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Rework pattern and expression nonterminal kinds.
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Merge `PatParam`/`PatWithOr`, and `Expr`/`Expr2021`, for a few reasons.

- It's conceptually nice, because the two pattern kinds and the two
  expression kinds are very similar.

- With expressions in particular, there are several places where both
  expression kinds get the same treatment.

- It removes one unreachable match arm.

- Most importantly, for #124141 I will need to introduce a new type
  `MetaVarKind` that is very similar to `NonterminalKind`, but records a
  couple of extra fields for expression metavars. It's nicer to have a
  single `MetaVarKind::Expr` expression variant to hold those extra
  fields instead of duplicating them across two variants
  `MetaVarKind::{Expr,Expr2021}`. And then it makes sense for patterns
  to be treated the same way, and for `NonterminalKind` to also be
  treated the same way.

I also clarified the comments, because I have long found them a little
hard to understand.
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@nnethercote
nnethercote committed Jun 23, 2024
1 parent 70fa67c commit e2aa38e
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Showing 5 changed files with 71 additions and 60 deletions.
73 changes: 44 additions & 29 deletions compiler/rustc_ast/src/token.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
pub use BinOpToken::*;
pub use LitKind::*;
pub use Nonterminal::*;
pub use NtExprKind::*;
pub use NtPatKind::*;
pub use TokenKind::*;

use crate::ast;
Expand Down Expand Up @@ -871,6 +873,27 @@ impl PartialEq<TokenKind> for Token {
}
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Encodable, Decodable)]
pub enum NtPatKind {
// Matches or-patterns. Was written using `pat` in edition 2021 or later.
PatWithOr,
// Doesn't match or-patterns.
// - `inferred`: was written using `pat` in edition 2015 or 2018.
// - `!inferred`: was written using `pat_param`.
PatParam { inferred: bool },
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Encodable, Decodable)]
pub enum NtExprKind {
// Matches expressions using the post-edition 2024. Was written using
// `expr` in edition 2024 or later.
Expr,
// Matches expressions using the pre-edition 2024 rules.
// - `inferred`: was written using `expr` in edition 2021 or earlier.
// - `!inferred`: was written using `expr_2021`.
Expr2021 { inferred: bool },
}

#[derive(Clone, Encodable, Decodable)]
/// For interpolation during macro expansion.
pub enum Nonterminal {
Expand All @@ -892,19 +915,8 @@ pub enum NonterminalKind {
Item,
Block,
Stmt,
PatParam {
/// Keep track of whether the user used `:pat_param` or `:pat` and we inferred it from the
/// edition of the span. This is used for diagnostics.
inferred: bool,
},
PatWithOr,
Expr,
/// Matches an expression using the rules from edition 2021 and earlier.
Expr2021 {
/// Keep track of whether the user used `:expr` or `:expr_2021` and we inferred it from the
/// edition of the span. This is used for diagnostics AND feature gating.
inferred: bool,
},
Pat(NtPatKind),
Expr(NtExprKind),
Ty,
Ident,
Lifetime,
Expand All @@ -926,20 +938,22 @@ impl NonterminalKind {
sym::item => NonterminalKind::Item,
sym::block => NonterminalKind::Block,
sym::stmt => NonterminalKind::Stmt,
sym::pat => match edition() {
Edition::Edition2015 | Edition::Edition2018 => {
NonterminalKind::PatParam { inferred: true }
sym::pat => {
if edition().at_least_rust_2021() {
NonterminalKind::Pat(PatWithOr)
} else {
NonterminalKind::Pat(PatParam { inferred: true })
}
Edition::Edition2021 | Edition::Edition2024 => NonterminalKind::PatWithOr,
},
sym::pat_param => NonterminalKind::PatParam { inferred: false },
sym::expr => match edition() {
Edition::Edition2015 | Edition::Edition2018 | Edition::Edition2021 => {
NonterminalKind::Expr2021 { inferred: true }
}
sym::pat_param => NonterminalKind::Pat(PatParam { inferred: false }),
sym::expr => {
if edition().at_least_rust_2024() {
NonterminalKind::Expr(Expr)
} else {
NonterminalKind::Expr(Expr2021 { inferred: true })
}
Edition::Edition2024 => NonterminalKind::Expr,
},
sym::expr_2021 => NonterminalKind::Expr2021 { inferred: false },
}
sym::expr_2021 => NonterminalKind::Expr(Expr2021 { inferred: false }),
sym::ty => NonterminalKind::Ty,
sym::ident => NonterminalKind::Ident,
sym::lifetime => NonterminalKind::Lifetime,
Expand All @@ -951,15 +965,16 @@ impl NonterminalKind {
_ => return None,
})
}

fn symbol(self) -> Symbol {
match self {
NonterminalKind::Item => sym::item,
NonterminalKind::Block => sym::block,
NonterminalKind::Stmt => sym::stmt,
NonterminalKind::PatParam { inferred: false } => sym::pat_param,
NonterminalKind::PatParam { inferred: true } | NonterminalKind::PatWithOr => sym::pat,
NonterminalKind::Expr | NonterminalKind::Expr2021 { inferred: true } => sym::expr,
NonterminalKind::Expr2021 { inferred: false } => sym::expr_2021,
NonterminalKind::Pat(PatParam { inferred: true } | PatWithOr) => sym::pat,
NonterminalKind::Pat(PatParam { inferred: false }) => sym::pat_param,
NonterminalKind::Expr(Expr2021 { inferred: true } | Expr) => sym::expr,
NonterminalKind::Expr(Expr2021 { inferred: false }) => sym::expr_2021,
NonterminalKind::Ty => sym::ty,
NonterminalKind::Ident => sym::ident,
NonterminalKind::Lifetime => sym::lifetime,
Expand Down
20 changes: 10 additions & 10 deletions compiler/rustc_expand/src/mbe/macro_rules.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,9 @@ use crate::mbe::transcribe::transcribe;

use ast::token::IdentIsRaw;
use rustc_ast as ast;
use rustc_ast::token::{self, Delimiter, NonterminalKind, Token, TokenKind, TokenKind::*};
use rustc_ast::token::{
self, Delimiter, NonterminalKind, NtPatKind::*, Token, TokenKind, TokenKind::*,
};
use rustc_ast::tokenstream::{DelimSpan, TokenStream};
use rustc_ast::{NodeId, DUMMY_NODE_ID};
use rustc_ast_pretty::pprust;
Expand Down Expand Up @@ -1145,7 +1147,7 @@ fn check_matcher_core<'tt>(
// Macros defined in the current crate have a real node id,
// whereas macros from an external crate have a dummy id.
if def.id != DUMMY_NODE_ID
&& matches!(kind, NonterminalKind::PatParam { inferred: true })
&& matches!(kind, NonterminalKind::Pat(PatParam { inferred: true }))
&& matches!(
next_token,
TokenTree::Token(token) if token.kind == BinOp(token::BinOpToken::Or)
Expand All @@ -1155,7 +1157,7 @@ fn check_matcher_core<'tt>(
let suggestion = quoted_tt_to_string(&TokenTree::MetaVarDecl(
span,
name,
Some(NonterminalKind::PatParam { inferred: false }),
Some(NonterminalKind::Pat(PatParam { inferred: false })),
));
sess.psess.buffer_lint(
RUST_2021_INCOMPATIBLE_OR_PATTERNS,
Expand Down Expand Up @@ -1188,14 +1190,14 @@ fn check_matcher_core<'tt>(
);
err.span_label(sp, format!("not allowed after `{kind}` fragments"));

if kind == NonterminalKind::PatWithOr
if kind == NonterminalKind::Pat(PatWithOr)
&& sess.psess.edition.at_least_rust_2021()
&& next_token.is_token(&BinOp(token::BinOpToken::Or))
{
let suggestion = quoted_tt_to_string(&TokenTree::MetaVarDecl(
span,
name,
Some(NonterminalKind::PatParam { inferred: false }),
Some(NonterminalKind::Pat(PatParam { inferred: false })),
));
err.span_suggestion(
span,
Expand Down Expand Up @@ -1295,9 +1297,7 @@ fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
// maintain
IsInFollow::Yes
}
NonterminalKind::Stmt
| NonterminalKind::Expr
| NonterminalKind::Expr2021 { inferred: _ } => {
NonterminalKind::Stmt | NonterminalKind::Expr(_) => {
const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
match tok {
TokenTree::Token(token) => match token.kind {
Expand All @@ -1307,7 +1307,7 @@ fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
_ => IsInFollow::No(TOKENS),
}
}
NonterminalKind::PatParam { .. } => {
NonterminalKind::Pat(PatParam { .. }) => {
const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
match tok {
TokenTree::Token(token) => match token.kind {
Expand All @@ -1320,7 +1320,7 @@ fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
_ => IsInFollow::No(TOKENS),
}
}
NonterminalKind::PatWithOr => {
NonterminalKind::Pat(PatWithOr) => {
const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`if`", "`in`"];
match tok {
TokenTree::Token(token) => match token.kind {
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_expand/src/mbe/quoted.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ use crate::errors;
use crate::mbe::macro_parser::count_metavar_decls;
use crate::mbe::{Delimited, KleeneOp, KleeneToken, MetaVarExpr, SequenceRepetition, TokenTree};

use rustc_ast::token::{self, Delimiter, IdentIsRaw, NonterminalKind, Token};
use rustc_ast::token::{self, Delimiter, IdentIsRaw, NonterminalKind, NtExprKind::*, Token};
use rustc_ast::{tokenstream, NodeId};
use rustc_ast_pretty::pprust;
use rustc_feature::Features;
Expand Down Expand Up @@ -109,7 +109,7 @@ pub(super) fn parse(
});
NonterminalKind::Ident
});
if kind == (NonterminalKind::Expr2021 { inferred: false })
if kind == NonterminalKind::Expr(Expr2021 { inferred: false })
&& !features.expr_fragment_specifier_2024
{
rustc_session::parse::feature_err(
Expand Down
28 changes: 12 additions & 16 deletions compiler/rustc_parse/src/parser/nonterminal.rs
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, Nonterminal::*, NonterminalKind, Token};
use rustc_ast::token::{
self, Delimiter, Nonterminal::*, NonterminalKind, NtExprKind::*, NtPatKind::*, Token,
};
use rustc_ast::HasTokens;
use rustc_ast_pretty::pprust;
use rustc_data_structures::sync::Lrc;
Expand Down Expand Up @@ -36,14 +38,14 @@ impl<'a> Parser<'a> {
}

match kind {
NonterminalKind::Expr2021 { inferred: _ } => {
NonterminalKind::Expr(Expr2021 { .. }) => {
token.can_begin_expr()
// This exception is here for backwards compatibility.
&& !token.is_keyword(kw::Let)
// This exception is here for backwards compatibility.
&& !token.is_keyword(kw::Const)
}
NonterminalKind::Expr => {
NonterminalKind::Expr(Expr) => {
token.can_begin_expr()
// This exception is here for backwards compatibility.
&& !token.is_keyword(kw::Let)
Expand Down Expand Up @@ -74,7 +76,7 @@ impl<'a> Parser<'a> {
token::Interpolated(nt) => may_be_ident(nt),
_ => false,
},
NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr => match &token.kind {
NonterminalKind::Pat(pat_kind) => match &token.kind {
// box, ref, mut, and other identifiers (can stricten)
token::Ident(..) | token::NtIdent(..) |
token::OpenDelim(Delimiter::Parenthesis) | // tuple pattern
Expand All @@ -89,7 +91,7 @@ impl<'a> Parser<'a> {
token::Lt | // path (UFCS constant)
token::BinOp(token::Shl) => true, // path (double UFCS)
// leading vert `|` or-pattern
token::BinOp(token::Or) => matches!(kind, NonterminalKind::PatWithOr),
token::BinOp(token::Or) => matches!(pat_kind, PatWithOr),
token::Interpolated(nt) => may_be_ident(nt),
_ => false,
},
Expand Down Expand Up @@ -135,31 +137,25 @@ impl<'a> Parser<'a> {
.create_err(UnexpectedNonterminal::Statement(self.token.span)));
}
},
NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr => {
NtPat(self.collect_tokens_no_attrs(|this| match kind {
NonterminalKind::PatParam { .. } => this.parse_pat_no_top_alt(None, None),
NonterminalKind::PatWithOr => this.parse_pat_allow_top_alt(
NonterminalKind::Pat(pat_kind) => {
NtPat(self.collect_tokens_no_attrs(|this| match pat_kind {
PatParam { .. } => this.parse_pat_no_top_alt(None, None),
PatWithOr => this.parse_pat_allow_top_alt(
None,
RecoverComma::No,
RecoverColon::No,
CommaRecoveryMode::EitherTupleOrPipe,
),
_ => unreachable!(),
})?)
}

NonterminalKind::Expr | NonterminalKind::Expr2021 { inferred: _ } => {
NtExpr(self.parse_expr_force_collect()?)
}
NonterminalKind::Expr(_) => NtExpr(self.parse_expr_force_collect()?),
NonterminalKind::Literal => {
// The `:literal` matcher does not support attributes
NtLiteral(self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?)
}

NonterminalKind::Ty => {
NtTy(self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?)
}

// this could be handled like a token, since it is one
NonterminalKind::Ident => {
return if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
Expand Down
6 changes: 3 additions & 3 deletions src/tools/rustfmt/src/parse/macros/mod.rs
View file
Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use rustc_ast::token::{Delimiter, NonterminalKind, TokenKind};
use rustc_ast::token::{Delimiter, NonterminalKind, NtExprKind::*, NtPatKind::*, TokenKind};
use rustc_ast::tokenstream::TokenStream;
use rustc_ast::{ast, ptr};
use rustc_parse::parser::{ForceCollect, Parser, Recovery};
Expand Down Expand Up @@ -48,7 +48,7 @@ fn parse_macro_arg<'a, 'b: 'a>(parser: &'a mut Parser<'b>) -> Option<MacroArg> {

parse_macro_arg!(
Expr,
NonterminalKind::Expr,
NonterminalKind::Expr(Expr),
|parser: &mut Parser<'b>| parser.parse_expr(),
|x: ptr::P<ast::Expr>| Some(x)
);
Expand All @@ -60,7 +60,7 @@ fn parse_macro_arg<'a, 'b: 'a>(parser: &'a mut Parser<'b>) -> Option<MacroArg> {
);
parse_macro_arg!(
Pat,
NonterminalKind::PatParam { inferred: false },
NonterminalKind::Pat(PatParam { inferred: false }),
|parser: &mut Parser<'b>| parser.parse_pat_no_top_alt(None, None),
|x: ptr::P<ast::Pat>| Some(x)
);
Expand Down

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