// Copyright 2012 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.

//! The CodeMap tracks all the source code used within a single crate, mapping
//! from integer byte positions to the original source code location. Each bit
//! of source parsed during crate parsing (typically files, in-memory strings,
//! or various bits of macro expansion) cover a continuous range of bytes in the
//! CodeMap and are represented by FileMaps. Byte positions are stored in
//! `spans` and used pervasively in the compiler. They are absolute positions
//! within the CodeMap, which upon request can be converted to line and column
//! information, source code snippets, etc.


pub use syntax_pos::*;
pub use syntax_pos::hygiene::{ExpnFormat, ExpnInfo, NameAndSpan};
pub use self::ExpnFormat::*;

use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::StableHasher;
use std::cell::{RefCell, Ref};
use std::hash::Hash;
use std::path::{Path, PathBuf};
use std::rc::Rc;

use std::env;
use std::fs;
use std::io::{self, Read};
use errors::CodeMapper;

/// Return the span itself if it doesn't come from a macro expansion,
/// otherwise return the call site span up to the `enclosing_sp` by
/// following the `expn_info` chain.
pub fn original_sp(sp: Span, enclosing_sp: Span) -> Span {
    let call_site1 = sp.ctxt().outer().expn_info().map(|ei| ei.call_site);
    let call_site2 = enclosing_sp.ctxt().outer().expn_info().map(|ei| ei.call_site);
    match (call_site1, call_site2) {
        (None, _) => sp,
        (Some(call_site1), Some(call_site2)) if call_site1 == call_site2 => sp,
        (Some(call_site1), _) => original_sp(call_site1, enclosing_sp),
    }
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
pub struct Spanned<T> {
    pub node: T,
    pub span: Span,
}

pub fn respan<T>(sp: Span, t: T) -> Spanned<T> {
    Spanned {node: t, span: sp}
}

pub fn dummy_spanned<T>(t: T) -> Spanned<T> {
    respan(DUMMY_SP, t)
}

// _____________________________________________________________________________
// FileMap, MultiByteChar, FileName, FileLines
//

/// An abstraction over the fs operations used by the Parser.
pub trait FileLoader {
    /// Query the existence of a file.
    fn file_exists(&self, path: &Path) -> bool;

    /// Return an absolute path to a file, if possible.
    fn abs_path(&self, path: &Path) -> Option<PathBuf>;

    /// Read the contents of an UTF-8 file into memory.
    fn read_file(&self, path: &Path) -> io::Result<String>;
}

/// A FileLoader that uses std::fs to load real files.
pub struct RealFileLoader;

impl FileLoader for RealFileLoader {
    fn file_exists(&self, path: &Path) -> bool {
        fs::metadata(path).is_ok()
    }

    fn abs_path(&self, path: &Path) -> Option<PathBuf> {
        if path.is_absolute() {
            Some(path.to_path_buf())
        } else {
            env::current_dir()
                .ok()
                .map(|cwd| cwd.join(path))
        }
    }

    fn read_file(&self, path: &Path) -> io::Result<String> {
        let mut src = String::new();
        fs::File::open(path)?.read_to_string(&mut src)?;
        Ok(src)
    }
}

// This is a FileMap identifier that is used to correlate FileMaps between
// subsequent compilation sessions (which is something we need to do during
// incremental compilation).
#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
pub struct StableFilemapId(u128);

impl StableFilemapId {
    pub fn new(filemap: &FileMap) -> StableFilemapId {
        let mut hasher = StableHasher::new();

        filemap.name.hash(&mut hasher);
        filemap.name_was_remapped.hash(&mut hasher);
        filemap.unmapped_path.hash(&mut hasher);

        StableFilemapId(hasher.finish())
    }
}

// _____________________________________________________________________________
// CodeMap
//

pub struct CodeMap {
    pub(super) files: RefCell<Vec<Rc<FileMap>>>,
    file_loader: Box<FileLoader>,
    // This is used to apply the file path remapping as specified via
    // -Zremap-path-prefix to all FileMaps allocated within this CodeMap.
    path_mapping: FilePathMapping,
    stable_id_to_filemap: RefCell<FxHashMap<StableFilemapId, Rc<FileMap>>>,
    /// In case we are in a doctest, replace all file names with the PathBuf,
    /// and add the given offsets to the line info
    doctest_offset: Option<(FileName, isize)>,
}

impl CodeMap {
    pub fn new(path_mapping: FilePathMapping) -> CodeMap {
        CodeMap {
            files: RefCell::new(Vec::new()),
            file_loader: Box::new(RealFileLoader),
            path_mapping,
            stable_id_to_filemap: RefCell::new(FxHashMap()),
            doctest_offset: None,
        }
    }

    pub fn new_doctest(path_mapping: FilePathMapping,
                       file: FileName, line: isize) -> CodeMap {
        CodeMap {
            doctest_offset: Some((file, line)),
            ..CodeMap::new(path_mapping)
        }

    }

    pub fn with_file_loader(file_loader: Box<FileLoader>,
                            path_mapping: FilePathMapping)
                            -> CodeMap {
        CodeMap {
            files: RefCell::new(Vec::new()),
            file_loader,
            path_mapping,
            stable_id_to_filemap: RefCell::new(FxHashMap()),
            doctest_offset: None,
        }
    }

    pub fn path_mapping(&self) -> &FilePathMapping {
        &self.path_mapping
    }

    pub fn file_exists(&self, path: &Path) -> bool {
        self.file_loader.file_exists(path)
    }

    pub fn load_file(&self, path: &Path) -> io::Result<Rc<FileMap>> {
        let src = self.file_loader.read_file(path)?;
        let filename = if let Some((ref name, _)) = self.doctest_offset {
            name.clone()
        } else {
            path.to_owned().into()
        };
        Ok(self.new_filemap(filename, src))
    }

    pub fn files(&self) -> Ref<Vec<Rc<FileMap>>> {
        self.files.borrow()
    }

    pub fn filemap_by_stable_id(&self, stable_id: StableFilemapId) -> Option<Rc<FileMap>> {
        self.stable_id_to_filemap.borrow().get(&stable_id).map(|fm| fm.clone())
    }

    fn next_start_pos(&self) -> usize {
        let files = self.files.borrow();
        match files.last() {
            None => 0,
            // Add one so there is some space between files. This lets us distinguish
            // positions in the codemap, even in the presence of zero-length files.
            Some(last) => last.end_pos.to_usize() + 1,
        }
    }

    /// Creates a new filemap without setting its line information. If you don't
    /// intend to set the line information yourself, you should use new_filemap_and_lines.
    pub fn new_filemap(&self, filename: FileName, src: String) -> Rc<FileMap> {
        let start_pos = self.next_start_pos();
        let mut files = self.files.borrow_mut();

        // The path is used to determine the directory for loading submodules and
        // include files, so it must be before remapping.
        // Note that filename may not be a valid path, eg it may be `<anon>` etc,
        // but this is okay because the directory determined by `path.pop()` will
        // be empty, so the working directory will be used.
        let unmapped_path = filename.clone();

        let (filename, was_remapped) = match filename {
            FileName::Real(filename) => {
                let (filename, was_remapped) = self.path_mapping.map_prefix(filename);
                (FileName::Real(filename), was_remapped)
            },
            other => (other, false),
        };
        let filemap = Rc::new(FileMap::new(
            filename,
            was_remapped,
            unmapped_path,
            src,
            Pos::from_usize(start_pos),
        ));

        files.push(filemap.clone());

        self.stable_id_to_filemap
            .borrow_mut()
            .insert(StableFilemapId::new(&filemap), filemap.clone());

        filemap
    }

    /// Creates a new filemap and sets its line information.
    pub fn new_filemap_and_lines(&self, filename: &Path, src: &str) -> Rc<FileMap> {
        let fm = self.new_filemap(filename.to_owned().into(), src.to_owned());
        let mut byte_pos: u32 = fm.start_pos.0;
        for line in src.lines() {
            // register the start of this line
            fm.next_line(BytePos(byte_pos));

            // update byte_pos to include this line and the \n at the end
            byte_pos += line.len() as u32 + 1;
        }
        fm
    }


    /// Allocates a new FileMap representing a source file from an external
    /// crate. The source code of such an "imported filemap" is not available,
    /// but we still know enough to generate accurate debuginfo location
    /// information for things inlined from other crates.
    pub fn new_imported_filemap(&self,
                                filename: FileName,
                                name_was_remapped: bool,
                                crate_of_origin: u32,
                                src_hash: u128,
                                name_hash: u128,
                                source_len: usize,
                                mut file_local_lines: Vec<BytePos>,
                                mut file_local_multibyte_chars: Vec<MultiByteChar>,
                                mut file_local_non_narrow_chars: Vec<NonNarrowChar>)
                                -> Rc<FileMap> {
        let start_pos = self.next_start_pos();
        let mut files = self.files.borrow_mut();

        let end_pos = Pos::from_usize(start_pos + source_len);
        let start_pos = Pos::from_usize(start_pos);

        for pos in &mut file_local_lines {
            *pos = *pos + start_pos;
        }

        for mbc in &mut file_local_multibyte_chars {
            mbc.pos = mbc.pos + start_pos;
        }

        for swc in &mut file_local_non_narrow_chars {
            *swc = *swc + start_pos;
        }

        let filemap = Rc::new(FileMap {
            name: filename,
            name_was_remapped,
            unmapped_path: None,
            crate_of_origin,
            src: None,
            src_hash,
            external_src: RefCell::new(ExternalSource::AbsentOk),
            start_pos,
            end_pos,
            lines: RefCell::new(file_local_lines),
            multibyte_chars: RefCell::new(file_local_multibyte_chars),
            non_narrow_chars: RefCell::new(file_local_non_narrow_chars),
            name_hash,
        });

        files.push(filemap.clone());

        self.stable_id_to_filemap
            .borrow_mut()
            .insert(StableFilemapId::new(&filemap), filemap.clone());

        filemap
    }

    pub fn mk_substr_filename(&self, sp: Span) -> String {
        let pos = self.lookup_char_pos(sp.lo());
        (format!("<{}:{}:{}>",
                 pos.file.name,
                 pos.line,
                 pos.col.to_usize() + 1)).to_string()
    }

    // If there is a doctest_offset, apply it to the line
    pub fn doctest_offset_line(&self, mut orig: usize) -> usize {
        if let Some((_, line)) = self.doctest_offset {
            if line >= 0 {
                orig = orig + line as usize;
            } else {
                orig = orig - (-line) as usize;
            }
        }
        orig
    }

    /// Lookup source information about a BytePos
    pub fn lookup_char_pos(&self, pos: BytePos) -> Loc {
        let chpos = self.bytepos_to_file_charpos(pos);
        match self.lookup_line(pos) {
            Ok(FileMapAndLine { fm: f, line: a }) => {
                let line = a + 1; // Line numbers start at 1
                let linebpos = (*f.lines.borrow())[a];
                let linechpos = self.bytepos_to_file_charpos(linebpos);
                let col = chpos - linechpos;

                let col_display = {
                    let non_narrow_chars = f.non_narrow_chars.borrow();
                    let start_width_idx = non_narrow_chars
                        .binary_search_by_key(&linebpos, |x| x.pos())
                        .unwrap_or_else(|x| x);
                    let end_width_idx = non_narrow_chars
                        .binary_search_by_key(&pos, |x| x.pos())
                        .unwrap_or_else(|x| x);
                    let special_chars = end_width_idx - start_width_idx;
                    let non_narrow: usize =
                        non_narrow_chars[start_width_idx..end_width_idx]
                        .into_iter()
                        .map(|x| x.width())
                        .sum();
                    col.0 - special_chars + non_narrow
                };
                debug!("byte pos {:?} is on the line at byte pos {:?}",
                       pos, linebpos);
                debug!("char pos {:?} is on the line at char pos {:?}",
                       chpos, linechpos);
                debug!("byte is on line: {}", line);
                assert!(chpos >= linechpos);
                Loc {
                    file: f,
                    line,
                    col,
                    col_display,
                }
            }
            Err(f) => {
                let col_display = {
                    let non_narrow_chars = f.non_narrow_chars.borrow();
                    let end_width_idx = non_narrow_chars
                        .binary_search_by_key(&pos, |x| x.pos())
                        .unwrap_or_else(|x| x);
                    let non_narrow: usize =
                        non_narrow_chars[0..end_width_idx]
                        .into_iter()
                        .map(|x| x.width())
                        .sum();
                    chpos.0 - end_width_idx + non_narrow
                };
                Loc {
                    file: f,
                    line: 0,
                    col: chpos,
                    col_display,
                }
            }
        }
    }

    // If the relevant filemap is empty, we don't return a line number.
    pub fn lookup_line(&self, pos: BytePos) -> Result<FileMapAndLine, Rc<FileMap>> {
        let idx = self.lookup_filemap_idx(pos);

        let files = self.files.borrow();
        let f = (*files)[idx].clone();

        match f.lookup_line(pos) {
            Some(line) => Ok(FileMapAndLine { fm: f, line: line }),
            None => Err(f)
        }
    }

    pub fn lookup_char_pos_adj(&self, pos: BytePos) -> LocWithOpt {
        let loc = self.lookup_char_pos(pos);
        LocWithOpt {
            filename: loc.file.name.clone(),
            line: loc.line,
            col: loc.col,
            file: Some(loc.file)
        }
    }

    /// Returns `Some(span)`, a union of the lhs and rhs span.  The lhs must precede the rhs. If
    /// there are gaps between lhs and rhs, the resulting union will cross these gaps.
    /// For this to work, the spans have to be:
    ///
    ///    * the ctxt of both spans much match
    ///    * the lhs span needs to end on the same line the rhs span begins
    ///    * the lhs span must start at or before the rhs span
    pub fn merge_spans(&self, sp_lhs: Span, sp_rhs: Span) -> Option<Span> {
        // make sure we're at the same expansion id
        if sp_lhs.ctxt() != sp_rhs.ctxt() {
            return None;
        }

        let lhs_end = match self.lookup_line(sp_lhs.hi()) {
            Ok(x) => x,
            Err(_) => return None
        };
        let rhs_begin = match self.lookup_line(sp_rhs.lo()) {
            Ok(x) => x,
            Err(_) => return None
        };

        // if we must cross lines to merge, don't merge
        if lhs_end.line != rhs_begin.line {
            return None;
        }

        // ensure these follow the expected order and we don't overlap
        if (sp_lhs.lo() <= sp_rhs.lo()) && (sp_lhs.hi() <= sp_rhs.lo()) {
            Some(sp_lhs.to(sp_rhs))
        } else {
            None
        }
    }

    pub fn span_to_string(&self, sp: Span) -> String {
        if self.files.borrow().is_empty() && sp.source_equal(&DUMMY_SP) {
            return "no-location".to_string();
        }

        let lo = self.lookup_char_pos_adj(sp.lo());
        let hi = self.lookup_char_pos_adj(sp.hi());
        return (format!("{}:{}:{}: {}:{}",
                        lo.filename,
                        lo.line,
                        lo.col.to_usize() + 1,
                        hi.line,
                        hi.col.to_usize() + 1)).to_string()
    }

    pub fn span_to_filename(&self, sp: Span) -> FileName {
        self.lookup_char_pos(sp.lo()).file.name.clone()
    }

    pub fn span_to_unmapped_path(&self, sp: Span) -> FileName {
        self.lookup_char_pos(sp.lo()).file.unmapped_path.clone()
            .expect("CodeMap::span_to_unmapped_path called for imported FileMap?")
    }

    pub fn is_multiline(&self, sp: Span) -> bool {
        let lo = self.lookup_char_pos(sp.lo());
        let hi = self.lookup_char_pos(sp.hi());
        lo.line != hi.line
    }

    pub fn span_to_lines(&self, sp: Span) -> FileLinesResult {
        debug!("span_to_lines(sp={:?})", sp);

        if sp.lo() > sp.hi() {
            return Err(SpanLinesError::IllFormedSpan(sp));
        }

        let lo = self.lookup_char_pos(sp.lo());
        debug!("span_to_lines: lo={:?}", lo);
        let hi = self.lookup_char_pos(sp.hi());
        debug!("span_to_lines: hi={:?}", hi);

        if lo.file.start_pos != hi.file.start_pos {
            return Err(SpanLinesError::DistinctSources(DistinctSources {
                begin: (lo.file.name.clone(), lo.file.start_pos),
                end: (hi.file.name.clone(), hi.file.start_pos),
            }));
        }
        assert!(hi.line >= lo.line);

        let mut lines = Vec::with_capacity(hi.line - lo.line + 1);

        // The span starts partway through the first line,
        // but after that it starts from offset 0.
        let mut start_col = lo.col;

        // For every line but the last, it extends from `start_col`
        // and to the end of the line. Be careful because the line
        // numbers in Loc are 1-based, so we subtract 1 to get 0-based
        // lines.
        for line_index in lo.line-1 .. hi.line-1 {
            let line_len = lo.file.get_line(line_index)
                                  .map(|s| s.chars().count())
                                  .unwrap_or(0);
            lines.push(LineInfo { line_index,
                                  start_col,
                                  end_col: CharPos::from_usize(line_len) });
            start_col = CharPos::from_usize(0);
        }

        // For the last line, it extends from `start_col` to `hi.col`:
        lines.push(LineInfo { line_index: hi.line - 1,
                              start_col,
                              end_col: hi.col });

        Ok(FileLines {file: lo.file, lines: lines})
    }

    pub fn span_to_snippet(&self, sp: Span) -> Result<String, SpanSnippetError> {
        if sp.lo() > sp.hi() {
            return Err(SpanSnippetError::IllFormedSpan(sp));
        }

        let local_begin = self.lookup_byte_offset(sp.lo());
        let local_end = self.lookup_byte_offset(sp.hi());

        if local_begin.fm.start_pos != local_end.fm.start_pos {
            return Err(SpanSnippetError::DistinctSources(DistinctSources {
                begin: (local_begin.fm.name.clone(),
                        local_begin.fm.start_pos),
                end: (local_end.fm.name.clone(),
                      local_end.fm.start_pos)
            }));
        } else {
            self.ensure_filemap_source_present(local_begin.fm.clone());

            let start_index = local_begin.pos.to_usize();
            let end_index = local_end.pos.to_usize();
            let source_len = (local_begin.fm.end_pos -
                              local_begin.fm.start_pos).to_usize();

            if start_index > end_index || end_index > source_len {
                return Err(SpanSnippetError::MalformedForCodemap(
                    MalformedCodemapPositions {
                        name: local_begin.fm.name.clone(),
                        source_len,
                        begin_pos: local_begin.pos,
                        end_pos: local_end.pos,
                    }));
            }

            if let Some(ref src) = local_begin.fm.src {
                return Ok((&src[start_index..end_index]).to_string());
            } else if let Some(src) = local_begin.fm.external_src.borrow().get_source() {
                return Ok((&src[start_index..end_index]).to_string());
            } else {
                return Err(SpanSnippetError::SourceNotAvailable {
                    filename: local_begin.fm.name.clone()
                });
            }
        }
    }

    /// Given a `Span`, try to get a shorter span ending before the first occurrence of `c` `char`
    pub fn span_until_char(&self, sp: Span, c: char) -> Span {
        match self.span_to_snippet(sp) {
            Ok(snippet) => {
                let snippet = snippet.split(c).nth(0).unwrap_or("").trim_right();
                if !snippet.is_empty() && !snippet.contains('\n') {
                    sp.with_hi(BytePos(sp.lo().0 + snippet.len() as u32))
                } else {
                    sp
                }
            }
            _ => sp,
        }
    }

    /// Given a `Span`, try to get a shorter span ending just after the first
    /// occurrence of `char` `c`.
    pub fn span_through_char(&self, sp: Span, c: char) -> Span {
        if let Ok(snippet) = self.span_to_snippet(sp) {
            if let Some(offset) = snippet.find(c) {
                return sp.with_hi(BytePos(sp.lo().0 + (offset + c.len_utf8()) as u32));
            }
        }
        sp
    }

    pub fn def_span(&self, sp: Span) -> Span {
        self.span_until_char(sp, '{')
    }

    pub fn get_filemap(&self, filename: &FileName) -> Option<Rc<FileMap>> {
        for fm in self.files.borrow().iter() {
            if *filename == fm.name {
                return Some(fm.clone());
            }
        }
        None
    }

    /// For a global BytePos compute the local offset within the containing FileMap
    pub fn lookup_byte_offset(&self, bpos: BytePos) -> FileMapAndBytePos {
        let idx = self.lookup_filemap_idx(bpos);
        let fm = (*self.files.borrow())[idx].clone();
        let offset = bpos - fm.start_pos;
        FileMapAndBytePos {fm: fm, pos: offset}
    }

    /// Converts an absolute BytePos to a CharPos relative to the filemap.
    pub fn bytepos_to_file_charpos(&self, bpos: BytePos) -> CharPos {
        let idx = self.lookup_filemap_idx(bpos);
        let files = self.files.borrow();
        let map = &(*files)[idx];

        // The number of extra bytes due to multibyte chars in the FileMap
        let mut total_extra_bytes = 0;

        for mbc in map.multibyte_chars.borrow().iter() {
            debug!("{}-byte char at {:?}", mbc.bytes, mbc.pos);
            if mbc.pos < bpos {
                // every character is at least one byte, so we only
                // count the actual extra bytes.
                total_extra_bytes += mbc.bytes - 1;
                // We should never see a byte position in the middle of a
                // character
                assert!(bpos.to_usize() >= mbc.pos.to_usize() + mbc.bytes);
            } else {
                break;
            }
        }

        assert!(map.start_pos.to_usize() + total_extra_bytes <= bpos.to_usize());
        CharPos(bpos.to_usize() - map.start_pos.to_usize() - total_extra_bytes)
    }

    // Return the index of the filemap (in self.files) which contains pos.
    pub fn lookup_filemap_idx(&self, pos: BytePos) -> usize {
        let files = self.files.borrow();
        let files = &*files;
        let count = files.len();

        // Binary search for the filemap.
        let mut a = 0;
        let mut b = count;
        while b - a > 1 {
            let m = (a + b) / 2;
            if files[m].start_pos > pos {
                b = m;
            } else {
                a = m;
            }
        }

        assert!(a < count, "position {} does not resolve to a source location", pos.to_usize());

        return a;
    }

    pub fn count_lines(&self) -> usize {
        self.files().iter().fold(0, |a, f| a + f.count_lines())
    }
}

impl CodeMapper for CodeMap {
    fn lookup_char_pos(&self, pos: BytePos) -> Loc {
        self.lookup_char_pos(pos)
    }
    fn span_to_lines(&self, sp: Span) -> FileLinesResult {
        self.span_to_lines(sp)
    }
    fn span_to_string(&self, sp: Span) -> String {
        self.span_to_string(sp)
    }
    fn span_to_filename(&self, sp: Span) -> FileName {
        self.span_to_filename(sp)
    }
    fn merge_spans(&self, sp_lhs: Span, sp_rhs: Span) -> Option<Span> {
        self.merge_spans(sp_lhs, sp_rhs)
    }
    fn call_span_if_macro(&self, sp: Span) -> Span {
        if self.span_to_filename(sp.clone()).is_macros() {
            let v = sp.macro_backtrace();
            if let Some(use_site) = v.last() {
                return use_site.call_site;
            }
        }
        sp
    }
    fn ensure_filemap_source_present(&self, file_map: Rc<FileMap>) -> bool {
        file_map.add_external_src(
            || match file_map.name {
                FileName::Real(ref name) => self.file_loader.read_file(name).ok(),
                _ => None,
            }
        )
    }
    fn doctest_offset_line(&self, line: usize) -> usize {
        self.doctest_offset_line(line)
    }
}

#[derive(Clone)]
pub struct FilePathMapping {
    mapping: Vec<(PathBuf, PathBuf)>,
}

impl FilePathMapping {
    pub fn empty() -> FilePathMapping {
        FilePathMapping {
            mapping: vec![]
        }
    }

    pub fn new(mapping: Vec<(PathBuf, PathBuf)>) -> FilePathMapping {
        FilePathMapping {
            mapping,
        }
    }

    /// Applies any path prefix substitution as defined by the mapping.
    /// The return value is the remapped path and a boolean indicating whether
    /// the path was affected by the mapping.
    pub fn map_prefix(&self, path: PathBuf) -> (PathBuf, bool) {
        // NOTE: We are iterating over the mapping entries from last to first
        //       because entries specified later on the command line should
        //       take precedence.
        for &(ref from, ref to) in self.mapping.iter().rev() {
            if let Ok(rest) = path.strip_prefix(from) {
                return (to.join(rest), true);
            }
        }

        (path, false)
    }
}

// _____________________________________________________________________________
// Tests
//

#[cfg(test)]
mod tests {
    use super::*;
    use std::borrow::Cow;
    use std::rc::Rc;

    #[test]
    fn t1 () {
        let cm = CodeMap::new(FilePathMapping::empty());
        let fm = cm.new_filemap(PathBuf::from("blork.rs").into(),
                                "first line.\nsecond line".to_string());
        fm.next_line(BytePos(0));
        // Test we can get lines with partial line info.
        assert_eq!(fm.get_line(0), Some(Cow::from("first line.")));
        // TESTING BROKEN BEHAVIOR: line break declared before actual line break.
        fm.next_line(BytePos(10));
        assert_eq!(fm.get_line(1), Some(Cow::from(".")));
        fm.next_line(BytePos(12));
        assert_eq!(fm.get_line(2), Some(Cow::from("second line")));
    }

    #[test]
    #[should_panic]
    fn t2 () {
        let cm = CodeMap::new(FilePathMapping::empty());
        let fm = cm.new_filemap(PathBuf::from("blork.rs").into(),
                                "first line.\nsecond line".to_string());
        // TESTING *REALLY* BROKEN BEHAVIOR:
        fm.next_line(BytePos(0));
        fm.next_line(BytePos(10));
        fm.next_line(BytePos(2));
    }

    fn init_code_map() -> CodeMap {
        let cm = CodeMap::new(FilePathMapping::empty());
        let fm1 = cm.new_filemap(PathBuf::from("blork.rs").into(),
                                 "first line.\nsecond line".to_string());
        let fm2 = cm.new_filemap(PathBuf::from("empty.rs").into(),
                                 "".to_string());
        let fm3 = cm.new_filemap(PathBuf::from("blork2.rs").into(),
                                 "first line.\nsecond line".to_string());

        fm1.next_line(BytePos(0));
        fm1.next_line(BytePos(12));
        fm2.next_line(fm2.start_pos);
        fm3.next_line(fm3.start_pos);
        fm3.next_line(fm3.start_pos + BytePos(12));

        cm
    }

    #[test]
    fn t3() {
        // Test lookup_byte_offset
        let cm = init_code_map();

        let fmabp1 = cm.lookup_byte_offset(BytePos(23));
        assert_eq!(fmabp1.fm.name, PathBuf::from("blork.rs").into());
        assert_eq!(fmabp1.pos, BytePos(23));

        let fmabp1 = cm.lookup_byte_offset(BytePos(24));
        assert_eq!(fmabp1.fm.name, PathBuf::from("empty.rs").into());
        assert_eq!(fmabp1.pos, BytePos(0));

        let fmabp2 = cm.lookup_byte_offset(BytePos(25));
        assert_eq!(fmabp2.fm.name, PathBuf::from("blork2.rs").into());
        assert_eq!(fmabp2.pos, BytePos(0));
    }

    #[test]
    fn t4() {
        // Test bytepos_to_file_charpos
        let cm = init_code_map();

        let cp1 = cm.bytepos_to_file_charpos(BytePos(22));
        assert_eq!(cp1, CharPos(22));

        let cp2 = cm.bytepos_to_file_charpos(BytePos(25));
        assert_eq!(cp2, CharPos(0));
    }

    #[test]
    fn t5() {
        // Test zero-length filemaps.
        let cm = init_code_map();

        let loc1 = cm.lookup_char_pos(BytePos(22));
        assert_eq!(loc1.file.name, PathBuf::from("blork.rs").into());
        assert_eq!(loc1.line, 2);
        assert_eq!(loc1.col, CharPos(10));

        let loc2 = cm.lookup_char_pos(BytePos(25));
        assert_eq!(loc2.file.name, PathBuf::from("blork2.rs").into());
        assert_eq!(loc2.line, 1);
        assert_eq!(loc2.col, CharPos(0));
    }

    fn init_code_map_mbc() -> CodeMap {
        let cm = CodeMap::new(FilePathMapping::empty());
        // € is a three byte utf8 char.
        let fm1 =
            cm.new_filemap(PathBuf::from("blork.rs").into(),
                           "fir€st €€€€ line.\nsecond line".to_string());
        let fm2 = cm.new_filemap(PathBuf::from("blork2.rs").into(),
                                 "first line€€.\n€ second line".to_string());

        fm1.next_line(BytePos(0));
        fm1.next_line(BytePos(28));
        fm2.next_line(fm2.start_pos);
        fm2.next_line(fm2.start_pos + BytePos(20));

        fm1.record_multibyte_char(BytePos(3), 3);
        fm1.record_multibyte_char(BytePos(9), 3);
        fm1.record_multibyte_char(BytePos(12), 3);
        fm1.record_multibyte_char(BytePos(15), 3);
        fm1.record_multibyte_char(BytePos(18), 3);
        fm2.record_multibyte_char(fm2.start_pos + BytePos(10), 3);
        fm2.record_multibyte_char(fm2.start_pos + BytePos(13), 3);
        fm2.record_multibyte_char(fm2.start_pos + BytePos(18), 3);

        cm
    }

    #[test]
    fn t6() {
        // Test bytepos_to_file_charpos in the presence of multi-byte chars
        let cm = init_code_map_mbc();

        let cp1 = cm.bytepos_to_file_charpos(BytePos(3));
        assert_eq!(cp1, CharPos(3));

        let cp2 = cm.bytepos_to_file_charpos(BytePos(6));
        assert_eq!(cp2, CharPos(4));

        let cp3 = cm.bytepos_to_file_charpos(BytePos(56));
        assert_eq!(cp3, CharPos(12));

        let cp4 = cm.bytepos_to_file_charpos(BytePos(61));
        assert_eq!(cp4, CharPos(15));
    }

    #[test]
    fn t7() {
        // Test span_to_lines for a span ending at the end of filemap
        let cm = init_code_map();
        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
        let file_lines = cm.span_to_lines(span).unwrap();

        assert_eq!(file_lines.file.name, PathBuf::from("blork.rs").into());
        assert_eq!(file_lines.lines.len(), 1);
        assert_eq!(file_lines.lines[0].line_index, 1);
    }

    /// Given a string like " ~~~~~~~~~~~~ ", produces a span
    /// converting that range. The idea is that the string has the same
    /// length as the input, and we uncover the byte positions.  Note
    /// that this can span lines and so on.
    fn span_from_selection(input: &str, selection: &str) -> Span {
        assert_eq!(input.len(), selection.len());
        let left_index = selection.find('~').unwrap() as u32;
        let right_index = selection.rfind('~').map(|x|x as u32).unwrap_or(left_index);
        Span::new(BytePos(left_index), BytePos(right_index + 1), NO_EXPANSION)
    }

    /// Test span_to_snippet and span_to_lines for a span converting 3
    /// lines in the middle of a file.
    #[test]
    fn span_to_snippet_and_lines_spanning_multiple_lines() {
        let cm = CodeMap::new(FilePathMapping::empty());
        let inputtext = "aaaaa\nbbbbBB\nCCC\nDDDDDddddd\neee\n";
        let selection = "     \n    ~~\n~~~\n~~~~~     \n   \n";
        cm.new_filemap_and_lines(Path::new("blork.rs"), inputtext);
        let span = span_from_selection(inputtext, selection);

        // check that we are extracting the text we thought we were extracting
        assert_eq!(&cm.span_to_snippet(span).unwrap(), "BB\nCCC\nDDDDD");

        // check that span_to_lines gives us the complete result with the lines/cols we expected
        let lines = cm.span_to_lines(span).unwrap();
        let expected = vec![
            LineInfo { line_index: 1, start_col: CharPos(4), end_col: CharPos(6) },
            LineInfo { line_index: 2, start_col: CharPos(0), end_col: CharPos(3) },
            LineInfo { line_index: 3, start_col: CharPos(0), end_col: CharPos(5) }
            ];
        assert_eq!(lines.lines, expected);
    }

    #[test]
    fn t8() {
        // Test span_to_snippet for a span ending at the end of filemap
        let cm = init_code_map();
        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
        let snippet = cm.span_to_snippet(span);

        assert_eq!(snippet, Ok("second line".to_string()));
    }

    #[test]
    fn t9() {
        // Test span_to_str for a span ending at the end of filemap
        let cm = init_code_map();
        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
        let sstr =  cm.span_to_string(span);

        assert_eq!(sstr, "blork.rs:2:1: 2:12");
    }

    /// Test failing to merge two spans on different lines
    #[test]
    fn span_merging_fail() {
        let cm = CodeMap::new(FilePathMapping::empty());
        let inputtext  = "bbbb BB\ncc CCC\n";
        let selection1 = "     ~~\n      \n";
        let selection2 = "       \n   ~~~\n";
        cm.new_filemap_and_lines(Path::new("blork.rs"), inputtext);
        let span1 = span_from_selection(inputtext, selection1);
        let span2 = span_from_selection(inputtext, selection2);

        assert!(cm.merge_spans(span1, span2).is_none());
    }

    /// Returns the span corresponding to the `n`th occurrence of
    /// `substring` in `source_text`.
    trait CodeMapExtension {
        fn span_substr(&self,
                    file: &Rc<FileMap>,
                    source_text: &str,
                    substring: &str,
                    n: usize)
                    -> Span;
    }

    impl CodeMapExtension for CodeMap {
        fn span_substr(&self,
                    file: &Rc<FileMap>,
                    source_text: &str,
                    substring: &str,
                    n: usize)
                    -> Span
        {
            println!("span_substr(file={:?}/{:?}, substring={:?}, n={})",
                    file.name, file.start_pos, substring, n);
            let mut i = 0;
            let mut hi = 0;
            loop {
                let offset = source_text[hi..].find(substring).unwrap_or_else(|| {
                    panic!("source_text `{}` does not have {} occurrences of `{}`, only {}",
                        source_text, n, substring, i);
                });
                let lo = hi + offset;
                hi = lo + substring.len();
                if i == n {
                    let span = Span::new(
                        BytePos(lo as u32 + file.start_pos.0),
                        BytePos(hi as u32 + file.start_pos.0),
                        NO_EXPANSION,
                    );
                    assert_eq!(&self.span_to_snippet(span).unwrap()[..],
                            substring);
                    return span;
                }
                i += 1;
            }
        }
    }
}