From 98ea26129e9efb4198760e4504261e5dbbad658e Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 7 Oct 2024 16:47:45 +0200
Subject: [PATCH] Check valid punctuation character in Punct::new

Valid punctuation characters generated by:

    use proc_macro::{Punct, Spacing, TokenStream};
    use std::panic;

    #[proc_macro]
    pub fn punct_chars(_input: TokenStream) -> TokenStream {
        for ch in '\0'..=char::MAX {
            if let Ok(_) = panic::catch_unwind(|| {
                let _ = Punct::new(ch, Spacing::Alone);
            }) {
                eprintln!("{:?}", ch);
            }
        }
        TokenStream::new()
    }
---
 src/lib.rs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 0bce18e..ed38122 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -835,10 +835,16 @@ impl Punct {
     /// The returned `Punct` will have the default span of `Span::call_site()`
     /// which can be further configured with the `set_span` method below.
     pub fn new(ch: char, spacing: Spacing) -> Self {
-        Punct {
-            ch,
-            spacing,
-            span: Span::call_site(),
+        if let '!' | '#' | '$' | '%' | '&' | '\'' | '*' | '+' | ',' | '-' | '.' | '/' | ':' | ';'
+        | '<' | '=' | '>' | '?' | '@' | '^' | '|' | '~' = ch
+        {
+            Punct {
+                ch,
+                spacing,
+                span: Span::call_site(),
+            }
+        } else {
+            panic!("unsupported proc macro punctuation character {:?}", ch);
         }
     }