Pretty-printed diagnostics with traceback

21 files changed, 510 insertions, 332 deletions

diff --git a/src/diag.rs b/src/diag.rs
index 76d7c6b7..397a833f 100644
--- a/src/diag.rs
+++ b/src/diag.rs
@@ -16,10 +16,21 @@ pub type StrResult<T> = Result<T, String>;
 pub struct Error {
     /// The file that contains the error.
     pub file: FileId,
-    /// The erronous location in the source code.
+    /// The erroneous location in the source code.
     pub span: Span,
     /// A diagnostic message describing the problem.
     pub message: String,
+    /// The trace of function calls leading to the error.
+    pub trace: Vec<(FileId, Span, Tracepoint)>,
+}
+
+/// A part of an error's [trace](Error::trace).
+#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
+pub enum Tracepoint {
+    /// A function call.
+    Call(Option<String>),
+    /// A module import.
+    Import,
 }
 
 impl Error {
@@ -28,6 +39,7 @@ impl Error {
         Self {
             file,
             span: span.into(),
+            trace: vec![],
             message: message.into(),
         }
     }
diff --git a/src/eval/capture.rs b/src/eval/capture.rs
index 10f7ec83..a6e543f9 100644
--- a/src/eval/capture.rs
+++ b/src/eval/capture.rs
@@ -43,8 +43,8 @@ impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
         }
     }
 
-    fn visit_binding(&mut self, id: &'ast Ident) {
-        self.internal.def_mut(id.as_str(), Value::None);
+    fn visit_binding(&mut self, ident: &'ast Ident) {
+        self.internal.def_mut(ident.as_str(), Value::None);
     }
 
     fn visit_enter(&mut self) {
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index decd4281..8f5532eb 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -25,11 +25,12 @@ use std::mem;
 use std::path::Path;
 use std::rc::Rc;
 
-use crate::diag::{Error, StrResult, TypResult};
+use crate::diag::{Error, StrResult, Tracepoint, TypResult};
 use crate::geom::{Angle, Fractional, Length, Relative};
 use crate::image::ImageCache;
 use crate::loading::{FileId, Loader};
 use crate::parse::parse;
+use crate::source::{SourceFile, SourceMap};
 use crate::syntax::visit::Visit;
 use crate::syntax::*;
 use crate::util::EcoString;
@@ -67,6 +68,8 @@ pub trait Eval {
 pub struct EvalContext<'a> {
     /// The loader from which resources (files and images) are loaded.
     pub loader: &'a dyn Loader,
+    /// The store for source files.
+    pub sources: &'a mut SourceMap,
     /// The cache for decoded images.
     pub images: &'a mut ImageCache,
     /// The cache for loaded modules.
@@ -86,6 +89,7 @@ impl<'a> EvalContext<'a> {
     pub fn new(ctx: &'a mut Context, file: FileId) -> Self {
         Self {
             loader: ctx.loader.as_ref(),
+            sources: &mut ctx.sources,
             images: &mut ctx.images,
             modules: &mut ctx.modules,
             scopes: Scopes::new(Some(&ctx.std)),
@@ -106,49 +110,58 @@ impl<'a> EvalContext<'a> {
 
     /// Process an import of a module relative to the current location.
     pub fn import(&mut self, path: &str, span: Span) -> TypResult<FileId> {
-        let id = self.resolve(path, span)?;
+        let file = self.resolve(path, span)?;
 
         // Prevent cyclic importing.
-        if self.file == id || self.route.contains(&id) {
+        if self.file == file || self.route.contains(&file) {
             bail!(self.file, span, "cyclic import");
         }
 
         // Check whether the module was already loaded.
-        if self.modules.get(&id).is_some() {
-            return Ok(id);
+        if self.modules.get(&file).is_some() {
+            return Ok(file);
         }
 
         // Load the source file.
         let buffer = self
             .loader
-            .load_file(id)
+            .load_file(file)
             .map_err(|_| Error::boxed(self.file, span, "failed to load file"))?;
 
         // Decode UTF-8.
-        let string = std::str::from_utf8(&buffer)
+        let string = String::from_utf8(buffer)
             .map_err(|_| Error::boxed(self.file, span, "file is not valid utf-8"))?;
 
         // Parse the file.
-        let ast = parse(id, string)?;
+        let source = self.sources.insert(SourceFile::new(file, string));
+        let ast = parse(&source)?;
 
         // Prepare the new context.
         let new_scopes = Scopes::new(self.scopes.base);
         let old_scopes = mem::replace(&mut self.scopes, new_scopes);
         self.route.push(self.file);
-        self.file = id;
+        self.file = file;
 
         // Evaluate the module.
-        let template = Rc::new(ast).eval(self)?;
+        let result = Rc::new(ast).eval(self);
 
         // Restore the old context.
         let new_scopes = mem::replace(&mut self.scopes, old_scopes);
         self.file = self.route.pop().unwrap();
 
+        // Add a tracepoint to the errors.
+        let template = result.map_err(|mut errors| {
+            for error in errors.iter_mut() {
+                error.trace.push((self.file, span, Tracepoint::Import));
+            }
+            errors
+        })?;
+
         // Save the evaluated module.
         let module = Module { scope: new_scopes.top, template };
-        self.modules.insert(id, module);
+        self.modules.insert(file, module);
 
-        Ok(id)
+        Ok(file)
     }
 }
 
@@ -399,7 +412,22 @@ impl Eval for CallExpr {
             .map_err(Error::partial(ctx.file, self.callee.span()))?;
 
         let mut args = self.args.eval(ctx)?;
-        let returned = callee(ctx, &mut args)?;
+        let returned = callee(ctx, &mut args).map_err(|mut errors| {
+            for error in errors.iter_mut() {
+                // Skip errors directly related to arguments.
+                if error.file == ctx.file && self.span.contains(error.span) {
+                    continue;
+                }
+
+                error.trace.push((
+                    ctx.file,
+                    self.span,
+                    Tracepoint::Call(callee.name().map(Into::into)),
+                ));
+            }
+            errors
+        })?;
+
         args.finish()?;
 
         Ok(returned)
@@ -445,6 +473,7 @@ impl Eval for ClosureExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
+        let file = ctx.file;
         let params = Rc::clone(&self.params);
         let body = Rc::clone(&self.body);
 
@@ -459,7 +488,8 @@ impl Eval for ClosureExpr {
         let func = Function::new(name, move |ctx, args| {
             // Don't leak the scopes from the call site. Instead, we use the
             // scope of captured variables we collected earlier.
-            let prev = mem::take(&mut ctx.scopes);
+            let prev_scopes = mem::take(&mut ctx.scopes);
+            let prev_file = mem::replace(&mut ctx.file, file);
             ctx.scopes.top = captured.clone();
 
             for param in params.iter() {
@@ -468,7 +498,8 @@ impl Eval for ClosureExpr {
             }
 
             let result = body.eval(ctx);
-            ctx.scopes = prev;
+            ctx.scopes = prev_scopes;
+            ctx.file = prev_file;
             result
         });
 
@@ -630,8 +661,8 @@ impl Eval for ImportExpr {
             .cast::<EcoString>()
             .map_err(Error::partial(ctx.file, self.path.span()))?;
 
-        let id = ctx.import(&path, self.path.span())?;
-        let module = &ctx.modules[&id];
+        let file = ctx.import(&path, self.path.span())?;
+        let module = &ctx.modules[&file];
 
         match &self.imports {
             Imports::Wildcard => {
@@ -664,8 +695,8 @@ impl Eval for IncludeExpr {
             .cast::<EcoString>()
             .map_err(Error::partial(ctx.file, self.path.span()))?;
 
-        let id = ctx.import(&path, self.path.span())?;
-        let module = &ctx.modules[&id];
+        let file = ctx.import(&path, self.path.span())?;
+        let module = &ctx.modules[&file];
 
         Ok(Value::Template(module.template.clone()))
     }
diff --git a/src/font.rs b/src/font.rs
index 94548699..a609e934 100644
--- a/src/font.rs
+++ b/src/font.rs
@@ -325,12 +325,12 @@ impl FaceId {
     ///
     /// This should only be called with values returned by
     /// [`into_raw`](Self::into_raw).
-    pub fn from_raw(v: u64) -> Self {
+    pub const fn from_raw(v: u64) -> Self {
         Self(v)
     }
 
     /// Convert into the raw underlying value.
-    pub fn into_raw(self) -> u64 {
+    pub const fn into_raw(self) -> u64 {
         self.0
     }
 }
diff --git a/src/image.rs b/src/image.rs
index 93b95bda..f041fac1 100644
--- a/src/image.rs
+++ b/src/image.rs
@@ -112,12 +112,12 @@ impl ImageId {
     ///
     /// This should only be called with values returned by
     /// [`into_raw`](Self::into_raw).
-    pub fn from_raw(v: u64) -> Self {
+    pub const fn from_raw(v: u64) -> Self {
         Self(v)
     }
 
     /// Convert into the raw underlying value.
-    pub fn into_raw(self) -> u64 {
+    pub const fn into_raw(self) -> u64 {
         self.0
     }
 }
diff --git a/src/layout/frame.rs b/src/layout/frame.rs
index 82ac71a9..6d5cc2f3 100644
--- a/src/layout/frame.rs
+++ b/src/layout/frame.rs
@@ -146,9 +146,8 @@ impl Text {
     pub fn encode_glyphs_be(&self) -> Vec<u8> {
         let mut bytes = Vec::with_capacity(2 * self.glyphs.len());
         for glyph in &self.glyphs {
-            let id = glyph.id;
-            bytes.push((id >> 8) as u8);
-            bytes.push((id & 0xff) as u8);
+            bytes.push((glyph.id >> 8) as u8);
+            bytes.push((glyph.id & 0xff) as u8);
         }
         bytes
     }
diff --git a/src/layout/incremental.rs b/src/layout/incremental.rs
index e7d12d10..32353d6f 100644
--- a/src/layout/incremental.rs
+++ b/src/layout/incremental.rs
@@ -8,7 +8,7 @@ use super::*;
 ///
 /// _This is only available when the `layout-cache` feature is enabled._
 #[cfg(feature = "layout-cache")]
-#[derive(Debug, Default, Clone)]
+#[derive(Default, Clone)]
 pub struct LayoutCache {
     /// Maps from node hashes to the resulting frames and regions in which the
     /// frames are valid. The right hand side of the hash map is a vector of
@@ -70,9 +70,9 @@ impl LayoutCache {
     ) {
         let entry = FramesEntry::new(frames, level);
         match self.frames.entry(hash) {
-            Entry::Occupied(o) => o.into_mut().push(entry),
-            Entry::Vacant(v) => {
-                v.insert(vec![entry]);
+            Entry::Occupied(occupied) => occupied.into_mut().push(entry),
+            Entry::Vacant(vacant) => {
+                vacant.insert(vec![entry]);
             }
         }
     }
diff --git a/src/lib.rs b/src/lib.rs
index be99fb58..0f556989 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,6 +44,7 @@ pub mod loading;
 pub mod paper;
 pub mod parse;
 pub mod pretty;
+pub mod source;
 pub mod syntax;
 pub mod util;
 
@@ -57,18 +58,21 @@ use crate::image::ImageCache;
 use crate::layout::Frame;
 #[cfg(feature = "layout-cache")]
 use crate::layout::LayoutCache;
-use crate::loading::{FileId, Loader};
+use crate::loading::Loader;
+use crate::source::{SourceFile, SourceMap};
 
 /// The core context which holds the loader, configuration and cached artifacts.
 pub struct Context {
     /// The loader the context was created with.
     pub loader: Rc<dyn Loader>,
+    /// Stores loaded source files.
+    pub sources: SourceMap,
+    /// Caches evaluated modules.
+    pub modules: ModuleCache,
     /// Caches parsed font faces.
     pub fonts: FontCache,
     /// Caches decoded images.
     pub images: ImageCache,
-    /// Caches evaluated modules.
-    pub modules: ModuleCache,
     /// Caches layouting artifacts.
     #[cfg(feature = "layout-cache")]
     pub layouts: LayoutCache,
@@ -97,15 +101,12 @@ impl Context {
 
     /// Typeset a source file into a collection of layouted frames.
     ///
-    /// The `file` identifies the source file and is used to resolve relative
-    /// paths (for importing and image loading).
-    ///
     /// Returns either a vector of frames representing individual pages or
     /// diagnostics in the form of a vector of error message with file and span
     /// information.
-    pub fn typeset(&mut self, file: FileId, src: &str) -> TypResult<Vec<Rc<Frame>>> {
-        let ast = parse::parse(file, src)?;
-        let module = eval::eval(self, file, Rc::new(ast))?;
+    pub fn typeset(&mut self, source: &SourceFile) -> TypResult<Vec<Rc<Frame>>> {
+        let ast = parse::parse(source)?;
+        let module = eval::eval(self, source.file(), Rc::new(ast))?;
         let tree = exec::exec(self, &module.template);
         let frames = layout::layout(self, &tree);
         Ok(frames)
@@ -140,6 +141,7 @@ impl ContextBuilder {
     pub fn build(self, loader: Rc<dyn Loader>) -> Context {
         Context {
             loader: Rc::clone(&loader),
+            sources: SourceMap::new(),
             fonts: FontCache::new(Rc::clone(&loader)),
             images: ImageCache::new(loader),
             modules: ModuleCache::new(),
diff --git a/src/loading/fs.rs b/src/loading/fs.rs
index d41a7dc1..c3ca332e 100644
--- a/src/loading/fs.rs
+++ b/src/loading/fs.rs
@@ -1,4 +1,4 @@
-use std::cell::RefCell;
+use std::cell::{Ref, RefCell};
 use std::collections::HashMap;
 use std::fs::{self, File};
 use std::io;
@@ -92,6 +92,11 @@ impl FsLoader {
         }
     }
 
+    /// Return the path of a resolved file.
+    pub fn path(&self, id: FileId) -> Ref<Path> {
+        Ref::map(self.paths.borrow(), |paths| paths[&id].as_path())
+    }
+
     #[cfg(all(unix, not(target_os = "macos")))]
     fn search_system_impl(&mut self) {
         self.search_path("/usr/share/fonts");
diff --git a/src/loading/mod.rs b/src/loading/mod.rs
index ab52439d..65eb25c6 100644
--- a/src/loading/mod.rs
+++ b/src/loading/mod.rs
@@ -40,12 +40,12 @@ pub struct FileId(u64);
 
 impl FileId {
     /// Create a file id from a raw value.
-    pub fn from_raw(v: u64) -> Self {
+    pub const fn from_raw(v: u64) -> Self {
         Self(v)
     }
 
     /// Convert into the raw underlying value.
-    pub fn into_raw(self) -> u64 {
+    pub const fn into_raw(self) -> u64 {
         self.0
     }
 }
diff --git a/src/main.rs b/src/main.rs
index 7891082d..51a6d833 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,14 +1,33 @@
 use std::fs;
+use std::io::{self, Write};
+use std::ops::Range;
 use std::path::{Path, PathBuf};
+use std::process;
 
 use anyhow::{anyhow, bail, Context};
+use codespan_reporting::diagnostic::{Diagnostic, Label};
+use codespan_reporting::files::{self, Files};
+use codespan_reporting::term::{self, termcolor, Config, Styles};
 use same_file::is_same_file;
+use termcolor::{ColorChoice, StandardStream, WriteColor};
 
-fn main() -> anyhow::Result<()> {
+use typst::diag::{Error, Tracepoint};
+use typst::loading::{FileId, FsLoader};
+use typst::source::{SourceFile, SourceMap};
+
+fn main() {
+    if let Err(error) = try_main() {
+        print_error(error).unwrap();
+        process::exit(1);
+    }
+}
+
+/// The main compiler logic.
+fn try_main() -> anyhow::Result<()> {
     let args: Vec<_> = std::env::args().collect();
     if args.len() < 2 || args.len() > 3 {
-        println!("usage: typst src.typ [out.pdf]");
-        return Ok(());
+        print_usage().unwrap();
+        process::exit(2);
     }
 
     // Determine source and destination path.
@@ -36,12 +55,12 @@ fn main() -> anyhow::Result<()> {
 
     // Resolve the file id of the source file and read the file.
     let file = loader.resolve(src_path).context("source file not found")?;
-    let src = fs::read_to_string(&src_path)
-        .map_err(|_| anyhow!("failed to read source file"))?;
+    let string = fs::read_to_string(&src_path).context("failed to read source file")?;
+    let source = SourceFile::new(file, string);
 
     // Typeset.
-    let mut ctx = typst::Context::new(loader);
-    match ctx.typeset(file, &src) {
+    let mut ctx = typst::Context::new(loader.clone());
+    match ctx.typeset(&source) {
         // Export the PDF.
         Ok(document) => {
             let buffer = typst::export::pdf(&ctx, &document);
@@ -50,20 +69,132 @@ fn main() -> anyhow::Result<()> {
 
         // Print diagnostics.
         Err(errors) => {
-            let map = typst::parse::LineMap::new(&src);
-            for error in errors.iter() {
-                let start = map.location(error.span.start).unwrap();
-                let end = map.location(error.span.end).unwrap();
-                println!(
-                    "Error: {}:{}-{}: {}",
-                    src_path.display(),
-                    start,
-                    end,
-                    error.message,
-                );
-            }
+            ctx.sources.insert(source);
+            print_diagnostics(&loader, &ctx.sources, *errors)
+                .context("failed to print diagnostics")?;
+        }
+    }
+
+    Ok(())
+}
+
+/// Print a usage message.
+fn print_usage() -> io::Result<()> {
+    let mut writer = StandardStream::stderr(ColorChoice::Always);
+    let styles = Styles::default();
+
+    writer.set_color(&styles.header_help)?;
+    write!(writer, "usage")?;
+
+    writer.set_color(&styles.header_message)?;
+    writeln!(writer, ": typst document.typ [output.pdf]")?;
+
+    writer.reset()
+}
+
+/// Print an error outside of a source file.
+fn print_error(error: anyhow::Error) -> io::Result<()> {
+    let mut writer = StandardStream::stderr(ColorChoice::Always);
+    let styles = Styles::default();
+
+    for (i, cause) in error.chain().enumerate() {
+        writer.set_color(&styles.header_error)?;
+        write!(writer, "{}", if i == 0 { "error" } else { "cause" })?;
+
+        writer.set_color(&styles.header_message)?;
+        writeln!(writer, ": {}", cause)?;
+    }
+
+    writer.reset()
+}
+
+/// Print diagnostics messages to the terminal.
+fn print_diagnostics(
+    loader: &FsLoader,
+    sources: &SourceMap,
+    errors: Vec<Error>,
+) -> Result<(), files::Error> {
+    let mut writer = StandardStream::stderr(ColorChoice::Always);
+    let config = Config { tab_width: 2, ..Default::default() };
+    let files = FilesImpl(loader, sources);
+
+    for error in errors {
+        // The main diagnostic.
+        let main = Diagnostic::error()
+            .with_message(error.message)
+            .with_labels(vec![Label::primary(error.file, error.span.to_range())]);
+
+        term::emit(&mut writer, &config, &files, &main)?;
+
+        // Stacktrace-like helper diagnostics.
+        for (file, span, point) in error.trace {
+            let message = match point {
+                Tracepoint::Call(Some(name)) => {
+                    format!("error occured in this call of function `{}`", name)
+                }
+                Tracepoint::Call(None) => "error occured in this function call".into(),
+                Tracepoint::Import => "error occured while importing this module".into(),
+            };
+
+            let help = Diagnostic::help()
+                .with_message(message)
+                .with_labels(vec![Label::primary(file, span.to_range())]);
+
+            term::emit(&mut writer, &config, &files, &help)?;
         }
     }
 
     Ok(())
 }
+
+/// Required for error message formatting with codespan-reporting.
+struct FilesImpl<'a>(&'a FsLoader, &'a SourceMap);
+
+impl FilesImpl<'_> {
+    fn source(&self, id: FileId) -> Result<&SourceFile, files::Error> {
+        self.1.get(id).ok_or(files::Error::FileMissing)
+    }
+}
+
+impl<'a> Files<'a> for FilesImpl<'a> {
+    type FileId = FileId;
+    type Name = String;
+    type Source = &'a str;
+
+    fn name(&'a self, id: FileId) -> Result<Self::Name, files::Error> {
+        Ok(self.0.path(id).display().to_string())
+    }
+
+    fn source(&'a self, id: FileId) -> Result<Self::Source, files::Error> {
+        Ok(self.source(id)?.src())
+    }
+
+    fn line_index(
+        &'a self,
+        id: FileId,
+        byte_index: usize,
+    ) -> Result<usize, files::Error> {
+        let source = self.source(id)?;
+        source.pos_to_line(byte_index.into()).ok_or_else(|| {
+            let (given, max) = (byte_index, source.len_bytes());
+            if given <= max {
+                files::Error::InvalidCharBoundary { given }
+            } else {
+                files::Error::IndexTooLarge { given, max }
+            }
+        })
+    }
+
+    fn line_range(
+        &'a self,
+        id: FileId,
+        line_index: usize,
+    ) -> Result<Range<usize>, files::Error> {
+        let source = self.source(id)?;
+        let span = source.line_to_span(line_index).ok_or(files::Error::LineTooLarge {
+            given: line_index,
+            max: source.len_lines(),
+        })?;
+        Ok(span.to_range())
+    }
+}
diff --git a/src/parse/lines.rs b/src/parse/lines.rs
deleted file mode 100644
index 2d97a25c..00000000
--- a/src/parse/lines.rs
+++ /dev/null
@@ -1,145 +0,0 @@
-// FIXME:
-// Both `LineMap::location` and `search_column` can lead to quadratic compile
-// times for very long lines. We probably need some smart acceleration structure
-// to determine columns.
-
-use super::Scanner;
-use crate::syntax::{Location, Pos};
-
-/// Enables conversion of byte position to locations.
-pub struct LineMap<'s> {
-    src: &'s str,
-    line_starts: Vec<Pos>,
-}
-
-impl<'s> LineMap<'s> {
-    /// Create a new line map for a source string.
-    pub fn new(src: &'s str) -> Self {
-        let mut line_starts = vec![Pos::ZERO];
-        let mut s = Scanner::new(src);
-
-        while let Some(c) = s.eat_merging_crlf() {
-            if is_newline(c) {
-                line_starts.push(s.index().into());
-            }
-        }
-
-        Self { src, line_starts }
-    }
-
-    /// Convert a byte position to a location.
-    pub fn location(&self, pos: Pos) -> Option<Location> {
-        // Find the line which contains the position.
-        let line_index = match self.line_starts.binary_search(&pos) {
-            Ok(i) => i,
-            Err(i) => i - 1,
-        };
-
-        let start = self.line_starts.get(line_index)?;
-        let head = self.src.get(start.to_usize() .. pos.to_usize())?;
-
-        // TODO: What about tabs?
-        let column_index = head.chars().count();
-
-        Some(Location {
-            line: 1 + line_index as u32,
-            column: 1 + column_index as u32,
-        })
-    }
-
-    /// Convert a location to a byte position.
-    pub fn pos(&self, location: Location) -> Option<Pos> {
-        // Determine the boundaries of the line.
-        let line_idx = location.line.checked_sub(1)? as usize;
-        let line_start = *self.line_starts.get(line_idx)?;
-        let line_end = self
-            .line_starts
-            .get(location.line as usize)
-            .map_or(self.src.len(), |pos| pos.to_usize());
-
-        let line = self.src.get(line_start.to_usize() .. line_end)?;
-
-        // Find the index in the line. For the first column, the index is always
-        // zero. For other columns, we have to look at which byte the char
-        // directly before the column in question ends. We can't do
-        // `nth(column_idx)` directly since the column may be behind the last
-        // char.
-        let column_idx = location.column.checked_sub(1)? as usize;
-        let line_offset = if let Some(prev_idx) = column_idx.checked_sub(1) {
-            // TODO: What about tabs?
-            let (idx, prev) = line.char_indices().nth(prev_idx)?;
-            idx + prev.len_utf8()
-        } else {
-            0
-        };
-
-        Some(line_start + line_offset)
-    }
-}
-
-/// Count how many column the string would fill.
-pub fn count_columns(src: &str) -> usize {
-    let mut column = 0;
-    for c in src.chars().rev() {
-        if is_newline(c) {
-            break;
-        } else if c == '\t' {
-            // TODO: How many columns per tab?
-            column += 2;
-        } else {
-            column += 1;
-        }
-    }
-    column
-}
-
-/// Whether this character denotes a newline.
-#[inline]
-pub fn is_newline(character: char) -> bool {
-    matches!(
-        character,
-        // Line Feed, Vertical Tab, Form Feed, Carriage Return.
-        '\n' | '\x0B' | '\x0C' | '\r' |
-        // Next Line, Line Separator, Paragraph Separator.
-        '\u{0085}' | '\u{2028}' | '\u{2029}'
-    )
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    const TEST: &str = "äbcde\nf💛g\r\nhi\rjkl";
-
-    #[test]
-    fn test_line_map_new() {
-        let map = LineMap::new(TEST);
-        assert_eq!(map.line_starts, vec![Pos(0), Pos(7), Pos(15), Pos(18)]);
-    }
-
-    #[test]
-    fn test_line_map_location() {
-        let map = LineMap::new(TEST);
-        assert_eq!(map.location(Pos(0)), Some(Location::new(1, 1)));
-        assert_eq!(map.location(Pos(2)), Some(Location::new(1, 2)));
-        assert_eq!(map.location(Pos(6)), Some(Location::new(1, 6)));
-        assert_eq!(map.location(Pos(7)), Some(Location::new(2, 1)));
-        assert_eq!(map.location(Pos(8)), Some(Location::new(2, 2)));
-        assert_eq!(map.location(Pos(12)), Some(Location::new(2, 3)));
-        assert_eq!(map.location(Pos(21)), Some(Location::new(4, 4)));
-        assert_eq!(map.location(Pos(22)), None);
-    }
-
-    #[test]
-    fn test_line_map_pos() {
-        fn assert_round_trip(map: &LineMap, pos: Pos) {
-            assert_eq!(map.location(pos).and_then(|loc| map.pos(loc)), Some(pos));
-        }
-
-        let map = LineMap::new(TEST);
-        assert_round_trip(&map, Pos(0));
-        assert_round_trip(&map, Pos(7));
-        assert_round_trip(&map, Pos(12));
-        assert_round_trip(&map, Pos(21));
-    }
-}
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index c103c342..f033e01f 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -1,12 +1,10 @@
 //! Parsing and tokenization.
 
-mod lines;
 mod parser;
 mod resolve;
 mod scanner;
 mod tokens;
 
-pub use lines::*;
 pub use parser::*;
 pub use resolve::*;
 pub use scanner::*;
@@ -15,13 +13,13 @@ pub use tokens::*;
 use std::rc::Rc;
 
 use crate::diag::TypResult;
-use crate::loading::FileId;
+use crate::source::SourceFile;
 use crate::syntax::*;
 use crate::util::EcoString;
 
 /// Parse a string of source code.
-pub fn parse(file: FileId, src: &str) -> TypResult<SyntaxTree> {
-    let mut p = Parser::new(file, src);
+pub fn parse(source: &SourceFile) -> TypResult<SyntaxTree> {
+    let mut p = Parser::new(source);
     let tree = tree(&mut p);
     let errors = p.finish();
     if errors.is_empty() {
diff --git a/src/parse/parser.rs b/src/parse/parser.rs
index 0238c8be..6b478780 100644
--- a/src/parse/parser.rs
+++ b/src/parse/parser.rs
@@ -1,15 +1,15 @@
 use std::fmt::{self, Debug, Formatter};
 use std::ops::Range;
 
-use super::{count_columns, TokenMode, Tokens};
+use super::{TokenMode, Tokens};
 use crate::diag::Error;
-use crate::loading::FileId;
+use crate::source::SourceFile;
 use crate::syntax::{Pos, Span, Token};
 
 /// A convenient token-based parser.
 pub struct Parser<'s> {
     /// The id of the parsed file.
-    file: FileId,
+    source: &'s SourceFile,
     /// Parsing errors.
     errors: Vec<Error>,
     /// An iterator over the source tokens.
@@ -60,11 +60,11 @@ pub enum Group {
 
 impl<'s> Parser<'s> {
     /// Create a new parser for the source string.
-    pub fn new(file: FileId, src: &'s str) -> Self {
-        let mut tokens = Tokens::new(src, TokenMode::Markup);
+    pub fn new(source: &'s SourceFile) -> Self {
+        let mut tokens = Tokens::new(source.src(), TokenMode::Markup);
         let next = tokens.next();
         Self {
-            file,
+            source,
             errors: vec![],
             tokens,
             groups: vec![],
@@ -82,11 +82,7 @@ impl<'s> Parser<'s> {
 
     /// Add an error with location and message.
     pub fn error(&mut self, span: impl Into<Span>, message: impl Into<String>) {
-        self.errors.push(Error {
-            file: self.file,
-            span: span.into(),
-            message: message.into(),
-        });
+        self.errors.push(Error::new(self.source.file(), span, message));
     }
 
     /// Eat the next token and add an error that it is not the expected `thing`.
@@ -324,7 +320,7 @@ impl<'s> Parser<'s> {
 
     /// Determine the column for the given index in the source.
     pub fn column(&self, index: usize) -> usize {
-        count_columns(self.tokens.scanner().get(.. index))
+        self.source.pos_to_column(index.into()).unwrap()
     }
 
     /// The span from `start` to [`self.prev_end()`](Self::prev_end).
diff --git a/src/parse/resolve.rs b/src/parse/resolve.rs
index f97d5383..7bd160f9 100644
--- a/src/parse/resolve.rs
+++ b/src/parse/resolve.rs
@@ -109,8 +109,11 @@ fn split_lines(text: &str) -> Vec<String> {
     let mut line = String::new();
     let mut lines = Vec::new();
 
-    while let Some(c) = s.eat_merging_crlf() {
+    while let Some(c) = s.eat() {
         if is_newline(c) {
+            if c == '\r' {
+                s.eat_if('\n');
+            }
             lines.push(std::mem::take(&mut line));
         } else {
             line.push(c);
@@ -173,14 +176,10 @@ mod tests {
             text: &str,
             block: bool,
         ) {
-            Span::without_cmp(|| {
-                assert_eq!(resolve_raw(Span::ZERO, raw, backticks), RawNode {
-                    span: Span::ZERO,
-                    lang: lang.and_then(|id| Ident::new(id, 0)),
-                    text: text.into(),
-                    block,
-                });
-            });
+            let node = resolve_raw(Span::ZERO, raw, backticks);
+            assert_eq!(node.lang.as_deref(), lang);
+            assert_eq!(node.text, text);
+            assert_eq!(node.block, block);
         }
 
         // Just one backtick.
diff --git a/src/parse/scanner.rs b/src/parse/scanner.rs
index 9ee7641c..bb827255 100644
--- a/src/parse/scanner.rs
+++ b/src/parse/scanner.rs
@@ -47,17 +47,6 @@ impl<'s> Scanner<'s> {
         debug_assert_eq!(next, Some(c));
     }
 
-    /// Consume the next char, coalescing `\r\n` to just `\n`.
-    #[inline]
-    pub fn eat_merging_crlf(&mut self) -> Option<char> {
-        if self.rest().starts_with("\r\n") {
-            self.index += 2;
-            Some('\n')
-        } else {
-            self.eat()
-        }
-    }
-
     /// Eat chars while the condition is true.
     #[inline]
     pub fn eat_while<F>(&mut self, mut f: F) -> &'s str
@@ -168,3 +157,15 @@ impl Debug for Scanner<'_> {
         write!(f, "Scanner({}|{})", self.eaten(), self.rest())
     }
 }
+
+/// Whether this character denotes a newline.
+#[inline]
+pub fn is_newline(character: char) -> bool {
+    matches!(
+        character,
+        // Line Feed, Vertical Tab, Form Feed, Carriage Return.
+        '\n' | '\x0B' | '\x0C' | '\r' |
+        // Next Line, Line Separator, Paragraph Separator.
+        '\u{0085}' | '\u{2028}' | '\u{2029}'
+    )
+}
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 356a2f96..9fd13ecc 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -198,13 +198,16 @@ impl<'s> Tokens<'s> {
 
         // Count the number of newlines.
         let mut newlines = 0;
-        while let Some(c) = self.s.eat_merging_crlf() {
+        while let Some(c) = self.s.eat() {
             if !c.is_whitespace() {
                 self.s.uneat();
                 break;
             }
 
             if is_newline(c) {
+                if c == '\r' {
+                    self.s.eat_if('\n');
+                }
                 newlines += 1;
             }
         }
@@ -484,8 +487,8 @@ impl Debug for Tokens<'_> {
     }
 }
 
-fn keyword(id: &str) -> Option<Token<'static>> {
-    Some(match id {
+fn keyword(ident: &str) -> Option<Token<'static>> {
+    Some(match ident {
         "not" => Token::Not,
         "and" => Token::And,
         "or" => Token::Or,
diff --git a/src/pretty.rs b/src/pretty.rs
index a4e9b334..2f3a6ef9 100644
--- a/src/pretty.rs
+++ b/src/pretty.rs
@@ -610,6 +610,7 @@ mod tests {
     use super::*;
     use crate::loading::FileId;
     use crate::parse::parse;
+    use crate::source::SourceFile;
 
     #[track_caller]
     fn roundtrip(src: &str) {
@@ -618,7 +619,8 @@ mod tests {
 
     #[track_caller]
     fn test_parse(src: &str, exp: &str) {
-        let ast = parse(FileId::from_raw(0), src).unwrap();
+        let source = SourceFile::new(FileId::from_raw(0), src.into());
+        let ast = parse(&source).unwrap();
         let found = pretty(&ast);
         if exp != found {
             println!("tree:     {:#?}", ast);
diff --git a/src/source.rs b/src/source.rs
new file mode 100644
index 00000000..abd3c246
--- /dev/null
+++ b/src/source.rs
@@ -0,0 +1,195 @@
+//! Source files.
+
+use std::collections::{hash_map::Entry, HashMap};
+
+use crate::loading::FileId;
+use crate::parse::{is_newline, Scanner};
+use crate::syntax::{Pos, Span};
+
+/// A store for loaded source files.
+#[derive(Default)]
+pub struct SourceMap {
+    sources: HashMap<FileId, SourceFile>,
+}
+
+impl SourceMap {
+    /// Create a new, empty source map
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Get a source file by id.
+    pub fn get(&self, file: FileId) -> Option<&SourceFile> {
+        self.sources.get(&file)
+    }
+
+    /// Insert a sources.
+    pub fn insert(&mut self, source: SourceFile) -> &SourceFile {
+        match self.sources.entry(source.file) {
+            Entry::Occupied(mut entry) => {
+                entry.insert(source);
+                entry.into_mut()
+            }
+            Entry::Vacant(entry) => entry.insert(source),
+        }
+    }
+
+    /// Remove all sources.
+    pub fn clear(&mut self) {
+        self.sources.clear();
+    }
+}
+
+/// A single source file.
+pub struct SourceFile {
+    file: FileId,
+    src: String,
+    line_starts: Vec<Pos>,
+}
+
+impl SourceFile {
+    /// Create a new source file from  string.
+    pub fn new(file: FileId, src: String) -> Self {
+        let mut line_starts = vec![Pos::ZERO];
+        let mut s = Scanner::new(&src);
+
+        while let Some(c) = s.eat() {
+            if is_newline(c) {
+                if c == '\r' {
+                    s.eat_if('\n');
+                }
+                line_starts.push(s.index().into());
+            }
+        }
+
+        Self { file, src, line_starts }
+    }
+
+    /// The file id.
+    pub fn file(&self) -> FileId {
+        self.file
+    }
+
+    /// The whole source as a string slice.
+    pub fn src(&self) -> &str {
+        &self.src
+    }
+
+    /// Get the length of the file in bytes.
+    pub fn len_bytes(&self) -> usize {
+        self.src.len()
+    }
+
+    /// Get the length of the file in lines.
+    pub fn len_lines(&self) -> usize {
+        self.line_starts.len()
+    }
+
+    /// Slice out the part of the source code enclosed by the span.
+    pub fn get(&self, span: Span) -> Option<&str> {
+        self.src.get(span.to_range())
+    }
+
+    /// Return the index of the line that contains the given byte position.
+    pub fn pos_to_line(&self, byte_pos: Pos) -> Option<usize> {
+        (byte_pos.to_usize() <= self.src.len()).then(|| {
+            match self.line_starts.binary_search(&byte_pos) {
+                Ok(i) => i,
+                Err(i) => i - 1,
+            }
+        })
+    }
+
+    /// Return the column of the byte index.
+    ///
+    /// Tabs are counted as occupying two columns.
+    pub fn pos_to_column(&self, byte_pos: Pos) -> Option<usize> {
+        let line = self.pos_to_line(byte_pos)?;
+        let start = self.line_to_pos(line)?;
+        let head = self.get(Span::new(start, byte_pos))?;
+        Some(head.chars().map(width).sum())
+    }
+
+    /// Return the byte position at which the given line starts.
+    pub fn line_to_pos(&self, line_idx: usize) -> Option<Pos> {
+        self.line_starts.get(line_idx).copied()
+    }
+
+    /// Return the span which encloses the given line.
+    pub fn line_to_span(&self, line_idx: usize) -> Option<Span> {
+        let start = self.line_to_pos(line_idx)?;
+        let end = self.line_to_pos(line_idx + 1).unwrap_or(self.src.len().into());
+        Some(Span::new(start, end))
+    }
+
+    /// Return the byte position of the given (line, column) pair.
+    ///
+    /// Tabs are counted as occupying two columns.
+    pub fn line_column_to_pos(&self, line_idx: usize, column_idx: usize) -> Option<Pos> {
+        let span = self.line_to_span(line_idx)?;
+        let line = self.get(span)?;
+
+        if column_idx == 0 {
+            return Some(span.start);
+        }
+
+        let mut column = 0;
+        for (i, c) in line.char_indices() {
+            column += width(c);
+            if column >= column_idx {
+                return Some(span.start + Pos::from(i + c.len_utf8()));
+            }
+        }
+
+        None
+    }
+}
+
+/// The display width of the character.
+fn width(c: char) -> usize {
+    if c == '\t' { 2 } else { 1 }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const ID: FileId = FileId::from_raw(0);
+    const TEST: &str = "äbcde\nf💛g\r\nhi\rjkl";
+
+    #[test]
+    fn test_source_file_new() {
+        let source = SourceFile::new(ID, TEST.into());
+        assert_eq!(source.line_starts, vec![Pos(0), Pos(7), Pos(15), Pos(18)]);
+    }
+
+    #[test]
+    fn test_source_file_pos_to_line() {
+        let source = SourceFile::new(ID, TEST.into());
+        assert_eq!(source.pos_to_line(Pos(0)), Some(0));
+        assert_eq!(source.pos_to_line(Pos(2)), Some(0));
+        assert_eq!(source.pos_to_line(Pos(6)), Some(0));
+        assert_eq!(source.pos_to_line(Pos(7)), Some(1));
+        assert_eq!(source.pos_to_line(Pos(8)), Some(1));
+        assert_eq!(source.pos_to_line(Pos(12)), Some(1));
+        assert_eq!(source.pos_to_line(Pos(21)), Some(3));
+        assert_eq!(source.pos_to_line(Pos(22)), None);
+    }
+
+    #[test]
+    fn test_source_file_roundtrip() {
+        #[track_caller]
+        fn roundtrip(source: &SourceFile, byte_pos: Pos) {
+            let line = source.pos_to_line(byte_pos).unwrap();
+            let column = source.pos_to_column(byte_pos).unwrap();
+            let result = source.line_column_to_pos(line, column).unwrap();
+            assert_eq!(result, byte_pos);
+        }
+
+        let source = SourceFile::new(ID, TEST.into());
+        roundtrip(&source, Pos(0));
+        roundtrip(&source, Pos(7));
+        roundtrip(&source, Pos(12));
+        roundtrip(&source, Pos(21));
+    }
+}
diff --git a/src/syntax/span.rs b/src/syntax/span.rs
index 8a630faa..800cca19 100644
--- a/src/syntax/span.rs
+++ b/src/syntax/span.rs
@@ -1,13 +1,8 @@
-use std::cell::Cell;
-use std::fmt::{self, Debug, Display, Formatter};
+use std::fmt::{self, Debug, Formatter};
 use std::ops::{Add, Range};
 
 use serde::{Deserialize, Serialize};
 
-thread_local! {
-    static CMP_SPANS: Cell<bool> = Cell::new(true);
-}
-
 /// A value with the span it corresponds to in the source code.
 #[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
 #[derive(Serialize, Deserialize)]
@@ -47,15 +42,17 @@ impl<T: Debug> Debug for Spanned<T> {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         self.v.fmt(f)?;
         if f.alternate() {
-            f.write_str(" ")?;
+            f.write_str(" <")?;
             self.span.fmt(f)?;
+            f.write_str(">")?;
         }
         Ok(())
     }
 }
 
 /// Bounds of a slice of source code.
-#[derive(Copy, Clone, Ord, PartialOrd, Serialize, Deserialize)]
+#[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Serialize, Deserialize)]
 pub struct Span {
     /// The inclusive start position.
     pub start: Pos,
@@ -90,34 +87,15 @@ impl Span {
         *self = self.join(other)
     }
 
+    /// Test whether one span complete contains the other span.
+    pub fn contains(self, other: Self) -> bool {
+        self.start <= other.start && self.end >= other.end
+    }
+
     /// Convert to a `Range<usize>` for indexing.
     pub fn to_range(self) -> Range<usize> {
         self.start.to_usize() .. self.end.to_usize()
     }
-
-    /// Run some code with span comparisons disabled.
-    pub fn without_cmp<F, T>(f: F) -> T
-    where
-        F: FnOnce() -> T,
-    {
-        let prev = Self::cmp();
-        Self::set_cmp(false);
-        let val = f();
-        Self::set_cmp(prev);
-        val
-    }
-
-    /// Whether spans will currently be compared.
-    fn cmp() -> bool {
-        CMP_SPANS.with(Cell::get)
-    }
-
-    /// Whether spans should be compared.
-    ///
-    /// When set to `false` comparisons with `PartialEq` ignore spans.
-    fn set_cmp(cmp: bool) {
-        CMP_SPANS.with(|cell| cell.set(cmp));
-    }
 }
 
 impl<T> From<T> for Span
@@ -138,28 +116,15 @@ where
     }
 }
 
-impl Default for Span {
-    fn default() -> Self {
-        Span::ZERO
-    }
-}
-
 impl Debug for Span {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "<{:?}-{:?}>", self.start, self.end)
-    }
-}
-
-impl Eq for Span {}
-
-impl PartialEq for Span {
-    fn eq(&self, other: &Self) -> bool {
-        !Self::cmp() || (self.start == other.start && self.end == other.end)
+        write!(f, "{:?}-{:?}", self.start, self.end)
     }
 }
 
 /// A byte position in source code.
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
+#[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Serialize, Deserialize)]
 pub struct Pos(pub u32);
 
 impl Pos {
@@ -178,12 +143,6 @@ impl From<u32> for Pos {
     }
 }
 
-impl From<i32> for Pos {
-    fn from(index: i32) -> Self {
-        Self(index as u32)
-    }
-}
-
 impl From<usize> for Pos {
     fn from(index: usize) -> Self {
         Self(index as u32)
@@ -206,31 +165,3 @@ where
         Pos(self.0 + rhs.into().0)
     }
 }
-
-/// A one-indexed line-column position in source code.
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
-pub struct Location {
-    /// The one-indexed line.
-    pub line: u32,
-    /// The one-indexed column.
-    pub column: u32,
-}
-
-impl Location {
-    /// Create a new location from line and column.
-    pub fn new(line: u32, column: u32) -> Self {
-        Self { line, column }
-    }
-}
-
-impl Display for Location {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "{}:{}", self.line, self.column)
-    }
-}
-
-impl Debug for Location {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        Display::fmt(self, f)
-    }
-}
diff --git a/src/util/eco.rs b/src/util/eco.rs
index 7fe1ac9c..00f87872 100644
--- a/src/util/eco.rs
+++ b/src/util/eco.rs
@@ -193,6 +193,24 @@ impl From<&String> for EcoString {
     }
 }
 
+impl From<EcoString> for String {
+    fn from(s: EcoString) -> Self {
+        match s.0 {
+            Repr::Small { .. } => s.as_str().to_owned(),
+            Repr::Large(rc) => match Rc::try_unwrap(rc) {
+                Ok(string) => string,
+                Err(rc) => (*rc).clone(),
+            },
+        }
+    }
+}
+
+impl From<&EcoString> for String {
+    fn from(s: &EcoString) -> Self {
+        s.as_str().to_owned()
+    }
+}
+
 impl Deref for EcoString {
     type Target = str;