[cfe-dev] How do I try out C++ modules with clang?

[Stephen Kelly]

Sean Silva <chisophugis at ...> writes:

> Stephen, thanks for being a brave guinea pig here :)

No problem!

With the define I get more errors of the form:

$ clang++ -E -fmodules -fmodules-cache-path=cache -D_USE_EXTENDED_LOCALES_
test.cpp 
# 1 "test.cpp"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 325 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "test.cpp" 2
While building module 'std' imported from test.cpp:6:
While building module 'Darwin' imported from
/Users/ske/dev/prefix/bin/../include/c++/v1/__config:23:
In file included from <module-includes>:3:
In file included from /usr/include/ctype.h:384:
/usr/include/xlocale/_ctype.h:35:50: error: unknown type name 'locale_t'
unsigned long           ___runetype_l(__darwin_ct_rune_t, locale_t);
                                                          ^
/usr/include/xlocale/_ctype.h:36:53: error: unknown type name 'locale_t'
__darwin_ct_rune_t      ___tolower_l(__darwin_ct_rune_t, locale_t);
                                                         ^


Actually I think I hit similar errors from files in /usr/include when I
tried this a few weeks ago on linux, and I think my solution was to add a
modulemap in /usr/include for a few things. I'll check that in a few days.

This patch allows me to build the libcxx module:

diff --git a/include/ios b/include/ios
index ff79998..e5dc654 100644
--- a/include/ios
+++ b/include/ios
@@ -213,6 +213,7 @@ storage-class-specifier const error_category&
iostream_category() noexcept;
 
 #include <__config>
 #include <iosfwd>
+#include <cstdlib>
 #include <__locale>
 #include <system_error>


Though this stuff is very fiddly, and I have not yet grokked the whole
connection/problem between modules and defines (I haven't passed the 'it
basically works' barrier yet in order to grok that :) ), so I don't know if
the above patch is the right approach.

I am surprised that this problem has survived as I thought it would be an
obvious "step 1" for anyone trying modules on mac. I guess either it's been
tested so far on a different kind of system, or whoever added the modulemap
for libcxx only tested it on linux. A unit test could be added in libcxx
which attempts to build a module for it, right?

Thanks,

Steve.