Struct rustc_span::Span

pub struct Span {
    base_or_index: u32,
    len_or_tag: u16,
    ctxt_or_tag: u16,
}

A compressed span.

Whereas 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_or_tag == span_data.ctxt (must be <= MAX_CTXT)

Interned format with inline SyntaxContext:

• 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_or_tag == 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_or_tag == CTXT_TAG

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.
• 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 numbers of bits for len are from 0 to 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_or_tag 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_or_tag, but larger crates might need more than 16 bits.

In order to reliably use parented spans in incremental compilation, the dependency to the parent definition’s span. This is performed using the callback SPAN_TRACK to access the query engine.

Fields

base_or_index: u32

len_or_tag: u16

ctxt_or_tag: u16

Implementations

impl Span

pub fn fresh_expansion(self, expn_id: LocalExpnId) -> Span

Creates a fresh expansion with given properties. Expansions are normally created by macros, but in some cases expansions are created for other compiler-generated code to set per-span properties like allowed unstable features. The returned span belongs to the created expansion and has the new properties, but its location is inherited from the current span.

pub fn mark_with_reason(
    self,
    allow_internal_unstable: Option<Lrc<[Symbol]>>,
    reason: DesugaringKind,
    edition: Edition,
    ctx: impl HashStableContext
) -> Span

Reuses the span but adds information like the kind of the desugaring and features that are allowed inside this span.

impl Span

pub fn new(
    lo: BytePos,
    hi: BytePos,
    ctxt: SyntaxContext,
    parent: Option<LocalDefId>
) -> Self

pub fn data(self) -> SpanData

pub fn data_untracked(self) -> SpanData

Internal function to translate between an encoded span and the expanded representation. This function must not be used outside the incremental engine.

pub fn ctxt(self) -> SyntaxContext

This function is used as a fast path when decoding the full SpanData is not necessary.

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 eq_ctxt(self, other: Span) -> bool

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

pub fn parent(self) -> Option<LocalDefId>

pub fn with_parent(self, ctxt: Option<LocalDefId>) -> Span

pub fn is_dummy(self) -> bool

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

pub fn is_visible(self, sm: &SourceMap) -> bool

pub fn from_expansion(self) -> bool

Returns true if this span comes from any kind of macro, desugaring or inlining.

pub fn in_macro_expansion_with_collapse_debuginfo(self) -> bool

Returns true if span originates in a macro’s expansion where debuginfo should be collapsed.

pub fn is_inlined(self) -> bool

Returns true if this span comes from MIR inlining.

pub fn in_derive_expansion(self) -> bool

Returns true if span originates in a derive-macro’s expansion.

pub fn can_be_used_for_suggestions(self) -> bool

Gate suggestions that would not be appropriate in a context the user didn’t write.

pub fn with_root_ctxt(lo: BytePos, hi: BytePos) -> Span

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 is_empty(self) -> bool

Returns true if hi == lo.

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

Returns true if self fully encloses other.

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

Returns true if self touches other.

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

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

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

pub fn source_callsite(self) -> Span

Returns the source span – this is either the supplied span, or the span for the macro callsite that expanded to it.

pub fn parent_callsite(self) -> Option<Span>

The Span for the tokens in the previous macro expansion from which self was generated, if any.

pub fn find_ancestor_inside(self, outer: Span) -> Option<Span>

Walk down the expansion ancestors to find a span that’s contained within outer.

pub fn find_ancestor_in_same_ctxt(self, other: Span) -> Option<Span>

Like find_ancestor_inside, but specifically for when spans might not overlaps. Take care when using this, and prefer find_ancestor_inside when you know that the spans are nested (modulo macro expansion).

pub fn edition(self) -> Edition

Edition of the crate from which this span came.

pub fn rust_2015(self) -> bool

pub fn rust_2018(self) -> bool

pub fn rust_2021(self) -> bool

pub fn rust_2024(self) -> bool

pub fn source_callee(self) -> Option<ExpnData>

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 allows_unstable(self, feature: Symbol) -> bool

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 is_desugaring(self, kind: DesugaringKind) -> bool

Checks if this span arises from a compiler desugaring of kind kind.

pub fn desugaring_kind(self) -> Option<DesugaringKind>

Returns the compiler desugaring that created this span, or None if this span is not from a desugaring.

pub fn allows_unsafe(self) -> bool

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 macro_backtrace(self) -> impl Iterator<Item = ExpnData>

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

Returns a Span that would enclose both self and end.

    ____             ___
    self lorem ipsum end
    ^^^^^^^^^^^^^^^^^^^^

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

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

    ____             ___
    self lorem ipsum end
        ^^^^^^^^^^^^^

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

Returns a Span from the beginning of self until the beginning of end.

    ____             ___
    self lorem ipsum end
    ^^^^^^^^^^^^^^^^^

pub fn from_inner(self, inner: InnerSpan) -> Span

pub fn with_def_site_ctxt(self, expn_id: ExpnId) -> Span

Equivalent of Span::def_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

Equivalent of Span::call_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

Equivalent of Span::mixed_site from the proc macro API, except that the location is taken from the self span.

pub fn with_ctxt_from_mark(
    self,
    expn_id: ExpnId,
    transparency: Transparency
) -> Span

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 apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> Span

pub fn remove_mark(&mut self) -> ExpnId

pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId>

pub fn normalize_to_macros_2_0_and_adjust(
    &mut self,
    expn_id: ExpnId
) -> Option<ExpnId>

pub fn glob_adjust(
    &mut self,
    expn_id: ExpnId,
    glob_span: Span
) -> Option<Option<ExpnId>>

pub fn reverse_glob_adjust(
    &mut self,
    expn_id: ExpnId,
    glob_span: Span
) -> Option<Option<ExpnId>>

pub fn normalize_to_macros_2_0(self) -> Span

pub fn normalize_to_macro_rules(self) -> Span

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 Debug for Span

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

Formats the value using the given formatter.

impl<D: Decoder> Decodable<D> for Span

default fn decode(s: &mut D) -> Span

impl Default for Span

fn default() -> Self

Returns the “default value” for a type.

impl<E: Encoder> Encodable<E> for Span

default fn encode(&self, s: &mut E)

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,
    Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<CTX> HashStable<CTX> for Spanwhere
    CTX: HashStableContext,

fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher)

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.

impl Ord for Span

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

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Selfwhere
    Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: Sized + PartialOrd<Self>,

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: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

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.

fn lt(&self, other: &Rhs) -> bool

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

fn le(&self, other: &Rhs) -> bool

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

fn gt(&self, other: &Rhs) -> bool

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

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 Copy for Span

impl Eq for Span

impl !Send for Span

impl StructuralEq for Span

impl StructuralPartialEq for Span

impl !Sync for Span

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.

Size: 8 bytes