3d735480bd
This is important especially for code that tries to traverse scopes as written in code, which is the contract SelectionTree tries to satisfy. Differential Revision: https://reviews.llvm.org/D112712
171 lines
7.3 KiB
C++
171 lines
7.3 KiB
C++
//===--- Selection.h - What's under the cursor? -------------------*-C++-*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// Many features are triggered at locations/ranges and operate on AST nodes.
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// (e.g. go-to-definition or code tweaks).
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// At a high level, such features need to work out which node is the correct
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// target.
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//
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// There are a few levels of ambiguity here:
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//
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// Which tokens are included:
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// int x = one + two; // what should "go to definition" do?
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// ^^^^^^
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//
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// Same token means multiple things:
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// string("foo") // class string, or a constructor?
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// ^
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//
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// Which level of the AST is interesting?
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// if (err) { // reference to 'err', or operator bool(),
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// ^ // or the if statement itself?
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//
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// Here we build and expose a data structure that allows features to resolve
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// these ambiguities in an appropriate way:
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// - we determine which low-level nodes are partly or completely covered
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// by the selection.
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// - we expose a tree of the selected nodes and their lexical parents.
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//
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// Sadly LSP specifies locations as being between characters, and this causes
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// some ambiguities we cannot cleanly resolve:
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// lhs+rhs // targeting '+' or 'lhs'?
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// ^ // in GUI editors, double-clicking 'lhs' yields this position!
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//
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// The best we can do in these cases is try both, which leads to the awkward
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// SelectionTree::createEach() API.
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
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#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
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#include "clang/AST/ASTTypeTraits.h"
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#include "clang/AST/PrettyPrinter.h"
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#include "clang/Tooling/Syntax/Tokens.h"
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#include "llvm/ADT/SmallVector.h"
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namespace clang {
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namespace clangd {
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// A selection can partially or completely cover several AST nodes.
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// The SelectionTree contains nodes that are covered, and their parents.
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// SelectionTree does not contain all AST nodes, rather only:
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// Decl, Stmt, TypeLoc, NestedNamespaceSpecifierLoc, CXXCtorInitializer.
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// (These are the nodes with source ranges that fit in DynTypedNode).
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//
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// Usually commonAncestor() is the place to start:
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// - it's the simplest answer to "what node is under the cursor"
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// - the selected Expr (for example) can be found by walking up the parent
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// chain and checking Node->ASTNode.
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// - if you want to traverse the selected nodes, they are all under
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// commonAncestor() in the tree.
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//
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// SelectionTree tries to behave sensibly in the presence of macros, but does
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// not model any preprocessor concepts: the output is a subset of the AST.
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// When a macro argument is specifically selected, only its first expansion is
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// selected in the AST. (Returning a selection forest is unreasonably difficult
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// for callers to handle correctly.)
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//
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// Comments, directives and whitespace are completely ignored.
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// Semicolons are also ignored, as the AST generally does not model them well.
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//
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// The SelectionTree owns the Node structures, but the ASTNode attributes
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// point back into the AST it was constructed with.
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class SelectionTree {
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public:
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// Create selection trees for the given range, and pass them to Func.
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//
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// There may be multiple possible selection trees:
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// - if the range is empty and borders two tokens, a tree for the right token
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// and a tree for the left token will be yielded.
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// - Func should return true on success (stop) and false on failure (continue)
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//
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// Always yields at least one tree. If no tokens are touched, it is empty.
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static bool createEach(ASTContext &AST, const syntax::TokenBuffer &Tokens,
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unsigned Begin, unsigned End,
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llvm::function_ref<bool(SelectionTree)> Func);
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// Create a selection tree for the given range.
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//
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// Where ambiguous (range is empty and borders two tokens), prefer the token
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// on the right.
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static SelectionTree createRight(ASTContext &AST,
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const syntax::TokenBuffer &Tokens,
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unsigned Begin, unsigned End);
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// Copies are no good - contain pointers to other nodes.
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SelectionTree(const SelectionTree &) = delete;
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SelectionTree &operator=(const SelectionTree &) = delete;
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// Moves are OK though - internal storage is pointer-stable when moved.
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SelectionTree(SelectionTree &&) = default;
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SelectionTree &operator=(SelectionTree &&) = default;
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// Describes to what extent an AST node is covered by the selection.
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enum Selection : unsigned char {
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// The AST node owns no characters covered by the selection.
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// Note that characters owned by children don't count:
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// if (x == 0) scream();
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// ^^^^^^
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// The IfStmt would be Unselected because all the selected characters are
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// associated with its children.
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// (Invisible nodes like ImplicitCastExpr are always unselected).
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Unselected,
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// The AST node owns selected characters, but is not completely covered.
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Partial,
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// The AST node owns characters, and is covered by the selection.
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Complete,
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};
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// An AST node that is implicated in the selection.
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// (Either selected directly, or some descendant is selected).
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struct Node {
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// The parent within the selection tree. nullptr for TranslationUnitDecl.
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Node *Parent;
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// Direct children within the selection tree.
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llvm::SmallVector<const Node *> Children;
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// The corresponding node from the full AST.
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DynTypedNode ASTNode;
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// The extent to which this node is covered by the selection.
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Selection Selected;
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// Walk up the AST to get the lexical DeclContext of this Node, which is not
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// the node itself.
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const DeclContext &getDeclContext() const;
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// Printable node kind, like "CXXRecordDecl" or "AutoTypeLoc".
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std::string kind() const;
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// If this node is a wrapper with no syntax (e.g. implicit cast), return
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// its contents. (If multiple wrappers are present, unwraps all of them).
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const Node &ignoreImplicit() const;
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// If this node is inside a wrapper with no syntax (e.g. implicit cast),
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// return that wrapper. (If multiple are present, unwraps all of them).
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const Node &outerImplicit() const;
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};
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// The most specific common ancestor of all the selected nodes.
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// Returns nullptr if the common ancestor is the root.
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// (This is to avoid accidentally traversing the TUDecl and thus preamble).
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const Node *commonAncestor() const;
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// The selection node corresponding to TranslationUnitDecl.
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const Node &root() const { return *Root; }
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private:
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// Creates a selection tree for the given range in the main file.
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// The range includes bytes [Start, End).
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SelectionTree(ASTContext &AST, const syntax::TokenBuffer &Tokens,
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unsigned Start, unsigned End);
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std::deque<Node> Nodes; // Stable-pointer storage.
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const Node *Root;
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clang::PrintingPolicy PrintPolicy;
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void print(llvm::raw_ostream &OS, const Node &N, int Indent) const;
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friend llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
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const SelectionTree &T) {
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T.print(OS, T.root(), 1);
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return OS;
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}
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};
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} // namespace clangd
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} // namespace clang
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#endif
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