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proc_macro::Group::span_open and span_close #53902

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merged 3 commits into from
Sep 9, 2018
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proc_macro::Group::span_open and span_close #53902

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proc_macro::Group::span_open and span_close
dtolnay Sep 2, 2018
a1dd39e
Track distinct spans for open and close delimiter
dtolnay Sep 9, 2018
57d6ada
Rename sp_lo to sp_open
dtolnay Sep 9, 2018
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43 changes: 42 additions & 1 deletion src/libproc_macro/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,7 @@ use syntax::errors::DiagnosticBuilder;
use syntax::parse::{self, token};
use syntax::symbol::Symbol;
use syntax::tokenstream;
use syntax_pos::{Pos, FileName};
use syntax_pos::{BytePos, Pos, FileName};

/// The main type provided by this crate, representing an abstract stream of
/// tokens, or, more specifically, a sequence of token trees.
Expand Down Expand Up @@ -671,11 +671,52 @@ impl Group {

/// Returns the span for the delimiters of this token stream, spanning the
/// entire `Group`.
///
/// ```text
/// pub fn span(&self) -> Span {
/// ^^^^^^^
/// ```
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub fn span(&self) -> Span {
self.span
}

/// Returns the span pointing to the opening delimiter of this group, or the
/// span of the entire group if this is a None-delimited group.
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Hmm, this sounds too specific.
Perhaps more general methods on Span like fn shrink_to_lo/fn shrink_to_hi in the compiler would be more useful?

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@petrochenkov petrochenkov Sep 2, 2018 •
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(Need to figure out specifics though, zero-character spans are still showed as single-character in errors, but positions may be +/-1 wrong depending on use case.)

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@dtolnay dtolnay Sep 2, 2018 •
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Either way works for me, but in my use case I don't really see this being called other than on the span of a Group. I opened #53904 with methods on Span.

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Some quick review of uses of shrink_to_lo/shrink_to_hi in the compiler:

  • Pointing to the private visibility / place to insert visibility (not a group).
  • Pointing at elided () return type in functions (group).
  • Pointing to the place to insert missing imports (not a group).
  • Pointing at the end of fn call to insert .as_ref() (group).
  • Pointing at the last missing argument in fn call (group).
  • Pointing at elided lifetime in &Type (not a group).
  • Pointing at missing lifetime argument at the start of generic argument list (not a group).
  • ... (ok, that's enough)

So, there are different possible uses for both groups and non-groups.

///
/// ```text
/// pub fn span_open(&self) -> Span {
/// ^
/// ```
#[unstable(feature = "proc_macro_span", issue = "38356")]
pub fn span_open(&self) -> Span {
if self.delimiter == Delimiter::None {
self.span
} else {
let lo = self.span.0.lo();
let new_hi = BytePos::from_usize(lo.to_usize() + 1);
Span(self.span.0.with_hi(new_hi))
}
}

/// Returns the span pointing to the closing delimiter of this group, or the
/// span of the entire group if this is a None-delimited group.
///
/// ```text
/// pub fn span_close(&self) -> Span {
/// ^
/// ```
#[unstable(feature = "proc_macro_span", issue = "38356")]
pub fn span_close(&self) -> Span {
let hi = self.span.0.hi();
if self.delimiter == Delimiter::None || hi.to_usize() == 0 {
self.span
} else {
let new_lo = BytePos::from_usize(hi.to_usize() - 1);
Span(self.span.0.with_lo(new_lo))
}
}

/// Configures the span for this `Group`'s delimiters, but not its internal
/// tokens.
///
Expand Down