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tame/tamer/src/span.rs

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// Source spans
//
// Copyright (C) 2014-2023 Ryan Specialty, LLC.
//
// This file is part of TAME.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//! Mapping to source input byte intervals.
//!
//! A [`Span`] is a mapping to a byte interval within a source file,
//! representing primarily where some IR entity originated.
//! This underpins the diagnostic system,
//! intended to:
//!
//! 1. Give the user specific information for debugging errors in their
//! programs; and
//! 2. Provide high-resolution information for source code inquiries,
//! such as "where is this identifier?" and "what exists at my cursor
//! position within this file"?
//!
//! A span contains a [`Context`] representing the source location.
//! A context's path is a [`PathSymbolId`],
//! which represents an interned string slice,
//! _not_ a [`PathBuf`](std::path::PathBuf) or
//! [`OsStr`](std::ffi::OsStr).
//!
//! ```
//! use tamer::span::{Span, Context};
//! use tamer::sym::GlobalSymbolIntern;
//!
//! // From raw parts
//! let ctx: Context = "some/path/foo".intern().into();
//! let span = Span::new(2, 6, ctx);
//!
//! assert_eq!(2, span.offset());
//! assert_eq!(6, span.len());
//! assert_eq!(ctx, span.context());
//!
//! // From a closed byte interval
//! let spani = Span::from_byte_interval((10, 25), "some/path/bar".intern());
//! assert_eq!(10, spani.offset());
//! assert_eq!(15, spani.len());
//!
//! // Freely copyable
//! let cp = span;
//! assert_eq!(cp, span);
//! ```
//!
//! Span is expected to be able to fit within a general-purpose CPU register
//! on a 64-bit system, and so does not exceed 8 bytes in length.
//!
//! Spans are one of the most common objects in TAMER,
//! competing only with [symbols](crate::sym).
//! But unlike symbols,
//! [`Span`]s are designed to be meaningfully identifiable and copyable
//! without interning.
//!
//! A span is ordered as such:
//!
//! 1. Spans group by [`Context`],
//! though the relative ordering of each [`Context`] isn't
//! necessarily meaningful;
//! 2. Spans are then ordered relative to their offset; and
//! 3. Spans are finally ordered by their length.
//!
//! Note that this means that a span beginning after but ending before
//! another span will still order higher,
//! as shown in the example below.
//!
//! ```
//! # use tamer::span::{Span, Context};
//! # use tamer::sym::GlobalSymbolIntern;
//! #
//! # let ctx: Context = "some/path/foo".intern().into();
//! #
//! // Visualization of spans:
//! // [....,....,....,....,]
//! // [A-+-] [B-+]|
//! // | [C-] |
//! // | [D-+-]
//! // | [E]
//! // [F----] |
//! // [G------]
//!
//! let A = Span::new(2, 6, ctx);
//! let B = Span::new(10, 5, ctx);
//! let C = Span::new(10, 4, ctx);
//! let D = Span::new(10, 6, ctx);
//! let E = Span::new(11, 3, ctx);
//! let F = Span::new(5, 7, ctx);
//! let G = Span::new(5, 8, ctx);
//!
//! let mut spans = vec![A, B, C, D, E, F, G];
//! spans.sort();
//!
//! assert_eq!(spans, vec![A, F, G, C, B, D, E]);
//! ```
//!
//! Design Rationale
//! ================
//! It is expected that spans will be created and copied frequently,
//! as they are propagated to every IR in the system.
//! It is further expected that the data within a span will only be
//! referenced for diagnostic purposes,
//! or for utilities operating on original source code
//! (such as code formatters).
//!
//! When a span is referenced,
//! it will either be to determine the exact location of a particular
//! entity,
//! or it will be to attempt to locate a similar entity in a higher-level
//! IR associated with the same region of code.
//! The latter requires that spans be comparable in a meaningful way,
//! exhibiting at least partial ordering.
//!
//! Spans are therefore optimized for three primary use cases:
//! - copying;
//! - comparison; and
//! - ordering.
//!
//! Span Structure
//! --------------
//! Spans are packed into 64-bit values that can be readily converted into a
//! [`u64`] value that is totally ordered relative to a given [`Context`],
//! byte offset, and byte length.
//! This means that sorting a collection of [`Span`]s will group spans by
//! their [`Context`];
//! will sort those spans relative to their starting offset within that
//! context; and
//! will sort again by the ending offset.
//!
//! This means that spans are [`Eq`] and [`Ord`],
//! and efficiently so by simply comparing the byte values of the entire
//! struct as a single [`u64`].
//! This allows spans to be sorted relative to their positions within a
//! context;
//! be placed into a binary tree for mapping back to higher-level IRs;
//! gives spans a meaningful unique identifier;
//! be freely copied without cost;
//! and more,
//! all very efficiently and without having to access individual
//! struct members.
//!
//! To accomplish this,
//! [`Span`] uses `repr(packed)` and orders the fields for little endian
//! systems like `x86_64`,
//! which is what our team uses.
//! The `packed` representation had to be used because the byte orderings
//! are [`u16`], [`u32`], [`u16`],
//! which makes the [`u32`] byte offset unaligned.
//! Note that,
//! while this _is_ unaligned,
//! this is _not_ unaligned _memory_ access,
//! since the entire [`Span`] will be retrieved from (aligned) memory at
//! once;
//! the unaligned fields within the [`u64`] do not incur a measurable
//! performance cost.
//!
//! Related Work
//! ============
//! This span is motivated by [rustc's compressed `Span`](rustc-span).
//! TAMER's span size relies on 16 bits being sufficient for holding
//! interned paths,
//! which _should_ be a very reasonable assumption unless the interner
//! ends up being shared with too many different things.
//! If ever that assumption becomes violated,
//! and it is deemed that packages containing so many symbols should be permitted,
//! TAMER's [`Span`] can accommodate in a similar with to rustc's by
//! interning the larger span data and tagging this span as such.
//!
//!
//! [rustc-span]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_span/struct.Span.html
use crate::{
debug_diagnostic_panic, global,
sym::{st16, ContextStaticSymbolId, GlobalSymbolResolve, SymbolId},
};
use std::{convert::TryInto, fmt::Display, path::Path};
/// A symbol size sufficient for holding interned paths.
pub type PathSymbolId = SymbolId<u16>;
/// Size of a [`Span`]'s `offset` field.
pub type SpanOffsetSize = global::SourceFileSize;
/// Size of a [`Span`]'s `len` field.
pub type SpanLenSize = global::FrontendTokenLength;
/// Description of a source location and byte interval for some object.
///
/// Spans represent byte intervals within a given source context.
/// A span should map to useful positions for helping users debug error
/// messages.
/// If code is generated, desugared, or otherwise manipulated,
/// the span ought to reference the original location of the code that can
/// be referenced and modified to correct any problems.
///
/// See the [module-level documentation](self) for more information.
#[cfg(target_endian = "little")]
#[repr(packed)]
#[derive(Debug, Clone, Copy)]
pub struct Span {
/// Token length (ending byte offset - `offset`).
len: SpanLenSize,
/// Starting 0-indexed byte position, inclusive.
offset: SpanOffsetSize,
/// Context onto which byte offsets are mapped,
/// such as a source file.
///
/// N.B.: This is an unaligned field,
/// and accessing it frequently may have a negative impact on
/// performance.
ctx: Context,
}
assert_eq_size!(Span, Option<Span>);
impl Span {
/// Create a new span from its constituent parts.
pub fn new<C: Into<Context>>(
offset: SpanOffsetSize,
len: SpanLenSize,
ctx: C,
) -> Self {
Self {
ctx: ctx.into(),
offset,
len,
}
}
/// Create a constant span from a static context.
pub const fn st_ctx(sym: ContextStaticSymbolId) -> Self {
Self {
ctx: Context(sym.as_sym()),
offset: 0,
len: 0,
}
}
/// Create a span from a byte interval and context.
///
/// Panics
/// ======
/// This will panic in the unlikely case that the difference between the
/// start and end of the interval exceeds the maximum of
/// [`global::FrontendTokenLength`].
///
/// If this error occurs,
/// the parser should consider splitting large tokens up into multiple
/// tokens;
/// increasing [`global::FrontendTokenLength`] should be a last
/// resort,
/// since it has wide-reaching implications on the size of
/// [`Span`].
///
/// The user is not expected to know how to recover from this error
/// without debugging the compiler.
/// It is not expected that this would occur on any valid inputs.
pub fn from_byte_interval<B, C>(interval: B, ctx: C) -> Self
where
B: Into<ClosedByteInterval>,
C: Into<Context>,
{
let binterval = interval.into();
Self {
offset: binterval.0,
len: (binterval.1 - binterval.0)
.try_into()
.expect("span length exceeds global::FrontendTokenLength"),
ctx: ctx.into(),
}
}
// A span represented uniquely as a totally ordered [`u64`].
//
// For more information on this important properly,
// see the documentation for [`Span`] itself.
pub fn as_u64(self) -> u64 {
// We take a number of precautions to make this safe (in the sense
// of correctness),
// through struct packing and a `cfg` directive for endianness.
// In any case,
// a `u64` isn't going to harm anyone.
unsafe { std::mem::transmute(self) }
}
/// Byte offset of the beginning of the span relative to its context.
pub fn offset(&self) -> SpanOffsetSize {
self.offset
}
/// Length of the span in bytes.
///
/// The interval of the span is `[offset, offset+len]`.
pub fn len(&self) -> SpanLenSize {
self.len
}
/// The context to which the span applies.
///
/// The context is, for example, a file.
pub fn context(&self) -> Context {
self.ctx
}
/// Further offset a span.
///
/// This attempts to offset a span relative to its current offset by the
/// provided value.
/// If the resulting offset exceeds [`SpanOffsetSize`],
/// the result will be [`None`].
pub const fn offset_add(self, value: SpanOffsetSize) -> Option<Self> {
match self.offset.checked_add(value) {
Some(offset) => Some(Self { offset, ..self }),
None => None,
}
}
/// Create two zero-length spans representing respectively the first and
/// last offsets in the span.
///
/// The second endpoint will be [`None`] if the offset cannot be
/// represented by [`SpanOffsetSize`].
///
/// ```
/// # use tamer::span::{Span, Context};
/// # use tamer::sym::GlobalSymbolIntern;
/// #
/// # let ctx: Context = "some/path/foo".intern().into();
/// #
/// // [0123456789]
/// // [---]
/// // 2 6
/// // A
/// let A = Span::new(2, 6, ctx);
///
/// assert_eq!(
/// A.endpoints(),
/// (
/// Span::new(2, 0, ctx),
/// Some(Span::new(8, 0, ctx)),
/// ),
/// );
/// ```
pub const fn endpoints(self) -> (Self, Option<Self>) {
(
// First endpoint.
Self {
offset: self.offset,
len: 0,
..self
},
// Second endpoint.
match self.offset.checked_add(self.len as u32) {
Some(offset) => Some(Self {
offset,
len: 0,
..self
}),
None => None,
},
)
}
/// Create two zero-length spans representing respectively the first and
/// last offsets in the span,
/// saturating the ending offset if it cannot be represented by
/// [`SpanOffsetSize`].
///
/// Aside from the saturation,
/// this is identical to [`Span::endpoints`].
pub fn endpoints_saturated(self) -> (Self, Self) {
let endpoints = self.endpoints();
(
endpoints.0,
endpoints.1.unwrap_or(Self {
offset: SpanOffsetSize::MAX,
..endpoints.0
}),
)
}
/// Create a new span that is a slice of this one.
///
/// If either `rel_offset` or `len` are too large,
/// then a copy of the span will be returned unsliced.
///
/// Panics (Debug Mode)
/// -------------------
/// If the offset and length exceeds the bounds of the span,
/// then the system has an arithmetic bug that ought to be corrected,
/// and so this will panic with a diagnostic message.
/// This check does not occur on release builds since this is not a
/// safety issue and should be caught by tests.
pub fn slice(self, rel_offset: usize, len: usize) -> Self {
let (irel_offset, ilen) = match (rel_offset.try_into(), len.try_into())
{
(Ok(x), Ok(y)) => (x, y),
_ => (0, self.len()),
};
// We shouldn't ignore slices that exceed the length of the span,
// since this represents a bug that'll cause nonsense diagnostic
// data and it represents an arithmetic bug in the system
// (but there are no safety concerns).
if ((irel_offset as usize).saturating_add(ilen as usize))
> self.len() as usize
{
#[cfg(debug_assertions)]
use crate::diagnose::Annotate;
debug_diagnostic_panic!(
self.error("attempting to slice this span").into(),
"length {len} at offset {rel_offset} \
exceeds bounds of span {self}",
);
}
Self {
ctx: self.ctx,
offset: self.offset.saturating_add(irel_offset),
len: ilen,
}
}
/// Adjust span such that its offset is relative to the provided span.
///
/// If the provide `rel_span` does not precede this span,
/// [`None`] will be returned.
///
/// If the two spans do not share the same [`Context`],
/// no comparison can be made and [`None`] will be returned.
pub fn relative_to(self, rel_span: Span) -> Option<Self> {
// Note that this is unaligned.
if self.context() != rel_span.context() {
return None;
}
if self.offset() < rel_span.offset() {
return None;
}
Some(Self {
ctx: self.ctx,
offset: self.offset.saturating_sub(rel_span.offset),
len: self.len,
})
}
/// Merge with another span `b` such that the combined span begins at
/// the offset of the earlier of the two spans and extends to the end
/// of the later of the two.
///
/// Both spans must have the same [`Context`],
/// otherwise the result will be [`None`].
/// Merged values beyond [`SpanOffsetSize`] and [`SpanLenSize`] will
/// also result in [`None`].
///
/// This properly handles overlapping spans,
/// including the case where one of the spans is entirely contained
/// within another.
/// See test cases for more information.
/// (TODO: Maybe we should move the test cases into these docs?)
pub fn merge<S: Into<Span>>(self, other: S) -> Option<Span> {
let b = other.into();
if self.context() != b.context() {
return None;
}
// Order arguments such that `self` is placed at or before `b`
// rather than having to worry about confounding accommodations
// below.
if self.offset() > b.offset() {
return b.merge(self);
}
let (_, end) = b.endpoints();
end.and_then(|Span { offset, .. }| {
SpanLenSize::try_from(offset - self.offset).ok()
})
.map(|new_len| Self {
ctx: self.ctx,
offset: self.offset,
len: self.len.max(new_len),
})
}
}
impl From<Span> for u64 {
fn from(val: Span) -> Self {
val.as_u64()
}
}
impl PartialEq for Span {
fn eq(&self, other: &Self) -> bool {
self.as_u64() == other.as_u64()
}
}
impl Eq for Span {}
impl PartialOrd for Span {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
Some(self.cmp(other))
}
}
impl Ord for Span {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
self.as_u64().cmp(&other.as_u64())
}
}
// This assertion verifies our above expectations.
// If this fails,
// then you have either modified [`global`] constants or you have modified
// the fields of [`Span`] itself,
// in which case you should read "Related Work" above to determine
// whether this was a good idea or if interned spans should be
// introduced.
// In any case,
// hopefully this was planned for,
// because otherwise your week has just been ruined.
assert_eq_size!(Span, u64);
impl From<Span> for (Span, Span) {
/// Expand a [`Span`] into a two-span.
///
/// A two-span `(A, B)` is equivalent to a span beginning at the start
/// of `A` and ending at the end of `B`.
///
/// We gain no resolution from performing this operation,
/// but it does allow for using a single span in contexts where a
/// higher resolution is supported.
fn from(span: Span) -> Self {
(span, span)
}
}
impl Display for Span {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
// Needed to avoid unaligned references since Span is packed.
let ctx = self.ctx;
let offset = self.offset as usize;
let end = offset + self.len as usize;
// Very primitive information to begin with; we'll have something
// more useful in the future.
write!(f, "[{} offset {}-{}]", ctx, offset, end)
}
}
/// A placeholder span indicating that a span is expected but is not yet
/// known.
pub const UNKNOWN_SPAN: Span = Span::st_ctx(st16::CTX_UNKNOWN);
/// Context for byte offsets (e.g. a source file).
///
/// A context is lifetime-free and [`Copy`]-able,
/// with the assumption that an interned [`PathSymbolId`] will only need
/// to be resolved to its underlying value in a diagnostic context where
/// the internment system is readily available.
///
/// Since this is used within [`Span`],
/// it must be kept as small as possible.
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
pub struct Context(PathSymbolId);
impl Context {
/// Produce a [`Span`] within the given context.
#[inline]
pub const fn span(self, offset: SpanOffsetSize, len: SpanLenSize) -> Span {
Span {
ctx: self,
offset,
len,
}
}
/// Attempt to produce a [`Span`] of the given length at the given
/// offset,
/// otherwise fall back to a `(0,0)` (ZZ) span.
///
/// If the offset cannot be stored,
/// then the length will always be `0` even if it could otherwise be
/// represented;
/// `(0,0)` indicates no span,
/// whereas `(0,N)` would indicate a span of length `N` at
/// offset `0`,
/// which would not be true.
///
/// If the offset can be represented but not the length,
/// then a zero-length span at that offset will be produced,
/// which still provides useful information.
/// This may be the case for very large objects,
/// like compiled text fragments.
///
/// The rationale here is that spans are intended to be informative.
/// If we are unable to provide that information due to exceptional
/// circumstances
/// (very large file or very large token),
/// then it's better to provide _some_ information than to bail out
/// with an error and interrupt the entire process,
/// potentially masking errors in the process.
#[inline]
pub fn span_or_zz(self, offset: usize, len: usize) -> Span {
self.span(offset.try_into().unwrap_or(0), len.try_into().unwrap_or(0))
}
}
/// A placeholder context indicating that a context is expected but is not
/// yet known.
pub const UNKNOWN_CONTEXT: Context = Context(st16::raw::CTX_UNKNOWN);
impl<P: Into<PathSymbolId>> From<P> for Context {
fn from(sym: P) -> Self {
Self(sym.into())
}
}
impl Display for Context {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.0.fmt(f)
}
}
impl AsRef<Path> for Context {
fn as_ref(&self) -> &Path {
Path::new(self.0.lookup_str())
}
}
/// A closed interval (range of values including its endpoints) representing
/// source bytes associated with a token.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub struct ClosedByteInterval<T = SpanOffsetSize>(pub T, pub T)
where
T: Copy + PartialOrd;
impl<T: Copy + PartialOrd> From<(T, T)> for ClosedByteInterval<T> {
/// Convert a tuple into a closed byte interval where the first index
/// represents the start of the interval and the second index the
/// end.
///
/// Panics
/// ======
/// The second value must be ≥ the first.
fn from(src: (T, T)) -> Self {
assert!(src.1 >= src.0);
Self(src.0, src.1)
}
}
assert_eq_size!(ClosedByteInterval, u64);
/// Dummy spans for testing.
#[cfg(test)]
pub mod dummy {
use super::{st16, Context, Span};
/// A dummy span that can be used in contexts where a span is expected
/// but is not important.
///
/// This is intended primarily for tests;
/// you should always use an appropriate span to permit sensible error
/// messages and source analysis.
/// For spans that are actually unknown,
/// use [`super::UNKNOWN_SPAN`].
///
/// Additional dummy spans can be derived from this one.
pub const DUMMY_SPAN: Span = Span::st_ctx(st16::CTX_DUMMY);
/// A dummy context that can be used where a span is expected but is not
/// important.
///
/// This is intended primarily for tests;
/// you should always use an appropriate span to permit sensible error
/// messages and source analysis.
/// For contexts that are actually unknown,
/// use [`super::UNKNOWN_CONTEXT`].
///
/// See also [`UNKNOWN_CONTEXT`].
pub const DUMMY_CONTEXT: Context = Context(st16::raw::CTX_DUMMY);
// This name is for brevity;
// we don't want to expose it because we don't want anyone to assume
// that a different name means that it's somehow different from
// `DUMMY_SPAN`.
const S0: Span = DUMMY_SPAN;
pub const S1: Span = S0.offset_add(1).unwrap();
pub const S2: Span = S0.offset_add(2).unwrap();
pub const S3: Span = S0.offset_add(3).unwrap();
pub const S4: Span = S0.offset_add(4).unwrap();
pub const S5: Span = S0.offset_add(5).unwrap();
pub const S6: Span = S0.offset_add(6).unwrap();
pub const S7: Span = S0.offset_add(7).unwrap();
pub const S8: Span = S0.offset_add(8).unwrap();
pub const S9: Span = S0.offset_add(9).unwrap();
pub const S10: Span = S0.offset_add(10).unwrap();
pub const S11: Span = S0.offset_add(11).unwrap();
pub const S12: Span = S0.offset_add(12).unwrap();
pub const S13: Span = S0.offset_add(13).unwrap();
pub const S14: Span = S0.offset_add(14).unwrap();
pub const S15: Span = S0.offset_add(15).unwrap();
pub const S16: Span = S0.offset_add(16).unwrap();
pub const S17: Span = S0.offset_add(17).unwrap();
pub const S18: Span = S0.offset_add(18).unwrap();
pub const S19: Span = S0.offset_add(19).unwrap();
pub const S20: Span = S0.offset_add(20).unwrap();
}
#[cfg(test)]
mod test {
use super::*;
// Little endian check.
//
// This ensures that the byte ordering is as expected,
// otherwise the resulting integer will not have the properties we
// require for sorting and comparison.
#[cfg(target_endian = "little")]
#[test]
fn span_pack_le() {
let span =
Span::new(0xA3A2A1A0, 0xB1B0, SymbolId::test_from_int(0xC1C0));
assert_eq!(
0xC1C0_A3A2A1A0_B1B0,
// ^ ^ ^
// ctx offset len
span.as_u64(),
"endianness check failed: {:X?}",
span.as_u64()
);
}
#[cfg(target_endian = "big")]
#[test]
fn span_pack_be_not_supported() {
panic!("Big-endian systems are not currently supported");
}
// The tests that follow are corollaries of the above, but the below
// tests do test that the implementations function as intended.
#[test]
fn span_at_later_offset_in_same_context_compares_greater() {
let ctx = Context::from("imaginary");
let first = ctx.span(10, 5);
let second = ctx.span(20, 5);
// These two assertions must be identical.
assert!(second > first);
assert!(second.as_u64() > first.as_u64());
}
#[test]
fn spans_order_by_context_start_and_len() {
let ctxa = Context::from("context a");
let ctxb = Context::from("context b");
// Sanity check, otherwise this test won't work as expected.
assert!(ctxa.0 < ctxb.0);
let sa1 = ctxa.span(10, 1);
let sa2 = ctxa.span(22, 1);
let sa3 = ctxa.span(35, 1);
let sb1 = ctxb.span(11, 1);
let sb2 = ctxb.span(20, 1);
let sb3 = ctxb.span(33, 1);
let mut spans = vec![sa3, sb2, sb1, sa2, sa1, sb3];
spans.sort();
assert_eq!(spans, vec![sa1, sa2, sa3, sb1, sb2, sb3]);
}
#[test]
fn retrieve_span_components() {
let ctx = Context::from("foo");
let offset = 100;
let len = 50;
let span = ctx.span(offset, len);
assert_eq!(
(offset, len, ctx),
(span.offset(), span.len(), span.context())
);
}
#[test]
fn span_offset_add() {
let ctx = Context::from("addtest");
let offset = 10;
let len = 5;
let span = ctx.span(offset, len);
// Successful add.
assert_eq!(
span.offset_add(10),
Some(Span {
offset: offset + 10,
len,
ctx
})
);
// Fail, do not wrap.
assert_eq!(span.offset_add(SpanOffsetSize::MAX), None);
}
#[test]
fn span_into_twospan() {
let ctx = Context::from("foo");
let span = ctx.span(10, 50);
assert_eq!((span, span), span.into());
}
#[test]
fn span_endpoints() {
let ctx = Context::from("end");
let span = ctx.span(10, 20);
let (start, end) = span.endpoints();
assert_eq!(start, Span::new(10, 0, ctx));
assert_eq!(end, Some(Span::new(30, 0, ctx)));
}
#[test]
fn span_endpoints_exceeding_max_offset() {
let ctx = Context::from("end");
let offset = SpanOffsetSize::MAX - 5;
let span = ctx.span(offset, 10);
let (start, end) = span.endpoints();
assert_eq!(start, Span::new(offset, 0, ctx));
assert_eq!(end, None);
}
#[test]
fn span_endpoints_saturated() {
let ctx = Context::from("end");
let offset = SpanOffsetSize::MAX - 5;
let span = ctx.span(offset, 10);
let (start, end) = span.endpoints_saturated();
assert_eq!(start, Span::new(offset, 0, ctx));
assert_eq!(end, Span::new(SpanOffsetSize::MAX, 0, ctx));
}
#[test]
fn span_slice_yields_slice_within_original() {
let ctx = Context::from("slice");
let span = ctx.span(10, 10);
assert_eq!(ctx.span(15, 5), span.slice(5, 5));
}
#[test]
fn span_slice_large_values_yield_original() {
let span = Context::from("slice").span(0, 50);
// Too large of an offset should return original even though legnth
// is okay.
assert_eq!(span, span.slice(usize::MAX, 5));
// Too large of length should return original even though offset is
// okay.
assert_eq!(span, span.slice(0, usize::MAX));
}
#[test]
fn span_merge_one_after_other() {
let ctx = Context::from("merge");
// "an example string"
// [-----] [----]
// 3 9 11 16
// | A B |
// [------------]
// 3 16
// C
let a = ctx.span(3, 7);
let b = ctx.span(11, 6);
let c = ctx.span(3, 14);
assert_eq!(a.merge(b), Some(c));
assert_eq!(b.merge(a), Some(c));
}
#[test]
fn span_merge_overlap() {
let ctx = Context::from("merge");
// "an example string"
// [---+-] |
// 3 | 9 |
// | A| |
// | [--------]
// | 7 16
// | B |
// [------------]
// 3 16
// C
let a = ctx.span(3, 7);
let b = ctx.span(7, 10);
let c = ctx.span(3, 14);
// We compare in both orders,
// so this will test when a span overlaps on either side.
assert_eq!(a.merge(b), Some(c));
assert_eq!(b.merge(a), Some(c));
}
#[test]
fn span_merge_overlap_within() {
let ctx = Context::from("merge");
// "an example string"
// |[----] |
// |1 6 |
// | B |
// [--------]
// 0 9
// C
let b = ctx.span(1, 6);
let c = ctx.span(0, 10);
assert_eq!(b.merge(c), Some(c));
assert_eq!(c.merge(b), Some(c));
}
// It doesn't make sense to merge two spans that are located in
// different contexts.
#[test]
fn span_merge_different_contexts() {
let ctx_a = Context::from("merge_a");
let ctx_b = Context::from("merge_b");
assert_eq!(ctx_a.span(0, 1).merge(ctx_b.span(1, 2)), None);
}
}
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