[gcc r17-2313] cobol: Replace NUL input with space, with diagnostic.

https://gcc.gnu.org/g:fe37b9c1c4ecb5dbb3762755ad1bd6eccf524afd

commit r17-2313-gfe37b9c1c4ecb5dbb3762755ad1bd6eccf524afd
Author: James K. Lowden <[email protected]>
Date:   Thu Jul 9 15:36:50 2026 -0400

    cobol: Replace NUL input with space, with diagnostic.
    
    Old-school COBOL input may embed NUL characters in alphanumeric
    literals. GNU Flex unfortunately treats NUL as end-of-file marker.
    
    Detect the situation in the lexio file-reader.  Replace NUL with
    SPACE, increment error count, and emit message. Fixes RT 3622.
    
            * lexio.h (parse_error_inc): Declare function.
            (struct filespan_t::next_line): Detect and remove NUL,

Diff:
---
 gcc/cobol/lexio.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/cobol/lexio.h b/gcc/cobol/lexio.h
index f58470d97e29..222a831fe6d4 100644
--- a/gcc/cobol/lexio.h
+++ b/gcc/cobol/lexio.h
@@ -112,7 +112,7 @@ struct bytespan_t {
   }
 };
 
-// YYLTYPE supplied by cbldiag.h.  Borrowed from parse.h as generated by Bison.
+size_t parse_error_inc();
 
 struct filespan_t : public bytespan_t {
   char *cur, *eol, *quote;
@@ -164,6 +164,19 @@ struct filespan_t : public bytespan_t {
 
     eol = std::find(cur, eodata, '\n');
 
+    char *nul = std::find(cur, eol, '\0');
+    if( nul != eol ) {
+      if( std::any_of( nul, eodata,
+                       []( char ch ) { return ch != '\0'; } ) ) {
+        int icol = nul - cur;
+        fprintf(stderr, "%s:%d:%d: error: NUL character detected in input\n%*s\n",
+                cobol_filename(), int(iline + 1), ++icol,
+                int(eol - cur), cur);
+        parse_error_inc();
+        std::replace(nul, eol, '\0', SPACE);
+      }
+    }
+
     if( eol < eodata ) {
       ++eol;
       ++iline;