[clang-tools-extra] [llvm] [llvm] add support for mustache templating language (PR #105893)

[Paul Kirth via cfe-commits]

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@@ -0,0 +1,113 @@
+//===--- 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 container class outputs the Mustache template string
+// and is main class for users. It stores all the lambdas and the ASTNode Tree.
+// When the Template is instantiated it tokenize 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"}};
+//   StringRef Rendered = Template.render(Data);
+//   // Rendered == "Hello, World!"
+//
+//   // Creating a template with a partial and rendering it
+//   auto Template = Template("{{>partial}}");
+//   Template.registerPartial("partial", "Hello, {{name}}!");
+//   Value Data = {{"name", "World"}};
+//   StringRef Rendered = Template.render(Data);
+//   // Rendered == "Hello, World!"
+//
+//   // Creating a template with a lambda and rendering it
+//   auto Template = Template("{{#lambda}}Hello, {{name}}!{{/lambda}}");
+//   Template.registerLambda("lambda", []() { return true; });
+//   Value Data = {{"name", "World"}};
+//   StringRef Rendered = Template.render(Data);
+//   // Rendered == "Hello, World!"
+// \endcode
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_MUSTACHE
+#define LLVM_SUPPORT_MUSTACHE
+
+#include "Error.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/JSON.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+
+namespace llvm {
+namespace mustache {
+
+using Accessor = SmallVector<SmallString<0>>;
+using Lambda = std::function<llvm::json::Value()>;
+using SectionLambda = std::function<llvm::json::Value(StringRef)>;
+
+class ASTNode;
+
+// A Template represents the container for the AST and the partials
+// and Lambdas that are registered with it.
+class Template {
+public:
+  Template(StringRef TemplateStr);
+
+  void render(llvm::json::Value &Data, llvm::raw_ostream &OS);
+
+  void registerPartial(StringRef Name, StringRef Partial);
+
+  void registerLambda(StringRef Name, Lambda Lambda);
+
+  void registerLambda(StringRef 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.
+  void registerEscape(DenseMap<char, StringRef> Escapes);
+
+private:
+  std::string Output;
+  StringMap<ASTNode *> Partials;
+  StringMap<Lambda> Lambdas;
+  StringMap<SectionLambda> SectionLambdas;
+  DenseMap<char, StringRef> Escapes;
+  // The allocator for the ASTNode Tree
+  llvm::BumpPtrAllocator Allocator;
+  // Allocator for each render call resets after each render
+  llvm::BumpPtrAllocator LocalAllocator;
----------------
ilovepi wrote:

```suggestion
  llvm::BumpPtrAllocator RenderAllocator;
```
Same idea as above.

https://github.com/llvm/llvm-project/pull/105893