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Simplify pattern grammar by allowing nested leading vert

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Along the way, we also implement a handful of diagnostics improvements
and fixes, particularly with respect to the special handling of `||` in
place of `|` and when there are leading verts in function params, which
don't allow top-level or-patterns anyway.
This commit is contained in:
mark 2021-02-07 20:40:33 -06:00
parent d1206f950f
commit aee1e59e6f
18 changed files with 189 additions and 303 deletions
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2
compiler/rustc_parse/src/parser/diagnostics.rs
View file

@ -1654,7 +1654,7 @@ impl<'a> Parser<'a> {
}
pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
let pat = self.parse_pat(Some("argument name"))?;
let pat = self.parse_pat_no_top_alt(Some("argument name"))?;
self.expect(&token::Colon)?;
let ty = self.parse_ty()?;

8
compiler/rustc_parse/src/parser/expr.rs
View file

@ -1726,7 +1726,7 @@ impl<'a> Parser<'a> {
let lo = self.token.span;
let attrs = self.parse_outer_attributes()?;
self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
let pat = this.parse_pat(PARAM_EXPECTED)?;
let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
let ty = if this.eat(&token::Colon) {
this.parse_ty()?
} else {
@ -1803,7 +1803,7 @@ impl<'a> Parser<'a> {
/// The `let` token has already been eaten.
fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
let lo = self.prev_token.span;
let pat = self.parse_top_pat(GateOr::No, RecoverComma::Yes)?;
let pat = self.parse_pat_allow_top_alt(None, GateOr::No, RecoverComma::Yes)?;
self.expect(&token::Eq)?;
let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
@ -1866,7 +1866,7 @@ impl<'a> Parser<'a> {
_ => None,
};
let pat = self.parse_top_pat(GateOr::Yes, RecoverComma::Yes)?;
let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::Yes)?;
if !self.eat_keyword(kw::In) {
self.error_missing_in_for_loop();
}
@ -1977,7 +1977,7 @@ impl<'a> Parser<'a> {
let attrs = self.parse_outer_attributes()?;
self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
let lo = this.token.span;
let pat = this.parse_top_pat(GateOr::No, RecoverComma::Yes)?;
let pat = this.parse_pat_allow_top_alt(None, GateOr::No, RecoverComma::Yes)?;
let guard = if this.eat_keyword(kw::If) {
let if_span = this.prev_token.span;
let cond = this.parse_expr()?;

1
compiler/rustc_parse/src/parser/mod.rs
View file

@ -14,6 +14,7 @@ use crate::lexer::UnmatchedBrace;
pub use attr_wrapper::AttrWrapper;
pub use diagnostics::AttemptLocalParseRecovery;
use diagnostics::Error;
pub use pat::{GateOr, RecoverComma};
pub use path::PathStyle;
use rustc_ast::ptr::P;

4
compiler/rustc_parse/src/parser/nonterminal.rs
View file

@ -120,9 +120,9 @@ impl<'a> Parser<'a> {
},
NonterminalKind::Pat2018 { .. } | NonterminalKind::Pat2021 { .. } => {
token::NtPat(self.collect_tokens_no_attrs(|this| match kind {
NonterminalKind::Pat2018 { .. } => this.parse_pat(None),
NonterminalKind::Pat2018 { .. } => this.parse_pat_no_top_alt(None),
NonterminalKind::Pat2021 { .. } => {
this.parse_top_pat(GateOr::Yes, RecoverComma::No)
this.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
}
_ => unreachable!(),
})?)

185
compiler/rustc_parse/src/parser/pat.rs
View file

@ -19,14 +19,14 @@ const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here"
/// Whether or not an or-pattern should be gated when occurring in the current context.
#[derive(PartialEq, Clone, Copy)]
pub(super) enum GateOr {
pub enum GateOr {
Yes,
No,
}
/// Whether or not to recover a `,` when parsing or-patterns.
#[derive(PartialEq, Copy, Clone)]
pub(super) enum RecoverComma {
pub enum RecoverComma {
Yes,
No,
}
@ -37,80 +37,57 @@ impl<'a> Parser<'a> {
/// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
/// at the top level. Used when parsing the parameters of lambda expressions,
/// functions, function pointers, and `pat` macro fragments.
pub fn parse_pat(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
pub fn parse_pat_no_top_alt(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
self.parse_pat_with_range_pat(true, expected)
}
/// Entry point to the main pattern parser.
/// Parses a pattern.
///
/// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
pub(super) fn parse_top_pat(
&mut self,
gate_or: GateOr,
rc: RecoverComma,
) -> PResult<'a, P<Pat>> {
// Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
let gated_leading_vert = self.eat_or_separator(None) && gate_or == GateOr::Yes;
let leading_vert_span = self.prev_token.span;
// Parse the possibly-or-pattern.
let pat = self.parse_pat_with_or(None, gate_or, rc)?;
// If we parsed a leading `|` which should be gated,
// and no other gated or-pattern has been parsed thus far,
// then we should really gate the leading `|`.
// This complicated procedure is done purely for diagnostics UX.
if gated_leading_vert && self.sess.gated_spans.is_ungated(sym::or_patterns) {
self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
}
Ok(pat)
}
/// Parse the pattern for a function or function pointer parameter.
/// Special recovery is provided for or-patterns and leading `|`.
pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
self.recover_leading_vert(None, "not allowed in a parameter pattern");
let pat = self.parse_pat_with_or(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
if let PatKind::Or(..) = &pat.kind {
self.ban_illegal_fn_param_or_pat(&pat);
}
Ok(pat)
}
/// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
let msg = "wrap the pattern in parenthesis";
let fix = format!("({})", pprust::pat_to_string(pat));
self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parenthesis")
.span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
.emit();
}
/// Parses a pattern, that may be a or-pattern (e.g. `Foo | Bar` in `Some(Foo | Bar)`).
/// Corresponds to `pat<allow_top_alt>` in RFC 2535.
fn parse_pat_with_or(
/// Used for parsing patterns in all cases when `pat<no_top_alt>` is not used.
///
/// Note that after the FCP in <https://github.com/rust-lang/rust/issues/81415>,
/// a leading vert is allowed in nested or-patterns, too. This allows us to
/// simplify the grammar somewhat.
pub fn parse_pat_allow_top_alt(
&mut self,
expected: Expected,
gate_or: GateOr,
rc: RecoverComma,
) -> PResult<'a, P<Pat>> {
// Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
let leading_vert_span =
if self.eat_or_separator(None) { Some(self.prev_token.span) } else { None };
// Parse the first pattern (`p_0`).
let first_pat = self.parse_pat(expected)?;
let first_pat = self.parse_pat_no_top_alt(expected)?;
self.maybe_recover_unexpected_comma(first_pat.span, rc, gate_or)?;
// If the next token is not a `|`,
// this is not an or-pattern and we should exit here.
if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
// If we parsed a leading `|` which should be gated,
// then we should really gate the leading `|`.
// This complicated procedure is done purely for diagnostics UX.
if let Some(leading_vert_span) = leading_vert_span {
if gate_or == GateOr::Yes && self.sess.gated_spans.is_ungated(sym::or_patterns) {
self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
}
// If there was a leading vert, treat this as an or-pattern. This improves
// diagnostics.
let span = leading_vert_span.to(self.prev_token.span);
return Ok(self.mk_pat(span, PatKind::Or(vec![first_pat])));
}
return Ok(first_pat);
}
// Parse the patterns `p_1 | ... | p_n` where `n > 0`.
let lo = first_pat.span;
let lo = leading_vert_span.unwrap_or(first_pat.span);
let mut pats = vec![first_pat];
while self.eat_or_separator(Some(lo)) {
let pat = self.parse_pat(expected).map_err(|mut err| {
let pat = self.parse_pat_no_top_alt(expected).map_err(|mut err| {
err.span_label(lo, WHILE_PARSING_OR_MSG);
err
})?;
@ -127,6 +104,62 @@ impl<'a> Parser<'a> {
Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
}
/// Parse the pattern for a function or function pointer parameter.
pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
// We actually do _not_ allow top-level or-patterns in function params, but we use
// `parse_pat_allow_top_alt` anyway so that we can detect when a user tries to use it. This
// allows us to print a better error message.
//
// In order to get good UX, we first recover in the case of a leading vert for an illegal
// top-level or-pat. Normally, this means recovering both `|` and `||`, but in this case,
// a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
// separately.
if let token::OrOr = self.token.kind {
let span = self.token.span;
let mut err = self.struct_span_err(span, "unexpected `||` before function parameter");
err.span_suggestion(
span,
"remove the `||`",
String::new(),
Applicability::MachineApplicable,
);
err.note("alternatives in or-patterns are separated with `|`, not `||`");
err.emit();
self.bump();
}
let pat = self.parse_pat_allow_top_alt(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
if let PatKind::Or(..) = &pat.kind {
self.ban_illegal_fn_param_or_pat(&pat);
}
Ok(pat)
}
/// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
// If all we have a leading vert, then print a special message. This is the case if
// `parse_pat_allow_top_alt` returns an or-pattern with one variant.
let (msg, fix) = match &pat.kind {
PatKind::Or(pats) if pats.len() == 1 => {
let msg = "remove the leading `|`";
let fix = pprust::pat_to_string(pat);
(msg, fix)
}
_ => {
let msg = "wrap the pattern in parentheses";
let fix = format!("({})", pprust::pat_to_string(pat));
(msg, fix)
}
};
self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parentheses")
.span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
.emit();
}
/// Eat the or-pattern `|` separator.
/// If instead a `||` token is encountered, recover and pretend we parsed `|`.
fn eat_or_separator(&mut self, lo: Option<Span>) -> bool {
@ -179,7 +212,7 @@ impl<'a> Parser<'a> {
/// We have parsed `||` instead of `|`. Error and suggest `|` instead.
fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
let mut err = self.struct_span_err(self.token.span, "unexpected token `||` after pattern");
let mut err = self.struct_span_err(self.token.span, "unexpected token `||` in pattern");
err.span_suggestion(
self.token.span,
"use a single `|` to separate multiple alternative patterns",
@ -244,7 +277,7 @@ impl<'a> Parser<'a> {
/// sequence of patterns until `)` is reached.
fn skip_pat_list(&mut self) -> PResult<'a, ()> {
while !self.check(&token::CloseDelim(token::Paren)) {
self.parse_pat(None)?;
self.parse_pat_no_top_alt(None)?;
if !self.eat(&token::Comma) {
return Ok(());
}
@ -252,22 +285,6 @@ impl<'a> Parser<'a> {
Ok(())
}
/// Recursive possibly-or-pattern parser with recovery for an erroneous leading `|`.
/// See `parse_pat_with_or` for details on parsing or-patterns.
fn parse_pat_with_or_inner(&mut self) -> PResult<'a, P<Pat>> {
self.recover_leading_vert(None, "only allowed in a top-level pattern");
self.parse_pat_with_or(None, GateOr::Yes, RecoverComma::No)
}
/// Recover if `|` or `||` is here.
/// The user is thinking that a leading `|` is allowed in this position.
fn recover_leading_vert(&mut self, lo: Option<Span>, ctx: &str) {
if let token::BinOp(token::Or) | token::OrOr = self.token.kind {
self.ban_illegal_vert(lo, "leading", ctx);
self.bump();
}
}
/// A `|` or possibly `||` token shouldn't be here. Ban it.
fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
let span = self.token.span;
@ -305,8 +322,9 @@ impl<'a> Parser<'a> {
self.parse_pat_tuple_or_parens()?
} else if self.check(&token::OpenDelim(token::Bracket)) {
// Parse `[pat, pat,...]` as a slice pattern.
let (pats, _) =
self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat_with_or_inner())?;
let (pats, _) = self.parse_delim_comma_seq(token::Bracket, |p| {
p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
})?;
PatKind::Slice(pats)
} else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
// A rest pattern `..`.
@ -429,7 +447,7 @@ impl<'a> Parser<'a> {
// At this point we attempt to parse `@ $pat_rhs` and emit an error.
self.bump(); // `@`
let mut rhs = self.parse_pat(None)?;
let mut rhs = self.parse_pat_no_top_alt(None)?;
let sp = lhs.span.to(rhs.span);
if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
@ -518,8 +536,9 @@ impl<'a> Parser<'a> {
/// Parse a tuple or parenthesis pattern.
fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
let (fields, trailing_comma) =
self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
})?;
// Here, `(pat,)` is a tuple pattern.
// For backward compatibility, `(..)` is a tuple pattern as well.
@ -548,7 +567,7 @@ impl<'a> Parser<'a> {
}
// Parse the pattern we hope to be an identifier.
let mut pat = self.parse_pat(Some("identifier"))?;
let mut pat = self.parse_pat_no_top_alt(Some("identifier"))?;
// If we don't have `mut $ident (@ pat)?`, error.
if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind {
@ -793,7 +812,7 @@ impl<'a> Parser<'a> {
fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
let ident = self.parse_ident()?;
let sub = if self.eat(&token::At) {
Some(self.parse_pat(Some("binding pattern"))?)
Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
} else {
None
};
@ -832,7 +851,9 @@ impl<'a> Parser<'a> {
if qself.is_some() {
return self.error_qpath_before_pat(&path, "(");
}
let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
let (fields, _) = self.parse_paren_comma_seq(|p| {
p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
})?;
Ok(PatKind::TupleStruct(path, fields))
}
@ -998,7 +1019,7 @@ impl<'a> Parser<'a> {
// Parsing a pattern of the form `fieldname: pat`.
let fieldname = self.parse_field_name()?;
self.bump();
let pat = self.parse_pat_with_or_inner()?;
let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)?;
hi = pat.span;
(pat, fieldname, false)
} else {

2
compiler/rustc_parse/src/parser/stmt.rs
View file

@ -220,7 +220,7 @@ impl<'a> Parser<'a> {
/// Parses a local variable declaration.
fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
let lo = self.prev_token.span;
let pat = self.parse_top_pat(GateOr::Yes, RecoverComma::Yes)?;
let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::Yes)?;
let (err, ty) = if self.eat(&token::Colon) {
// Save the state of the parser before parsing type normally, in case there is a `:`