Avoid "-Wzero-as-null-pointer-constant" warnings on the generated code.

Reported in
<https://lists.gnu.org/archive/html/bug-gnulib/2024-11/msg00123.html>.

* src/output.cc (Output::output_lookup_function_body): To denote a null
pointer, emit a cast expression instead of plain "0".
* tests/c-parse.exp, tests/charsets.exp, tests/chill.exp,
tests/cplusplus.exp, tests/gpc.exp, tests/incomplete.exp,
tests/java.exp, tests/languages.exp, tests/modula2.exp, tests/objc.exp,
tests/permut2.exp, tests/permut3.exp, tests/permutc2.exp,
tests/test-4.exp: Update.

ChangeLog

@@ -1,3 +1,16 @@
+2024-11-16  Bruno Haible  <bruno@clisp.org>
+
+	Avoid "-Wzero-as-null-pointer-constant" warnings on the generated code.
+	Reported in
+	<https://lists.gnu.org/archive/html/bug-gnulib/2024-11/msg00123.html>.
+	* src/output.cc (Output::output_lookup_function_body): To denote a null
+	pointer, emit a cast expression instead of plain "0".
+	* tests/c-parse.exp, tests/charsets.exp, tests/chill.exp,
+	tests/cplusplus.exp, tests/gpc.exp, tests/incomplete.exp,
+	tests/java.exp, tests/languages.exp, tests/modula2.exp, tests/objc.exp,
+	tests/permut2.exp, tests/permut3.exp, tests/permutc2.exp,
+	tests/test-4.exp: Update.
+
 2024-10-28  Bruno Haible  <bruno@clisp.org>
 
 	doc: Improve text rendering in PDF output.

src/output.cc

@@ -1,5 +1,5 @@
 /* Output routines.
-   Copyright (C) 1989-1998, 2000, 2002-2004, 2006-2007, 2009, 2011-2012, 2016, 2018, 2021, 2023 Free Software Foundation, Inc.
+   Copyright (C) 1989-2024 Free Software Foundation, Inc.
    Written by Douglas C. Schmidt <schmidt@ics.uci.edu>
    and Bruno Haible <bruno@clisp.org>.
 
@@ -1707,6 +1707,17 @@ output_switches (KeywordExt_List *list, int num_switches, int size, int min_hash
 void
 Output::output_lookup_function_body (const Output_Compare& comparison) const
 {
+  /* An expression equivalent to NULL, of type _return_type.
+     We don't use plain "0", because that would trigger a gcc 15 warning
+     if the warning option -Wzero-as-null-pointer-constant is in use.
+     In C++, using "nullptr" if __cplusplus >= 201103L would be possible,
+     but is not worth the trouble.  */
+  char *null_expression = new char[17 + strlen (_return_type) + 1];
+  if (option[CPLUSPLUS])
+    sprintf (null_expression, "static_cast<%s> (0)", _return_type);
+  else
+    sprintf (null_expression, "(%s) 0", _return_type);
+
   printf ("  if (len <= %sMAX_WORD_LENGTH && len >= %sMIN_WORD_LENGTH)\n"
           "    {\n"
           "      %sunsigned int key = %s (str, len);\n\n",
@@ -1755,7 +1766,8 @@ Output::output_lookup_function_body (const Output_Compare& comparison) const
 
       output_switches (_head, num_switches, switch_size, _min_hash_value, _max_hash_value, 10);
 
-      printf ("          return 0;\n");
+      printf ("          return %s;\n",
+              null_expression);
       if (option[DUP] && _total_duplicates > 0)
         {
           int indent = 8;
@@ -1798,8 +1810,8 @@ Output::output_lookup_function_body (const Output_Compare& comparison) const
                     indent, "");
           printf ("%*s      wordptr++;\n"
                   "%*s    }\n"
-                  "%*s  return 0;\n",
+                  "%*s  return %s;\n",
-                  indent, "", indent, "", indent, "");
+                  indent, "", indent, "", indent, "", null_expression);
         }
       printf ("        compare:\n");
       if (option[TYPE])
@@ -2020,7 +2032,10 @@ Output::output_lookup_function_body (const Output_Compare& comparison) const
         }
     }
   printf ("    }\n"
-          "  return 0;\n");
+          "  return %s;\n",
+          null_expression);
+
+  delete[] null_expression;
 }
 
 /* Generates C code for the lookup function.  */

tests/c-parse.exp

@@ -219,5 +219,5 @@ is_reserved_word (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/charsets.exp

@@ -1878,6 +1878,6 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct charset *) 0;
 }
 

tests/chill.exp

@@ -1550,7 +1550,7 @@ in_word_set (str, len)
                 resword = &wordlist[299];
                 goto compare;
             }
-          return 0;
+          return (struct resword *) 0;
         compare:
           {
             register const char *s = resword->name;
@@ -1560,5 +1560,5 @@ in_word_set (str, len)
           }
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/cplusplus.exp

@@ -269,5 +269,5 @@ is_reserved_word (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/gpc.exp

@@ -153,5 +153,5 @@ is_reserved_word (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/incomplete.exp

@@ -121,5 +121,5 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct month *) 0;
 }

tests/java.exp

@@ -199,5 +199,5 @@ java_keyword (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct java_keyword *) 0;
 }

tests/languages.exp

@@ -1495,7 +1495,7 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct language *) 0;
 }
 
 

tests/modula2.exp

@@ -246,5 +246,5 @@ in_word_set (register const char *str, register size_t len)
               return s;
           }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/objc.exp

@@ -194,5 +194,5 @@ is_reserved_word (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/permut2.exp

@@ -104,5 +104,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/permut3.exp

@@ -104,5 +104,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/permutc2.exp

@@ -153,5 +153,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/test-4.exp

@@ -230,5 +230,5 @@ in_word_set (register const char *str, register size_t len)
             }
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }