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THRIFT-2429 #93

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100 changes: 100 additions & 0 deletions compiler/cpp/src/generate/t_cpp_generator.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,20 @@ using std::vector;

static const string endl = "\n"; // avoid ostream << std::endl flushes

namespace {


enum TerseWrites { TW_DISABLED = 0, TW_SAFE = 1, TW_ALL = 2 };

template <class Options>
TerseWrites parseTerseWrites(const Options& options) {
auto iter = options.find("terse_writes");
return (iter == options.end()) ? TW_DISABLED :
(iter->second == "safe") ? TW_SAFE : TW_ALL;
}

} // namespace

/**
* C++ code generator. This is legitimacy incarnate.
*
Expand Down Expand Up @@ -81,6 +95,8 @@ class t_cpp_generator : public t_oop_generator {
gen_templates_only_ =
(iter != parsed_options.end() && iter->second == "only");

terse_writes_ = parseTerseWrites(parsed_options);

out_dir_base_ = "gen-cpp";
}

Expand Down Expand Up @@ -217,6 +233,8 @@ class t_cpp_generator : public t_oop_generator {
std::string argument_list(t_struct* tstruct, bool name_params=true, bool start_comma=false);
std::string type_to_enum(t_type* ttype);
std::string local_reflection_name(const char*, t_type* ttype, bool external=false);
bool try_terse_write_predicate(ofstream& out, t_field* t, bool pointers, TerseWrites terse_writes,
string& predicate);

void generate_enum_constant_list(std::ofstream& f,
const vector<t_enum_value*>& constants,
Expand Down Expand Up @@ -291,6 +309,15 @@ class t_cpp_generator : public t_oop_generator {
*/
bool gen_no_default_operators_;

/*
* Should write function avoid emitting values that are unchanged
* from default, if not explicitly optional/required?
* Caveats, when whitelisted:
* - don't change default values when turned on.
* - read() should be done into fresh or __clear()ed objects.
*/
TerseWrites terse_writes_;

/**
* Strings for namespace, computed once up front then used directly
*/
Expand Down Expand Up @@ -1379,6 +1406,70 @@ void t_cpp_generator::generate_struct_reader(ofstream& out,
"}" << endl << endl;
}

/**
* Generates a terse write predicate - checks if the value
* has changed from its initial value.
*/
bool t_cpp_generator::try_terse_write_predicate(
ofstream& out, t_field* tfield, bool pointers, TerseWrites terse_writes,
string& predicate) {
if (terse_writes == TW_DISABLED) {
return false;
}

// Only do terse writes for fields where required/optional isn't specified.
if (tfield->get_req() == t_field::T_REQUIRED ||
tfield->get_req() == t_field::T_OPTIONAL) {
return false;
}
t_type* type = get_true_type(tfield->get_type());
t_const_value* tval = tfield->get_value();

// Terse write is unsafe to use without explicitly setting default value,
// as in PHP / Python that would change result of deserialization (comparing
// with the case when terse_writes is not used): field set in C++ to default
// value would be deserialized as null / None.
if (terse_writes == TW_SAFE && tval == nullptr) {
return false;
}

if (type->is_struct() || type->is_xception() ||
// no support for void.
(type->is_base_type() && ((t_base_type*)type)->is_void()) ||
// only support string, if default empty.
(type->is_base_type() && ((t_base_type*)type)->is_string() &&
tval != nullptr && !tval->get_string().empty()) ||
// only support container, if default empty.
(type->is_container() && tval != nullptr &&
((tval->get_type() == t_const_value::CV_LIST &&
!tval->get_list().empty()) ||
(tval->get_type() == t_const_value::CV_MAP &&
!tval->get_map().empty())))
) {
return false;
}

// Containers -> "if (!x.empty())"
if (type->is_container() ||
(type->is_base_type() && ((t_base_type*)type)->is_string())) {
predicate = "!this->" + tfield->get_name() +
(pointers ? "->empty()" : ".empty()");
return true;
}
// ints, enum -> "if (x != default value)
if (type->is_base_type() || type->is_enum()) {
std::string const_value = "0";
if (tval != NULL) {
const_value = render_const_value(out, "", type, tval);
}
predicate = (pointers ? "*(this->" : "this->") +
tfield->get_name() + (pointers ? ") != " : " != ") +
const_value;
return true;
}
return false;
}

/**
* Generates the write function.
*
Expand All @@ -1391,6 +1482,9 @@ void t_cpp_generator::generate_struct_writer(ofstream& out,
string name = tstruct->get_name();
const vector<t_field*>& fields = tstruct->get_sorted_members();
vector<t_field*>::const_iterator f_iter;
string predicate;
const TerseWrites terse_writes =
std::max(terse_writes_, parseTerseWrites(tstruct->annotations_));

if (gen_templates_) {
out <<
Expand All @@ -1416,6 +1510,11 @@ void t_cpp_generator::generate_struct_writer(ofstream& out,
if (check_if_set) {
out << endl << indent() << "if (this->__isset." << (*f_iter)->get_name() << ") {" << endl;
indent_up();
} else if (try_terse_write_predicate(out, *f_iter, pointers, terse_writes,
predicate)) {
indent(out) << "if (" << predicate << ") {" << endl;
indent_up();
check_if_set = true;
} else {
out << endl;
}
Expand Down Expand Up @@ -4682,5 +4781,6 @@ THRIFT_REGISTER_GENERATOR(cpp, "C++",
" pure_enums: Generate pure enums instead of wrapper classes.\n"
" dense: Generate type specifications for the dense protocol.\n"
" include_prefix: Use full include paths in generated files.\n"
" terse_writes: Suppress writes for fields holding default values.\n"
)

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