Write error messages to pager, if attached

closes #946

src/bin/bat/main.rs

@@ -210,7 +210,8 @@ fn main() {
 
     match result {
         Err(error) => {
-            default_error_handler(&error);
+            let stderr = std::io::stderr();
+            default_error_handler(&error, &mut stderr.lock());
             process::exit(1);
         }
         Ok(false) => {

src/controller.rs

@@ -31,7 +31,7 @@ impl<'b> Controller<'b> {
     pub fn run_with_error_handler(
         &self,
         inputs: Vec<Input>,
-        handle_error: impl Fn(&Error),
+        handle_error: impl Fn(&Error, &mut dyn Write),
     ) -> Result<bool> {
         let mut output_type;
 
@@ -62,13 +62,23 @@ impl<'b> Controller<'b> {
             output_type = OutputType::stdout();
         }
 
+        let attached_to_pager = output_type.is_pager();
         let writer = output_type.handle()?;
         let mut no_errors: bool = true;
 
+        let stderr = io::stderr();
+        let print_error = |error: &Error, write: &mut dyn Write| {
+            if attached_to_pager {
+                handle_error(error, write);
+            } else {
+                handle_error(error, &mut stderr.lock());
+            }
+        };
+
         for input in inputs.into_iter() {
             match input.open(io::stdin().lock()) {
                 Err(error) => {
-                    handle_error(&error);
+                    print_error(&error, writer);
                     no_errors = false;
                 }
                 Ok(mut opened_input) => {
@@ -123,7 +133,7 @@ impl<'b> Controller<'b> {
                     );
 
                     if let Err(error) = result {
-                        handle_error(&error);
+                        print_error(&error, writer);
                         no_errors = false;
                     }
                 }
@@ -138,8 +148,7 @@ impl<'b> Controller<'b> {
         printer: &mut dyn Printer,
         writer: &mut dyn Write,
         input: &mut OpenedInput,
-        #[cfg(feature = "git")]
-        line_changes: &Option<LineChanges>,
+        #[cfg(feature = "git")] line_changes: &Option<LineChanges>,
     ) -> Result<()> {
         if !input.reader.first_line.is_empty() || self.config.style_components.header() {
             printer.print_header(writer, input)?;

src/error.rs

@@ -1,4 +1,5 @@
 use error_chain::error_chain;
+use std::io::Write;
 
 error_chain! {
     foreign_links {
@@ -11,7 +12,7 @@ error_chain! {
     }
 }
 
-pub fn default_error_handler(error: &Error) {
+pub fn default_error_handler(error: &Error, output: &mut dyn Write) {
     use ansi_term::Colour::Red;
 
     match error {
@@ -21,14 +22,16 @@ pub fn default_error_handler(error: &Error) {
             ::std::process::exit(0);
         }
         Error(ErrorKind::SerdeYamlError(_), _) => {
-            eprintln!(
+            writeln!(
+                output,
                 "{}: Error while parsing metadata.yaml file: {}",
                 Red.paint("[bat error]"),
                 error
-            );
+            )
+            .ok();
         }
         _ => {
-            eprintln!("{}: {}", Red.paint("[bat error]"), error);
+            writeln!(output, "{}: {}", Red.paint("[bat error]"), error).ok();
         }
     };
 }

src/output.rs

@@ -125,6 +125,20 @@ impl OutputType {
         OutputType::Stdout(io::stdout())
     }
 
+    #[cfg(feature = "paging")]
+    pub(crate) fn is_pager(&self) -> bool {
+        if let OutputType::Pager(_) = self {
+            true
+        } else {
+            false
+        }
+    }
+
+    #[cfg(not(feature = "paging"))]
+    pub(crate) fn is_pager(&self) -> bool {
+        false
+    }
+
     pub fn handle(&mut self) -> Result<&mut dyn Write> {
         Ok(match *self {
             #[cfg(feature = "paging")]