From e1b5f21a582495b8f5f52a6edc54cc3f4e8338be Mon Sep 17 00:00:00 2001
From: Ross Smyth <crs2017@gmail.com>
Date: Sat, 2 Mar 2024 20:55:48 -0500
Subject: [PATCH] Add postfix match MatchSource to HIR

---
 compiler/rustc_ast_lowering/src/expr.rs                  | 7 +++++--
 compiler/rustc_hir/src/hir.rs                            | 3 +++
 compiler/rustc_mir_build/src/thir/pattern/check_match.rs | 1 +
 compiler/rustc_passes/src/check_const.rs                 | 2 +-
 4 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index b8c2bc06fd6aa..51738fa241223 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -184,10 +184,13 @@ 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 {
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 78e7c636a3e74..b510e14d5109e 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2004,6 +2004,8 @@ pub enum LocalSource {
 pub enum MatchSource {
     /// A `match _ { .. }`.
     Normal,
+    /// A `expr.match { .. }`.
+    Postfix,
     /// A desugared `for _ in _ { .. }` loop.
     ForLoopDesugar,
     /// A desugared `?` operator.
@@ -2020,6 +2022,7 @@ impl MatchSource {
         use MatchSource::*;
         match self {
             Normal => "match",
+            Postfix => ".match",
             ForLoopDesugar => "for",
             TryDesugar(_) => "?",
             AwaitDesugar => ".await",
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index a0235f20a0570..1eb066bb700c6 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -477,6 +477,7 @@ 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
diff --git a/compiler/rustc_passes/src/check_const.rs b/compiler/rustc_passes/src/check_const.rs
index 02792491f5ed0..de123a16859ea 100644
--- a/compiler/rustc_passes/src/check_const.rs
+++ b/compiler/rustc_passes/src/check_const.rs
@@ -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)