From d25c8a8ade05384e9ca84866be8672a97896826d Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Fri, 11 Apr 2025 10:45:14 +1000
Subject: [PATCH] Handle a negated literal in `eat_token_lit`.

Fixes #139495.
---
 compiler/rustc_parse/src/parser/expr.rs          | 13 +++++++++----
 tests/ui/macros/reparse-expr-issue-139495.rs     |  7 +++++++
 tests/ui/macros/reparse-expr-issue-139495.stderr | 13 +++++++++++++
 3 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 tests/ui/macros/reparse-expr-issue-139495.rs
 create mode 100644 tests/ui/macros/reparse-expr-issue-139495.stderr

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 9c457f150a3..d52e36fcfac 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2166,10 +2166,15 @@ impl<'a> Parser<'a> {
                 let expr = self
                     .eat_metavar_seq(mv_kind, |this| this.parse_expr())
                     .expect("metavar seq expr");
-                let ast::ExprKind::Lit(token_lit) = expr.kind else {
-                    panic!("didn't reparse an expr");
-                };
-                Some(token_lit)
+                if let ast::ExprKind::Lit(token_lit) = expr.kind {
+                    Some(token_lit)
+                } else if let ast::ExprKind::Unary(UnOp::Neg, inner) = &expr.kind
+                    && let ast::Expr { kind: ast::ExprKind::Lit(_), .. } = **inner
+                {
+                    None
+                } else {
+                    panic!("unexpected reparsed expr: {:?}", expr.kind);
+                }
             }
             _ => None,
         }
diff --git a/tests/ui/macros/reparse-expr-issue-139495.rs b/tests/ui/macros/reparse-expr-issue-139495.rs
new file mode 100644
index 00000000000..38d24573a53
--- /dev/null
+++ b/tests/ui/macros/reparse-expr-issue-139495.rs
@@ -0,0 +1,7 @@
+macro_rules! m {
+  ($abi : expr) => { extern $abi } //~ ERROR expected expression, found keyword `extern`
+}
+
+fn main() {
+    m!(-2)
+}
diff --git a/tests/ui/macros/reparse-expr-issue-139495.stderr b/tests/ui/macros/reparse-expr-issue-139495.stderr
new file mode 100644
index 00000000000..73a8ed87ba0
--- /dev/null
+++ b/tests/ui/macros/reparse-expr-issue-139495.stderr
@@ -0,0 +1,13 @@
+error: expected expression, found keyword `extern`
+  --> $DIR/reparse-expr-issue-139495.rs:2:22
+   |
+LL |   ($abi : expr) => { extern $abi }
+   |                      ^^^^^^ expected expression
+...
+LL |     m!(-2)
+   |     ------ in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+