Added --keep-prefix to not strip schema include path in C++ includes.

Change-Id: I3c6356fc6664072796f273096df64829108b4a34
Tested: on Linux.

docs/source/Compiler.md

@@ -123,5 +123,7 @@ Additional options:
 -   `--include-prefix PATH` : Prefix this path to any generated include
     statements.
 
+-   `--keep-prefix` : Keep original prefix of schema include statement.
+
 NOTE: short-form options for generators are deprecated, use the long form
 whenever possible.

include/flatbuffers/idl.h

@@ -358,6 +358,7 @@ struct IDLOptions {
   bool union_value_namespacing;
   bool allow_non_utf8;
   std::string include_prefix;
+  bool keep_include_path;
   bool binary_schema_comments;
   bool skip_flatbuffers_import;
   std::string go_namespace;
@@ -403,6 +404,7 @@ struct IDLOptions {
       cpp_object_api_pointer_type("std::unique_ptr"),
       union_value_namespacing(true),
       allow_non_utf8(false),
+      keep_include_path(false),
       binary_schema_comments(false),
       skip_flatbuffers_import(false),
       reexport_ts_modules(true),

src/flatc.cpp

@@ -103,6 +103,7 @@ std::string FlatCompiler::GetUsageString(const char* program_name) const {
       "    PATH             \n"
       "  --include-prefix   Prefix this path to any generated include statements.\n"
       "    PATH\n"
+      "  --keep-prefix      Keep original prefix of schema include statement.\n"
       "  --no-fb-import     Don't include flatbuffers import statement for TypeScript.\n"
       "  --no-ts-reexport   Don't re-export imported dependencies for TypeScript.\n"
       "FILEs may be schemas, or JSON files (conforming to preceding schema)\n"
@@ -155,6 +156,8 @@ int FlatCompiler::Compile(int argc, const char** argv) {
         opts.include_prefix = argv[argi];
         if (opts.include_prefix.back() != '/' &&
             opts.include_prefix.back() != '\\') opts.include_prefix += "/";
+      } else if(arg == "--keep-prefix") {
+        opts.keep_include_path = true;
       } else if(arg == "--strict-json") {
         opts.strict_json = true;
       } else if(arg == "--allow-non-utf8") {

src/idl_gen_cpp.cpp

@@ -72,8 +72,9 @@ class CppGenerator : public BaseGenerator {
     }
     for (auto it = parser_.included_files_.begin();
          it != parser_.included_files_.end(); ++it) {
-      const auto basename =
-          flatbuffers::StripPath(flatbuffers::StripExtension(it->first));
+      auto basename = flatbuffers::StripExtension(it->first);
+      if (!parser_.opts.keep_include_path)
+        basename = flatbuffers::StripPath(basename);
       if (basename != file_name_) {
         code_ += "#include \"" + parser_.opts.include_prefix + basename +
                  "_generated.h\"";