Add async generators support via AST transformation #1657

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trossimel-sc wants to merge 19 commits into facebook:static_h from trossimel-sc:async-generators

API/hermes/hermes.cpp

-Original file line number
+Diff line change
@@ Expand Up / @@ -197,6 +197,7 @@ class HermesRuntimeImpl final : public HermesRuntime, @@
         compileFlags_.enableGenerator = runtimeConfig.getEnableGenerator();
         compileFlags_.enableES6BlockScoping = runtimeConfig.getES6BlockScoping();
+        compileFlags_.enableAsyncGenerators = runtimeConfig.getEnableAsyncGenerators();
         compileFlags_.emitAsyncBreakCheck =
             runtimeConfig.getAsyncBreakCheckInEval();
         runtime_.addCustomRootsFunction(
@@ Expand Down @@

include/hermes/AST/AsyncGenerator.h

-Original file line number
+Diff line change
@@ -0,0 +1,14 @@
+    #ifndef HERMES_AST_ASYNCGENERATORS_H
+    #define HERMES_AST_ASYNCGENERATORS_H
+    #include "hermes/AST/ESTree.h"
+    namespace hermes {
+    /// Recursively transforms the ESTree Node tree such that async generators
+    /// are converted into generators
+    ESTree::Node* transformAsyncGenerators(Context &context, ESTree::Node *node);
+    } // namespace hermes
+    #endif

include/hermes/AST/Context.h

-Original file line number
+Diff line change
@@ Expand Up / @@ -242,6 +242,9 @@ class Context { @@
       /// Whether to parse TypeScript syntax.
       bool parseTS_{false};
+      /// Whether to enable support for async generators
+      bool enableAsyncGenerators_{false};
       /// Whether to enable support for ES6 block scoping.
       /// TODO: This is intended to provide a temporary way to configure block
       ///       scoping until we have debugger support for it.
@@ Expand Down Expand Up / @@ -433,6 +436,14 @@ class Context { @@
         return parseTS_;
       }
+      void setEnableAsyncGenerators(bool enableAsyncGenerators) {
+        enableAsyncGenerators_ = enableAsyncGenerators;
+      }
+      bool getEnableAsyncGenerators() const {
+        return enableAsyncGenerators_;
+      }
       void setEnableES6BlockScoping(bool enableES6BlockScoping) {
         enableES6BlockScoping_ = enableES6BlockScoping;
       }
@@ Expand Down @@

include/hermes/AST/TransformAST.h

-Original file line number
+Diff line change
@@ -0,0 +1,25 @@
+    /*
+     * Copyright (c) Meta Platforms, Inc. and affiliates.
+     *
+     * This source code is licensed under the MIT license found in the
+     * LICENSE file in the root directory of this source tree.
+     */
+    #pragma once
+    #include "hermes/AST/Context.h"
+    #include "hermes/AST/ESTree.h"
+    namespace hermes {
+    /// General purpose AST transformation which will be applied before running
+    /// semantic resolution in the compiler pipeline.
+    /// Allows adding functionality/transforms in a general way directly to the AST
+    /// in a way that works for lazy compilation, debugger eval, etc.
+    ///
+    /// \return the transformed node, which should be used for the remainder of
+    ///   compilation. On failure, report an error and return nullptr.
+    ///   The returned Node must be the same kind as the original \p root.
+    ESTree::Node *transformASTForCompilation(Context &context, ESTree::Node *root);
+    } // namespace hermes

include/hermes/AST/TransformationsBase.h

-Original file line number
+Diff line change
@@ -0,0 +1,146 @@
+    #include "hermes/AST/RecursiveVisitor.h"
+    #include "hermes/Parser/JSLexer.h"
+    #include "llvh/ADT/StringRef.h"
+    namespace {
+    using namespace hermes;
+    /// Mutable vector that helps dealing with arrays of nodes safely.
+    /// Once done with the vector, it can create an ESTree::NodeList
+    /// representation which is used by the ESTree API in several places.
+    class NodeVector {
+     public:
+      using Storage = llvh::SmallVector<ESTree::Node *, 8>;
+      NodeVector() = default;
+      NodeVector(std::initializer_list<ESTree::Node *> nodes) {
+        for (auto &node : nodes) {
+          _storage.push_back(node);
+        }
+      }
+      NodeVector(ESTree::NodeList &list) {
+        for (auto &node : list) {
+          _storage.push_back(&node);
+        }
+      }
+      ~NodeVector() = default;
+      size_t size() const {
+        return _storage.size();
+      }
+      Storage::const_iterator begin() const {
+        return _storage.begin();
+      }
+      Storage::const_iterator end() const {
+        return _storage.end();
+      }
+      void append(ESTree::Node *node) {
+        _storage.emplace_back(node);
+      }
+      void prepend(ESTree::Node *node) {
+        _storage.insert(_storage.begin(), node);
+      }
+      ESTree::NodeList toNodeList() const {
+        ESTree::NodeList nodeList;
+        for (auto &node : _storage) {
+          nodeList.push_back(*node);
+        }
+        return nodeList;
+      }
+     private:
+      Storage _storage;
+    };
+    class TransformationsBase
+        : public ESTree::RecursionDepthTracker<TransformationsBase> {
+     public:
+      static constexpr bool kEnableNodeListMutation = true;
+      TransformationsBase(Context &context)
+          : context_(context),
+            identVar_(context.getIdentifier("var").getUnderlyingPointer()) {}
+      void recursionDepthExceeded(ESTree::Node *n) {
+        context_.getSourceErrorManager().error(
+            n->getEndLoc(), "Too many nested expressions/statements/declarations");
+      }
+     protected:
+      Context &context_;
+      UniqueString *const identVar_;
+      void doCopyLocation(ESTree::Node *src, ESTree::Node *dest) {
+        if (src != nullptr) {
+          dest->setStartLoc(src->getStartLoc());
+          dest->setEndLoc(src->getEndLoc());
+          dest->setDebugLoc(src->getDebugLoc());
+        }
+      }
+      template <typename T>
+      T *copyLocation(ESTree::Node *src, T *dest) {
+        doCopyLocation(src, dest);
+        return dest;
+      }
+      template <typename T, typename... Args>
+      T *createTransformedNode(ESTree::Node *src, Args &&...args) {
+        auto *node = new (context_) T(std::forward<Args>(args)...);
+        return copyLocation(src, node);
+      }
+      ESTree::IdentifierNode *makeIdentifierNode(
+          ESTree::Node *srcNode,
+          UniqueString *name) {
+        return createTransformedNode<ESTree::IdentifierNode>(
+            srcNode, name, nullptr, false);
+      }
+      ESTree::IdentifierNode *makeIdentifierNode(
+          ESTree::Node *srcNode,
+          llvh::StringRef name) {
+        return makeIdentifierNode(
+            srcNode, context_.getIdentifier(name).getUnderlyingPointer());
+      }
+      ESTree::Node *makeSingleVarDecl(
+          ESTree::Node *srcNode,
+          ESTree::Node *identifier,
+          ESTree::Node *value) {
+        auto *variableDeclarator =
+            createTransformedNode<ESTree::VariableDeclaratorNode>(
+                srcNode, value, identifier);
+        ESTree::NodeList variableList;
+        variableList.push_back(*variableDeclarator);
+        return createTransformedNode<ESTree::VariableDeclarationNode>(
+            srcNode, identVar_, std::move(variableList));
+      }
+      ESTree::Node *makeHermesInternalCall(
+          ESTree::Node *srcNode,
+          llvh::StringRef methodName,
+          const NodeVector &parameters) {
+        auto hermesInternalIdentifier = getHermesInternalIdentifier(srcNode);
+        auto methodIdentifier = makeIdentifierNode(srcNode, methodName);
+        auto *getPropertyNode = createTransformedNode<ESTree::MemberExpressionNode>(
+            srcNode, hermesInternalIdentifier, methodIdentifier, false);
+        return createTransformedNode<ESTree::CallExpressionNode>(
+            srcNode, getPropertyNode, nullptr, parameters.toNodeList());
+      }
+      virtual ESTree::Node *getHermesInternalIdentifier(ESTree::Node *srcNode) {
+        return nullptr;
+      };
+      virtual ~TransformationsBase() = default;
+    };
+    } // namespace

include/hermes/BCGen/HBC/HBC.h

-Original file line number
+Diff line change
@@ Expand Up / @@ -68,6 +68,8 @@ struct CompileFlags { @@
       bool enableGenerator{true};
       /// Enable ES6 block scoping support
       bool enableES6BlockScoping{false};
+      /// Enable async generators support
+      bool enableAsyncGenerators{false};
       /// Define the output format of the generated bytecode. For instance, whether
       /// the bytecode is intended for execution or serialisation.
       OutputFormatKind format{Execute};
@@ Expand Down @@

include/hermes/CompilerDriver/CompilerDriver.h

-Original file line number
+Diff line change
@@ Expand Up / @@ -102,5 +102,6 @@ extern llvh::cl::opt<bool> EmitAsyncBreakCheck; @@
     extern llvh::cl::list<std::string> InputFilenames;
     extern llvh::cl::opt<bool> OptimizedEval;
     extern llvh::cl::opt<bool> PrintCompilerTiming;
+    extern llvh::cl::opt<bool> EnableAsyncGenerators;
     } // namespace cl
     #endif

include/hermes/FrontEndDefs/Builtins.def

-Original file line number
+Diff line change
@@ Expand Up / @@ -156,6 +156,7 @@ PRIVATE_BUILTIN(functionPrototypeCall) @@
     JS_BUILTIN(spawnAsync)
     MARK_FIRST_JS_BUILTIN(spawnAsync)
+    JS_BUILTIN(makeAsyncIterator)
     #undef NORMAL_OBJECT
     #undef NORMAL_METHOD
@@ Expand Down @@

include/hermes/VM/NativeFunctions.def

-Original file line number
+Diff line change
@@ Expand Up / @@ -164,6 +164,7 @@ NATIVE_FUNCTION(hermesInternalIsProxy) @@
     NATIVE_FUNCTION(hermesInternalHasPromise)
     NATIVE_FUNCTION(hermesInternalTTIReached)
     NATIVE_FUNCTION(hermesInternalTTRCReached)
+    NATIVE_FUNCTION(hermesInternalHasAsyncGenerators)
     NATIVE_FUNCTION(hermesInternalSetPromiseRejectionTrackingHook)
     NATIVE_FUNCTION(hermesInternalEnablePromiseRejectionTracker)
@@ Expand Down @@

include/hermes/VM/PredefinedStrings.def

-Original file line number
+Diff line change
@@ Expand Up / @@ -430,6 +430,7 @@ STR(HermesInternal, "HermesInternal") @@
     STR(detachArrayBuffer, "detachArrayBuffer")
     STR(createHeapSnapshot, "createHeapSnapshot")
     STR(hasPromise, "hasPromise")
+    STR(hasAsyncGenerators, "hasAsyncGenerators")
     STR(useEngineQueue, "useEngineQueue")
     STR(enqueueJob, "enqueueJob")
     STR(drainJobs, "drainJobs")
@@ Expand Down Expand Up / @@ -463,6 +464,7 @@ STR(fileName, "fileName") @@
     STR(setPromiseRejectionTrackingHook, "setPromiseRejectionTrackingHook")
     STR(enablePromiseRejectionTracker, "enablePromiseRejectionTracker")
     STR(spawnAsync, "spawnAsync") /* NOLINT */
+    STR(makeAsyncIterator, "makeAsyncIterator") /* NOLINT */
     STR(SHBuiltin, "$SHBuiltin")
@@ Expand Down @@

include/hermes/VM/Runtime.h

-Original file line number
+Diff line change
@@ Expand Up @@
         return hasES6Proxy_;
       }
+      bool hasAsyncGenerators() const {
+        return hasAsyncGenerators_;
+      }
       bool hasES6BlockScoping() const {
         return hasES6BlockScoping_;
       }
@@ Expand Down Expand Up @@
       /// Set to true if we should enable ES6 Proxy.
       const bool hasES6Proxy_;
+      /// Set to true if we should enable async generators.
+      const bool hasAsyncGenerators_;
       /// Set to true if we should enable ES6 block scoping.
       const bool hasES6BlockScoping_;
@@ Expand Down @@

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