Refactor fuzzer transform generation

Also splits out various utility classes from tint_common_fuzzer and
uses consistent naming for utility classes.

BUG=tint:1106

Change-Id: Ic343741eea799366850c46834865d50885554a84
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/65301
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

fuzzers/data_builder.h

@@ -0,0 +1,142 @@
+// Copyright 2021 The Tint Authors.
+//
+// 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 FUZZERS_DATA_BUILDER_H_
+#define FUZZERS_DATA_BUILDER_H_
+
+#include <cassert>
+#include <functional>
+#include <string>
+#include <vector>
+
+#include "fuzzers/random_generator.h"
+
+namespace tint {
+namespace fuzzers {
+
+/// Builder for generic pseudo-random data using a data buffer as seed
+class DataBuilder {
+ public:
+  /// @brief Initialize random number generations
+  /// @param data - pointer to a data buffer to use as a seed
+  /// @param size - size of data buffer
+  explicit DataBuilder(const uint8_t* data, size_t size)
+      : generator_(data, size) {}
+
+  ~DataBuilder() {}
+
+  /// Generate pseudo-random data of a specific type
+  /// @tparam T - type of data to produce
+  /// @returns pseudo-random data of type T
+  template <typename T>
+  T build() {
+    return BuildImpl<T>::impl(this);
+  }
+
+  /// Generate pseudo-random data of a specific type in a vector
+  /// @tparam T - data type held vector
+  /// @returns pseudo-random data of type std::vector<T>
+  template <typename T>
+  std::vector<T> vector() {
+    auto count = build<uint8_t>();
+    std::vector<T> out(count);
+    for (uint8_t i = 0; i < count; i++) {
+      out[i] = build<T>();
+    }
+    return out;
+  }
+
+  /// Generate complex pseudo-random data of a specific type in a vector
+  /// @tparam T - data type held vector
+  /// @tparam Callback - callback that takes in a DataBuilder* and returns a T
+  /// @param generate - callback for generating each instance of T
+  /// @returns pseudo-random data of type std::vector<T>
+  template <typename T, typename Callback>
+  std::vector<T> vector(Callback generate) {
+    auto count = build<uint8_t>();
+    std::vector<T> out(count);
+    for (size_t i = 0; i < count; i++) {
+      out[i] = generate(this);
+    }
+    return out;
+  }
+
+  /// Generate an pseudo-random entry to a enum class.
+  /// Assumes enum is tightly packed starting at 0.
+  /// @tparam T - type of enum class
+  /// @param count - number of entries in enum class
+  /// @returns a random enum class entry
+  template <typename T>
+  T enum_class(uint32_t count) {
+    return static_cast<T>(generator_.Get4Bytes() % count);
+  }
+
+ private:
+  RandomGenerator generator_;
+
+  /// Get N bytes of pseudo-random data
+  /// @param out - pointer to location to save data
+  /// @param n - number of bytes to get
+  void build(void* out, size_t n) {
+    assert(out != nullptr && "|out| cannot be nullptr");
+    assert(n > 0 && "|n| must be > 0");
+
+    generator_.GetNBytes(reinterpret_cast<uint8_t*>(out), n);
+  }
+
+  /// Implementation of ::build<T>()
+  /// @tparam T - type of data to produce
+  template <typename T>
+  struct BuildImpl {
+    /// Generate a pseudo-random variable of type T
+    /// @param b - data builder to use
+    /// @returns a variable of type T filled with pseudo-random data
+    static T impl(DataBuilder* b) {
+      T out{};
+      b->build(&out, sizeof(T));
+      return out;
+    }
+  };
+
+  /// Specialization for std::string
+  template <>
+  struct BuildImpl<std::string> {
+    /// Generate a pseudo-random string
+    /// @param b - data builder to use
+    /// @returns a string filled with pseudo-random data
+    static std::string impl(DataBuilder* b) {
+      auto count = b->build<uint8_t>();
+      if (count == 0) {
+        return "";
+      }
+      std::vector<uint8_t> source(count);
+      b->build(source.data(), count);
+      return std::string(source.begin(), source.end());
+    }
+  };
+
+  /// Specialization for bool
+  template <>
+  struct BuildImpl<bool> {
+    /// Generate a pseudo-random bool
+    /// @param b - data builder to use
+    /// @returns a boolean with even odds of being true or false
+    static bool impl(DataBuilder* b) { return b->generator_.GetBool(); }
+  };
+};
+
+}  // namespace fuzzers
+}  // namespace tint
+
+#endif  // FUZZERS_DATA_BUILDER_H_