Skip to content

Commit

Permalink
Clarify parse_dot_suffix_expr.
Browse files Browse the repository at this point in the history
For the `MiddleDot` case, current behaviour:
- For a case like `1.2`, `sym1` is `1` and `sym2` is `2`, and `self.token`
  holds `1.2`.
- It creates a new ident token from `sym1` that it puts into `self.token`.
- Then it does `bump_with` with a new dot token, which moves the `sym1`
  token into `prev_token`.
- Then it does `bump_with` with a new ident token from `sym2`, which moves the
  `dot` token into `prev_token` and discards the `sym1` token.
- Then it does `bump`, which puts whatever is next into `self.token`,
  moves the `sym2` token into `prev_token`, and discards the `dot` token
  altogether.

New behaviour:
- Skips creating and inserting the `sym1` and dot tokens, because they are
  unnecessary.
- This also demonstrates that the comment about `Spacing::Alone` is
  wrong -- that value is never used. That comment was added in #77250,
  and AFAICT it has always been incorrect.

The commit also expands comments. I found this code hard to read
previously, the examples in comments make it easier.
  • Loading branch information
nnethercote committed Mar 22, 2024
1 parent f311ef0 commit 421d9c1
Showing 1 changed file with 19 additions and 19 deletions.
38 changes: 19 additions & 19 deletions compiler/rustc_parse/src/parser/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,6 @@ use core::mem;
use core::ops::ControlFlow;
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, Token, TokenKind};
use rustc_ast::tokenstream::Spacing;
use rustc_ast::util::case::Case;
use rustc_ast::util::classify;
use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
Expand Down Expand Up @@ -999,6 +998,8 @@ impl<'a> Parser<'a> {
}

pub fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
// At this point we've consumed something like `expr.` and `self.token` holds the token
// after the dot.
match self.token.uninterpolate().kind {
token::Ident(..) => self.parse_dot_suffix(base, lo),
token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
Expand All @@ -1008,41 +1009,40 @@ impl<'a> Parser<'a> {
}
token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
Ok(match self.break_up_float(symbol, self.token.span) {
// 1e2
DestructuredFloat::Single(sym, _sp) => {
// `foo.1e2`: a single complete dot access, fully consumed. We end up with
// the `1e2` token in `self.prev_token` and the following token in
// `self.token`.
let ident_span = self.token.span;
self.bump();
self.mk_expr_tuple_field_access(lo, ident_span, base, sym, suffix)
}
// 1.
DestructuredFloat::TrailingDot(sym, ident_span, dot_span) => {
// `foo.1.`: a single complete dot access and the start of another.
// We end up with the `sym` (`1`) token in `self.prev_token` and a dot in
// `self.token`.
assert!(suffix.is_none());
self.token = Token::new(token::Ident(sym, IdentIsRaw::No), ident_span);
let ident_span = self.token.span;
self.bump_with((Token::new(token::Dot, dot_span), self.token_spacing));
self.mk_expr_tuple_field_access(lo, ident_span, base, sym, None)
}
// 1.2 | 1.2e3
DestructuredFloat::MiddleDot(
symbol1,
sym1,
ident1_span,
dot_span,
symbol2,
_dot_span,
sym2,
ident2_span,
) => {
self.token = Token::new(token::Ident(symbol1, IdentIsRaw::No), ident1_span);
// This needs to be `Spacing::Alone` to prevent regressions.
// See issue #76399 and PR #76285 for more details
let ident_span = self.token.span;
self.bump_with((Token::new(token::Dot, dot_span), Spacing::Alone));
let base1 =
self.mk_expr_tuple_field_access(lo, ident_span, base, symbol1, None);
// `foo.1.2` (or `foo.1.2e3`): two complete dot accesses. We end up with
// the `sym2` (`2` or `2e3`) token in `self.prev_token` and the following
// token in `self.token`.
let next_token2 =
Token::new(token::Ident(symbol2, IdentIsRaw::No), ident2_span);
self.bump_with((next_token2, self.token_spacing)); // `.`
let ident_span = self.token.span;
Token::new(token::Ident(sym2, IdentIsRaw::No), ident2_span);
self.bump_with((next_token2, self.token_spacing));
self.bump();
self.mk_expr_tuple_field_access(lo, ident_span, base1, symbol2, suffix)
let base1 =
self.mk_expr_tuple_field_access(lo, ident1_span, base, sym1, None);
self.mk_expr_tuple_field_access(lo, ident2_span, base1, sym2, suffix)
}
DestructuredFloat::Error => base,
})
Expand Down

0 comments on commit 421d9c1

Please sign in to comment.