[Bug #21111] Find C++ programs at runtime

Author: nobu

lib/mkmf.rb

@@ -3020,13 +3020,74 @@ def self.[]=(name, mod)
                    "$(CXXFLAGS) $(src) $(LIBPATH) $(LDFLAGS) $(ARCH_FLAG) $(LOCAL_LIBS) $(LIBS)"
 
     def have_devel?
+      if config_string('CXX') == 'false'
+        return @have_devel = false unless progs = find_cxx_progs
+        MAKEFILE_CONFIG.update(progs)
+        CONFIG.update(progs)
+      end
       unless defined? @have_devel
         @have_devel = true
         @have_devel = try_link(MAIN_DOES_NOTHING)
       end
       @have_devel
     end
 
+    def check_prog_for_cc(stem, repl, cc)
+      cxx = cc.sub(/#{stem}(?=[^\/]*\z)/, repl)
+      cxx if find_executable0(cxx)
+    end
+
+    # Find C++ programs at runtime, according to CONFIG['CC'].
+    def find_cxx_progs
+      cc, = config_string('CC').shellsplit
+      case File.basename(cc)
+      when 'cc' # /(?:\A|[ \/])cc(?: |\z)/
+        # Don't try g++/clang++ when CC=cc
+        {
+          'CXX' => %w[cl.exe CC c++].find {|cc| find_executable0(cc)},
+        }
+      when /icc/
+        # Intel C++ has interprocedural optimizations.  It tends to come with its
+        # own linker etc.
+        {
+          'AR' => check_prog_for_cc("icc", "xiar", cc),
+          'CXX' => check_prog_for_cc("icc", "icpc", cc),
+          'LD' => check_prog_for_cc("icc", "xild", cc),
+        }
+      when /gcc/
+        # Ditto for GCC.
+        {
+          'LD' => check_prog_for_cc("gcc", "ld", cc),
+          'AR' => check_prog_for_cc("gcc", "gcc-ar", cc),
+          'CXX' => check_prog_for_cc("gcc", "g++", cc),
+          'NM' => check_prog_for_cc("gcc", "gcc-nm", cc),
+          'RANLIB' => check_prog_for_cc("gcc", "gcc-ranlib", cc),
+        }
+      when /clang/
+        # Ditto for LLVM.  Note however that llvm-as is a LLVM-IR to LLVM bitcode
+        # assembler that does not target your machine native binary.
+
+        # Xcode has its own version tools that may be incompatible with
+        # genuine LLVM tools, use the tools in the same directory.
+
+        llvm_prefix = IO.popen([cc, *%w"-E -dM -xc -"], in: :close, &:read)
+        llvm_prefix = llvm_prefix.include?("__apple_build_version__") ? "" : "llvm-"
+        {
+          'LD' => check_prog_for_cc("clang", "ld", cc), # ... maybe try lld ?
+          'AR' => check_prog_for_cc("clang", "#{llvm_prefix}ar", cc),
+          # 'AS' => check_prog_for_cc("clang", "#{llvm_prefix}as", cc),
+          'CXX' => check_prog_for_cc("clang", "clang++", cc),
+          'NM' => check_prog_for_cc("clang", "#{llvm_prefix}nm", cc),
+          'OBJCOPY' => check_prog_for_cc("clang", "#{llvm_prefix}objcopy", cc),
+          'OBJDUMP' => check_prog_for_cc("clang", "#{llvm_prefix}objdump", cc),
+          'RANLIB' => check_prog_for_cc("clang", "#{llvm_prefix}ranlib", cc),
+          'STRIP' => check_prog_for_cc("clang", "#{llvm_prefix}strip", cc),
+        }
+      else
+        return
+      end.compact
+    end
+
     def conftest_source
       CONFTEST_CXX
     end