Add option to change preprocessor -CC to -C

See #37.

include/cppast/libclang_parser.hpp

@@ -27,6 +27,8 @@ namespace cppast
             static bool write_preprocessed(const libclang_compile_config& config);
 
             static bool fast_preprocessing(const libclang_compile_config& config);
+
+            static bool remove_comments_in_macro(const libclang_compile_config& config);
         };
 
         void for_each_file(const libclang_compilation_database& database, void* user_data,
@@ -144,6 +146,15 @@ namespace cppast
             fast_preprocessing_ = b;
         }
 
+        /// \effects Sets whether or not documentation comments generated by macros are removed.
+        /// Default value is `false`.
+        /// \notes If this leads to an error due to preprocessing and comments, you have to enable it.
+        /// \notes If this is `true`, `clang` will be invoked with `-CC`, otherwise `-C`.
+        void remove_comments_in_macro(bool b) noexcept
+        {
+            remove_comments_in_macro_ = b;
+        }
+
     private:
         void do_set_flags(cpp_standard standard, compile_flags flags) override;
 
@@ -162,6 +173,7 @@ namespace cppast
         int         clang_version_;
         bool        write_preprocessed_ : 1;
         bool        fast_preprocessing_ : 1;
+        bool        remove_comments_in_macro_ : 1;
 
         friend detail::libclang_compile_config_access;
     };

src/libclang/libclang_parser.cpp

@@ -48,6 +48,12 @@ bool detail::libclang_compile_config_access::fast_preprocessing(
     return config.fast_preprocessing_;
 }
 
+bool detail::libclang_compile_config_access::remove_comments_in_macro(
+    const libclang_compile_config& config)
+{
+    return config.remove_comments_in_macro_;
+}
+
 libclang_compilation_database::libclang_compilation_database(const std::string& build_directory)
 {
     static_assert(std::is_same<database, CXCompilationDatabase>::value, "forgot to update type");
@@ -88,7 +94,10 @@ namespace
 }
 
 libclang_compile_config::libclang_compile_config()
-: compile_config({}), write_preprocessed_(false), fast_preprocessing_(false)
+: compile_config({}),
+  write_preprocessed_(false),
+  fast_preprocessing_(false),
+  remove_comments_in_macro_(false)
 {
     // set given clang binary
     auto ptr   = CPPAST_CLANG_VERSION_STRING;

src/libclang/preprocessor.cpp

@@ -200,9 +200,15 @@ namespace
     {
         // -x c++: force C++ as input language
         // -E: print preprocessor output
-        // -CC: keep comments, even in macro
         // -dD: keep macros
-        auto flags = std::string("-x c++ -E -CC -dD");
+        auto flags = std::string("-x c++ -E -dD");
+
+        // -CC: keep comments, even in macro
+        // -C: keep comments, but not in macro
+        if (!detail::libclang_compile_config_access::remove_comments_in_macro(c))
+            flags += " -CC";
+        else
+            flags += " -C";
 
         if (macro_file_path)
             // -no*: disable default include search paths

tool/main.cpp

@@ -210,7 +210,8 @@ int main(int argc, char* argv[]) try
         ("gnu_extensions", "enable GNU extensions (equivalent to -std=gnu++XX)")
         ("msvc_extensions", "enable MSVC extensions (equivalent to -fms-extensions)")
         ("msvc_compatibility", "enable MSVC compatibility (equivalent to -fms-compatibility)")
-        ("fast_preprocessing", "enable fast preprocessing, be careful, this breaks if you e.g. redefine macros in the same file!");
+        ("fast_preprocessing", "enable fast preprocessing, be careful, this breaks if you e.g. redefine macros in the same file!")
+        ("remove_comments_in_macro", "whether or not comments generated by macro are kept, enable if you run into errors");
     // clang-format on
     options.parse_positional("file");
     options.parse(argc, argv);
@@ -252,6 +253,9 @@ int main(int argc, char* argv[]) try
         if (options.count("fast_preprocessing"))
             config.fast_preprocessing(true);
 
+        if (options.count("remove_comments_in_macro"))
+            config.remove_comments_in_macro(true);
+
         if (options.count("include_directory"))
             for (auto& include : options["include_directory"].as<std::vector<std::string>>())
                 config.add_include_dir(include);