Rename directories for some crates from `syntax_x` to `rustc_x`

`syntax_expand` -> `rustc_expand`
`syntax_pos` -> `rustc_span`
`syntax_ext` -> `rustc_builtin_macros`

1 files changed, 1672 insertions, 0 deletions

diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
new file mode 100644
index 00000000000..a58c12f2350
--- /dev/null
+++ b/src/librustc_span/lib.rs
@@ -0,0 +1,1672 @@
+//! The source positions and related helper functions.
+//!
+//! ## Note
+//!
+//! This API is completely unstable and subject to change.
+
+#![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
+#![feature(const_fn)]
+#![feature(crate_visibility_modifier)]
+#![feature(nll)]
+#![feature(optin_builtin_traits)]
+#![feature(rustc_attrs)]
+#![feature(specialization)]
+#![feature(step_trait)]
+
+use rustc_data_structures::AtomicRef;
+use rustc_macros::HashStable_Generic;
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+
+mod caching_source_map_view;
+pub mod source_map;
+pub use self::caching_source_map_view::CachingSourceMapView;
+
+pub mod edition;
+use edition::Edition;
+pub mod hygiene;
+use hygiene::Transparency;
+pub use hygiene::{DesugaringKind, ExpnData, ExpnId, ExpnKind, MacroKind, SyntaxContext};
+
+mod span_encoding;
+pub use span_encoding::{Span, DUMMY_SP};
+
+pub mod symbol;
+pub use symbol::{sym, Symbol};
+
+mod analyze_source_file;
+pub mod fatal_error;
+
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::sync::{Lock, Lrc};
+
+use std::borrow::Cow;
+use std::cell::RefCell;
+use std::cmp::{self, Ordering};
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use std::ops::{Add, Sub};
+use std::path::PathBuf;
+
+#[cfg(test)]
+mod tests;
+
+pub struct Globals {
+    symbol_interner: Lock<symbol::Interner>,
+    span_interner: Lock<span_encoding::SpanInterner>,
+    hygiene_data: Lock<hygiene::HygieneData>,
+}
+
+impl Globals {
+    pub fn new(edition: Edition) -> Globals {
+        Globals {
+            symbol_interner: Lock::new(symbol::Interner::fresh()),
+            span_interner: Lock::new(span_encoding::SpanInterner::default()),
+            hygiene_data: Lock::new(hygiene::HygieneData::new(edition)),
+        }
+    }
+}
+
+scoped_tls::scoped_thread_local!(pub static GLOBALS: Globals);
+
+/// Differentiates between real files and common virtual files.
+#[derive(
+    Debug,
+    Eq,
+    PartialEq,
+    Clone,
+    Ord,
+    PartialOrd,
+    Hash,
+    RustcDecodable,
+    RustcEncodable,
+    HashStable_Generic
+)]
+pub enum FileName {
+    Real(PathBuf),
+    /// A macro. This includes the full name of the macro, so that there are no clashes.
+    Macros(String),
+    /// Call to `quote!`.
+    QuoteExpansion(u64),
+    /// Command line.
+    Anon(u64),
+    /// Hack in `src/libsyntax/parse.rs`.
+    // FIXME(jseyfried)
+    MacroExpansion(u64),
+    ProcMacroSourceCode(u64),
+    /// Strings provided as `--cfg [cfgspec]` stored in a `crate_cfg`.
+    CfgSpec(u64),
+    /// Strings provided as crate attributes in the CLI.
+    CliCrateAttr(u64),
+    /// Custom sources for explicit parser calls from plugins and drivers.
+    Custom(String),
+    DocTest(PathBuf, isize),
+}
+
+impl std::fmt::Display for FileName {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use FileName::*;
+        match *self {
+            Real(ref path) => write!(fmt, "{}", path.display()),
+            Macros(ref name) => write!(fmt, "<{} macros>", name),
+            QuoteExpansion(_) => write!(fmt, "<quote expansion>"),
+            MacroExpansion(_) => write!(fmt, "<macro expansion>"),
+            Anon(_) => write!(fmt, "<anon>"),
+            ProcMacroSourceCode(_) => write!(fmt, "<proc-macro source code>"),
+            CfgSpec(_) => write!(fmt, "<cfgspec>"),
+            CliCrateAttr(_) => write!(fmt, "<crate attribute>"),
+            Custom(ref s) => write!(fmt, "<{}>", s),
+            DocTest(ref path, _) => write!(fmt, "{}", path.display()),
+        }
+    }
+}
+
+impl From<PathBuf> for FileName {
+    fn from(p: PathBuf) -> Self {
+        assert!(!p.to_string_lossy().ends_with('>'));
+        FileName::Real(p)
+    }
+}
+
+impl FileName {
+    pub fn is_real(&self) -> bool {
+        use FileName::*;
+        match *self {
+            Real(_) => true,
+            Macros(_)
+            | Anon(_)
+            | MacroExpansion(_)
+            | ProcMacroSourceCode(_)
+            | CfgSpec(_)
+            | CliCrateAttr(_)
+            | Custom(_)
+            | QuoteExpansion(_)
+            | DocTest(_, _) => false,
+        }
+    }
+
+    pub fn is_macros(&self) -> bool {
+        use FileName::*;
+        match *self {
+            Real(_)
+            | Anon(_)
+            | MacroExpansion(_)
+            | ProcMacroSourceCode(_)
+            | CfgSpec(_)
+            | CliCrateAttr(_)
+            | Custom(_)
+            | QuoteExpansion(_)
+            | DocTest(_, _) => false,
+            Macros(_) => true,
+        }
+    }
+
+    pub fn quote_expansion_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::QuoteExpansion(hasher.finish())
+    }
+
+    pub fn macro_expansion_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::MacroExpansion(hasher.finish())
+    }
+
+    pub fn anon_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::Anon(hasher.finish())
+    }
+
+    pub fn proc_macro_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::ProcMacroSourceCode(hasher.finish())
+    }
+
+    pub fn cfg_spec_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::QuoteExpansion(hasher.finish())
+    }
+
+    pub fn cli_crate_attr_source_code(src: &str) -> FileName {
+        let mut hasher = StableHasher::new();
+        src.hash(&mut hasher);
+        FileName::CliCrateAttr(hasher.finish())
+    }
+
+    pub fn doc_test_source_code(path: PathBuf, line: isize) -> FileName {
+        FileName::DocTest(path, line)
+    }
+}
+
+/// Spans represent a region of code, used for error reporting. Positions in spans
+/// are *absolute* positions from the beginning of the source_map, not positions
+/// relative to `SourceFile`s. Methods on the `SourceMap` can be used to relate spans back
+/// to the original source.
+/// You must be careful if the span crosses more than one file - you will not be
+/// able to use many of the functions on spans in source_map and you cannot assume
+/// that the length of the `span = hi - lo`; there may be space in the `BytePos`
+/// range between files.
+///
+/// `SpanData` is public because `Span` uses a thread-local interner and can't be
+/// sent to other threads, but some pieces of performance infra run in a separate thread.
+/// Using `Span` is generally preferred.
+#[derive(Clone, Copy, Hash, PartialEq, Eq, Ord, PartialOrd)]
+pub struct SpanData {
+    pub lo: BytePos,
+    pub hi: BytePos,
+    /// Information about where the macro came from, if this piece of
+    /// code was created by a macro expansion.
+    pub ctxt: SyntaxContext,
+}
+
+impl SpanData {
+    #[inline]
+    pub fn with_lo(&self, lo: BytePos) -> Span {
+        Span::new(lo, self.hi, self.ctxt)
+    }
+    #[inline]
+    pub fn with_hi(&self, hi: BytePos) -> Span {
+        Span::new(self.lo, hi, self.ctxt)
+    }
+    #[inline]
+    pub fn with_ctxt(&self, ctxt: SyntaxContext) -> Span {
+        Span::new(self.lo, self.hi, ctxt)
+    }
+}
+
+// The interner is pointed to by a thread local value which is only set on the main thread
+// with parallelization is disabled. So we don't allow `Span` to transfer between threads
+// to avoid panics and other errors, even though it would be memory safe to do so.
+#[cfg(not(parallel_compiler))]
+impl !Send for Span {}
+#[cfg(not(parallel_compiler))]
+impl !Sync for Span {}
+
+impl PartialOrd for Span {
+    fn partial_cmp(&self, rhs: &Self) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&self.data(), &rhs.data())
+    }
+}
+impl Ord for Span {
+    fn cmp(&self, rhs: &Self) -> Ordering {
+        Ord::cmp(&self.data(), &rhs.data())
+    }
+}
+
+/// A collection of spans. Spans have two orthogonal attributes:
+///
+/// - They can be *primary spans*. In this case they are the locus of
+///   the error, and would be rendered with `^^^`.
+/// - They can have a *label*. In this case, the label is written next
+///   to the mark in the snippet when we render.
+#[derive(Clone, Debug, Hash, PartialEq, Eq, RustcEncodable, RustcDecodable)]
+pub struct MultiSpan {
+    primary_spans: Vec<Span>,
+    span_labels: Vec<(Span, String)>,
+}
+
+impl Span {
+    #[inline]
+    pub fn lo(self) -> BytePos {
+        self.data().lo
+    }
+    #[inline]
+    pub fn with_lo(self, lo: BytePos) -> Span {
+        self.data().with_lo(lo)
+    }
+    #[inline]
+    pub fn hi(self) -> BytePos {
+        self.data().hi
+    }
+    #[inline]
+    pub fn with_hi(self, hi: BytePos) -> Span {
+        self.data().with_hi(hi)
+    }
+    #[inline]
+    pub fn ctxt(self) -> SyntaxContext {
+        self.data().ctxt
+    }
+    #[inline]
+    pub fn with_ctxt(self, ctxt: SyntaxContext) -> Span {
+        self.data().with_ctxt(ctxt)
+    }
+
+    /// Returns `true` if this is a dummy span with any hygienic context.
+    #[inline]
+    pub fn is_dummy(self) -> bool {
+        let span = self.data();
+        span.lo.0 == 0 && span.hi.0 == 0
+    }
+
+    /// Returns `true` if this span comes from a macro or desugaring.
+    #[inline]
+    pub fn from_expansion(self) -> bool {
+        self.ctxt() != SyntaxContext::root()
+    }
+
+    #[inline]
+    pub fn with_root_ctxt(lo: BytePos, hi: BytePos) -> Span {
+        Span::new(lo, hi, SyntaxContext::root())
+    }
+
+    /// Returns a new span representing an empty span at the beginning of this span
+    #[inline]
+    pub fn shrink_to_lo(self) -> Span {
+        let span = self.data();
+        span.with_hi(span.lo)
+    }
+    /// Returns a new span representing an empty span at the end of this span.
+    #[inline]
+    pub fn shrink_to_hi(self) -> Span {
+        let span = self.data();
+        span.with_lo(span.hi)
+    }
+
+    /// Returns `self` if `self` is not the dummy span, and `other` otherwise.
+    pub fn substitute_dummy(self, other: Span) -> Span {
+        if self.is_dummy() { other } else { self }
+    }
+
+    /// Returns `true` if `self` fully encloses `other`.
+    pub fn contains(self, other: Span) -> bool {
+        let span = self.data();
+        let other = other.data();
+        span.lo <= other.lo && other.hi <= span.hi
+    }
+
+    /// Returns `true` if `self` touches `other`.
+    pub fn overlaps(self, other: Span) -> bool {
+        let span = self.data();
+        let other = other.data();
+        span.lo < other.hi && other.lo < span.hi
+    }
+
+    /// Returns `true` if the spans are equal with regards to the source text.
+    ///
+    /// Use this instead of `==` when either span could be generated code,
+    /// and you only care that they point to the same bytes of source text.
+    pub fn source_equal(&self, other: &Span) -> bool {
+        let span = self.data();
+        let other = other.data();
+        span.lo == other.lo && span.hi == other.hi
+    }
+
+    /// Returns `Some(span)`, where the start is trimmed by the end of `other`.
+    pub fn trim_start(self, other: Span) -> Option<Span> {
+        let span = self.data();
+        let other = other.data();
+        if span.hi > other.hi { Some(span.with_lo(cmp::max(span.lo, other.hi))) } else { None }
+    }
+
+    /// Returns the source span -- this is either the supplied span, or the span for
+    /// the macro callsite that expanded to it.
+    pub fn source_callsite(self) -> Span {
+        let expn_data = self.ctxt().outer_expn_data();
+        if !expn_data.is_root() { expn_data.call_site.source_callsite() } else { self }
+    }
+
+    /// The `Span` for the tokens in the previous macro expansion from which `self` was generated,
+    /// if any.
+    pub fn parent(self) -> Option<Span> {
+        let expn_data = self.ctxt().outer_expn_data();
+        if !expn_data.is_root() { Some(expn_data.call_site) } else { None }
+    }
+
+    /// Edition of the crate from which this span came.
+    pub fn edition(self) -> edition::Edition {
+        self.ctxt().outer_expn_data().edition
+    }
+
+    #[inline]
+    pub fn rust_2015(&self) -> bool {
+        self.edition() == edition::Edition::Edition2015
+    }
+
+    #[inline]
+    pub fn rust_2018(&self) -> bool {
+        self.edition() >= edition::Edition::Edition2018
+    }
+
+    /// Returns the source callee.
+    ///
+    /// Returns `None` if the supplied span has no expansion trace,
+    /// else returns the `ExpnData` for the macro definition
+    /// corresponding to the source callsite.
+    pub fn source_callee(self) -> Option<ExpnData> {
+        fn source_callee(expn_data: ExpnData) -> ExpnData {
+            let next_expn_data = expn_data.call_site.ctxt().outer_expn_data();
+            if !next_expn_data.is_root() { source_callee(next_expn_data) } else { expn_data }
+        }
+        let expn_data = self.ctxt().outer_expn_data();
+        if !expn_data.is_root() { Some(source_callee(expn_data)) } else { None }
+    }
+
+    /// Checks if a span is "internal" to a macro in which `#[unstable]`
+    /// items can be used (that is, a macro marked with
+    /// `#[allow_internal_unstable]`).
+    pub fn allows_unstable(&self, feature: Symbol) -> bool {
+        self.ctxt().outer_expn_data().allow_internal_unstable.map_or(false, |features| {
+            features
+                .iter()
+                .any(|&f| f == feature || f == sym::allow_internal_unstable_backcompat_hack)
+        })
+    }
+
+    /// Checks if this span arises from a compiler desugaring of kind `kind`.
+    pub fn is_desugaring(&self, kind: DesugaringKind) -> bool {
+        match self.ctxt().outer_expn_data().kind {
+            ExpnKind::Desugaring(k) => k == kind,
+            _ => false,
+        }
+    }
+
+    /// Returns the compiler desugaring that created this span, or `None`
+    /// if this span is not from a desugaring.
+    pub fn desugaring_kind(&self) -> Option<DesugaringKind> {
+        match self.ctxt().outer_expn_data().kind {
+            ExpnKind::Desugaring(k) => Some(k),
+            _ => None,
+        }
+    }
+
+    /// Checks if a span is "internal" to a macro in which `unsafe`
+    /// can be used without triggering the `unsafe_code` lint
+    //  (that is, a macro marked with `#[allow_internal_unsafe]`).
+    pub fn allows_unsafe(&self) -> bool {
+        self.ctxt().outer_expn_data().allow_internal_unsafe
+    }
+
+    pub fn macro_backtrace(mut self) -> Vec<MacroBacktrace> {
+        let mut prev_span = DUMMY_SP;
+        let mut result = vec![];
+        loop {
+            let expn_data = self.ctxt().outer_expn_data();
+            if expn_data.is_root() {
+                break;
+            }
+            // Don't print recursive invocations.
+            if !expn_data.call_site.source_equal(&prev_span) {
+                let (pre, post) = match expn_data.kind {
+                    ExpnKind::Root => break,
+                    ExpnKind::Desugaring(..) => ("desugaring of ", ""),
+                    ExpnKind::AstPass(..) => ("", ""),
+                    ExpnKind::Macro(macro_kind, _) => match macro_kind {
+                        MacroKind::Bang => ("", "!"),
+                        MacroKind::Attr => ("#[", "]"),
+                        MacroKind::Derive => ("#[derive(", ")]"),
+                    },
+                };
+                result.push(MacroBacktrace {
+                    call_site: expn_data.call_site,
+                    macro_decl_name: format!("{}{}{}", pre, expn_data.kind.descr(), post),
+                    def_site_span: expn_data.def_site,
+                });
+            }
+
+            prev_span = self;
+            self = expn_data.call_site;
+        }
+        result
+    }
+
+    /// Returns a `Span` that would enclose both `self` and `end`.
+    pub fn to(self, end: Span) -> Span {
+        let span_data = self.data();
+        let end_data = end.data();
+        // FIXME(jseyfried): `self.ctxt` should always equal `end.ctxt` here (cf. issue #23480).
+        // Return the macro span on its own to avoid weird diagnostic output. It is preferable to
+        // have an incomplete span than a completely nonsensical one.
+        if span_data.ctxt != end_data.ctxt {
+            if span_data.ctxt == SyntaxContext::root() {
+                return end;
+            } else if end_data.ctxt == SyntaxContext::root() {
+                return self;
+            }
+            // Both spans fall within a macro.
+            // FIXME(estebank): check if it is the *same* macro.
+        }
+        Span::new(
+            cmp::min(span_data.lo, end_data.lo),
+            cmp::max(span_data.hi, end_data.hi),
+            if span_data.ctxt == SyntaxContext::root() { end_data.ctxt } else { span_data.ctxt },
+        )
+    }
+
+    /// Returns a `Span` between the end of `self` to the beginning of `end`.
+    pub fn between(self, end: Span) -> Span {
+        let span = self.data();
+        let end = end.data();
+        Span::new(
+            span.hi,
+            end.lo,
+            if end.ctxt == SyntaxContext::root() { end.ctxt } else { span.ctxt },
+        )
+    }
+
+    /// Returns a `Span` between the beginning of `self` to the beginning of `end`.
+    pub fn until(self, end: Span) -> Span {
+        let span = self.data();
+        let end = end.data();
+        Span::new(
+            span.lo,
+            end.lo,
+            if end.ctxt == SyntaxContext::root() { end.ctxt } else { span.ctxt },
+        )
+    }
+
+    pub fn from_inner(self, inner: InnerSpan) -> Span {
+        let span = self.data();
+        Span::new(
+            span.lo + BytePos::from_usize(inner.start),
+            span.lo + BytePos::from_usize(inner.end),
+            span.ctxt,
+        )
+    }
+
+    /// Equivalent of `Span::def_site` from the proc macro API,
+    /// except that the location is taken from the `self` span.
+    pub fn with_def_site_ctxt(self, expn_id: ExpnId) -> Span {
+        self.with_ctxt_from_mark(expn_id, Transparency::Opaque)
+    }
+
+    /// Equivalent of `Span::call_site` from the proc macro API,
+    /// except that the location is taken from the `self` span.
+    pub fn with_call_site_ctxt(&self, expn_id: ExpnId) -> Span {
+        self.with_ctxt_from_mark(expn_id, Transparency::Transparent)
+    }
+
+    /// Equivalent of `Span::mixed_site` from the proc macro API,
+    /// except that the location is taken from the `self` span.
+    pub fn with_mixed_site_ctxt(&self, expn_id: ExpnId) -> Span {
+        self.with_ctxt_from_mark(expn_id, Transparency::SemiTransparent)
+    }
+
+    /// Produces a span with the same location as `self` and context produced by a macro with the
+    /// given ID and transparency, assuming that macro was defined directly and not produced by
+    /// some other macro (which is the case for built-in and procedural macros).
+    pub fn with_ctxt_from_mark(self, expn_id: ExpnId, transparency: Transparency) -> Span {
+        self.with_ctxt(SyntaxContext::root().apply_mark(expn_id, transparency))
+    }
+
+    #[inline]
+    pub fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> Span {
+        let span = self.data();
+        span.with_ctxt(span.ctxt.apply_mark(expn_id, transparency))
+    }
+
+    #[inline]
+    pub fn remove_mark(&mut self) -> ExpnId {
+        let mut span = self.data();
+        let mark = span.ctxt.remove_mark();
+        *self = Span::new(span.lo, span.hi, span.ctxt);
+        mark
+    }
+
+    #[inline]
+    pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
+        let mut span = self.data();
+        let mark = span.ctxt.adjust(expn_id);
+        *self = Span::new(span.lo, span.hi, span.ctxt);
+        mark
+    }
+
+    #[inline]
+    pub fn modernize_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
+        let mut span = self.data();
+        let mark = span.ctxt.modernize_and_adjust(expn_id);
+        *self = Span::new(span.lo, span.hi, span.ctxt);
+        mark
+    }
+
+    #[inline]
+    pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
+        let mut span = self.data();
+        let mark = span.ctxt.glob_adjust(expn_id, glob_span);
+        *self = Span::new(span.lo, span.hi, span.ctxt);
+        mark
+    }
+
+    #[inline]
+    pub fn reverse_glob_adjust(
+        &mut self,
+        expn_id: ExpnId,
+        glob_span: Span,
+    ) -> Option<Option<ExpnId>> {
+        let mut span = self.data();
+        let mark = span.ctxt.reverse_glob_adjust(expn_id, glob_span);
+        *self = Span::new(span.lo, span.hi, span.ctxt);
+        mark
+    }
+
+    #[inline]
+    pub fn modern(self) -> Span {
+        let span = self.data();
+        span.with_ctxt(span.ctxt.modern())
+    }
+
+    #[inline]
+    pub fn modern_and_legacy(self) -> Span {
+        let span = self.data();
+        span.with_ctxt(span.ctxt.modern_and_legacy())
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct SpanLabel {
+    /// The span we are going to include in the final snippet.
+    pub span: Span,
+
+    /// Is this a primary span? This is the "locus" of the message,
+    /// and is indicated with a `^^^^` underline, versus `----`.
+    pub is_primary: bool,
+
+    /// What label should we attach to this span (if any)?
+    pub label: Option<String>,
+}
+
+impl Default for Span {
+    fn default() -> Self {
+        DUMMY_SP
+    }
+}
+
+impl rustc_serialize::UseSpecializedEncodable for Span {
+    fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        let span = self.data();
+        s.emit_struct("Span", 2, |s| {
+            s.emit_struct_field("lo", 0, |s| span.lo.encode(s))?;
+
+            s.emit_struct_field("hi", 1, |s| span.hi.encode(s))
+        })
+    }
+}
+
+impl rustc_serialize::UseSpecializedDecodable for Span {
+    fn default_decode<D: Decoder>(d: &mut D) -> Result<Span, D::Error> {
+        d.read_struct("Span", 2, |d| {
+            let lo = d.read_struct_field("lo", 0, Decodable::decode)?;
+            let hi = d.read_struct_field("hi", 1, Decodable::decode)?;
+            Ok(Span::with_root_ctxt(lo, hi))
+        })
+    }
+}
+
+pub fn default_span_debug(span: Span, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    f.debug_struct("Span")
+        .field("lo", &span.lo())
+        .field("hi", &span.hi())
+        .field("ctxt", &span.ctxt())
+        .finish()
+}
+
+impl fmt::Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (*SPAN_DEBUG)(*self, f)
+    }
+}
+
+impl fmt::Debug for SpanData {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (*SPAN_DEBUG)(Span::new(self.lo, self.hi, self.ctxt), f)
+    }
+}
+
+impl MultiSpan {
+    #[inline]
+    pub fn new() -> MultiSpan {
+        MultiSpan { primary_spans: vec![], span_labels: vec![] }
+    }
+
+    pub fn from_span(primary_span: Span) -> MultiSpan {
+        MultiSpan { primary_spans: vec![primary_span], span_labels: vec![] }
+    }
+
+    pub fn from_spans(vec: Vec<Span>) -> MultiSpan {
+        MultiSpan { primary_spans: vec, span_labels: vec![] }
+    }
+
+    pub fn push_span_label(&mut self, span: Span, label: String) {
+        self.span_labels.push((span, label));
+    }
+
+    /// Selects the first primary span (if any).
+    pub fn primary_span(&self) -> Option<Span> {
+        self.primary_spans.first().cloned()
+    }
+
+    /// Returns all primary spans.
+    pub fn primary_spans(&self) -> &[Span] {
+        &self.primary_spans
+    }
+
+    /// Returns `true` if any of the primary spans are displayable.
+    pub fn has_primary_spans(&self) -> bool {
+        self.primary_spans.iter().any(|sp| !sp.is_dummy())
+    }
+
+    /// Returns `true` if this contains only a dummy primary span with any hygienic context.
+    pub fn is_dummy(&self) -> bool {
+        let mut is_dummy = true;
+        for span in &self.primary_spans {
+            if !span.is_dummy() {
+                is_dummy = false;
+            }
+        }
+        is_dummy
+    }
+
+    /// Replaces all occurrences of one Span with another. Used to move `Span`s in areas that don't
+    /// display well (like std macros). Returns whether replacements occurred.
+    pub fn replace(&mut self, before: Span, after: Span) -> bool {
+        let mut replacements_occurred = false;
+        for primary_span in &mut self.primary_spans {
+            if *primary_span == before {
+                *primary_span = after;
+                replacements_occurred = true;
+            }
+        }
+        for span_label in &mut self.span_labels {
+            if span_label.0 == before {
+                span_label.0 = after;
+                replacements_occurred = true;
+            }
+        }
+        replacements_occurred
+    }
+
+    /// Returns the strings to highlight. We always ensure that there
+    /// is an entry for each of the primary spans -- for each primary
+    /// span `P`, if there is at least one label with span `P`, we return
+    /// those labels (marked as primary). But otherwise we return
+    /// `SpanLabel` instances with empty labels.
+    pub fn span_labels(&self) -> Vec<SpanLabel> {
+        let is_primary = |span| self.primary_spans.contains(&span);
+
+        let mut span_labels = self
+            .span_labels
+            .iter()
+            .map(|&(span, ref label)| SpanLabel {
+                span,
+                is_primary: is_primary(span),
+                label: Some(label.clone()),
+            })
+            .collect::<Vec<_>>();
+
+        for &span in &self.primary_spans {
+            if !span_labels.iter().any(|sl| sl.span == span) {
+                span_labels.push(SpanLabel { span, is_primary: true, label: None });
+            }
+        }
+
+        span_labels
+    }
+
+    /// Returns `true` if any of the span labels is displayable.
+    pub fn has_span_labels(&self) -> bool {
+        self.span_labels.iter().any(|(sp, _)| !sp.is_dummy())
+    }
+}
+
+impl From<Span> for MultiSpan {
+    fn from(span: Span) -> MultiSpan {
+        MultiSpan::from_span(span)
+    }
+}
+
+impl From<Vec<Span>> for MultiSpan {
+    fn from(spans: Vec<Span>) -> MultiSpan {
+        MultiSpan::from_spans(spans)
+    }
+}
+
+/// Identifies an offset of a multi-byte character in a `SourceFile`.
+#[derive(Copy, Clone, RustcEncodable, RustcDecodable, Eq, PartialEq, Debug)]
+pub struct MultiByteChar {
+    /// The absolute offset of the character in the `SourceMap`.
+    pub pos: BytePos,
+    /// The number of bytes, `>= 2`.
+    pub bytes: u8,
+}
+
+/// Identifies an offset of a non-narrow character in a `SourceFile`.
+#[derive(Copy, Clone, RustcEncodable, RustcDecodable, Eq, PartialEq, Debug)]
+pub enum NonNarrowChar {
+    /// Represents a zero-width character.
+    ZeroWidth(BytePos),
+    /// Represents a wide (full-width) character.
+    Wide(BytePos),
+    /// Represents a tab character, represented visually with a width of 4 characters.
+    Tab(BytePos),
+}
+
+impl NonNarrowChar {
+    fn new(pos: BytePos, width: usize) -> Self {
+        match width {
+            0 => NonNarrowChar::ZeroWidth(pos),
+            2 => NonNarrowChar::Wide(pos),
+            4 => NonNarrowChar::Tab(pos),
+            _ => panic!("width {} given for non-narrow character", width),
+        }
+    }
+
+    /// Returns the absolute offset of the character in the `SourceMap`.
+    pub fn pos(&self) -> BytePos {
+        match *self {
+            NonNarrowChar::ZeroWidth(p) | NonNarrowChar::Wide(p) | NonNarrowChar::Tab(p) => p,
+        }
+    }
+
+    /// Returns the width of the character, 0 (zero-width) or 2 (wide).
+    pub fn width(&self) -> usize {
+        match *self {
+            NonNarrowChar::ZeroWidth(_) => 0,
+            NonNarrowChar::Wide(_) => 2,
+            NonNarrowChar::Tab(_) => 4,
+        }
+    }
+}
+
+impl Add<BytePos> for NonNarrowChar {
+    type Output = Self;
+
+    fn add(self, rhs: BytePos) -> Self {
+        match self {
+            NonNarrowChar::ZeroWidth(pos) => NonNarrowChar::ZeroWidth(pos + rhs),
+            NonNarrowChar::Wide(pos) => NonNarrowChar::Wide(pos + rhs),
+            NonNarrowChar::Tab(pos) => NonNarrowChar::Tab(pos + rhs),
+        }
+    }
+}
+
+impl Sub<BytePos> for NonNarrowChar {
+    type Output = Self;
+
+    fn sub(self, rhs: BytePos) -> Self {
+        match self {
+            NonNarrowChar::ZeroWidth(pos) => NonNarrowChar::ZeroWidth(pos - rhs),
+            NonNarrowChar::Wide(pos) => NonNarrowChar::Wide(pos - rhs),
+            NonNarrowChar::Tab(pos) => NonNarrowChar::Tab(pos - rhs),
+        }
+    }
+}
+
+/// Identifies an offset of a character that was normalized away from `SourceFile`.
+#[derive(Copy, Clone, RustcEncodable, RustcDecodable, Eq, PartialEq, Debug)]
+pub struct NormalizedPos {
+    /// The absolute offset of the character in the `SourceMap`.
+    pub pos: BytePos,
+    /// The difference between original and normalized string at position.
+    pub diff: u32,
+}
+
+/// The state of the lazy external source loading mechanism of a `SourceFile`.
+#[derive(PartialEq, Eq, Clone)]
+pub enum ExternalSource {
+    /// The external source has been loaded already.
+    Present(String),
+    /// No attempt has been made to load the external source.
+    AbsentOk,
+    /// A failed attempt has been made to load the external source.
+    AbsentErr,
+    /// No external source has to be loaded, since the `SourceFile` represents a local crate.
+    Unneeded,
+}
+
+impl ExternalSource {
+    pub fn is_absent(&self) -> bool {
+        match *self {
+            ExternalSource::Present(_) => false,
+            _ => true,
+        }
+    }
+
+    pub fn get_source(&self) -> Option<&str> {
+        match *self {
+            ExternalSource::Present(ref src) => Some(src),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct OffsetOverflowError;
+
+/// A single source in the `SourceMap`.
+#[derive(Clone)]
+pub struct SourceFile {
+    /// The name of the file that the source came from. Source that doesn't
+    /// originate from files has names between angle brackets by convention
+    /// (e.g., `<anon>`).
+    pub name: FileName,
+    /// `true` if the `name` field above has been modified by `--remap-path-prefix`.
+    pub name_was_remapped: bool,
+    /// The unmapped path of the file that the source came from.
+    /// Set to `None` if the `SourceFile` was imported from an external crate.
+    pub unmapped_path: Option<FileName>,
+    /// Indicates which crate this `SourceFile` was imported from.
+    pub crate_of_origin: u32,
+    /// The complete source code.
+    pub src: Option<Lrc<String>>,
+    /// The source code's hash.
+    pub src_hash: u128,
+    /// The external source code (used for external crates, which will have a `None`
+    /// value as `self.src`.
+    pub external_src: Lock<ExternalSource>,
+    /// The start position of this source in the `SourceMap`.
+    pub start_pos: BytePos,
+    /// The end position of this source in the `SourceMap`.
+    pub end_pos: BytePos,
+    /// Locations of lines beginnings in the source code.
+    pub lines: Vec<BytePos>,
+    /// Locations of multi-byte characters in the source code.
+    pub multibyte_chars: Vec<MultiByteChar>,
+    /// Width of characters that are not narrow in the source code.
+    pub non_narrow_chars: Vec<NonNarrowChar>,
+    /// Locations of characters removed during normalization.
+    pub normalized_pos: Vec<NormalizedPos>,
+    /// A hash of the filename, used for speeding up hashing in incremental compilation.
+    pub name_hash: u128,
+}
+
+impl Encodable for SourceFile {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_struct("SourceFile", 8, |s| {
+            s.emit_struct_field("name", 0, |s| self.name.encode(s))?;
+            s.emit_struct_field("name_was_remapped", 1, |s| self.name_was_remapped.encode(s))?;
+            s.emit_struct_field("src_hash", 2, |s| self.src_hash.encode(s))?;
+            s.emit_struct_field("start_pos", 3, |s| self.start_pos.encode(s))?;
+            s.emit_struct_field("end_pos", 4, |s| self.end_pos.encode(s))?;
+            s.emit_struct_field("lines", 5, |s| {
+                let lines = &self.lines[..];
+                // Store the length.
+                s.emit_u32(lines.len() as u32)?;
+
+                if !lines.is_empty() {
+                    // In order to preserve some space, we exploit the fact that
+                    // the lines list is sorted and individual lines are
+                    // probably not that long. Because of that we can store lines
+                    // as a difference list, using as little space as possible
+                    // for the differences.
+                    let max_line_length = if lines.len() == 1 {
+                        0
+                    } else {
+                        lines.windows(2).map(|w| w[1] - w[0]).map(|bp| bp.to_usize()).max().unwrap()
+                    };
+
+                    let bytes_per_diff: u8 = match max_line_length {
+                        0..=0xFF => 1,
+                        0x100..=0xFFFF => 2,
+                        _ => 4,
+                    };
+
+                    // Encode the number of bytes used per diff.
+                    bytes_per_diff.encode(s)?;
+
+                    // Encode the first element.
+                    lines[0].encode(s)?;
+
+                    let diff_iter = (&lines[..]).windows(2).map(|w| (w[1] - w[0]));
+
+                    match bytes_per_diff {
+                        1 => {
+                            for diff in diff_iter {
+                                (diff.0 as u8).encode(s)?
+                            }
+                        }
+                        2 => {
+                            for diff in diff_iter {
+                                (diff.0 as u16).encode(s)?
+                            }
+                        }
+                        4 => {
+                            for diff in diff_iter {
+                                diff.0.encode(s)?
+                            }
+                        }
+                        _ => unreachable!(),
+                    }
+                }
+
+                Ok(())
+            })?;
+            s.emit_struct_field("multibyte_chars", 6, |s| self.multibyte_chars.encode(s))?;
+            s.emit_struct_field("non_narrow_chars", 7, |s| self.non_narrow_chars.encode(s))?;
+            s.emit_struct_field("name_hash", 8, |s| self.name_hash.encode(s))?;
+            s.emit_struct_field("normalized_pos", 9, |s| self.normalized_pos.encode(s))
+        })
+    }
+}
+
+impl Decodable for SourceFile {
+    fn decode<D: Decoder>(d: &mut D) -> Result<SourceFile, D::Error> {
+        d.read_struct("SourceFile", 8, |d| {
+            let name: FileName = d.read_struct_field("name", 0, |d| Decodable::decode(d))?;
+            let name_was_remapped: bool =
+                d.read_struct_field("name_was_remapped", 1, |d| Decodable::decode(d))?;
+            let src_hash: u128 = d.read_struct_field("src_hash", 2, |d| Decodable::decode(d))?;
+            let start_pos: BytePos =
+                d.read_struct_field("start_pos", 3, |d| Decodable::decode(d))?;
+            let end_pos: BytePos = d.read_struct_field("end_pos", 4, |d| Decodable::decode(d))?;
+            let lines: Vec<BytePos> = d.read_struct_field("lines", 5, |d| {
+                let num_lines: u32 = Decodable::decode(d)?;
+                let mut lines = Vec::with_capacity(num_lines as usize);
+
+                if num_lines > 0 {
+                    // Read the number of bytes used per diff.
+                    let bytes_per_diff: u8 = Decodable::decode(d)?;
+
+                    // Read the first element.
+                    let mut line_start: BytePos = Decodable::decode(d)?;
+                    lines.push(line_start);
+
+                    for _ in 1..num_lines {
+                        let diff = match bytes_per_diff {
+                            1 => d.read_u8()? as u32,
+                            2 => d.read_u16()? as u32,
+                            4 => d.read_u32()?,
+                            _ => unreachable!(),
+                        };
+
+                        line_start = line_start + BytePos(diff);
+
+                        lines.push(line_start);
+                    }
+                }
+
+                Ok(lines)
+            })?;
+            let multibyte_chars: Vec<MultiByteChar> =
+                d.read_struct_field("multibyte_chars", 6, |d| Decodable::decode(d))?;
+            let non_narrow_chars: Vec<NonNarrowChar> =
+                d.read_struct_field("non_narrow_chars", 7, |d| Decodable::decode(d))?;
+            let name_hash: u128 = d.read_struct_field("name_hash", 8, |d| Decodable::decode(d))?;
+            let normalized_pos: Vec<NormalizedPos> =
+                d.read_struct_field("normalized_pos", 9, |d| Decodable::decode(d))?;
+            Ok(SourceFile {
+                name,
+                name_was_remapped,
+                unmapped_path: None,
+                // `crate_of_origin` has to be set by the importer.
+                // This value matches up with `rustc::hir::def_id::INVALID_CRATE`.
+                // That constant is not available here, unfortunately.
+                crate_of_origin: std::u32::MAX - 1,
+                start_pos,
+                end_pos,
+                src: None,
+                src_hash,
+                external_src: Lock::new(ExternalSource::AbsentOk),
+                lines,
+                multibyte_chars,
+                non_narrow_chars,
+                normalized_pos,
+                name_hash,
+            })
+        })
+    }
+}
+
+impl fmt::Debug for SourceFile {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "SourceFile({})", self.name)
+    }
+}
+
+impl SourceFile {
+    pub fn new(
+        name: FileName,
+        name_was_remapped: bool,
+        unmapped_path: FileName,
+        mut src: String,
+        start_pos: BytePos,
+    ) -> Result<SourceFile, OffsetOverflowError> {
+        let normalized_pos = normalize_src(&mut src, start_pos);
+
+        let src_hash = {
+            let mut hasher: StableHasher = StableHasher::new();
+            hasher.write(src.as_bytes());
+            hasher.finish::<u128>()
+        };
+        let name_hash = {
+            let mut hasher: StableHasher = StableHasher::new();
+            name.hash(&mut hasher);
+            hasher.finish::<u128>()
+        };
+        let end_pos = start_pos.to_usize() + src.len();
+        if end_pos > u32::max_value() as usize {
+            return Err(OffsetOverflowError);
+        }
+
+        let (lines, multibyte_chars, non_narrow_chars) =
+            analyze_source_file::analyze_source_file(&src[..], start_pos);
+
+        Ok(SourceFile {
+            name,
+            name_was_remapped,
+            unmapped_path: Some(unmapped_path),
+            crate_of_origin: 0,
+            src: Some(Lrc::new(src)),
+            src_hash,
+            external_src: Lock::new(ExternalSource::Unneeded),
+            start_pos,
+            end_pos: Pos::from_usize(end_pos),
+            lines,
+            multibyte_chars,
+            non_narrow_chars,
+            normalized_pos,
+            name_hash,
+        })
+    }
+
+    /// Returns the `BytePos` of the beginning of the current line.
+    pub fn line_begin_pos(&self, pos: BytePos) -> BytePos {
+        let line_index = self.lookup_line(pos).unwrap();
+        self.lines[line_index]
+    }
+
+    /// Add externally loaded source.
+    /// If the hash of the input doesn't match or no input is supplied via None,
+    /// it is interpreted as an error and the corresponding enum variant is set.
+    /// The return value signifies whether some kind of source is present.
+    pub fn add_external_src<F>(&self, get_src: F) -> bool
+    where
+        F: FnOnce() -> Option<String>,
+    {
+        if *self.external_src.borrow() == ExternalSource::AbsentOk {
+            let src = get_src();
+            let mut external_src = self.external_src.borrow_mut();
+            // Check that no-one else have provided the source while we were getting it
+            if *external_src == ExternalSource::AbsentOk {
+                if let Some(src) = src {
+                    let mut hasher: StableHasher = StableHasher::new();
+                    hasher.write(src.as_bytes());
+
+                    if hasher.finish::<u128>() == self.src_hash {
+                        *external_src = ExternalSource::Present(src);
+                        return true;
+                    }
+                } else {
+                    *external_src = ExternalSource::AbsentErr;
+                }
+
+                false
+            } else {
+                self.src.is_some() || external_src.get_source().is_some()
+            }
+        } else {
+            self.src.is_some() || self.external_src.borrow().get_source().is_some()
+        }
+    }
+
+    /// Gets a line from the list of pre-computed line-beginnings.
+    /// The line number here is 0-based.
+    pub fn get_line(&self, line_number: usize) -> Option<Cow<'_, str>> {
+        fn get_until_newline(src: &str, begin: usize) -> &str {
+            // We can't use `lines.get(line_number+1)` because we might
+            // be parsing when we call this function and thus the current
+            // line is the last one we have line info for.
+            let slice = &src[begin..];
+            match slice.find('\n') {
+                Some(e) => &slice[..e],
+                None => slice,
+            }
+        }
+
+        let begin = {
+            let line = if let Some(line) = self.lines.get(line_number) {
+                line
+            } else {
+                return None;
+            };
+            let begin: BytePos = *line - self.start_pos;
+            begin.to_usize()
+        };
+
+        if let Some(ref src) = self.src {
+            Some(Cow::from(get_until_newline(src, begin)))
+        } else if let Some(src) = self.external_src.borrow().get_source() {
+            Some(Cow::Owned(String::from(get_until_newline(src, begin))))
+        } else {
+            None
+        }
+    }
+
+    pub fn is_real_file(&self) -> bool {
+        self.name.is_real()
+    }
+
+    pub fn is_imported(&self) -> bool {
+        self.src.is_none()
+    }
+
+    pub fn byte_length(&self) -> u32 {
+        self.end_pos.0 - self.start_pos.0
+    }
+    pub fn count_lines(&self) -> usize {
+        self.lines.len()
+    }
+
+    /// Finds the line containing the given position. The return value is the
+    /// index into the `lines` array of this `SourceFile`, not the 1-based line
+    /// number. If the source_file is empty or the position is located before the
+    /// first line, `None` is returned.
+    pub fn lookup_line(&self, pos: BytePos) -> Option<usize> {
+        if self.lines.len() == 0 {
+            return None;
+        }
+
+        let line_index = lookup_line(&self.lines[..], pos);
+        assert!(line_index < self.lines.len() as isize);
+        if line_index >= 0 { Some(line_index as usize) } else { None }
+    }
+
+    pub fn line_bounds(&self, line_index: usize) -> (BytePos, BytePos) {
+        if self.start_pos == self.end_pos {
+            return (self.start_pos, self.end_pos);
+        }
+
+        assert!(line_index < self.lines.len());
+        if line_index == (self.lines.len() - 1) {
+            (self.lines[line_index], self.end_pos)
+        } else {
+            (self.lines[line_index], self.lines[line_index + 1])
+        }
+    }
+
+    #[inline]
+    pub fn contains(&self, byte_pos: BytePos) -> bool {
+        byte_pos >= self.start_pos && byte_pos <= self.end_pos
+    }
+
+    /// Calculates the original byte position relative to the start of the file
+    /// based on the given byte position.
+    pub fn original_relative_byte_pos(&self, pos: BytePos) -> BytePos {
+        // Diff before any records is 0. Otherwise use the previously recorded
+        // diff as that applies to the following characters until a new diff
+        // is recorded.
+        let diff = match self.normalized_pos.binary_search_by(|np| np.pos.cmp(&pos)) {
+            Ok(i) => self.normalized_pos[i].diff,
+            Err(i) if i == 0 => 0,
+            Err(i) => self.normalized_pos[i - 1].diff,
+        };
+
+        BytePos::from_u32(pos.0 - self.start_pos.0 + diff)
+    }
+}
+
+/// Normalizes the source code and records the normalizations.
+fn normalize_src(src: &mut String, start_pos: BytePos) -> Vec<NormalizedPos> {
+    let mut normalized_pos = vec![];
+    remove_bom(src, &mut normalized_pos);
+    normalize_newlines(src, &mut normalized_pos);
+
+    // Offset all the positions by start_pos to match the final file positions.
+    for np in &mut normalized_pos {
+        np.pos.0 += start_pos.0;
+    }
+
+    normalized_pos
+}
+
+/// Removes UTF-8 BOM, if any.
+fn remove_bom(src: &mut String, normalized_pos: &mut Vec<NormalizedPos>) {
+    if src.starts_with("\u{feff}") {
+        src.drain(..3);
+        normalized_pos.push(NormalizedPos { pos: BytePos(0), diff: 3 });
+    }
+}
+
+/// Replaces `\r\n` with `\n` in-place in `src`.
+///
+/// Returns error if there's a lone `\r` in the string
+fn normalize_newlines(src: &mut String, normalized_pos: &mut Vec<NormalizedPos>) {
+    if !src.as_bytes().contains(&b'\r') {
+        return;
+    }
+
+    // We replace `\r\n` with `\n` in-place, which doesn't break utf-8 encoding.
+    // While we *can* call `as_mut_vec` and do surgery on the live string
+    // directly, let's rather steal the contents of `src`. This makes the code
+    // safe even if a panic occurs.
+
+    let mut buf = std::mem::replace(src, String::new()).into_bytes();
+    let mut gap_len = 0;
+    let mut tail = buf.as_mut_slice();
+    let mut cursor = 0;
+    let original_gap = normalized_pos.last().map_or(0, |l| l.diff);
+    loop {
+        let idx = match find_crlf(&tail[gap_len..]) {
+            None => tail.len(),
+            Some(idx) => idx + gap_len,
+        };
+        tail.copy_within(gap_len..idx, 0);
+        tail = &mut tail[idx - gap_len..];
+        if tail.len() == gap_len {
+            break;
+        }
+        cursor += idx - gap_len;
+        gap_len += 1;
+        normalized_pos.push(NormalizedPos {
+            pos: BytePos::from_usize(cursor + 1),
+            diff: original_gap + gap_len as u32,
+        });
+    }
+
+    // Account for removed `\r`.
+    // After `set_len`, `buf` is guaranteed to contain utf-8 again.
+    let new_len = buf.len() - gap_len;
+    unsafe {
+        buf.set_len(new_len);
+        *src = String::from_utf8_unchecked(buf);
+    }
+
+    fn find_crlf(src: &[u8]) -> Option<usize> {
+        let mut search_idx = 0;
+        while let Some(idx) = find_cr(&src[search_idx..]) {
+            if src[search_idx..].get(idx + 1) != Some(&b'\n') {
+                search_idx += idx + 1;
+                continue;
+            }
+            return Some(search_idx + idx);
+        }
+        None
+    }
+
+    fn find_cr(src: &[u8]) -> Option<usize> {
+        src.iter().position(|&b| b == b'\r')
+    }
+}
+
+// _____________________________________________________________________________
+// Pos, BytePos, CharPos
+//
+
+pub trait Pos {
+    fn from_usize(n: usize) -> Self;
+    fn to_usize(&self) -> usize;
+    fn from_u32(n: u32) -> Self;
+    fn to_u32(&self) -> u32;
+}
+
+/// A byte offset. Keep this small (currently 32-bits), as AST contains
+/// a lot of them.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
+pub struct BytePos(pub u32);
+
+/// A character offset. Because of multibyte UTF-8 characters, a byte offset
+/// is not equivalent to a character offset. The `SourceMap` will convert `BytePos`
+/// values to `CharPos` values as necessary.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
+pub struct CharPos(pub usize);
+
+// FIXME: lots of boilerplate in these impls, but so far my attempts to fix
+// have been unsuccessful.
+
+impl Pos for BytePos {
+    #[inline(always)]
+    fn from_usize(n: usize) -> BytePos {
+        BytePos(n as u32)
+    }
+
+    #[inline(always)]
+    fn to_usize(&self) -> usize {
+        self.0 as usize
+    }
+
+    #[inline(always)]
+    fn from_u32(n: u32) -> BytePos {
+        BytePos(n)
+    }
+
+    #[inline(always)]
+    fn to_u32(&self) -> u32 {
+        self.0
+    }
+}
+
+impl Add for BytePos {
+    type Output = BytePos;
+
+    #[inline(always)]
+    fn add(self, rhs: BytePos) -> BytePos {
+        BytePos((self.to_usize() + rhs.to_usize()) as u32)
+    }
+}
+
+impl Sub for BytePos {
+    type Output = BytePos;
+
+    #[inline(always)]
+    fn sub(self, rhs: BytePos) -> BytePos {
+        BytePos((self.to_usize() - rhs.to_usize()) as u32)
+    }
+}
+
+impl Encodable for BytePos {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_u32(self.0)
+    }
+}
+
+impl Decodable for BytePos {
+    fn decode<D: Decoder>(d: &mut D) -> Result<BytePos, D::Error> {
+        Ok(BytePos(d.read_u32()?))
+    }
+}
+
+impl Pos for CharPos {
+    #[inline(always)]
+    fn from_usize(n: usize) -> CharPos {
+        CharPos(n)
+    }
+
+    #[inline(always)]
+    fn to_usize(&self) -> usize {
+        self.0
+    }
+
+    #[inline(always)]
+    fn from_u32(n: u32) -> CharPos {
+        CharPos(n as usize)
+    }
+
+    #[inline(always)]
+    fn to_u32(&self) -> u32 {
+        self.0 as u32
+    }
+}
+
+impl Add for CharPos {
+    type Output = CharPos;
+
+    #[inline(always)]
+    fn add(self, rhs: CharPos) -> CharPos {
+        CharPos(self.to_usize() + rhs.to_usize())
+    }
+}
+
+impl Sub for CharPos {
+    type Output = CharPos;
+
+    #[inline(always)]
+    fn sub(self, rhs: CharPos) -> CharPos {
+        CharPos(self.to_usize() - rhs.to_usize())
+    }
+}
+
+// _____________________________________________________________________________
+// Loc, SourceFileAndLine, SourceFileAndBytePos
+//
+
+/// A source code location used for error reporting.
+#[derive(Debug, Clone)]
+pub struct Loc {
+    /// Information about the original source.
+    pub file: Lrc<SourceFile>,
+    /// The (1-based) line number.
+    pub line: usize,
+    /// The (0-based) column offset.
+    pub col: CharPos,
+    /// The (0-based) column offset when displayed.
+    pub col_display: usize,
+}
+
+// Used to be structural records.
+#[derive(Debug)]
+pub struct SourceFileAndLine {
+    pub sf: Lrc<SourceFile>,
+    pub line: usize,
+}
+#[derive(Debug)]
+pub struct SourceFileAndBytePos {
+    pub sf: Lrc<SourceFile>,
+    pub pos: BytePos,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct LineInfo {
+    /// Index of line, starting from 0.
+    pub line_index: usize,
+
+    /// Column in line where span begins, starting from 0.
+    pub start_col: CharPos,
+
+    /// Column in line where span ends, starting from 0, exclusive.
+    pub end_col: CharPos,
+}
+
+pub struct FileLines {
+    pub file: Lrc<SourceFile>,
+    pub lines: Vec<LineInfo>,
+}
+
+pub static SPAN_DEBUG: AtomicRef<fn(Span, &mut fmt::Formatter<'_>) -> fmt::Result> =
+    AtomicRef::new(&(default_span_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
+
+#[derive(Debug)]
+pub struct MacroBacktrace {
+    /// span where macro was applied to generate this code
+    pub call_site: Span,
+
+    /// name of macro that was applied (e.g., "foo!" or "#[derive(Eq)]")
+    pub macro_decl_name: String,
+
+    /// span where macro was defined (possibly dummy)
+    pub def_site_span: Span,
+}
+
+// _____________________________________________________________________________
+// SpanLinesError, SpanSnippetError, DistinctSources, MalformedSourceMapPositions
+//
+
+pub type FileLinesResult = Result<FileLines, SpanLinesError>;
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum SpanLinesError {
+    DistinctSources(DistinctSources),
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum SpanSnippetError {
+    IllFormedSpan(Span),
+    DistinctSources(DistinctSources),
+    MalformedForSourcemap(MalformedSourceMapPositions),
+    SourceNotAvailable { filename: FileName },
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct DistinctSources {
+    pub begin: (FileName, BytePos),
+    pub end: (FileName, BytePos),
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct MalformedSourceMapPositions {
+    pub name: FileName,
+    pub source_len: usize,
+    pub begin_pos: BytePos,
+    pub end_pos: BytePos,
+}
+
+/// Range inside of a `Span` used for diagnostics when we only have access to relative positions.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct InnerSpan {
+    pub start: usize,
+    pub end: usize,
+}
+
+impl InnerSpan {
+    pub fn new(start: usize, end: usize) -> InnerSpan {
+        InnerSpan { start, end }
+    }
+}
+
+// Given a slice of line start positions and a position, returns the index of
+// the line the position is on. Returns -1 if the position is located before
+// the first line.
+fn lookup_line(lines: &[BytePos], pos: BytePos) -> isize {
+    match lines.binary_search(&pos) {
+        Ok(line) => line as isize,
+        Err(line) => line as isize - 1,
+    }
+}
+
+/// Requirements for a `StableHashingContext` to be used in this crate.
+/// This is a hack to allow using the `HashStable_Generic` derive macro
+/// instead of implementing everything in librustc.
+pub trait HashStableContext {
+    fn hash_spans(&self) -> bool;
+    fn byte_pos_to_line_and_col(
+        &mut self,
+        byte: BytePos,
+    ) -> Option<(Lrc<SourceFile>, usize, BytePos)>;
+}
+
+impl<CTX> HashStable<CTX> for Span
+where
+    CTX: HashStableContext,
+{
+    /// Hashes a span in a stable way. We can't directly hash the span's `BytePos`
+    /// fields (that would be similar to hashing pointers, since those are just
+    /// offsets into the `SourceMap`). Instead, we hash the (file name, line, column)
+    /// triple, which stays the same even if the containing `SourceFile` has moved
+    /// within the `SourceMap`.
+    /// Also note that we are hashing byte offsets for the column, not unicode
+    /// codepoint offsets. For the purpose of the hash that's sufficient.
+    /// Also, hashing filenames is expensive so we avoid doing it twice when the
+    /// span starts and ends in the same file, which is almost always the case.
+    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
+        const TAG_VALID_SPAN: u8 = 0;
+        const TAG_INVALID_SPAN: u8 = 1;
+        const TAG_EXPANSION: u8 = 0;
+        const TAG_NO_EXPANSION: u8 = 1;
+
+        if !ctx.hash_spans() {
+            return;
+        }
+
+        if *self == DUMMY_SP {
+            return std::hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
+        }
+
+        // If this is not an empty or invalid span, we want to hash the last
+        // position that belongs to it, as opposed to hashing the first
+        // position past it.
+        let span = self.data();
+        let (file_lo, line_lo, col_lo) = match ctx.byte_pos_to_line_and_col(span.lo) {
+            Some(pos) => pos,
+            None => {
+                return std::hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
+            }
+        };
+
+        if !file_lo.contains(span.hi) {
+            return std::hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
+        }
+
+        std::hash::Hash::hash(&TAG_VALID_SPAN, hasher);
+        // We truncate the stable ID hash and line and column numbers. The chances
+        // of causing a collision this way should be minimal.
+        std::hash::Hash::hash(&(file_lo.name_hash as u64), hasher);
+
+        let col = (col_lo.0 as u64) & 0xFF;
+        let line = ((line_lo as u64) & 0xFF_FF_FF) << 8;
+        let len = ((span.hi - span.lo).0 as u64) << 32;
+        let line_col_len = col | line | len;
+        std::hash::Hash::hash(&line_col_len, hasher);
+
+        if span.ctxt == SyntaxContext::root() {
+            TAG_NO_EXPANSION.hash_stable(ctx, hasher);
+        } else {
+            TAG_EXPANSION.hash_stable(ctx, hasher);
+
+            // Since the same expansion context is usually referenced many
+            // times, we cache a stable hash of it and hash that instead of
+            // recursing every time.
+            thread_local! {
+                static CACHE: RefCell<FxHashMap<hygiene::ExpnId, u64>> = Default::default();
+            }
+
+            let sub_hash: u64 = CACHE.with(|cache| {
+                let expn_id = span.ctxt.outer_expn();
+
+                if let Some(&sub_hash) = cache.borrow().get(&expn_id) {
+                    return sub_hash;
+                }
+
+                let mut hasher = StableHasher::new();
+                expn_id.expn_data().hash_stable(ctx, &mut hasher);
+                let sub_hash: Fingerprint = hasher.finish();
+                let sub_hash = sub_hash.to_smaller_hash();
+                cache.borrow_mut().insert(expn_id, sub_hash);
+                sub_hash
+            });
+
+            sub_hash.hash_stable(ctx, hasher);
+        }
+    }
+}