Fix warnings for invalid C++ option with `enable_cxx_abi`; ref #3618, #4703

lib/mruby/build.rb

@@ -162,7 +162,7 @@ module MRuby
       compilers.each { |c|
         c.defines += %w(MRB_ENABLE_CXX_EXCEPTION MRB_ENABLE_CXX_ABI)
         c.flags << c.cxx_compile_flag
-        c.flags.delete('-std=gnu99')
+        c.flags = c.flags.flatten - c.cxx_invalid_flags.flatten
       }
       linker.command = cxx.command if toolchains.find { |v| v == 'gcc' }
       @cxx_abi_enabled = true

lib/mruby/build/command.rb

@@ -41,7 +41,7 @@ module MRuby
   class Command::Compiler < Command
     attr_accessor :flags, :include_paths, :defines, :source_exts
     attr_accessor :compile_options, :option_define, :option_include_path, :out_ext
-    attr_accessor :cxx_compile_flag, :cxx_exception_flag
+    attr_accessor :cxx_compile_flag, :cxx_exception_flag, :cxx_invalid_flags
 
     def initialize(build, source_exts=[])
       super(build)
@@ -53,6 +53,7 @@ module MRuby
       @option_include_path = '-I%s'
       @option_define = '-D%s'
       @compile_options = '%{flags} -o %{outfile} -c %{infile}'
+      @cxx_invalid_flags = []
     end
 
     alias header_search_paths include_paths

tasks/toolchains/gcc.rake

 MRuby::Toolchain.new(:gcc) do |conf, params|
   default_command = params[:default_command] || 'gcc'
-  compile_flags = %w(-g -O3 -Wall -Wundef -Werror-implicit-function-declaration)
+  compiler_flags = %w(-g -O3 -Wall -Wundef)
+  c_mandatory_flags = %w(-std=gnu99)
+  cxx_invalid_flags = %w(-Wdeclaration-after-statement -Werror-implicit-function-declaration)
 
   [conf.cc, conf.objc, conf.asm, conf.cxx].each do |compiler|
     if compiler == conf.cxx
       compiler.command = ENV['CXX'] || default_command.sub(/cc|$/, '++')
-      compiler.flags = [ENV['CXXFLAGS'] || ENV['CFLAGS'] || compile_flags]
+      compiler.flags = [ENV['CXXFLAGS'] || ENV['CFLAGS'] || compiler_flags]
     else
       compiler.command = ENV['CC'] || default_command
-      compiler.flags = ['-std=gnu99', ENV['CFLAGS'] || [compile_flags, %w(-Wdeclaration-after-statement -Wwrite-strings)]]
+      compiler.flags = [c_mandatory_flags, ENV['CFLAGS'] || [compiler_flags, cxx_invalid_flags, %w(-Wwrite-strings)]]
     end
     compiler.option_include_path = '-I%s'
     compiler.option_define = '-D%s'
     compiler.compile_options = '%{flags} -MMD -o %{outfile} -c %{infile}'
     compiler.cxx_compile_flag = '-x c++ -std=c++03'
     compiler.cxx_exception_flag = '-fexceptions'
+    compiler.cxx_invalid_flags = c_mandatory_flags + cxx_invalid_flags
   end
 
   conf.linker do |linker|

travis_config.rb

@@ -40,7 +40,7 @@ MRuby::Build.new('cxx_abi') do |conf|
   toolchain :gcc
 
   conf.gembox 'full-core'
-  conf.cc.flags += %w(-Werror=declaration-after-statement -fpermissive)
+  conf.cc.flags += %w(-fpermissive)
   conf.compilers.each do |c|
     c.defines += %w(MRB_GC_FIXED_ARENA)
   end