Would it be possible to do this without changing how name mangling works?
#include <string.h>
__prefix__ str; /* in scope: "","str" */
strlen("Hi!"); /* try "strlen",done,ignore "strstrlen" */
len("Bye"); /* no "len",try "strlen",done */
__prefix__(foo_) { void bar(void); } /* "foo_bar" */Namespaces don't need to be mangled at all if they are interpreted as symbol prefixes.
I'd prefer that, say, namespace foo::bar resolved into foo_bar for all symbols (even that meant risking namespace naming collisions) to not having any support for namespaces in C.
In fact, this approach is already used to implement pseudo-namespaces, so that wouldn't be much of a stretch.
It seems like you want the language to be more complicated for no benefit. Why not use C++ at that point?
You're missing the whole point of namespaces. The goal is not to replace foo_bar with foo::bar. The whole point is that within a scope you can type bar instead of foo::bar, or bar instead of foo::baz::qux::bar, because you might have multiple identifiers that might share a name albeit they are expected to be distinct symbols.
using namespace kind::ofa::long_name;
or
using kind::ofa::long_name::bar;
is the point.