[gcc r14-1954] libcpp: reject codepoints above 0x10FFFF

[gcc r14-1954] libcpp: reject codepoints above 0x10FFFF

[Jason Merrill]

https://gcc.gnu.org/g:c1dbaa6656acc62c586dad1018f06113cde2d8a4

commit r14-1954-gc1dbaa6656acc62c586dad1018f06113cde2d8a4
Author: Ben Boeckel <ben.boeckel@kitware.com>
Date:   Tue Jun 6 16:50:22 2023 -0400

    libcpp: reject codepoints above 0x10FFFF
    
    Unicode does not support such values because they are unrepresentable in
    UTF-16.
    
    libcpp/
    
            * charset.cc: Reject encodings of codepoints above 0x10FFFF.
            UTF-16 does not support such codepoints and therefore all
            Unicode rejects such values.
    
    Signed-off-by: Ben Boeckel <ben.boeckel@kitware.com>

Diff:
---
 libcpp/charset.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/libcpp/charset.cc b/libcpp/charset.cc
index d7f323b2cd5..d4f573e365f 100644
--- a/libcpp/charset.cc
+++ b/libcpp/charset.cc
@@ -1886,6 +1886,13 @@ cpp_valid_utf8_p (const char *buffer, size_t num_bytes)
       int err = one_utf8_to_cppchar (&iter, &bytesleft, &cp);
       if (err)
 	return false;
+
+      /* Additionally, Unicode declares that all codepoints above 0010FFFF are
+	 invalid because they cannot be represented in UTF-16.
+
+	 Reject such values.*/
+      if (cp >= UCS_LIMIT)
+	return false;
     }
   /* No problems encountered.  */
   return true;