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Adjust parsing of Slice, Tuple, TupleStruct patterns.

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This commit is contained in:
Mazdak Farrokhzad 2019-07-09 10:36:14 +02:00
parent 7e1b671f8a
commit 62b29a1e17
1 changed files with 26 additions and 127 deletions
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153
src/libsyntax/parse/parser.rs
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@ -3535,122 +3535,6 @@ impl<'a> Parser<'a> {
};
}
// Parses a parenthesized list of patterns like
// `()`, `(p)`, `(p,)`, `(p, q)`, or `(p, .., q)`. Returns:
// - a vector of the patterns that were parsed
// - an option indicating the index of the `..` element
// - a boolean indicating whether a trailing comma was present.
// Trailing commas are significant because (p) and (p,) are different patterns.
fn parse_parenthesized_pat_list(&mut self) -> PResult<'a, (Vec<P<Pat>>, Option<usize>, bool)> {
self.expect(&token::OpenDelim(token::Paren))?;
let result = match self.parse_pat_list() {
Ok(result) => result,
Err(mut err) => { // recover from parse error in tuple pattern list
err.emit();
self.consume_block(token::Paren);
return Ok((vec![], Some(0), false));
}
};
self.expect(&token::CloseDelim(token::Paren))?;
Ok(result)
}
fn parse_pat_list(&mut self) -> PResult<'a, (Vec<P<Pat>>, Option<usize>, bool)> {
let mut fields = Vec::new();
let mut ddpos = None;
let mut prev_dd_sp = None;
let mut trailing_comma = false;
loop {
if self.eat(&token::DotDot) {
if ddpos.is_none() {
ddpos = Some(fields.len());
prev_dd_sp = Some(self.prev_span);
} else {
// Emit a friendly error, ignore `..` and continue parsing
let mut err = self.struct_span_err(
self.prev_span,
"`..` can only be used once per tuple or tuple struct pattern",
);
err.span_label(self.prev_span, "can only be used once per pattern");
if let Some(sp) = prev_dd_sp {
err.span_label(sp, "previously present here");
}
err.emit();
}
} else if !self.check(&token::CloseDelim(token::Paren)) {
fields.push(self.parse_pat(None)?);
} else {
break
}
trailing_comma = self.eat(&token::Comma);
if !trailing_comma {
break
}
}
if ddpos == Some(fields.len()) && trailing_comma {
// `..` needs to be followed by `)` or `, pat`, `..,)` is disallowed.
let msg = "trailing comma is not permitted after `..`";
self.struct_span_err(self.prev_span, msg)
.span_label(self.prev_span, msg)
.emit();
}
Ok((fields, ddpos, trailing_comma))
}
fn parse_pat_vec_elements(
&mut self,
) -> PResult<'a, (Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>)> {
let mut before = Vec::new();
let mut slice = None;
let mut after = Vec::new();
let mut first = true;
let mut before_slice = true;
while self.token != token::CloseDelim(token::Bracket) {
if first {
first = false;
} else {
self.expect(&token::Comma)?;
if self.token == token::CloseDelim(token::Bracket)
&& (before_slice || !after.is_empty()) {
break
}
}
if before_slice {
if self.eat(&token::DotDot) {
if self.check(&token::Comma) ||
self.check(&token::CloseDelim(token::Bracket)) {
slice = Some(P(Pat {
id: ast::DUMMY_NODE_ID,
node: PatKind::Wild,
span: self.prev_span,
}));
before_slice = false;
}
continue
}
}
let subpat = self.parse_pat(None)?;
if before_slice && self.eat(&token::DotDot) {
slice = Some(subpat);
before_slice = false;
} else if before_slice {
before.push(subpat);
} else {
after.push(subpat);
}
}
Ok((before, slice, after))
}
fn parse_pat_field(
&mut self,
lo: Span,
@ -3862,6 +3746,17 @@ impl<'a> Parser<'a> {
}))
}
/// Parse a parentesized comma separated sequence of patterns until `delim` is reached.
fn parse_recover_pat_list(&mut self) -> PResult<'a, ()> {
while !self.check(&token::CloseDelim(token::Paren)) {
self.parse_pat(None)?;
if !self.eat(&token::Comma) {
return Ok(())
}
}
Ok(())
}
/// A wrapper around `parse_pat` with some special error handling for the
/// "top-level" patterns in a match arm, `for` loop, `let`, &c. (in contrast
/// to subpatterns within such).
@ -3875,7 +3770,7 @@ impl<'a> Parser<'a> {
// later.
let comma_span = self.token.span;
self.bump();
if let Err(mut err) = self.parse_pat_list() {
if let Err(mut err) = self.parse_recover_pat_list() {
// We didn't expect this to work anyway; we just wanted
// to advance to the end of the comma-sequence so we know
// the span to suggest parenthesizing
@ -3933,20 +3828,24 @@ impl<'a> Parser<'a> {
pat = PatKind::Ref(subpat, mutbl);
}
token::OpenDelim(token::Paren) => {
// Parse (pat,pat,pat,...) as tuple pattern
let (fields, ddpos, trailing_comma) = self.parse_parenthesized_pat_list()?;
pat = if fields.len() == 1 && ddpos.is_none() && !trailing_comma {
// Parse `(pat, pat, pat, ...)` as tuple pattern.
let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| p.parse_pat(None))?;
pat = if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
PatKind::Paren(fields.into_iter().nth(0).unwrap())
} else {
PatKind::Tuple(fields, ddpos)
PatKind::Tuple(fields)
};
}
token::OpenDelim(token::Bracket) => {
// Parse [pat,pat,...] as slice pattern
// Parse `[pat, pat,...]` as a slice pattern.
let (slice, _) = self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat(None))?;
pat = PatKind::Slice(slice);
}
token::DotDot => {
// Parse `..`.
self.bump();
let (before, slice, after) = self.parse_pat_vec_elements()?;
self.expect(&token::CloseDelim(token::Bracket))?;
pat = PatKind::Slice(before, slice, after);
pat = PatKind::Rest;
}
// At this point, token != &, &&, (, [
_ => if self.eat_keyword(kw::Underscore) {
@ -4044,8 +3943,8 @@ impl<'a> Parser<'a> {
return Err(err);
}
// Parse tuple struct or enum pattern
let (fields, ddpos, _) = self.parse_parenthesized_pat_list()?;
pat = PatKind::TupleStruct(path, fields, ddpos)
let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat(None))?;
pat = PatKind::TupleStruct(path, fields)
}
_ => pat = PatKind::Path(qself, path),
}