Reorganize C++ exceptions; ref #3470

There are 3 levels of C++ exception handling:
* default - no C++ exception (use setjmp/longjmp)
* enable_cxx_exception (use C++ exceptions with C ABI)
* enable_cxx_abi (use C++ ABI including exceptions)

8 files changed, 55 insertions, 32 deletions

diff --git a/doc/guides/compile.md b/doc/guides/compile.md
index 9ca61c6fd..2aaf6f1fe 100644
--- a/doc/guides/compile.md
+++ b/doc/guides/compile.md
@@ -241,13 +241,15 @@ conf.enable_bintest
 
 ### C++ ABI
 
-mruby can use C++ exception to raise exception internally.
-By using C++ exception it can release C++ stack object correctly.
+By default, mruby uses setjmp/longjmp to implement its
+exceptions. But it doesn't release C++ stack object
+correctly. To support mrbgems written in C++, mruby can be
+configured to use C++ exception.
 
 There are two levels of C++ exception handling. The one is
-C++ exception enabled (but still C files are compiled by C
-compiler), and the other is C++ ABI mode where all files are
-compiled by C++ compiler.
+```enable_cxx_exception``` that enables C++ exception, but
+uses C ABI. The other is ```enable_cxx_abi``` where all
+files are compiled by C++ compiler.
 
 When you mix C++ code, C++ exception would be enabled automatically.
 If you need to enable C++ exception explicitly add the following:
@@ -255,23 +257,16 @@ If you need to enable C++ exception explicitly add the following:
 conf.enable_cxx_exception
 ```
 
-If you need to enable C++ ABI mode explicitly add the following:
-```ruby
-conf.enable_cxx_abi
-```
-
 #### C++ exception disabling.
 
-
-If you need to force C++ exception disable
-(For example using a compiler option to disable C++ exception),
-but still want to use C++ ABI mode,
-add following:
+If your compiler does not support C++ and you want to ensure
+you don't use mrbgem written in C++, you can explicitly disable
+C++ exception, add following:
 ```ruby
 conf.disable_cxx_exception
 ```
-
-Note that it must be called before ```enable_cxx_abi``` or ```gem``` method.
+and you will get an error when you try to use C++ gem.
+Note that it must be called before ```enable_cxx_exception``` or ```gem``` method.
 
 ### Debugging mode
 
diff --git a/include/mruby/throw.h b/include/mruby/throw.h
index 010793027..5d3d214e7 100644
--- a/include/mruby/throw.h
+++ b/include/mruby/throw.h
@@ -7,8 +7,10 @@
 #ifndef MRB_THROW_H
 #define MRB_THROW_H
 
-#if defined(MRB_ENABLE_CXX_EXCEPTION) && !defined(__cplusplus)
-#error Trying to use C++ exception handling in C code
+#if defined(MRB_ENABLE_CXX_ABI)
+# if !defined(__cplusplus)
+#  error Trying to use C++ exception handling in C code
+# endif
 #endif
 
 #if defined(MRB_ENABLE_CXX_EXCEPTION) && defined(__cplusplus)
diff --git a/mrbgems/mruby-bin-mruby/mrbgem.rake b/mrbgems/mruby-bin-mruby/mrbgem.rake
index ba7fad1fa..243b413eb 100644
--- a/mrbgems/mruby-bin-mruby/mrbgem.rake
+++ b/mrbgems/mruby-bin-mruby/mrbgem.rake
@@ -4,4 +4,10 @@ MRuby::Gem::Specification.new('mruby-bin-mruby') do |spec|
   spec.summary = 'mruby command'
   spec.bins = %w(mruby)
   spec.add_dependency('mruby-compiler', :core => 'mruby-compiler')
+  spec.add_dependency('mruby-error', :core => 'mruby-error')
+
+  if build.cxx_exception_enabled?
+    @objs << build.compile_as_cxx("#{spec.dir}/tools/mruby/mruby.c", "#{spec.build_dir}/tools/mruby/mruby.cxx")
+    @objs.delete_if { |v| v == objfile("#{spec.build_dir}/tools/mruby/mruby") }
+  end
 end
diff --git a/mrbgems/mruby-compiler/mrbgem.rake b/mrbgems/mruby-compiler/mrbgem.rake
index 3a22762fa..3bf6d6ae3 100644
--- a/mrbgems/mruby-compiler/mrbgem.rake
+++ b/mrbgems/mruby-compiler/mrbgem.rake
@@ -8,11 +8,11 @@ MRuby::Gem::Specification.new 'mruby-compiler' do |spec|
 
   lex_def = "#{current_dir}/core/lex.def"
   core_objs = Dir.glob("#{current_dir}/core/*.c").map { |f|
-    next nil if build.cxx_abi_enabled? and f =~ /(codegen).c$/
+    next nil if build.cxx_exception_enabled? and f =~ /(codegen).c$/
     objfile(f.pathmap("#{current_build_dir}/core/%n"))
   }.compact
 
-  if build.cxx_abi_enabled?
+  if build.cxx_exception_enabled?
     core_objs <<
       build.compile_as_cxx("#{current_build_dir}/core/y.tab.c", "#{current_build_dir}/core/y.tab.cxx",
                            objfile("#{current_build_dir}/y.tab"), ["#{current_dir}/core"]) <<
diff --git a/mrbgems/mruby-error/mrbgem.rake b/mrbgems/mruby-error/mrbgem.rake
index b8281b17e..30a4259a8 100644
--- a/mrbgems/mruby-error/mrbgem.rake
+++ b/mrbgems/mruby-error/mrbgem.rake
@@ -3,7 +3,7 @@ MRuby::Gem::Specification.new('mruby-error') do |spec|
   spec.author  = 'mruby developers'
   spec.summary = 'extensional error handling'
 
-  if build.cxx_abi_enabled?
+  if build.cxx_exception_enabled?
     @objs << build.compile_as_cxx("#{spec.dir}/src/exception.c", "#{spec.build_dir}/src/exception.cxx")
     @objs.delete_if { |v| v == objfile("#{spec.build_dir}/src/exception") }
   end
diff --git a/src/mruby_core.rake b/src/mruby_core.rake
index abde441d5..4558493d9 100644
--- a/src/mruby_core.rake
+++ b/src/mruby_core.rake
@@ -4,11 +4,11 @@ MRuby.each_target do
   current_build_dir = "#{build_dir}/#{relative_from_root}"
 
   objs = Dir.glob("#{current_dir}/*.c").map { |f|
-    next nil if cxx_abi_enabled? and f =~ /(error|vm).c$/
+    next nil if cxx_exception_enabled? and f =~ /(error|vm).c$/
     objfile(f.pathmap("#{current_build_dir}/%n"))
   }.compact
 
-  if cxx_abi_enabled?
+  if cxx_exception_enabled?
     objs += %w(vm error).map { |v| compile_as_cxx "#{current_dir}/#{v}.c", "#{current_build_dir}/#{v}.cxx" }
   end
   self.libmruby << objs
diff --git a/src/vm.c b/src/vm.c
index 458968524..c05afca9d 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -2583,3 +2583,7 @@ mrb_top_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int sta
 
   return v;
 }
+
+#if defined(MRB_ENABLE_CXX_EXCEPTION) && defined(__cplusplus)
+mrb_int mrb_jmpbuf::jmpbuf_id = 0;
+#endif
diff --git a/tasks/mruby_build.rake b/tasks/mruby_build.rake
index 46459cf6c..f5d4374d1 100644
--- a/tasks/mruby_build.rake
+++ b/tasks/mruby_build.rake
@@ -83,8 +83,9 @@ module MRuby
         @bins = []
         @gems, @libmruby = MRuby::Gem::List.new, []
         @build_mrbtest_lib_only = false
-        @cxx_abi_enabled = false
+        @cxx_exception_enabled = false
         @cxx_exception_disabled = false
+        @cxx_abi_enabled = false
         @enable_bintest = false
         @enable_test = false
         @toolchains = []
@@ -110,15 +111,28 @@ module MRuby
     end
 
     def disable_cxx_exception
+      if @cxx_exception_enabled or @cxx_abi_enabled
+        raise "cxx_exception already enabled"
+      end
       @cxx_exception_disabled = true
     end
 
     def enable_cxx_exception
-      @cxx_exception_disabled = false
+      return if @cxx_exception_enabled
+      return if @cxx_abi_enabled
+      if @cxx_exception_disabled
+        raise "cxx_exception disabled"
+      end
+      @cxx_exception_enabled = true
       compilers.each { |c|
         c.defines += %w(MRB_ENABLE_CXX_EXCEPTION)
         c.flags << c.cxx_exception_flag
       }
+      linker.command = cxx.command if toolchains.find { |v| v == 'gcc' }
+    end
+
+    def cxx_exception_enabled?
+      @cxx_exception_enabled
     end
 
     def cxx_abi_enabled?
@@ -127,9 +141,13 @@ module MRuby
 
     def enable_cxx_abi
       return if @cxx_abi_enabled
-      unless @cxx_exception_disabled
-        enable_cxx_exception
+      if @cxx_exception_enabled
+        raise "cxx_exception already enabled"
       end
+      compilers.each { |c|
+        c.defines += %w(MRB_ENABLE_CXX_EXCEPTION MRB_ENABLE_CXX_ABI)
+        c.flags << c.cxx_compile_flag
+      }
       compilers.each { |c| c.flags << c.cxx_compile_flag }
       linker.command = cxx.command if toolchains.find { |v| v == 'gcc' }
       @cxx_abi_enabled = true
@@ -146,15 +164,13 @@ module MRuby
 #define __STDC_CONSTANT_MACROS
 #define __STDC_LIMIT_MACROS
 
-#ifndef MRB_ENABLE_CXX_EXCEPTION
+#ifndef MRB_ENABLE_CXX_ABI
 extern "C" {
 #endif
 #include "#{src}"
-#ifndef MRB_ENABLE_CXX_EXCEPTION
+#ifndef MRB_ENABLE_CXX_ABI
 }
 #endif
-
-#{src == "#{MRUBY_ROOT}/src/error.c"? 'mrb_int mrb_jmpbuf::jmpbuf_id = 0;' : ''}
 EOS
       end