https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118112
Bug ID: 118112
Summary: Unhelpful "too many arguments to function" error
message
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: dmalcolm at gcc dot gnu.org
Target Milestone: ---
Seen attempting to build 389-ds-base with gcc 15:
https://bugzilla.redhat.com/show_bug.cgi?id=2333039
I see this failure:
ldap/servers/slapd/compare.c: In function 'do_compare':
ldap/servers/slapd/compare.c:184:19: error: too many arguments to function
'be->be_database->plg_un.plg_un_db.plg_un_db_compare'
184 | rc = (*be->be_compare)(pb);
| ~^~~~~~~~~~~~~~~~
whereas the build succeeded with gcc 14.
There is no note from c-typeck.cc's inform_declaration as we don't have a
funcdecl, just an expression that's a callback field of function type.
Looking at the source I see:
slap.h:1467:#define be_compare be_database->plg_compare
struct slapdplugin *be_database; /* single plugin */
#define plg_compare plg_un.plg_un_db.plg_un_db_compare
slap.h:1074: IFP plg_un_db_compare; /* compare */
where slapi-private.h has:
/* JCMREPL - IFP and CFP should be defined centrally */
#ifndef _IFP
#define _IFP
typedef int (*IFP)(); /* takes undefined arguments */
#endif
I believe this is due to GCC 15 defaulting to -std=gnu23, whereas GCC 14
defaulted to -std=gnu17, and C23 is stricter about function prototypes than
C17.
I'm not sure exactly what the chapter-and-verse here is in terms of the C
standard, but the UX here is poor. Ideas for improvement:
- tell the user how many arguments were expected vs how many were used
- if we have a field of callback type, show the decl of the field
- if it's a typedef, show the typedef
- show where the surplus arguments begin at the callsite, and their types
- special-case for the migration-to-C23 case?
