Added support for mini-reflection tables.

Change-Id: I83453d074685fa57bbf1c7c87b1d9392ce972085
Tested: on Linux.

include/flatbuffers/flatbuffers.h

@@ -2066,6 +2066,73 @@ inline int LookupEnum(const char **names, const char *name) {
   #error Unknown compiler, please define structure alignment macros
 #endif
 
+// Minimal reflection via code generation.
+// Besides full-fat reflection (see reflection.h) and parsing/printing by
+// loading schemas (see idl.h), we can also have code generation for mimimal
+// reflection data which allows pretty-printing and other uses without needing
+// a schema or a parser.
+// Generate code with --reflect-types (types only) or --reflect-names (names
+// also) to enable.
+// See minireflect.h for utilities using this functionality.
+
+// These types are organized slightly differently as the ones in idl.h.
+enum SequenceType { ST_TABLE, ST_STRUCT, ST_UNION, ST_ENUM };
+
+// Scalars have the same order as in idl.h
+#define FLATBUFFERS_GEN_ELEMENTARY_TYPES(ET) \
+  ET(ET_UTYPE) \
+  ET(ET_BOOL) \
+  ET(ET_CHAR) \
+  ET(ET_UCHAR) \
+  ET(ET_SHORT) \
+  ET(ET_USHORT) \
+  ET(ET_INT) \
+  ET(ET_UINT) \
+  ET(ET_LONG) \
+  ET(ET_ULONG) \
+  ET(ET_FLOAT) \
+  ET(ET_DOUBLE) \
+  ET(ET_STRING) \
+  ET(ET_SEQUENCE)  // See SequenceType.
+
+enum ElementaryType {
+  #define FLATBUFFERS_ET(E) E,
+    FLATBUFFERS_GEN_ELEMENTARY_TYPES(FLATBUFFERS_ET)
+  #undef FLATBUFFERS_ET
+};
+
+inline const char **ElementaryTypeNames() {
+  static const char *names[] = {
+    #define FLATBUFFERS_ET(E) #E,
+      FLATBUFFERS_GEN_ELEMENTARY_TYPES(FLATBUFFERS_ET)
+    #undef FLATBUFFERS_ET
+  };
+  return names;
+}
+
+// Basic type info cost just 16bits per field!
+struct TypeCode {
+  uint16_t base_type : 4;      // ElementaryType
+  uint16_t is_vector : 1;
+  int16_t sequence_ref : 11;   // Index into type_refs below, or -1 for none.
+};
+
+static_assert(sizeof(TypeCode) == 2, "TypeCode");
+
+struct TypeTable;
+
+// Signature of the static method present in each type.
+typedef TypeTable *(*TypeFunction)();
+
+struct TypeTable {
+  SequenceType st;
+  size_t num_elems;  // of each of the arrays below.
+  const TypeCode *type_codes;
+  const TypeFunction *type_refs;
+  const int32_t *values;  // Only set for non-consecutive enum/union or structs.
+  const char **names;  // Only set if compiled with --reflect-names.
+};
+
 // String which identifies the current version of FlatBuffers.
 // flatbuffer_version_string is used by Google developers to identify which
 // applications uploaded to Google Play are using this library.  This allows

include/flatbuffers/idl.h

@@ -396,6 +396,10 @@ struct IDLOptions {
 
   Language lang;
 
+  enum MiniReflect { kNone, kTypes, kTypesAndNames };
+
+  MiniReflect mini_reflect;
+
   // The corresponding language bit will be set if a language is included
   // for code generation.
   unsigned long lang_to_generate;
@@ -426,6 +430,7 @@ struct IDLOptions {
       reexport_ts_modules(true),
       protobuf_ascii_alike(false),
       lang(IDLOptions::kJava),
+      mini_reflect(IDLOptions::kNone),
       lang_to_generate(0) {}
 };
 

include/flatbuffers/minireflect.h

@@ -0,0 +1,352 @@
+/*
+ * Copyright 2017 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FLATBUFFERS_MINIREFLECT_H_
+#define FLATBUFFERS_MINIREFLECT_H_
+
+#include "flatbuffers/flatbuffers.h"
+#include "flatbuffers/util.h"
+
+namespace flatbuffers {
+
+// Utilities that can be used with the "mini reflection" tables present
+// in generated code with --reflect-types (only types) or --reflect-names
+// (also names).
+// This allows basic reflection functionality such as pretty-printing
+// that does not require the use of the schema parser or loading of binary
+// schema files at runtime (reflection.h).
+
+// For any of the functions below that take `const TypeTable *`, you pass
+// `FooTypeTable()` if the type of the root is `Foo`.
+
+// First, a generic iterator that can be used by multiple algorithms.
+
+struct IterationVisitor {
+  // These mark the scope of a table or struct.
+  virtual void StartSequence() {}
+  virtual void EndSequence() {}
+  // Called for each field regardless of wether it is present or not.
+  // If not present, val == nullptr. set_idx is the index of all set fields.
+  virtual void Field(size_t /*field_idx*/, size_t /*set_idx*/,
+                     ElementaryType /*type*/, bool /*is_vector*/,
+                     const TypeTable * /*type_table*/, const char * /*name*/,
+                     const uint8_t * /*val*/) {}
+  // Called for a value that is actually present, after a field, or as part
+  // of a vector.
+  virtual void UType(uint8_t, const char *) {}
+  virtual void Bool(bool) {}
+  virtual void Char(int8_t, const char *) {}
+  virtual void UChar(uint8_t, const char *) {}
+  virtual void Short(int16_t, const char *) {}
+  virtual void UShort(uint16_t, const char *) {}
+  virtual void Int(int32_t, const char *) {}
+  virtual void UInt(uint32_t, const char *) {}
+  virtual void Long(int64_t) {}
+  virtual void ULong(uint64_t) {}
+  virtual void Float(float) {}
+  virtual void Double(double) {}
+  virtual void String(const String *) {}
+  virtual void Unknown(const uint8_t *) {}  // From a future version.
+  // These mark the scope of a vector.
+  virtual void StartVector() {}
+  virtual void EndVector() {}
+  virtual void Element(size_t /*i*/, ElementaryType /*type*/,
+                       const TypeTable * /*type_table*/,
+                       const uint8_t * /*val*/)
+  {}
+  virtual ~IterationVisitor() {}
+};
+
+inline size_t InlineSize(ElementaryType type, const TypeTable *type_table) {
+  switch (type) {
+    case ET_UTYPE:
+    case ET_BOOL:
+    case ET_CHAR:
+    case ET_UCHAR:
+      return 1;
+    case ET_SHORT:
+    case ET_USHORT:
+      return 2;
+    case ET_INT:
+    case ET_UINT:
+    case ET_FLOAT:
+    case ET_STRING:
+      return 4;
+    case ET_LONG:
+    case ET_ULONG:
+    case ET_DOUBLE:
+      return 8;
+    case ET_SEQUENCE:
+      switch (type_table->st) {
+        case ST_TABLE:
+        case ST_UNION:
+          return 4;
+        case ST_STRUCT:
+          return type_table->values[type_table->num_elems];
+        default:
+          assert(false);
+          return 1;
+      }
+    default:
+      assert(false);
+      return 1;
+  }
+}
+
+inline int32_t LookupEnum(int32_t enum_val, const int32_t *values,
+                          size_t num_values) {
+  if (!values) return enum_val;
+  for (size_t i = 0; i < num_values; i++) {
+    if (enum_val == values[i]) return static_cast<int32_t>(i);
+  }
+  return -1;  // Unknown enum value.
+}
+
+template<typename T> const char *EnumName(T tval, const TypeTable *type_table) {
+  if (!type_table || !type_table->names) return nullptr;
+  auto i = LookupEnum(static_cast<int32_t>(tval), type_table->values,
+                                  type_table->num_elems);
+  if (i >= 0 && i < static_cast<int32_t>(type_table->num_elems)) {
+    return type_table->names[i];
+  }
+  return nullptr;
+}
+
+void IterateObject(const uint8_t *obj, const TypeTable *type_table,
+                  IterationVisitor *visitor);
+
+inline void IterateValue(ElementaryType type, const uint8_t *val,
+                         const TypeTable *type_table,
+                         const uint8_t *prev_val,
+                         soffset_t vector_index,
+                         IterationVisitor *visitor) {
+  switch (type) {
+    case ET_UTYPE: {
+      auto tval = *reinterpret_cast<const uint8_t *>(val);
+      visitor->UType(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_BOOL: {
+      visitor->Bool(*reinterpret_cast<const uint8_t *>(val) != 0);
+      break;
+    }
+    case ET_CHAR: {
+      auto tval = *reinterpret_cast<const int8_t *>(val);
+      visitor->Char(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_UCHAR: {
+      auto tval = *reinterpret_cast<const uint8_t *>(val);
+      visitor->UChar(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_SHORT: {
+      auto tval = *reinterpret_cast<const int16_t *>(val);
+      visitor->Short(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_USHORT: {
+      auto tval = *reinterpret_cast<const uint16_t *>(val);
+      visitor->UShort(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_INT: {
+      auto tval = *reinterpret_cast<const int32_t *>(val);
+      visitor->Int(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_UINT: {
+      auto tval = *reinterpret_cast<const uint32_t *>(val);
+      visitor->UInt(tval, EnumName(tval, type_table));
+      break;
+    }
+    case ET_LONG: {
+      visitor->Long(*reinterpret_cast<const int64_t *>(val));
+      break;
+    }
+    case ET_ULONG: {
+      visitor->ULong(*reinterpret_cast<const uint64_t *>(val));
+      break;
+    }
+    case ET_FLOAT: {
+      visitor->Float(*reinterpret_cast<const float *>(val));
+      break;
+    }
+    case ET_DOUBLE: {
+      visitor->Double(*reinterpret_cast<const double *>(val));
+      break;
+    }
+    case ET_STRING: {
+      val += ReadScalar<uoffset_t>(val);
+      visitor->String(reinterpret_cast<const String *>(val));
+      break;
+    }
+    case ET_SEQUENCE: {
+      switch (type_table->st) {
+        case ST_TABLE:
+          val += ReadScalar<uoffset_t>(val);
+          IterateObject(val, type_table, visitor);
+          break;
+        case ST_STRUCT:
+          IterateObject(val, type_table, visitor);
+          break;
+        case ST_UNION: {
+          val += ReadScalar<uoffset_t>(val);
+          assert(prev_val);
+          auto union_type = *prev_val;  // Always a uint8_t.
+          if (vector_index >= 0) {
+            auto type_vec = reinterpret_cast<const Vector<uint8_t> *>(prev_val);
+            union_type = type_vec->Get(static_cast<uoffset_t>(vector_index));
+          }
+          auto type_code_idx = LookupEnum(union_type, type_table->values,
+                                          type_table->num_elems);
+          if (type_code_idx >= 0 && type_code_idx <
+              static_cast<int32_t>(type_table->num_elems)) {
+            auto type_code = type_table->type_codes[type_code_idx];
+            switch (type_code.base_type) {
+              case ET_SEQUENCE: {
+                auto ref = type_table->type_refs[type_code.sequence_ref]();
+                IterateObject(val, ref, visitor);
+                break;
+              }
+              case ET_STRING:
+                visitor->String(reinterpret_cast<const String *>(val));
+                break;
+              default:
+                visitor->Unknown(val);
+            }
+          } else {
+            visitor->Unknown(val);
+          }
+          break;
+        }
+        case ST_ENUM:
+          assert(false);
+          break;
+      }
+      break;
+    }
+    default: {
+      visitor->Unknown(val);
+      break;
+    }
+  }
+}
+
+inline void IterateObject(const uint8_t *obj, const TypeTable *type_table,
+                          IterationVisitor *visitor) {
+  visitor->StartSequence();
+  const uint8_t *prev_val = nullptr;
+  size_t set_idx = 0;
+  for (size_t i = 0; i < type_table->num_elems; i++) {
+    auto type_code = type_table->type_codes[i];
+    auto type = static_cast<ElementaryType>(type_code.base_type);
+    auto is_vector = type_code.is_vector != 0;
+    auto ref_idx = type_code.sequence_ref;
+    const TypeTable *ref = nullptr;
+    if (ref_idx >= 0) {
+      ref = type_table->type_refs[ref_idx]();
+    }
+    auto name = type_table->names ? type_table->names[i] : nullptr;
+    const uint8_t *val = nullptr;
+    if (type_table->st == ST_TABLE) {
+      val = reinterpret_cast<const Table *>(obj)->GetAddressOf(
+              FieldIndexToOffset(static_cast<voffset_t>(i)));
+    } else {
+      val = obj + type_table->values[i];
+    }
+    visitor->Field(i, set_idx, type, is_vector, ref, name, val);
+    if (val) {
+      set_idx++;
+      if (is_vector) {
+        val += ReadScalar<uoffset_t>(val);
+        auto vec = reinterpret_cast<const Vector<uint8_t> *>(val);
+        visitor->StartVector();
+        auto elem_ptr = vec->Data();
+        for (size_t j = 0; j < vec->size(); j++) {
+          visitor->Element(j, type, ref, elem_ptr);
+          IterateValue(type, elem_ptr, ref, prev_val, static_cast<soffset_t>(j),
+                       visitor);
+          elem_ptr += InlineSize(type, ref);
+        }
+        visitor->EndVector();
+      } else {
+        IterateValue(type, val, ref, prev_val, -1, visitor);
+      }
+    }
+    prev_val = val;
+  }
+  visitor->EndSequence();
+}
+
+inline void IterateFlatBuffer(const uint8_t *buffer,
+                              const TypeTable *type_table,
+                              IterationVisitor *callback) {
+  IterateObject(GetRoot<uint8_t>(buffer), type_table, callback);
+}
+
+// Outputting a Flatbuffer to a string. Tries to conform as close to JSON /
+// the output generated by idl_gen_text.cpp.
+
+struct ToStringVisitor : public IterationVisitor {
+  std::string s;
+  void StartSequence() { s += "{ "; }
+  void EndSequence() { s += " }"; }
+  void Field(size_t /*field_idx*/, size_t set_idx, ElementaryType /*type*/,
+             bool /*is_vector*/, const TypeTable * /*type_table*/,
+             const char *name, const uint8_t *val) {
+    if (!val) return;
+    if (set_idx) s += ", ";
+    if (name) { s += name; s += ": "; }
+  }
+  template<typename T> void Named(T x, const char *name) {
+    if (name) s+= name;
+    else s+= NumToString(x);
+  }
+  void UType(uint8_t x, const char *name) { Named(x, name); }
+  void Bool(bool x) { s+= x ? "true" : "false"; }
+  void Char(int8_t x, const char *name) { Named(x, name); }
+  void UChar(uint8_t x, const char *name) { Named(x, name); }
+  void Short(int16_t x, const char *name) { Named(x, name); }
+  void UShort(uint16_t x, const char *name) { Named(x, name); }
+  void Int(int32_t x, const char *name) { Named(x, name); }
+  void UInt(uint32_t x, const char *name) { Named(x, name); }
+  void Long(int64_t x) { s+= NumToString(x); }
+  void ULong(uint64_t x) { s+= NumToString(x); }
+  void Float(float x) { s+= NumToString(x); }
+  void Double(double x) { s+= NumToString(x); }
+  void String(const struct String *str) {
+    EscapeString(str->c_str(), str->size(), &s, true);
+  }
+  void Unknown(const uint8_t *) { s += "(?)"; }
+  void StartVector() { s += "[ "; }
+  void EndVector() { s += " ]"; }
+  void Element(size_t i, ElementaryType /*type*/,
+               const TypeTable * /*type_table*/, const uint8_t * /*val*/) {
+    if (i) s += ", ";
+  }
+};
+
+inline std::string FlatBufferToString(const uint8_t *buffer,
+                                      const TypeTable *type_table) {
+  ToStringVisitor tostring_visitor;
+  IterateFlatBuffer(buffer, type_table, &tostring_visitor);
+  return tostring_visitor.s;
+}
+
+}  // namespace flatbuffers
+
+#endif  // FLATBUFFERS_MINIREFLECT_H_