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

[via cfe-commits]

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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 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 <vector>
+
+namespace llvm {
+namespace mustache {
+
+using Accessor = SmallVector<SmallString<128>>;
+using Lambda = std::function<llvm::json::Value()>;
+using SectionLambda = std::function<llvm::json::Value(StringRef)>;
+
+class Token {
+public:
+  enum class Type {
+    Text,
+    Variable,
+    Partial,
+    SectionOpen,
+    SectionClose,
+    InvertSectionOpen,
+    UnescapeVariable,
+    Comment,
+  };
+
+  Token(StringRef Str);
+
+  Token(StringRef RawBody, StringRef Str, char Identifier);
+
+  StringRef getTokenBody() const { return TokenBody; };
+
+  StringRef getRawBody() const { return RawBody; };
+
+  void setTokenBody(SmallString<128> NewBody) { TokenBody = NewBody; };
+
+  Accessor getAccessor() const { return Accessor; };
+
+  Type getType() const { return TokenType; };
+
+  static Type getTokenType(char Identifier);
+
+private:
+  Type TokenType;
+  SmallString<128> RawBody;
+  Accessor Accessor;
+  SmallString<128> TokenBody;
+};
+
+class ASTNode {
+public:
+  enum Type {
+    Root,
+    Text,
+    Partial,
+    Variable,
+    UnescapeVariable,
+    Section,
+    InvertSection,
+  };
+
+  ASTNode() : T(Type::Root), LocalContext(nullptr) {};
+
+  ASTNode(StringRef Body, ASTNode *Parent)
+      : T(Type::Text), Body(Body), Parent(Parent), LocalContext(nullptr) {};
+
+  // Constructor for Section/InvertSection/Variable/UnescapeVariable
+  ASTNode(Type T, Accessor Accessor, ASTNode *Parent)
+      : T(T), Parent(Parent), Children({}), Accessor(Accessor),
+        LocalContext(nullptr) {};
+
+  void addChild(ASTNode *Child) { Children.emplace_back(Child); };
+
+  SmallString<128> getBody() const { return Body; };
+
+  void setBody(StringRef NewBody) { Body = NewBody; };
+
+  void setRawBody(StringRef NewBody) { RawBody = NewBody; };
+
+  SmallString<128> render(llvm::json::Value Data,
+                          llvm::BumpPtrAllocator &Allocator,
+                          DenseMap<StringRef, ASTNode *> &Partials,
+                          DenseMap<StringRef, Lambda> &Lambdas,
+                          DenseMap<StringRef, SectionLambda> &SectionLambdas,
+                          DenseMap<char, StringRef> &Escapes);
+
+private:
+  llvm::json::Value findContext();
+  Type T;
+  SmallString<128> RawBody;
+  SmallString<128> Body;
+  ASTNode *Parent;
+  std::vector<ASTNode *> Children;
+  const Accessor Accessor;
+  llvm::json::Value LocalContext;
+};
+
+// A Template represents the container for the AST and the partials
+// and Lambdas that are registered with it.
+class Template {
+public:
+  Template(StringRef TemplateStr);
+
+  SmallString<128> render(llvm::json::Value Data);
+
+  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.
----------------
PeterChou1 wrote:

It might be useful in languages where escaping html wouldn't be helpful like Latex or Markdown

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