Mustache.h

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//===--- Mustache.h ---------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Implementation of the Mustache templating language supports version 1.4.2
// currently relies on llvm::json::Value for data input.
// See the Mustache spec for more information
// (https://mustache.github.io/mustache.5.html).
//
// Current Features Supported:
// - Variables
// - Sections
// - Inverted Sections
// - Partials
// - Comments
// - Lambdas
// - Unescaped Variables
//
// Features Not Supported:
// - Set Delimiter
// - Blocks
// - Parents
// - Dynamic Names
//
// The Template class is a container class that outputs the Mustache template
// string and is the main class for users. It stores all the lambdas and the
// ASTNode Tree. When the Template is instantiated it tokenizes the Template
// String and creates a vector of Tokens. Then it calls a basic recursive
// descent parser to construct the ASTNode Tree. The ASTNodes are all stored
// in an arena allocator which is freed once the template class goes out of
// scope.
//
// Usage:
// \code
//   // Creating a simple template and rendering it
//   auto Template = Template("Hello, {{name}}!");
//   Value Data = {{"name", "World"}};
//   std::string Out;
//   raw_string_ostream OS(Out);
//   T.render(Data, OS);
//   // Out == "Hello, World!"
//
//   // Creating a template with a partial and rendering it
//   auto Template = Template("{{>partial}}");
//   Template.registerPartial("partial", "Hello, {{name}}!");
//   Value Data = {{"name", "World"}};
//   std::string Out;
//   raw_string_ostream OS(Out);
//   T.render(Data, OS);
//   // Out == "Hello, World!"
//
//   // Creating a template with a lambda and rendering it
//   Value D = Object{};
//   auto T = Template("Hello, {{lambda}}!");
//   Lambda L = []() -> llvm::json::Value { return "World"; };
//   T.registerLambda("lambda", L);
//   std::string Out;
//   raw_string_ostream OS(Out);
//   T.render(D, OS);
//   // Out == "Hello, World!"
// \endcode
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SUPPORT_MUSTACHE
#define LLVM_SUPPORT_MUSTACHE
 
#include "Error.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/JSON.h"
#include "llvm/Support/StringSaver.h"
#include <functional>
#include <vector>
 
namespace llvm::mustache {
 
using Lambda = std::function<llvm::json::Value()>;
using SectionLambda = std::function<llvm::json::Value(std::string)>;
 
class ASTNode;
using AstPtr = ASTNode *;
using EscapeMap = DenseMap<char, std::string>;
using ASTNodeList = iplist<ASTNode>;
 
struct MustacheContext {
  MustacheContext(BumpPtrAllocator &Allocator, StringSaver &Saver)
      : Allocator(Allocator), Saver(Saver) {}
  BumpPtrAllocator &Allocator;
  StringSaver &Saver;
  StringMap<AstPtr> Partials;
  StringMap<Lambda> Lambdas;
  StringMap<SectionLambda> SectionLambdas;
  EscapeMap Escapes;
};
 
// A Template represents the container for the AST and the partials
// and Lambdas that are registered with it.
class Template {
public:
  LLVM_ABI Template(StringRef TemplateStr, MustacheContext &Ctx);
 
  Template(const Template &) = delete;
 
  Template &operator=(const Template &) = delete;
 
  LLVM_ABI Template(Template &&Other) noexcept;
 
  // Define this in the cpp file to  work around ASTNode being an incomplete
  // type.
  LLVM_ABI ~Template();
 
  Template &operator=(Template &&) = delete;
 
  LLVM_ABI void render(const llvm::json::Value &Data, llvm::raw_ostream &OS);
 
  LLVM_ABI void registerPartial(std::string Name, std::string Partial);
 
  LLVM_ABI void registerLambda(std::string Name, Lambda Lambda);
 
  LLVM_ABI void registerLambda(std::string Name, SectionLambda Lambda);
 
  // By default the Mustache Spec Specifies that HTML special characters
  // should be escaped. This function allows the user to specify which
  // characters should be escaped.
  LLVM_ABI void overrideEscapeCharacters(DenseMap<char, std::string> Escapes);
 
private:
  MustacheContext &Ctx;
  AstPtr Tree;
};
} // namespace llvm::mustache
 
#endif // LLVM_SUPPORT_MUSTACHE