open stdin for pager")?,
+                .ok_or("Could not open stdin for pager")?,
             OutputType::Stdout(ref mut handle) => handle,
         })
     }

src/printer.rs

@@ -174,7 +174,7 @@ impl<'a> InteractivePrinter<'a> {
             let syntax_in_set =
                 match assets.get_syntax(config.language, input, &config.syntax_mapping) {
                     Ok(syntax_in_set) => syntax_in_set,
-                    Err(Error(ErrorKind::UndetectedSyntax(_), _)) => {
+                    Err(Error::UndetectedSyntax(_)) => {
                         let syntax_set = assets.get_syntax_set()?;
                         let syntax = syntax_set.find_syntax_plain_text();
                         SyntaxReferenceInSet { syntax, syntax_set }