Our current base compiler will abort with an error if it finds a typedef
being redefined, even if the new definition is no different from the one
it knows about.
Allowing this kind of type redefinition is a new C11 feature, which some
third-party software has already started using. Moreover, recent gcc
compilers will indeed accept this, even in non-c11 mode, with an
optional warning.
Consider the following testcase:
$ cat type.c
typedef unsigned char uint8_t;
typedef unsigned char char_t;
/* the following should not cause errors */
typedef unsigned char uint8_t;
typedef char_t uint8_t;
/* the following should cause errors */
typedef unsigned int uint8_t;
$
With the current in-tree compiler, it will produce these errors:
type.c:5: error: redefinition of typedef 'uint8_t'
type.c:1: error: previous declaration of 'uint8_t' was here
type.c:6: error: redefinition of typedef 'uint8_t'
type.c:5: error: previous declaration of 'uint8_t' was here
type.c:9: error: conflicting types for 'uint8_t'
type.c:6: error: previous declaration of 'uint8_t' was here
with the diff I am proposing below, it will only produce these errors:
type.c:9: error: conflicting types for 'uint8_t'
type.c:6: error: previous declaration of 'uint8_t' was here
and adding -pedantic will produce these warnings:
type.c:5: warning: redefinition of typedef 'uint8_t'
type.c:6: warning: redefinition of typedef 'uint8_t'
Any objections?
Index: c-decl.c
===================================================================
RCS file: /OpenBSD/src/gnu/gcc/gcc/c-decl.c,v
retrieving revision 1.2
diff -u -p -r1.2 c-decl.c
--- c-decl.c 29 Apr 2010 18:37:37 -0000 1.2
+++ c-decl.c 2 May 2015 14:35:28 -0000
@@ -1285,9 +1285,17 @@ diagnose_mismatched_decls (tree newdecl,
if (DECL_IN_SYSTEM_HEADER (newdecl) || DECL_IN_SYSTEM_HEADER (olddecl))
return true; /* Allow OLDDECL to continue in use. */
- error ("redefinition of typedef %q+D", newdecl);
- locate_old_decl (olddecl, error);
- return false;
+ if (pedantic)
+ {
+ pedwarn ("redefinition of typedef %q+D", newdecl);
+ if (flag_pedantic_errors)
+ {
+ locate_old_decl (olddecl, error);
+ return false;
+ }
+ }
+
+ return true;
}
/* Function declarations can either be 'static' or 'extern' (no
