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Rollup merge of rust-lang#121619 - RossSmyth:pfix_match, r=petrochenkov
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Experimental feature postfix match

This has a basic experimental implementation for the RFC postfix match (rust-lang/rfcs#3295, rust-lang#121618). [Liaison is](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Postfix.20Match.20Liaison/near/423301844) ``@scottmcm`` with the lang team's [experimental feature gate process](https://github.com/rust-lang/lang-team/blob/master/src/how_to/experiment.md).

This feature has had an RFC for a while, and there has been discussion on it for a while. It would probably be valuable to see it out in the field rather than continue discussing it. This feature also allows to see how popular postfix expressions like this are for the postfix macros RFC, as those will take more time to implement.

It is entirely implemented in the parser, so it should be relatively easy to remove if needed.

This PR is split in to 5 commits to ease review.

1. The implementation of the feature & gating.
2. Add a MatchKind field, fix uses, fix pretty.
3. Basic rustfmt impl, as rustfmt crashes upon seeing this syntax without a fix.
4. Add new MatchSource to HIR for Clippy & other HIR consumers
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matthiaskrgr authored Mar 22, 2024
2 parents 7762adc + 567c98b commit efde155
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Showing 34 changed files with 367 additions and 41 deletions.
11 changes: 10 additions & 1 deletion compiler/rustc_ast/src/ast.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1441,7 +1441,7 @@ pub enum ExprKind {
/// `'label: loop { block }`
Loop(P<Block>, Option<Label>, Span),
/// A `match` block.
Match(P<Expr>, ThinVec<Arm>),
Match(P<Expr>, ThinVec<Arm>, MatchKind),
/// A closure (e.g., `move |a, b, c| a + b + c`).
Closure(Box<Closure>),
/// A block (`'label: { ... }`).
Expand Down Expand Up @@ -1766,6 +1766,15 @@ pub enum StrStyle {
Raw(u8),
}

/// The kind of match expression
#[derive(Clone, Copy, Encodable, Decodable, Debug, PartialEq)]
pub enum MatchKind {
/// match expr { ... }
Prefix,
/// expr.match { ... }
Postfix,
}

/// A literal in a meta item.
#[derive(Clone, Encodable, Decodable, Debug, HashStable_Generic)]
pub struct MetaItemLit {
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_ast/src/mut_visit.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1425,7 +1425,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
visit_opt(label, |label| vis.visit_label(label));
vis.visit_span(span);
}
ExprKind::Match(expr, arms) => {
ExprKind::Match(expr, arms, _kind) => {
vis.visit_expr(expr);
arms.flat_map_in_place(|arm| vis.flat_map_arm(arm));
}
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_ast/src/visit.rs
Original file line number Diff line number Diff line change
Expand Up @@ -923,7 +923,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) -> V
visit_opt!(visitor, visit_label, opt_label);
try_visit!(visitor.visit_block(block));
}
ExprKind::Match(subexpression, arms) => {
ExprKind::Match(subexpression, arms, _kind) => {
try_visit!(visitor.visit_expr(subexpression));
walk_list!(visitor, visit_arm, arms);
}
Expand Down
7 changes: 5 additions & 2 deletions compiler/rustc_ast_lowering/src/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -181,10 +181,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
)
}),
ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
ExprKind::Match(expr, arms) => hir::ExprKind::Match(
ExprKind::Match(expr, arms, kind) => hir::ExprKind::Match(
self.lower_expr(expr),
self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
hir::MatchSource::Normal,
match kind {
MatchKind::Prefix => hir::MatchSource::Normal,
MatchKind::Postfix => hir::MatchSource::Postfix,
},
),
ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
ExprKind::Closure(box Closure {
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_ast_passes/src/feature_gate.rs
Original file line number Diff line number Diff line change
Expand Up @@ -564,6 +564,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
gate_all!(generic_const_items, "generic const items are experimental");
gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
gate_all!(fn_delegation, "functions delegation is not yet fully implemented");
gate_all!(postfix_match, "postfix match is experimental");

if !visitor.features.never_patterns {
if let Some(spans) = spans.get(&sym::never_patterns) {
Expand Down
20 changes: 15 additions & 5 deletions compiler/rustc_ast_pretty/src/pprust/state/expr.rs
Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use crate::pp::Breaks::Inconsistent;
use crate::pprust::state::{AnnNode, PrintState, State, INDENT_UNIT};
use ast::ForLoopKind;
use ast::{ForLoopKind, MatchKind};
use itertools::{Itertools, Position};
use rustc_ast::ptr::P;
use rustc_ast::token;
Expand Down Expand Up @@ -589,12 +589,22 @@ impl<'a> State<'a> {
self.word_nbsp("loop");
self.print_block_with_attrs(blk, attrs);
}
ast::ExprKind::Match(expr, arms) => {
ast::ExprKind::Match(expr, arms, match_kind) => {
self.cbox(0);
self.ibox(0);
self.word_nbsp("match");
self.print_expr_as_cond(expr);
self.space();

match match_kind {
MatchKind::Prefix => {
self.word_nbsp("match");
self.print_expr_as_cond(expr);
self.space();
}
MatchKind::Postfix => {
self.print_expr_as_cond(expr);
self.word_nbsp(".match");
}
}

self.bopen();
self.print_inner_attributes_no_trailing_hardbreak(attrs);
for arm in arms {
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/assert/context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -245,7 +245,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
ExprKind::Let(_, local_expr, _, _) => {
self.manage_cond_expr(local_expr);
}
ExprKind::Match(local_expr, _) => {
ExprKind::Match(local_expr, ..) => {
self.manage_cond_expr(local_expr);
}
ExprKind::MethodCall(call) => {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,7 @@ fn cs_partial_cmp(
// Reference: https://github.com/rust-lang/rust/pull/103659#issuecomment-1328126354

if !tag_then_data
&& let ExprKind::Match(_, arms) = &mut expr1.kind
&& let ExprKind::Match(_, arms, _) = &mut expr1.kind
&& let Some(last) = arms.last_mut()
&& let PatKind::Wild = last.pat.kind
{
Expand Down
3 changes: 1 addition & 2 deletions compiler/rustc_builtin_macros/src/deriving/debug.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,7 @@ use crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::path_std;

use ast::EnumDef;
use rustc_ast::{self as ast, MetaItem};
use rustc_ast::{self as ast, EnumDef, MetaItem};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::Span;
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_expand/src/build.rs
Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use crate::base::ExtCtxt;
use rustc_ast::ptr::P;
use rustc_ast::{self as ast, AttrVec, BlockCheckMode, Expr, LocalKind, PatKind, UnOp};
use rustc_ast::{self as ast, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp};
use rustc_ast::{attr, token, util::literal};
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
Expand Down Expand Up @@ -524,7 +524,7 @@ impl<'a> ExtCtxt<'a> {
}

pub fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: ThinVec<ast::Arm>) -> P<Expr> {
self.expr(span, ast::ExprKind::Match(arg, arms))
self.expr(span, ast::ExprKind::Match(arg, arms, MatchKind::Prefix))
}

pub fn expr_if(
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/unstable.rs
Original file line number Diff line number Diff line change
Expand Up @@ -559,6 +559,8 @@ declare_features! (
(unstable, offset_of_nested, "1.77.0", Some(120140)),
/// Allows using `#[optimize(X)]`.
(unstable, optimize_attribute, "1.34.0", Some(54882)),
/// Allows postfix match `expr.match { ... }`
(unstable, postfix_match, "CURRENT_RUSTC_VERSION", Some(121618)),
/// Allows macro attributes on expressions, statements and non-inline modules.
(unstable, proc_macro_hygiene, "1.30.0", Some(54727)),
/// Allows `&raw const $place_expr` and `&raw mut $place_expr` expressions.
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_hir/src/hir.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2019,6 +2019,8 @@ pub enum LocalSource {
pub enum MatchSource {
/// A `match _ { .. }`.
Normal,
/// A `expr.match { .. }`.
Postfix,
/// A desugared `for _ in _ { .. }` loop.
ForLoopDesugar,
/// A desugared `?` operator.
Expand All @@ -2035,6 +2037,7 @@ impl MatchSource {
use MatchSource::*;
match self {
Normal => "match",
Postfix => ".match",
ForLoopDesugar => "for",
TryDesugar(_) => "?",
AwaitDesugar => ".await",
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_lint/src/unused.rs
Original file line number Diff line number Diff line change
Expand Up @@ -865,7 +865,7 @@ trait UnusedDelimLint {
(iter, UnusedDelimsCtx::ForIterExpr, true, None, Some(body.span.lo()), true)
}

Match(ref head, _) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
Match(ref head, ..) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
let left = e.span.lo() + rustc_span::BytePos(5);
(head, UnusedDelimsCtx::MatchScrutineeExpr, true, Some(left), None, true)
}
Expand Down Expand Up @@ -1133,7 +1133,7 @@ impl EarlyLintPass for UnusedParens {
}
return;
}
ExprKind::Match(ref _expr, ref arm) => {
ExprKind::Match(ref _expr, ref arm, _) => {
for a in arm {
if let Some(body) = &a.body {
self.check_unused_delims_expr(
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_mir_build/src/thir/pattern/check_match.rs
Original file line number Diff line number Diff line change
Expand Up @@ -481,6 +481,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
// when the iterator is an uninhabited type. unreachable_code will trigger instead.
hir::MatchSource::ForLoopDesugar if arms.len() == 1 => {}
hir::MatchSource::ForLoopDesugar
| hir::MatchSource::Postfix
| hir::MatchSource::Normal
| hir::MatchSource::FormatArgs => report_arm_reachability(&cx, &report),
// Unreachable patterns in try and await expressions occur when one of
Expand Down
29 changes: 24 additions & 5 deletions compiler/rustc_parse/src/parser/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ use crate::errors;
use crate::maybe_recover_from_interpolated_ty_qpath;
use ast::mut_visit::{noop_visit_expr, MutVisitor};
use ast::token::IdentIsRaw;
use ast::{CoroutineKind, ForLoopKind, GenBlockKind, Pat, Path, PathSegment};
use ast::{CoroutineKind, ForLoopKind, GenBlockKind, MatchKind, Pat, Path, PathSegment};
use core::mem;
use core::ops::ControlFlow;
use rustc_ast::ptr::P;
Expand Down Expand Up @@ -1379,6 +1379,13 @@ impl<'a> Parser<'a> {
return Ok(self.mk_await_expr(self_arg, lo));
}

// Post-fix match
if self.eat_keyword(kw::Match) {
let match_span = self.prev_token.span;
self.psess.gated_spans.gate(sym::postfix_match, match_span);
return self.parse_match_block(lo, match_span, self_arg, MatchKind::Postfix);
}

let fn_span_lo = self.token.span;
let mut seg = self.parse_path_segment(PathStyle::Expr, None)?;
self.check_trailing_angle_brackets(&seg, &[&token::OpenDelim(Delimiter::Parenthesis)]);
Expand Down Expand Up @@ -2894,8 +2901,20 @@ impl<'a> Parser<'a> {
/// Parses a `match ... { ... }` expression (`match` token already eaten).
fn parse_expr_match(&mut self) -> PResult<'a, P<Expr>> {
let match_span = self.prev_token.span;
let lo = self.prev_token.span;
let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;

self.parse_match_block(match_span, match_span, scrutinee, MatchKind::Prefix)
}

/// Parses the block of a `match expr { ... }` or a `expr.match { ... }`
/// expression. This is after the match token and scrutinee are eaten
fn parse_match_block(
&mut self,
lo: Span,
match_span: Span,
scrutinee: P<Expr>,
match_kind: MatchKind,
) -> PResult<'a, P<Expr>> {
if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
if self.token == token::Semi {
e.span_suggestion_short(
Expand Down Expand Up @@ -2938,15 +2957,15 @@ impl<'a> Parser<'a> {
});
return Ok(self.mk_expr_with_attrs(
span,
ExprKind::Match(scrutinee, arms),
ExprKind::Match(scrutinee, arms, match_kind),
attrs,
));
}
}
}
let hi = self.token.span;
self.bump();
Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms, match_kind), attrs))
}

/// Attempt to recover from match arm body with statements and no surrounding braces.
Expand Down Expand Up @@ -3955,7 +3974,7 @@ impl MutVisitor for CondChecker<'_> {
| ExprKind::While(_, _, _)
| ExprKind::ForLoop { .. }
| ExprKind::Loop(_, _, _)
| ExprKind::Match(_, _)
| ExprKind::Match(_, _, _)
| ExprKind::Closure(_)
| ExprKind::Block(_, _)
| ExprKind::Gen(_, _, _)
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_passes/src/check_const.rs
Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ impl NonConstExpr {
Self::Match(TryDesugar(_)) => &[sym::const_try],

// All other expressions are allowed.
Self::Loop(Loop | While) | Self::Match(Normal | FormatArgs) => &[],
Self::Loop(Loop | While) | Self::Match(Normal | Postfix | FormatArgs) => &[],
};

Some(gates)
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1335,6 +1335,7 @@ symbols! {
poll,
poll_next,
post_dash_lto: "post-lto",
postfix_match,
powerpc_target_feature,
powf128,
powf16,
Expand Down
22 changes: 22 additions & 0 deletions src/doc/unstable-book/src/language-features/postfix-match.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
# `postfix-match`

`postfix-match` adds the feature for matching upon values postfix
the expressions that generate the values.

```rust,edition2021
#![feature(postfix_match)]
enum Foo {
Bar,
Baz
}
fn get_foo() -> Foo {
Foo::Bar
}
get_foo().match {
Foo::Bar => {},
Foo::Baz => panic!(),
}
```
2 changes: 1 addition & 1 deletion src/tools/clippy/clippy_lints/src/redundant_else.rs
Original file line number Diff line number Diff line change
Expand Up @@ -105,7 +105,7 @@ impl<'ast> Visitor<'ast> for BreakVisitor {
fn visit_expr(&mut self, expr: &'ast Expr) {
self.is_break = match expr.kind {
ExprKind::Break(..) | ExprKind::Continue(..) | ExprKind::Ret(..) => true,
ExprKind::Match(_, ref arms) => arms.iter().all(|arm|
ExprKind::Match(_, ref arms, _) => arms.iter().all(|arm|
arm.body.is_none() || arm.body.as_deref().is_some_and(|body| self.check_expr(body))
),
ExprKind::If(_, ref then, Some(ref els)) => self.check_block(then) && self.check_expr(els),
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -552,7 +552,7 @@ fn ident_difference_expr_with_base_location(
| (Gen(_, _, _), Gen(_, _, _))
| (Block(_, _), Block(_, _))
| (Closure(_), Closure(_))
| (Match(_, _), Match(_, _))
| (Match(_, _, _), Match(_, _, _))
| (Loop(_, _, _), Loop(_, _, _))
| (ForLoop { .. }, ForLoop { .. })
| (While(_, _, _), While(_, _, _))
Expand Down
2 changes: 1 addition & 1 deletion src/tools/clippy/clippy_utils/src/ast_utils.rs
Original file line number Diff line number Diff line change
Expand Up @@ -198,7 +198,7 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
},
(AssignOp(lo, lp, lv), AssignOp(ro, rp, rv)) => lo.node == ro.node && eq_expr(lp, rp) && eq_expr(lv, rv),
(Field(lp, lf), Field(rp, rf)) => eq_id(*lf, *rf) && eq_expr(lp, rp),
(Match(ls, la), Match(rs, ra)) => eq_expr(ls, rs) && over(la, ra, eq_arm),
(Match(ls, la, lkind), Match(rs, ra, rkind)) => (lkind == rkind) && eq_expr(ls, rs) && over(la, ra, eq_arm),
(
Closure(box ast::Closure {
binder: lb,
Expand Down
8 changes: 4 additions & 4 deletions src/tools/rustfmt/src/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ use std::cmp::min;

use itertools::Itertools;
use rustc_ast::token::{Delimiter, Lit, LitKind};
use rustc_ast::{ast, ptr, token, ForLoopKind};
use rustc_ast::{ast, ptr, token, ForLoopKind, MatchKind};
use rustc_span::{BytePos, Span};

use crate::chains::rewrite_chain;
Expand Down Expand Up @@ -170,8 +170,8 @@ pub(crate) fn format_expr(
}
}
}
ast::ExprKind::Match(ref cond, ref arms) => {
rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
ast::ExprKind::Match(ref cond, ref arms, kind) => {
rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs, kind)
}
ast::ExprKind::Path(ref qself, ref path) => {
rewrite_path(context, PathContext::Expr, qself, path, shape)
Expand Down Expand Up @@ -625,7 +625,7 @@ pub(crate) fn rewrite_cond(
shape: Shape,
) -> Option<String> {
match expr.kind {
ast::ExprKind::Match(ref cond, _) => {
ast::ExprKind::Match(ref cond, _, MatchKind::Prefix) => {
// `match `cond` {`
let cond_shape = match context.config.indent_style() {
IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
Expand Down
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