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//===--- 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.
//===----------------------------------------------------------------------===//
#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 "llvm/ADT/SmallVector.h"
namespace clang {
namespace clangd {
class ParsedAST;
// 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.
//
// The SelectionTree owns the Node structures, but the ASTNode attributes
// point back into the AST it was constructed with.
class SelectionTree {
public:
// Creates a selection tree at the given byte offset in the main file.
// This is approximately equivalent to a range of one character.
// (Usually, the character to the right of Offset, sometimes to the left).
SelectionTree(ASTContext &AST, unsigned Offset);
// Creates a selection tree for the given range in the main file.
// The range includes bytes [Start, End).
// If Start == End, uses the same heuristics as SelectionTree(AST, Start).
SelectionTree(ASTContext &AST, unsigned Start, unsigned End);
// Describes to what extent an AST node is covered by the selection.
enum Selection {
// The AST node owns no characters covered by the selection.
// Note that characters owned by children don't count:
// if (x == 0) scream();
// ^^^^^^
// The IfStmt would be Unselected because all the selected characters are
// associated with its children.
// (Invisible nodes like ImplicitCastExpr are always unselected).
Unselected,
// The AST node owns selected characters, but is not completely covered.
Partial,
// The AST node owns characters, and is covered by the selection.
Complete,
};
// An AST node that is implicated in the selection.
// (Either selected directly, or some descendant is selected).
struct Node {
// The parent within the selection tree. nullptr for TranslationUnitDecl.
Node *Parent;
// Direct children within the selection tree.
llvm::SmallVector<const Node *, 8> Children;
// The corresponding node from the full AST.
ast_type_traits::DynTypedNode ASTNode;
// The extent to which this node is covered by the selection.
Selection Selected;
// Walk up the AST to get the DeclContext of this Node,
// which is not the node itself.
const DeclContext& getDeclContext() const;
};
// The most specific common ancestor of all the selected nodes.
// If there is no selection, this is nullptr.
const Node *commonAncestor() const;
// The selection node corresponding to TranslationUnitDecl.
// If there is no selection, this is nullptr.
const Node *root() const { return Root; }
private:
std::deque<Node> Nodes; // Stable-pointer storage.
const Node *Root;
clang::PrintingPolicy PrintPolicy;
void print(llvm::raw_ostream &OS, const Node &N, int Indent) const;
friend llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
const SelectionTree &T) {
if (auto R = T.root())
T.print(OS, *R, 0);
else
OS << "(empty selection)\n";
return OS;
}
};
} // namespace clangd
} // namespace clang
#endif
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