Struct swc_common::Span

pub struct Span { /* fields omitted */ }

A compressed span.

SpanData is 12 bytes, which is a bit too big to stick everywhere. Span is a form that only takes up 8 bytes, with less space for the length and context. The vast majority (99.9%+) of SpanData instances will fit within those 8 bytes; any SpanData whose fields don't fit into a Span are stored in a separate interner table, and the Span will index into that table. Interning is rare enough that the cost is low, but common enough that the code is exercised regularly.

An earlier version of this code used only 4 bytes for Span, but that was slower because only 80--90% of spans could be stored inline (even less in very large crates) and so the interner was used a lot more.

Inline (compressed) format:

• span.base_or_index == span_data.lo
• span.len_or_tag == len == span_data.hi - span_data.lo (must be <= MAX_LEN)
• span.ctxt == span_data.ctxt (must be <= MAX_CTXT)

Interned format:

• span.base_or_index == index (indexes into the interner table)
• span.len_or_tag == LEN_TAG (high bit set, all other bits are zero)
• span.ctxt == 0

The inline form uses 0 for the tag value (rather than 1) so that we don't need to mask out the tag bit when getting the length, and so that the dummy span can be all zeroes.

Notes about the choice of field sizes:

• base is 32 bits in both Span and SpanData, which means that base values never cause interning. The number of bits needed for base depends on the crate size. 32 bits allows up to 4 GiB of code in a crate. script-servo is the largest crate in rustc-perf, requiring 26 bits for some spans.
• len is 15 bits in Span (a u16, minus 1 bit for the tag) and 32 bits in SpanData, which means that large len values will cause interning. The number of bits needed for len does not depend on the crate size. The most common number of bits for len are 0--7, with a peak usually at 3 or 4, and then it drops off quickly from 8 onwards. 15 bits is enough for 99.99%+ of cases, but larger values (sometimes 20+ bits) might occur dozens of times in a typical crate.
• ctxt is 16 bits in Span and 32 bits in SpanData, which means that large ctxt values will cause interning. The number of bits needed for ctxt values depend partly on the crate size and partly on the form of the code. No crates in rustc-perf need more than 15 bits for ctxt, but larger crates might need more than 16 bits.

Implementations

impl Span

pub fn new(lo: BytePos, hi: BytePos, ctxt: SyntaxContext) -> Self

pub fn data(self) -> SpanData

impl Span

pub fn lo(self) -> BytePos

pub fn with_lo(self, lo: BytePos) -> Span

pub fn hi(self) -> BytePos

pub fn with_hi(self, hi: BytePos) -> Span

pub fn ctxt(self) -> SyntaxContext

pub fn with_ctxt(self, ctxt: SyntaxContext) -> Span

pub fn is_dummy(self) -> bool

Returns true if this is a dummy span with any hygienic context.

pub fn shrink_to_lo(self) -> Span

Returns a new span representing an empty span at the beginning of this span

pub fn shrink_to_hi(self) -> Span

Returns a new span representing an empty span at the end of this span

pub fn substitute_dummy(self, other: Span) -> Span

Returns self if self is not the dummy span, and other otherwise.

pub fn contains(self, other: Span) -> bool

Return true if self fully encloses other.

pub fn source_equal(self, other: Span) -> bool

Return 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 trim_start(self, other: Span) -> Option<Span>

Returns Some(span), where the start is trimmed by the end of other

pub fn to(self, end: Span) -> Span

Return a Span that would enclose both self and end.

pub fn between(self, end: Span) -> Span

Return a Span between the end of self to the beginning of end.

pub fn until(self, end: Span) -> Span

Return a Span between the beginning of self to the beginning of end.

pub fn from_inner_byte_pos(self, start: usize, end: usize) -> Span

pub fn apply_mark(self, mark: Mark) -> Span

pub fn remove_mark(&mut self) -> Mark

pub fn adjust(&mut self, expansion: Mark) -> Option<Mark>

pub fn glob_adjust(
    &mut self,
    expansion: Mark,
    glob_ctxt: SyntaxContext
) -> Option<Option<Mark>>

pub fn reverse_glob_adjust(
    &mut self,
    expansion: Mark,
    glob_ctxt: SyntaxContext
) -> Option<Option<Mark>>

Trait Implementations

impl Clone for Span

fn clone(&self) -> Span

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Span

impl Debug for Span

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Default for Span

fn default() -> Self

Returns the "default value" for a type.

impl<'de> Deserialize<'de> for Span

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl Eq for Span

impl From<Span> for MultiSpan

fn from(span: Span) -> MultiSpan

Performs the conversion.

impl Hash for Span

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl Ord for Span

fn cmp(&self, rhs: &Self) -> Ordering

This method returns an [Ordering] between self and other.

#[must_use]fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]fn clamp(self, min: Self, max: Self) -> Self

🔬 This is a nightly-only experimental API. (clamp)

Restrict a value to a certain interval.

impl PartialEq<Span> for Span

fn eq(&self, other: &Span) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Span) -> bool

This method tests for !=.

impl PartialOrd<Span> for Span

fn partial_cmp(&self, rhs: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

#[must_use]fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

#[must_use]fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

#[must_use]fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

#[must_use]fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for Span

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl Spanned for Span

fn span(&self) -> Span

Get span of self.

impl StructuralEq for Span

impl StructuralPartialEq for Span