emitter.rs

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use self::Destination::*;

use syntax_pos::{COMMAND_LINE_SP, DUMMY_SP, FileMap, Span, MultiSpan, CharPos};

use {Level, CodeSuggestion, DiagnosticBuilder, SubDiagnostic, CodeMapper};
use RenderSpan::*;
use snippet::{StyledString, Style, Annotation, Line};
use styled_buffer::StyledBuffer;

use std::io::prelude::*;
use std::io;
use std::rc::Rc;
use term;

/// Emitter trait for emitting errors.
pub trait Emitter {
    /// Emit a structured diagnostic.
    fn emit(&mut self, db: &DiagnosticBuilder);
}

impl Emitter for EmitterWriter {
    fn emit(&mut self, db: &DiagnosticBuilder) {
        let mut primary_span = db.span.clone();
        let mut children = db.children.clone();
        self.fix_multispans_in_std_macros(&mut primary_span, &mut children);
        self.emit_messages_default(&db.level, &db.message, &db.code, &primary_span, &children);
    }
}

/// maximum number of lines we will print for each error; arbitrary.
pub const MAX_HIGHLIGHT_LINES: usize = 6;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum ColorConfig {
    Auto,
    Always,
    Never,
}

impl ColorConfig {
    fn use_color(&self) -> bool {
        match *self {
            ColorConfig::Always => true,
            ColorConfig::Never  => false,
            ColorConfig::Auto   => stderr_isatty(),
        }
    }
}

pub struct EmitterWriter {
    dst: Destination,
    cm: Option<Rc<CodeMapper>>,
}

struct FileWithAnnotatedLines {
    file: Rc<FileMap>,
    lines: Vec<Line>,
}


/// Do not use this for messages that end in `\n` – use `println_maybe_styled` instead. See
/// `EmitterWriter::print_maybe_styled` for details.
macro_rules! print_maybe_styled {
    ($dst: expr, $style: expr, $($arg: tt)*) => {
        $dst.print_maybe_styled(format_args!($($arg)*), $style, false)
    }
}

macro_rules! println_maybe_styled {
    ($dst: expr, $style: expr, $($arg: tt)*) => {
        $dst.print_maybe_styled(format_args!($($arg)*), $style, true)
    }
}

impl EmitterWriter {
    pub fn stderr(color_config: ColorConfig,
                  code_map: Option<Rc<CodeMapper>>)
                  -> EmitterWriter {
        if color_config.use_color() {
            let dst = Destination::from_stderr();
            EmitterWriter { dst: dst,
                            cm: code_map}
        } else {
            EmitterWriter { dst: Raw(Box::new(io::stderr())),
                            cm: code_map}
        }
    }

    pub fn new(dst: Box<Write + Send>,
               code_map: Option<Rc<CodeMapper>>)
               -> EmitterWriter {
        EmitterWriter { dst: Raw(dst),
                        cm: code_map}
    }

    fn preprocess_annotations(&self, msp: &MultiSpan) -> Vec<FileWithAnnotatedLines> {
        fn add_annotation_to_file(file_vec: &mut Vec<FileWithAnnotatedLines>,
                                    file: Rc<FileMap>,
                                    line_index: usize,
                                    ann: Annotation) {

            for slot in file_vec.iter_mut() {
                // Look through each of our files for the one we're adding to
                if slot.file.name == file.name {
                    // See if we already have a line for it
                    for line_slot in &mut slot.lines {
                        if line_slot.line_index == line_index {
                            line_slot.annotations.push(ann);
                            return;
                        }
                    }
                    // We don't have a line yet, create one
                    slot.lines.push(Line {
                        line_index: line_index,
                        annotations: vec![ann],
                    });
                    slot.lines.sort();
                    return;
                }
            }
            // This is the first time we're seeing the file
            file_vec.push(FileWithAnnotatedLines {
                file: file,
                lines: vec![Line {
                                line_index: line_index,
                                annotations: vec![ann],
                            }],
            });
        }

        let mut output = vec![];

        if let Some(ref cm) = self.cm {
            for span_label in msp.span_labels() {
                if span_label.span == DUMMY_SP || span_label.span == COMMAND_LINE_SP {
                    continue;
                }
                let lo = cm.lookup_char_pos(span_label.span.lo);
                let mut hi = cm.lookup_char_pos(span_label.span.hi);
                let mut is_minimized = false;

                // If the span is multi-line, simplify down to the span of one character
                if lo.line != hi.line {
                    hi.line = lo.line;
                    hi.col = CharPos(lo.col.0 + 1);
                    is_minimized = true;
                }

                // Watch out for "empty spans". If we get a span like 6..6, we
                // want to just display a `^` at 6, so convert that to
                // 6..7. This is degenerate input, but it's best to degrade
                // gracefully -- and the parser likes to supply a span like
                // that for EOF, in particular.
                if lo.col == hi.col {
                    hi.col = CharPos(lo.col.0 + 1);
                }

                add_annotation_to_file(&mut output,
                                        lo.file,
                                        lo.line,
                                        Annotation {
                                            start_col: lo.col.0,
                                            end_col: hi.col.0,
                                            is_primary: span_label.is_primary,
                                            is_minimized: is_minimized,
                                            label: span_label.label.clone(),
                                        });
            }
        }
        output
    }

    fn render_source_line(&self,
                          buffer: &mut StyledBuffer,
                          file: Rc<FileMap>,
                          line: &Line,
                          width_offset: usize) {
        let source_string = file.get_line(line.line_index - 1)
            .unwrap_or("");

        let line_offset = buffer.num_lines();

        // First create the source line we will highlight.
        buffer.puts(line_offset, width_offset, &source_string, Style::Quotation);
        buffer.puts(line_offset,
                    0,
                    &(line.line_index.to_string()),
                    Style::LineNumber);

        draw_col_separator(buffer, line_offset, width_offset - 2);

        if line.annotations.is_empty() {
            return;
        }

        // We want to display like this:
        //
        //      vec.push(vec.pop().unwrap());
        //      ---      ^^^               _ previous borrow ends here
        //      |        |
        //      |        error occurs here
        //      previous borrow of `vec` occurs here
        //
        // But there are some weird edge cases to be aware of:
        //
        //      vec.push(vec.pop().unwrap());
        //      --------                    - previous borrow ends here
        //      ||
        //      |this makes no sense
        //      previous borrow of `vec` occurs here
        //
        // For this reason, we group the lines into "highlight lines"
        // and "annotations lines", where the highlight lines have the `~`.

        // Sort the annotations by (start, end col)
        let mut annotations = line.annotations.clone();
        annotations.sort();

        // Next, create the highlight line.
        for annotation in &annotations {
            for p in annotation.start_col..annotation.end_col {
                if annotation.is_primary {
                    buffer.putc(line_offset + 1,
                                width_offset + p,
                                '^',
                                Style::UnderlinePrimary);
                    if !annotation.is_minimized {
                        buffer.set_style(line_offset,
                                            width_offset + p,
                                            Style::UnderlinePrimary);
                    }
                } else {
                    buffer.putc(line_offset + 1,
                                width_offset + p,
                                '-',
                                Style::UnderlineSecondary);
                    if !annotation.is_minimized {
                        buffer.set_style(line_offset,
                                            width_offset + p,
                                            Style::UnderlineSecondary);
                    }
                }
            }
        }
        draw_col_separator(buffer, line_offset + 1, width_offset - 2);

        // Now we are going to write labels in. To start, we'll exclude
        // the annotations with no labels.
        let (labeled_annotations, unlabeled_annotations): (Vec<_>, _) = annotations.into_iter()
            .partition(|a| a.label.is_some());

        // If there are no annotations that need text, we're done.
        if labeled_annotations.is_empty() {
            return;
        }
        // Now add the text labels. We try, when possible, to stick the rightmost
        // annotation at the end of the highlight line:
        //
        //      vec.push(vec.pop().unwrap());
        //      ---      ---               - previous borrow ends here
        //
        // But sometimes that's not possible because one of the other
        // annotations overlaps it. For example, from the test
        // `span_overlap_label`, we have the following annotations
        // (written on distinct lines for clarity):
        //
        //      fn foo(x: u32) {
        //      --------------
        //             -
        //
        // In this case, we can't stick the rightmost-most label on
        // the highlight line, or we would get:
        //
        //      fn foo(x: u32) {
        //      -------- x_span
        //      |
        //      fn_span
        //
        // which is totally weird. Instead we want:
        //
        //      fn foo(x: u32) {
        //      --------------
        //      |      |
        //      |      x_span
        //      fn_span
        //
        // which is...less weird, at least. In fact, in general, if
        // the rightmost span overlaps with any other span, we should
        // use the "hang below" version, so we can at least make it
        // clear where the span *starts*.
        let mut labeled_annotations = &labeled_annotations[..];
        match labeled_annotations.split_last().unwrap() {
            (last, previous) => {
                if previous.iter()
                    .chain(&unlabeled_annotations)
                    .all(|a| !overlaps(a, last)) {
                    // append the label afterwards; we keep it in a separate
                    // string
                    let highlight_label: String = format!(" {}", last.label.as_ref().unwrap());
                    if last.is_primary {
                        buffer.append(line_offset + 1, &highlight_label, Style::LabelPrimary);
                    } else {
                        buffer.append(line_offset + 1, &highlight_label, Style::LabelSecondary);
                    }
                    labeled_annotations = previous;
                }
            }
        }

        // If that's the last annotation, we're done
        if labeled_annotations.is_empty() {
            return;
        }

        for (index, annotation) in labeled_annotations.iter().enumerate() {
            // Leave:
            // - 1 extra line
            // - One line for each thing that comes after
            let comes_after = labeled_annotations.len() - index - 1;
            let blank_lines = 3 + comes_after;

            // For each blank line, draw a `|` at our column. The
            // text ought to be long enough for this.
            for index in 2..blank_lines {
                if annotation.is_primary {
                    buffer.putc(line_offset + index,
                                width_offset + annotation.start_col,
                                '|',
                                Style::UnderlinePrimary);
                } else {
                    buffer.putc(line_offset + index,
                                width_offset + annotation.start_col,
                                '|',
                                Style::UnderlineSecondary);
                }
                draw_col_separator(buffer, line_offset + index, width_offset - 2);
            }

            if annotation.is_primary {
                buffer.puts(line_offset + blank_lines,
                            width_offset + annotation.start_col,
                            annotation.label.as_ref().unwrap(),
                            Style::LabelPrimary);
            } else {
                buffer.puts(line_offset + blank_lines,
                            width_offset + annotation.start_col,
                            annotation.label.as_ref().unwrap(),
                            Style::LabelSecondary);
            }
            draw_col_separator(buffer, line_offset + blank_lines, width_offset - 2);
        }
    }

    fn get_multispan_max_line_num(&mut self, msp: &MultiSpan) -> usize {
        let mut max = 0;
        if let Some(ref cm) = self.cm {
            for primary_span in msp.primary_spans() {
                if primary_span != &DUMMY_SP && primary_span != &COMMAND_LINE_SP {
                    let hi = cm.lookup_char_pos(primary_span.hi);
                    if hi.line > max {
                        max = hi.line;
                    }
                }
            }
            for span_label in msp.span_labels() {
                if span_label.span != DUMMY_SP && span_label.span != COMMAND_LINE_SP {
                    let hi = cm.lookup_char_pos(span_label.span.hi);
                    if hi.line > max {
                        max = hi.line;
                    }
                }
            }
        }
        max
    }

    fn get_max_line_num(&mut self, span: &MultiSpan, children: &Vec<SubDiagnostic>) -> usize {
        let mut max = 0;

        let primary = self.get_multispan_max_line_num(span);
        max = if primary > max { primary } else { max };

        for sub in children {
            let sub_result = self.get_multispan_max_line_num(&sub.span);
            max = if sub_result > max { primary } else { max };
        }
        max
    }

    // This "fixes" MultiSpans that contain Spans that are pointing to locations inside of
    // <*macros>. Since these locations are often difficult to read, we move these Spans from
    // <*macros> to their corresponding use site.
    fn fix_multispan_in_std_macros(&mut self, span: &mut MultiSpan) -> bool {
        let mut spans_updated = false;

        if let Some(ref cm) = self.cm {
            let mut before_after: Vec<(Span, Span)> = vec![];
            let mut new_labels: Vec<(Span, String)> = vec![];

            // First, find all the spans in <*macros> and point instead at their use site
            for sp in span.primary_spans() {
                if (*sp == COMMAND_LINE_SP) || (*sp == DUMMY_SP) {
                    continue;
                }
                if cm.span_to_filename(sp.clone()).contains("macros>") {
                    let v = cm.macro_backtrace(sp.clone());
                    if let Some(use_site) = v.last() {
                        before_after.push((sp.clone(), use_site.call_site.clone()));
                    }
                }
                for trace in cm.macro_backtrace(sp.clone()).iter().rev() {
                    // Only show macro locations that are local
                    // and display them like a span_note
                    if let Some(def_site) = trace.def_site_span {
                        if (def_site == COMMAND_LINE_SP) || (def_site == DUMMY_SP) {
                            continue;
                        }
                        // Check to make sure we're not in any <*macros>
                        if !cm.span_to_filename(def_site).contains("macros>") &&
                            !trace.macro_decl_name.starts_with("#[")
                        {
                            new_labels.push((trace.call_site,
                                             "in this macro invocation".to_string()));
                            break;
                        }
                    }
                }
            }
            for (label_span, label_text) in new_labels {
                span.push_span_label(label_span, label_text);
            }
            for sp_label in span.span_labels() {
                if (sp_label.span == COMMAND_LINE_SP) || (sp_label.span == DUMMY_SP) {
                    continue;
                }
                if cm.span_to_filename(sp_label.span.clone()).contains("macros>") {
                    let v = cm.macro_backtrace(sp_label.span.clone());
                    if let Some(use_site) = v.last() {
                        before_after.push((sp_label.span.clone(), use_site.call_site.clone()));
                    }
                }
            }
            // After we have them, make sure we replace these 'bad' def sites with their use sites
            for (before, after) in before_after {
                span.replace(before, after);
                spans_updated = true;
            }
        }

        spans_updated
    }

    // This does a small "fix" for multispans by looking to see if it can find any that
    // point directly at <*macros>. Since these are often difficult to read, this
    // will change the span to point at the use site.
    fn fix_multispans_in_std_macros(&mut self,
                                    span: &mut MultiSpan,
                                    children: &mut Vec<SubDiagnostic>) {
        let mut spans_updated = self.fix_multispan_in_std_macros(span);
        for child in children.iter_mut() {
            spans_updated |= self.fix_multispan_in_std_macros(&mut child.span);
        }
        if spans_updated {
            children.push(SubDiagnostic {
                level: Level::Note,
                message: "this error originates in a macro from the standard library".to_string(),
                span: MultiSpan::new(),
                render_span: None
            });
        }
    }

    fn emit_message_default(&mut self,
                            msp: &MultiSpan,
                            msg: &str,
                            code: &Option<String>,
                            level: &Level,
                            max_line_num_len: usize,
                            is_secondary: bool)
                            -> io::Result<()> {
        let mut buffer = StyledBuffer::new();

        if msp.primary_spans().is_empty() && msp.span_labels().is_empty() && is_secondary {
            // This is a secondary message with no span info
            for _ in 0..max_line_num_len {
                buffer.prepend(0, " ", Style::NoStyle);
            }
            draw_note_separator(&mut buffer, 0, max_line_num_len + 1);
            buffer.append(0, &level.to_string(), Style::HeaderMsg);
            buffer.append(0, ": ", Style::NoStyle);
            buffer.append(0, msg, Style::NoStyle);
        }
        else {
            buffer.append(0, &level.to_string(), Style::Level(level.clone()));
            match code {
                &Some(ref code) => {
                    buffer.append(0, "[", Style::Level(level.clone()));
                    buffer.append(0, &code, Style::Level(level.clone()));
                    buffer.append(0, "]", Style::Level(level.clone()));
                }
                _ => {}
            }
            buffer.append(0, ": ", Style::HeaderMsg);
            buffer.append(0, msg, Style::HeaderMsg);
        }

        // Preprocess all the annotations so that they are grouped by file and by line number
        // This helps us quickly iterate over the whole message (including secondary file spans)
        let mut annotated_files = self.preprocess_annotations(msp);

        // Make sure our primary file comes first
        let primary_lo =
            if let (Some(ref cm), Some(ref primary_span)) = (self.cm.as_ref(),
                                                             msp.primary_span().as_ref()) {
                if primary_span != &&DUMMY_SP && primary_span != &&COMMAND_LINE_SP {
                    cm.lookup_char_pos(primary_span.lo)
                }
                else {
                    emit_to_destination(&buffer.render(), level, &mut self.dst)?;
                    return Ok(());
                }
            } else {
                // If we don't have span information, emit and exit
                emit_to_destination(&buffer.render(), level, &mut self.dst)?;
                return Ok(());
            };
        if let Ok(pos) =
                annotated_files.binary_search_by(|x| x.file.name.cmp(&primary_lo.file.name)) {
            annotated_files.swap(0, pos);
        }

        // Print out the annotate source lines that correspond with the error
        for annotated_file in annotated_files {
            // print out the span location and spacer before we print the annotated source
            // to do this, we need to know if this span will be primary
            let is_primary = primary_lo.file.name == annotated_file.file.name;
            if is_primary {
                // remember where we are in the output buffer for easy reference
                let buffer_msg_line_offset = buffer.num_lines();

                buffer.prepend(buffer_msg_line_offset, "--> ", Style::LineNumber);
                let loc = primary_lo.clone();
                buffer.append(buffer_msg_line_offset,
                                &format!("{}:{}:{}", loc.file.name, loc.line, loc.col.0 + 1),
                                Style::LineAndColumn);
                for _ in 0..max_line_num_len {
                    buffer.prepend(buffer_msg_line_offset, " ", Style::NoStyle);
                }
            } else {
                // remember where we are in the output buffer for easy reference
                let buffer_msg_line_offset = buffer.num_lines();

                // Add spacing line
                draw_col_separator(&mut buffer, buffer_msg_line_offset, max_line_num_len + 1);

                // Then, the secondary file indicator
                buffer.prepend(buffer_msg_line_offset + 1, "::: ", Style::LineNumber);
                buffer.append(buffer_msg_line_offset + 1,
                                &annotated_file.file.name,
                                Style::LineAndColumn);
                for _ in 0..max_line_num_len {
                    buffer.prepend(buffer_msg_line_offset + 1, " ", Style::NoStyle);
                }
            }

            // Put in the spacer between the location and annotated source
            let buffer_msg_line_offset = buffer.num_lines();
            draw_col_separator_no_space(&mut buffer, buffer_msg_line_offset, max_line_num_len + 1);

            // Next, output the annotate source for this file
            for line_idx in 0..annotated_file.lines.len() {
                self.render_source_line(&mut buffer,
                                        annotated_file.file.clone(),
                                        &annotated_file.lines[line_idx],
                                        3 + max_line_num_len);

                // check to see if we need to print out or elide lines that come between
                // this annotated line and the next one
                if line_idx < (annotated_file.lines.len() - 1) {
                    let line_idx_delta = annotated_file.lines[line_idx + 1].line_index -
                                            annotated_file.lines[line_idx].line_index;
                    if line_idx_delta > 2 {
                        let last_buffer_line_num = buffer.num_lines();
                        buffer.puts(last_buffer_line_num, 0, "...", Style::LineNumber);
                    } else if line_idx_delta == 2 {
                        let unannotated_line = annotated_file.file
                            .get_line(annotated_file.lines[line_idx].line_index)
                            .unwrap_or("");

                        let last_buffer_line_num = buffer.num_lines();

                        buffer.puts(last_buffer_line_num,
                                    0,
                                    &(annotated_file.lines[line_idx + 1].line_index - 1)
                                        .to_string(),
                                    Style::LineNumber);
                        draw_col_separator(&mut buffer, last_buffer_line_num, 1 + max_line_num_len);
                        buffer.puts(last_buffer_line_num,
                                    3 + max_line_num_len,
                                    &unannotated_line,
                                    Style::Quotation);
                    }
                }
            }
        }

        // final step: take our styled buffer, render it, then output it
        emit_to_destination(&buffer.render(), level, &mut self.dst)?;

        Ok(())
    }
    fn emit_suggestion_default(&mut self,
                               suggestion: &CodeSuggestion,
                               level: &Level,
                               msg: &str,
                               max_line_num_len: usize)
                               -> io::Result<()> {
        use std::borrow::Borrow;

        let primary_span = suggestion.msp.primary_span().unwrap();
        if let Some(ref cm) = self.cm {
            let mut buffer = StyledBuffer::new();

            buffer.append(0, &level.to_string(), Style::Level(level.clone()));
            buffer.append(0, ": ", Style::HeaderMsg);
            buffer.append(0, msg, Style::HeaderMsg);

            let lines = cm.span_to_lines(primary_span).unwrap();

            assert!(!lines.lines.is_empty());

            let complete = suggestion.splice_lines(cm.borrow());

            // print the suggestion without any line numbers, but leave
            // space for them. This helps with lining up with previous
            // snippets from the actual error being reported.
            let mut lines = complete.lines();
            let mut row_num = 1;
            for line in lines.by_ref().take(MAX_HIGHLIGHT_LINES) {
                draw_col_separator(&mut buffer, row_num, max_line_num_len + 1);
                buffer.append(row_num, line, Style::NoStyle);
                row_num += 1;
            }

            // if we elided some lines, add an ellipsis
            if let Some(_) = lines.next() {
                buffer.append(row_num, "...", Style::NoStyle);
            }
            emit_to_destination(&buffer.render(), level, &mut self.dst)?;
        }
        Ok(())
    }
    fn emit_messages_default(&mut self,
                             level: &Level,
                             message: &String,
                             code: &Option<String>,
                             span: &MultiSpan,
                             children: &Vec<SubDiagnostic>) {
        let max_line_num = self.get_max_line_num(span, children);
        let max_line_num_len = max_line_num.to_string().len();

        match self.emit_message_default(span,
                                        message,
                                        code,
                                        level,
                                        max_line_num_len,
                                        false) {
            Ok(()) => {
                if !children.is_empty() {
                    let mut buffer = StyledBuffer::new();
                    draw_col_separator_no_space(&mut buffer, 0, max_line_num_len + 1);
                    match emit_to_destination(&buffer.render(), level, &mut self.dst) {
                        Ok(()) => (),
                        Err(e) => panic!("failed to emit error: {}", e)
                    }
                }
                for child in children {
                    match child.render_span {
                        Some(FullSpan(ref msp)) => {
                            match self.emit_message_default(msp,
                                                            &child.message,
                                                            &None,
                                                            &child.level,
                                                            max_line_num_len,
                                                            true) {
                                Err(e) => panic!("failed to emit error: {}", e),
                                _ => ()
                            }
                        },
                        Some(Suggestion(ref cs)) => {
                            match self.emit_suggestion_default(cs,
                                                               &child.level,
                                                               &child.message,
                                                               max_line_num_len) {
                                Err(e) => panic!("failed to emit error: {}", e),
                                _ => ()
                            }
                        },
                        None => {
                            match self.emit_message_default(&child.span,
                                                            &child.message,
                                                            &None,
                                                            &child.level,
                                                            max_line_num_len,
                                                            true) {
                                Err(e) => panic!("failed to emit error: {}", e),
                                _ => ()
                            }
                        }
                    }
                }
            }
            Err(e) => panic!("failed to emit error: {}", e)
        }
        match write!(&mut self.dst, "\n") {
            Err(e) => panic!("failed to emit error: {}", e),
            _ => match self.dst.flush() {
                Err(e) => panic!("failed to emit error: {}", e),
                _ => ()
            }
        }
    }
}

fn draw_col_separator(buffer: &mut StyledBuffer, line: usize, col: usize) {
    buffer.puts(line, col, "| ", Style::LineNumber);
}

fn draw_col_separator_no_space(buffer: &mut StyledBuffer, line: usize, col: usize) {
    buffer.puts(line, col, "|", Style::LineNumber);
}

fn draw_note_separator(buffer: &mut StyledBuffer, line: usize, col: usize) {
    buffer.puts(line, col, "= ", Style::LineNumber);
}

fn overlaps(a1: &Annotation, a2: &Annotation) -> bool {
    (a2.start_col..a2.end_col).contains(a1.start_col) ||
    (a1.start_col..a1.end_col).contains(a2.start_col)
}

fn emit_to_destination(rendered_buffer: &Vec<Vec<StyledString>>,
        lvl: &Level,
        dst: &mut Destination) -> io::Result<()> {
    use lock;

    // In order to prevent error message interleaving, where multiple error lines get intermixed
    // when multiple compiler processes error simultaneously, we emit errors with additional
    // steps.
    //
    // On Unix systems, we write into a buffered terminal rather than directly to a terminal. When
    // the .flush() is called we take the buffer created from the buffered writes and write it at
    // one shot.  Because the Unix systems use ANSI for the colors, which is a text-based styling
    // scheme, this buffered approach works and maintains the styling.
    //
    // On Windows, styling happens through calls to a terminal API. This prevents us from using the
    // same buffering approach.  Instead, we use a global Windows mutex, which we acquire long
    // enough to output the full error message, then we release.
    let _buffer_lock = lock::acquire_global_lock("rustc_errors");
    for line in rendered_buffer {
        for part in line {
            dst.apply_style(lvl.clone(), part.style)?;
            write!(dst, "{}", part.text)?;
            dst.reset_attrs()?;
        }
        write!(dst, "\n")?;
    }
    dst.flush()?;
    Ok(())
}

#[cfg(unix)]
fn stderr_isatty() -> bool {
    use libc;
    unsafe { libc::isatty(libc::STDERR_FILENO) != 0 }
}
#[cfg(windows)]
fn stderr_isatty() -> bool {
    type DWORD = u32;
    type BOOL = i32;
    type HANDLE = *mut u8;
    const STD_ERROR_HANDLE: DWORD = -12i32 as DWORD;
    extern "system" {
        fn GetStdHandle(which: DWORD) -> HANDLE;
        fn GetConsoleMode(hConsoleHandle: HANDLE,
                          lpMode: *mut DWORD) -> BOOL;
    }
    unsafe {
        let handle = GetStdHandle(STD_ERROR_HANDLE);
        let mut out = 0;
        GetConsoleMode(handle, &mut out) != 0
    }
}

pub type BufferedStderr = term::Terminal<Output = BufferedWriter> + Send;

pub enum Destination {
    Terminal(Box<term::StderrTerminal>),
    BufferedTerminal(Box<BufferedStderr>),
    Raw(Box<Write + Send>),
}

/// Buffered writer gives us a way on Unix to buffer up an entire error message before we output
/// it.  This helps to prevent interleaving of multiple error messages when multiple compiler
/// processes error simultaneously
pub struct BufferedWriter {
    buffer: Vec<u8>,
}

impl BufferedWriter {
    // note: we use _new because the conditional compilation at its use site may make this
    // this function unused on some platforms
    fn _new() -> BufferedWriter {
        BufferedWriter {
            buffer: vec![]
        }
    }
}

impl Write for BufferedWriter {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        for b in buf {
            self.buffer.push(*b);
        }
        Ok(buf.len())
    }
    fn flush(&mut self) -> io::Result<()> {
        let mut stderr = io::stderr();
        let result = (|| {
            stderr.write_all(&self.buffer)?;
            stderr.flush()
        })();
        self.buffer.clear();
        result
    }
}

impl Destination {
    #[cfg(not(windows))]
    /// When not on Windows, prefer the buffered terminal so that we can buffer an entire error
    /// to be emitted at one time.
    fn from_stderr() -> Destination {
        let stderr: Option<Box<BufferedStderr>>  =
            term::TerminfoTerminal::new(BufferedWriter::_new())
                .map(|t| Box::new(t) as Box<BufferedStderr>);

        match stderr {
            Some(t) => BufferedTerminal(t),
            None    => Raw(Box::new(io::stderr())),
        }
    }

    #[cfg(windows)]
    /// Return a normal, unbuffered terminal when on Windows.
    fn from_stderr() -> Destination {
        let stderr: Option<Box<term::StderrTerminal>> =
            term::TerminfoTerminal::new(io::stderr())
                .map(|t| Box::new(t) as Box<term::StderrTerminal>)
                .or_else(|| term::WinConsole::new(io::stderr()).ok()
                    .map(|t| Box::new(t) as Box<term::StderrTerminal>));

        match stderr {
            Some(t) => Terminal(t),
            None    => Raw(Box::new(io::stderr())),
        }
    }

    fn apply_style(&mut self,
                   lvl: Level,
                   style: Style)
                   -> io::Result<()> {
        match style {
            Style::FileNameStyle | Style::LineAndColumn => {}
            Style::LineNumber => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(term::color::BRIGHT_BLUE)));
            }
            Style::ErrorCode => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(term::color::BRIGHT_MAGENTA)));
            }
            Style::Quotation => {}
            Style::OldSchoolNote => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(term::color::BRIGHT_GREEN)));
            }
            Style::OldSchoolNoteText | Style::HeaderMsg => {
                try!(self.start_attr(term::Attr::Bold));
            }
            Style::UnderlinePrimary | Style::LabelPrimary => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(lvl.color())));
            }
            Style::UnderlineSecondary |
            Style::LabelSecondary => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(term::color::BRIGHT_BLUE)));
            }
            Style::NoStyle => {}
            Style::Level(l) => {
                try!(self.start_attr(term::Attr::Bold));
                try!(self.start_attr(term::Attr::ForegroundColor(l.color())));
            }
        }
        Ok(())
    }

    fn start_attr(&mut self, attr: term::Attr) -> io::Result<()> {
        match *self {
            Terminal(ref mut t) => { t.attr(attr)?; }
            BufferedTerminal(ref mut t) => { t.attr(attr)?; }
            Raw(_) => { }
        }
        Ok(())
    }

    fn reset_attrs(&mut self) -> io::Result<()> {
        match *self {
            Terminal(ref mut t) => { t.reset()?; }
            BufferedTerminal(ref mut t) => { t.reset()?; }
            Raw(_) => { }
        }
        Ok(())
    }
}

impl Write for Destination {
    fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
        match *self {
            Terminal(ref mut t) => t.write(bytes),
            BufferedTerminal(ref mut t) => t.write(bytes),
            Raw(ref mut w) => w.write(bytes),
        }
    }
    fn flush(&mut self) -> io::Result<()> {
        match *self {
            Terminal(ref mut t) => t.flush(),
            BufferedTerminal(ref mut t) => t.flush(),
            Raw(ref mut w) => w.flush(),
        }
    }
}