hpb: Introduce Context

We set the stage for replacing bespoke `Output` calls with Protobuf's canonical io::Printer.

PiperOrigin-RevId: 684418174

hpb_generator/context.h

@@ -0,0 +1,73 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2024 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_HPB_CONTEXT_H__
+#define GOOGLE_PROTOBUF_COMPILER_HPB_CONTEXT_H__
+
+#include <memory>
+#include <utility>
+
+#include "absl/strings/string_view.h"
+#include "absl/types/source_location.h"
+#include "absl/types/span.h"
+#include "google/protobuf/io/printer.h"
+#include "google/protobuf/io/zero_copy_stream.h"
+namespace google::protobuf::hpb_generator {
+
+enum class Backend { UPB, CPP };
+
+struct Options {
+  Backend backend = Backend::UPB;
+};
+
+/**
+ * This Context object will be used throughout hpb generation.
+ * It is a thin wrapper around an io::Printer and can be easily extended
+ * to support more options.
+ *
+ * Expected usage is:
+ * SomeGenerationFunc(..., Context& context) {
+ *   context.Emit({{"some_key", some_computed_val}}, R"cc(
+ *   // hpb gencode ...
+ *  )cc);
+ * }
+ */
+class Context final {
+ public:
+  Context(std::unique_ptr<io::ZeroCopyOutputStream> stream,
+          const Options& options)
+      : stream_(std::move(stream)),
+        printer_(stream_.get()),
+        options_(options) {}
+
+  void Emit(absl::Span<const io::Printer::Sub> vars, absl::string_view format,
+            absl::SourceLocation loc = absl::SourceLocation::current()) {
+    printer_.Emit(vars, format, loc);
+  }
+
+  void Emit(absl::string_view format,
+            absl::SourceLocation loc = absl::SourceLocation::current()) {
+    printer_.Emit(format, loc);
+  }
+
+  const Options& options() { return options_; }
+
+  Context(const Context&) = delete;
+  Context& operator=(const Context&) = delete;
+  Context(Context&&) = delete;
+  Context& operator=(Context&&) = delete;
+
+ private:
+  std::unique_ptr<io::ZeroCopyOutputStream> stream_;
+  io::Printer printer_;
+  const Options& options_;
+};
+
+}  // namespace protobuf
+}  // namespace google::hpb_generator
+
+#endif  // GOOGLE_PROTOBUF_COMPILER_HPB_CONTEXT_H__