llvm/clang-tools-extra/clangd/Selection.h

//===--- Selection.h - What's under the cursor? -------------------*-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
//
//===----------------------------------------------------------------------===//
// Many features are triggered at locations/ranges and operate on AST nodes.
// (e.g. go-to-definition or code tweaks).
// At a high level, such features need to work out which node is the correct
// target.
//
// There are a few levels of ambiguity here:
//
// Which tokens are included:
//   int x = one + two;  // what should "go to definition" do?
//            ^^^^^^
//
// Same token means multiple things:
//   string("foo")       // class string, or a constructor?
//   ^
//
// Which level of the AST is interesting?
//   if (err) {          // reference to 'err', or operator bool(),
//       ^               // or the if statement itself?
//
// Here we build and expose a data structure that allows features to resolve
// these ambiguities in an appropriate way:
//   - we determine which low-level nodes are partly or completely covered
//     by the selection.
//   - we expose a tree of the selected nodes and their lexical parents.
//
// Sadly LSP specifies locations as being between characters, and this causes
// some ambiguities we cannot cleanly resolve:
//   lhs+rhs  // targeting '+' or 'lhs'?
//      ^     // in GUI editors, double-clicking 'lhs' yields this position!
//
// The best we can do in these cases is try both, which leads to the awkward
// SelectionTree::createEach() API.
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
#include "clang/AST/ASTTypeTraits.h"
#include "clang/AST/PrettyPrinter.h"
#include "clang/Tooling/Syntax/Tokens.h"
#include "llvm/ADT/SmallVector.h"
#include <stack>

namespace clang {
namespace clangd {

// A selection can partially or completely cover several AST nodes.
// The SelectionTree contains nodes that are covered, and their parents.
// SelectionTree does not contain all AST nodes, rather only:
//   Decl, Stmt, TypeLoc, NestedNamespaceSpecifierLoc, CXXCtorInitializer.
// (These are the nodes with source ranges that fit in DynTypedNode).
//
// Usually commonAncestor() is the place to start:
//  - it's the simplest answer to "what node is under the cursor"
//  - the selected Expr (for example) can be found by walking up the parent
//    chain and checking Node->ASTNode.
//  - if you want to traverse the selected nodes, they are all under
//    commonAncestor() in the tree.
//
// SelectionTree tries to behave sensibly in the presence of macros, but does
// not model any preprocessor concepts: the output is a subset of the AST.
// When a macro argument is specifically selected, only its first expansion is
// selected in the AST. (Returning a selection forest is unreasonably difficult
// for callers to handle correctly.)
//
// Comments, directives and whitespace are completely ignored.
// Semicolons are also ignored, as the AST generally does not model them well.
//
// The SelectionTree owns the Node structures, but the ASTNode attributes
// point back into the AST it was constructed with.
class SelectionTree { … };

} // namespace clangd
} // namespace clang
#endif