[SyntaxTree][Synthesis] Add support for Tree.

[eduucaldas]

add previous patch to allow pre-merge checks

clang/include/clang/Tooling/Syntax/BuildTree.h

 /// `TokenKind`.
 syntax::Leaf *createLeaf(syntax::Arena &A, tok::TokenKind K,
                          StringRef Spelling);
 
 /// Infer the token spelling from its `TokenKind`, then create `Leaf` from
 /// this token
 syntax::Leaf *createLeaf(syntax::Arena &A, tok::TokenKind K);
 
+// Synthesis of Trees
+syntax::Tree *
+foldChildren(Arena &A, std::vector<std::pair<syntax::Node *, syntax::NodeRole>>,
+             syntax::NodeKind);
+syntax::Tree *foldChildren(Arena &A, std::vector<syntax::Node *> Children,
+                           syntax::NodeKind K = NodeKind::UnknownExpression);
+syntax::Tree *createEmptyTree(Arena &A,
+                              syntax::NodeKind K = NodeKind::UnknownExpression);
+
 // Synthesis of Syntax Nodes
 clang::syntax::EmptyStatement *createEmptyStatement(clang::syntax::Arena &A);
 
 } // namespace syntax
 } // namespace clang
 #endif

clang/lib/Tooling/Syntax/Synthesis.cpp

 //===- Synthesis.cpp ------------------------------------------*- 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
 //
 //===----------------------------------------------------------------------===//
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Tooling/Syntax/BuildTree.h"
+#include "clang/Tooling/Syntax/Nodes.h"
 
 using namespace clang;
 
 /// Exposes private syntax tree APIs required to implement node synthesis.
 /// Should not be used for anything else.
 class clang::syntax::FactoryImpl {
 public:
   static void setCanModify(syntax::Node *N) { N->CanModify = true; }
syntax::Leaf *clang::syntax::createLeaf(syntax::Arena &A, tok::TokenKind K) {
   const auto *Spelling = tok::getPunctuatorSpelling(K);
   if (!Spelling)
     Spelling = tok::getKeywordSpelling(K);
   assert(Spelling &&
          "Cannot infer the spelling of the token from its token kind.");
   return createLeaf(A, K, Spelling);
 }
 
+syntax::Tree *clang::syntax::foldChildren(
+    syntax::Arena &A,
+    std::vector<std::pair<syntax::Node *, syntax::NodeRole>> Children,
+    syntax::NodeKind K) {
+  auto *T = new (A.getAllocator()) syntax::Tree(K);
+  FactoryImpl::setCanModify(T);
+  for (auto ChildIt = Children.rbegin(); ChildIt != Children.rend();
+       std::advance(ChildIt, 1))
+    FactoryImpl::prependChildLowLevel(T, ChildIt->first, ChildIt->second);
+
+  T->assertInvariants();
+  return T;
+}
+
+// For testing purposes
+syntax::Tree *clang::syntax::foldChildren(syntax::Arena &A,
+                                          std::vector<syntax::Node *> Children,
+                                          syntax::NodeKind K) {
+  auto *T = new (A.getAllocator()) syntax::Tree(K);
+  FactoryImpl::setCanModify(T);
+  for (auto ChildIt = Children.rbegin(); ChildIt != Children.rend();
+       std::advance(ChildIt, 1))
+    FactoryImpl::prependChildLowLevel(T, *ChildIt, NodeRole::Unknown);
+
+  T->assertInvariants();
+  return T;
+}
+
+syntax::Tree *clang::syntax::createEmptyTree(syntax::Arena &A,
+                                             syntax::NodeKind K) {
+  auto *T = new (A.getAllocator()) syntax::Tree(K);
+  FactoryImpl::setCanModify(T);
+  T->assertInvariants();
+  return T;
+}
+
 syntax::EmptyStatement *clang::syntax::createEmptyStatement(syntax::Arena &A) {
   auto *S = new (A.getAllocator()) syntax::EmptyStatement;
   FactoryImpl::setCanModify(S);
   FactoryImpl::prependChildLowLevel(S, createLeaf(A, tok::semi),
                                     NodeRole::Unknown);
   S->assertInvariants();
   return S;
 }

clang/unittests/Tooling/Syntax/SynthesisTest.cpp

TEST_P(SynthesisTest, Leaf_Number) {
 
   auto *C = createLeaf(*Arena, tok::numeric_constant, "1");
 
   EXPECT_TRUE(treeDumpEqual(C, R"txt(
 '1' Detached synthesized
   )txt"));
 }
 
+TEST_P(SynthesisTest, Tree_Empty) {
+  buildTree("", GetParam());
+
+  auto *Tree = createEmptyTree(*Arena);
+
+  EXPECT_TRUE(treeDumpEqual(Tree, R"txt(
+UnknownExpression Detached synthesized
+  )txt"));
+}
+
+TEST_P(SynthesisTest, Tree_Simple) {
+  buildTree("", GetParam());
+
+  auto *IdA = createLeaf(*Arena, tok::identifier, "a");
+  auto *Comma = createLeaf(*Arena, tok::comma);
+  auto *IdB = createLeaf(*Arena, tok::identifier, "b");
+  auto *Tree = foldChildren(*Arena, {IdA, Comma, IdB});
+
+  EXPECT_TRUE(treeDumpEqual(Tree, R"txt(
+UnknownExpression Detached synthesized
+|-'a' synthesized
+|-',' synthesized
+`-'b' synthesized
+  )txt"));
+}
+
 TEST_P(SynthesisTest, Statement_EmptyStatement) {
   buildTree("", GetParam());
 
   auto *S = createEmptyStatement(*Arena);
   EXPECT_TRUE(treeDumpEqual(S, R"txt(
 EmptyStatement Detached synthesized
 `-';' synthesized
   )txt"));
 }
 } // namespace