Add --gen-absl-hash option to generate AbslHashValue for structs.

Author: dbaileychess

include/flatbuffers/idl.h

@@ -664,6 +664,7 @@ struct IDLOptions {
   bool generate_name_strings;
   bool generate_object_based_api;
   bool gen_compare;
+  bool gen_absl_hash;
   std::string cpp_object_api_pointer_type;
   std::string cpp_object_api_string_type;
   bool cpp_object_api_string_flexible_constructor;
@@ -818,6 +819,7 @@ struct IDLOptions {
         generate_name_strings(false),
         generate_object_based_api(false),
         gen_compare(false),
+        gen_absl_hash(false),
         cpp_object_api_pointer_type("std::unique_ptr"),
         cpp_object_api_string_flexible_constructor(false),
         cpp_object_api_field_case_style(CaseStyle_Unchanged),

samples/monster_generated.h

@@ -236,6 +236,10 @@ inline bool operator!=(const Vec3 &lhs, const Vec3 &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Vec3 &obj) {
+  return H::combine(std::move(h), obj.x(), obj.y(), obj.z());
+}
 
 struct MonsterT : public ::flatbuffers::NativeTable {
   typedef Monster TableType;

scripts/generate_code.py

@@ -69,6 +69,7 @@ def glob(path, pattern):
 CPP_OPTS = [
     "--cpp",
     "--gen-compare",
+    "--gen-absl-hash",
 ] + (["--cpp-std", "c++0x"] if args.cpp_0x else [])
 
 CPP_17_OPTS = NO_INCL_OPTS + [

src/flatc.cpp

@@ -529,6 +529,8 @@ FlatCOptions FlatCompiler::ParseFromCommandLineArguments(int argc,
         opts.generate_object_based_api = true;
       } else if (arg == "--gen-compare") {
         opts.gen_compare = true;
+      } else if (arg == "--gen-absl-hash") {
+        opts.gen_absl_hash = true;
       } else if (arg == "--cpp-include") {
         if (++argi >= argc) Error("missing include following: " + arg, true);
         opts.cpp_includes.push_back(argv[argi]);

src/idl_gen_cpp.cpp

@@ -2311,6 +2311,34 @@ class CppGenerator : public BaseGenerator {
     code_ += "";
   }
 
+  void GenAbslHashValue(const StructDef& struct_def) {
+    code_ += "template <typename H>";
+    code_ += "inline H AbslHashValue(H h, const {{NATIVE_NAME}} &obj) {";
+    std::string combine_args;
+    for (const auto& field : struct_def.fields.vec) {
+      if (field->deprecated) {
+        continue;
+      }
+      if (IsArray(field->value.type)) {
+        const auto field_accessor = "obj." + Name(*field) + "()";
+        const auto& element_type = field->value.type.VectorType();
+        if (IsStruct(element_type)) {
+          code_ += "  for (const auto* element : *" + field_accessor + ") {";
+          code_ += "    h = H::combine(std::move(h), *element);";
+          code_ += "  }";
+        } else {
+          code_ += "  for (auto element : *" + field_accessor + ") {";
+          code_ += "    h = H::combine(std::move(h), element);";
+          code_ += "  }";
+        }
+      } else {
+        combine_args += ", obj." + Name(*field) + "()";
+      }
+    }
+    code_ += "  return H::combine(std::move(h)" + combine_args + ");";
+    code_ += "}";
+  }
+
   void GenOperatorNewDelete(const StructDef& struct_def) {
     if (auto native_custom_alloc =
             struct_def.attributes.Lookup("native_custom_alloc")) {
@@ -4281,7 +4309,12 @@ class CppGenerator : public BaseGenerator {
 
     code_.SetValue("STRUCT_BYTE_SIZE", NumToString(struct_def.bytesize));
     code_ += "FLATBUFFERS_STRUCT_END({{STRUCT_NAME}}, {{STRUCT_BYTE_SIZE}});";
-    if (opts_.gen_compare) GenCompareOperator(struct_def, "()");
+    if (opts_.gen_compare) {
+      GenCompareOperator(struct_def, "()");
+    }
+    if (opts_.gen_absl_hash) {
+      GenAbslHashValue(struct_def);
+    }
     code_ += "";
 
     // Definition for type traits for this table type. This allows querying var-

tests/BUILD.bazel

@@ -213,6 +213,7 @@ flatbuffer_cc_library(
 include_test_args = [
     "--gen-object-api",
     "--gen-compare",
+    "--gen-absl-hash",
     "--gen-mutable",
     "--reflect-names",
     "--cpp-ptr-type flatbuffers::unique_ptr",

tests/evolution_test/evolution_v1_generated.h

@@ -145,6 +145,10 @@ inline bool operator!=(const Struct &lhs, const Struct &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Struct &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b());
+}
 
 struct TableA FLATBUFFERS_FINAL_CLASS : private ::flatbuffers::Table {
   typedef TableABuilder Builder;

tests/evolution_test/evolution_v2_generated.h

@@ -161,6 +161,10 @@ inline bool operator!=(const Struct &lhs, const Struct &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Struct &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b());
+}
 
 struct TableA FLATBUFFERS_FINAL_CLASS : private ::flatbuffers::Table {
   typedef TableABuilder Builder;

tests/monster_test_generated.h

@@ -712,6 +712,10 @@ inline bool operator!=(const Test &lhs, const Test &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Test &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(8) Vec3 FLATBUFFERS_FINAL_CLASS {
  private:
@@ -810,6 +814,10 @@ inline bool operator!=(const Vec3 &lhs, const Vec3 &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Vec3 &obj) {
+  return H::combine(std::move(h), obj.x(), obj.y(), obj.z(), obj.test1(), obj.test2(), obj.test3());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) Ability FLATBUFFERS_FINAL_CLASS {
  private:
@@ -859,6 +867,10 @@ inline bool operator!=(const Ability &lhs, const Ability &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Ability &obj) {
+  return H::combine(std::move(h), obj.id(), obj.distance());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) StructOfStructs FLATBUFFERS_FINAL_CLASS {
  private:
@@ -912,6 +924,10 @@ inline bool operator!=(const StructOfStructs &lhs, const StructOfStructs &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const StructOfStructs &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b(), obj.c());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) StructOfStructsOfStructs FLATBUFFERS_FINAL_CLASS {
  private:
@@ -945,6 +961,10 @@ inline bool operator!=(const StructOfStructsOfStructs &lhs, const StructOfStruct
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const StructOfStructsOfStructs &obj) {
+  return H::combine(std::move(h), obj.a());
+}
 
 }  // namespace Example
 

tests/monster_test_suffix/ext_only/monster_test_generated.hpp

@@ -709,6 +709,10 @@ inline bool operator!=(const Test &lhs, const Test &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Test &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(8) Vec3 FLATBUFFERS_FINAL_CLASS {
  private:
@@ -807,6 +811,10 @@ inline bool operator!=(const Vec3 &lhs, const Vec3 &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Vec3 &obj) {
+  return H::combine(std::move(h), obj.x(), obj.y(), obj.z(), obj.test1(), obj.test2(), obj.test3());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) Ability FLATBUFFERS_FINAL_CLASS {
  private:
@@ -856,6 +864,10 @@ inline bool operator!=(const Ability &lhs, const Ability &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const Ability &obj) {
+  return H::combine(std::move(h), obj.id(), obj.distance());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) StructOfStructs FLATBUFFERS_FINAL_CLASS {
  private:
@@ -909,6 +921,10 @@ inline bool operator!=(const StructOfStructs &lhs, const StructOfStructs &rhs) {
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const StructOfStructs &obj) {
+  return H::combine(std::move(h), obj.a(), obj.b(), obj.c());
+}
 
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) StructOfStructsOfStructs FLATBUFFERS_FINAL_CLASS {
  private:
@@ -942,6 +958,10 @@ inline bool operator!=(const StructOfStructsOfStructs &lhs, const StructOfStruct
     return !(lhs == rhs);
 }
 
+template <typename H>
+inline H AbslHashValue(H h, const StructOfStructsOfStructs &obj) {
+  return H::combine(std::move(h), obj.a());
+}
 
 }  // namespace Example