Issue #11962 has been updated by Kenta Murata.


I found the other place to be fixed.
The following patch is the complete version.

```diff
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 7aabf5b..a2f42c8 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -620,7 +620,7 @@ int ruby_safe_level_2_warning(void) __attribute__((warning("$SAFE=2 to 4 are obs
 # ifdef RUBY_EXPORT
 #   define ruby_safe_level_2_warning() ruby_safe_level_2_error()
 # endif
-#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P) && !defined(__cplusplus)
 # define RUBY_SAFE_LEVEL_INVALID_P(level) \
     __extension__(\
        __builtin_choose_expr(\
@@ -874,7 +874,7 @@ struct RBasic {
 VALUE rb_obj_hide(VALUE obj);
 VALUE rb_obj_reveal(VALUE obj, VALUE klass); /* do not use this API to change klass information */

-#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P) && !defined(__cplusplus)
 # define RB_OBJ_WB_UNPROTECT_FOR(type, obj) \
     __extension__( \
        __builtin_choose_expr( \
@@ -1376,7 +1376,7 @@ rb_data_object_wrap_warning(VALUE klass, void *ptr, RUBY_DATA_FUNC mark, RUBY_DA
     return rb_data_object_wrap(klass, ptr, mark, free);
 }

-#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P) && !defined(__cplusplus)
 #define rb_data_object_wrap_warning(klass, ptr, mark, free) \
     __extension__( \
        __builtin_choose_expr( \
diff --git a/include/ruby/st.h b/include/ruby/st.h
index 190bad2..97c08b1 100644
--- a/include/ruby/st.h
+++ b/include/ruby/st.h
@@ -59,7 +59,7 @@ struct st_hash_type {

 #define ST_INDEX_BITS (sizeof(st_index_t) * CHAR_BIT)

-#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR) && defined(HAVE_BUILTIN___BUILTIN_TYPES_COMPATIBLE_P)
+#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR) && defined(HAVE_BUILTIN___BUILTIN_TYPES_COMPATIBLE_P) && !defined(__cplusplus)
 # define ST_DATA_COMPATIBLE_P(type) \
    __builtin_choose_expr(__builtin_types_compatible_p(type, st_data_t), 1, 0)
 #else
```

----------------------------------------
Bug #11962: Ruby 2.3.0 causing compile failure on extensions using a C++ compiler
https://bugs.ruby-lang.org/issues/11962#change-56007

* Author: Sameer Deshmukh
* Status: Open
* Priority: Normal
* Assignee: Nobuyoshi Nakada
* ruby -v: 2.3.0
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
Hello,

I'm a contributor with the SciRuby foundation, and we have a gem called [nmatrix](https://github.com/SciRuby/nmatrix), which is a ruby gem for linear algebra processing in Ruby.

For representing different types of data, nmatrix makes heavy use of C++ templates, which requires compilation with g++. Currently we wrap the code that defines ruby functions at C level in an `extern "C" {}` block in a .cpp file and use g++ to compile the file as a whole.

Upgrading to ruby 2.3.0 has caused a problem because of [this change implemented in the internals of the ruby C API](https://github.com/ruby/ruby/commit/334710c155ad19cfd947ce6bcd7127b97cbe37da#diff-3b256c5581538dcd834697c766a2b1aaR879).

As specified in the GCC docs (https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html) the function "__builtin_choose_expr" (that has been introduced in the latest Ruby C API) is available only for C. Thus the change is rendering our C++ extensions useless.

You can see the compile error being caused in nmatrix here: https://github.com/SciRuby/nmatrix/issues/429

I have come up with [a temporary fix for this](https://github.com/SciRuby/nmatrix/pull/432/files#diff-cc867f54069967617c44c1ca31a5969aR37), but its only patch work and will need to be done by every single extension employing a C++ compiler.

Looking forward to a positive response from you.



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