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150
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1 //===--- Selection.h - What's under the cursor? -------------------*-C++-*-===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 // Many features are triggered at locations/ranges and operate on AST nodes.
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9 // (e.g. go-to-definition or code tweaks).
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10 // At a high level, such features need to work out which node is the correct
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11 // target.
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12 //
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13 // There are a few levels of ambiguity here:
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14 //
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15 // Which tokens are included:
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16 // int x = one + two; // what should "go to definition" do?
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17 // ^^^^^^
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18 //
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19 // Same token means multiple things:
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20 // string("foo") // class string, or a constructor?
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21 // ^
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22 //
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23 // Which level of the AST is interesting?
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24 // if (err) { // reference to 'err', or operator bool(),
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25 // ^ // or the if statement itself?
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26 //
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27 // Here we build and expose a data structure that allows features to resolve
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28 // these ambiguities in an appropriate way:
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29 // - we determine which low-level nodes are partly or completely covered
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30 // by the selection.
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31 // - we expose a tree of the selected nodes and their lexical parents.
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173
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32 //
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33 // Sadly LSP specifies locations as being between characters, and this causes
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34 // some ambiguities we cannot cleanly resolve:
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35 // lhs+rhs // targeting '+' or 'lhs'?
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36 // ^ // in GUI editors, double-clicking 'lhs' yields this position!
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37 //
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38 // The best we can do in these cases is try both, which leads to the awkward
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39 // SelectionTree::createEach() API.
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150
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40 //===----------------------------------------------------------------------===//
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41
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42 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
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43 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SELECTION_H
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44 #include "clang/AST/ASTTypeTraits.h"
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45 #include "clang/AST/PrettyPrinter.h"
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46 #include "clang/Tooling/Syntax/Tokens.h"
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47 #include "llvm/ADT/SmallVector.h"
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48
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49 namespace clang {
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50 namespace clangd {
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51
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52 // A selection can partially or completely cover several AST nodes.
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53 // The SelectionTree contains nodes that are covered, and their parents.
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54 // SelectionTree does not contain all AST nodes, rather only:
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55 // Decl, Stmt, TypeLoc, NestedNamespaceSpecifierLoc, CXXCtorInitializer.
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56 // (These are the nodes with source ranges that fit in DynTypedNode).
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57 //
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58 // Usually commonAncestor() is the place to start:
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59 // - it's the simplest answer to "what node is under the cursor"
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60 // - the selected Expr (for example) can be found by walking up the parent
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61 // chain and checking Node->ASTNode.
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62 // - if you want to traverse the selected nodes, they are all under
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63 // commonAncestor() in the tree.
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64 //
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65 // SelectionTree tries to behave sensibly in the presence of macros, but does
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66 // not model any preprocessor concepts: the output is a subset of the AST.
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173
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67 // When a macro argument is specifically selected, only its first expansion is
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68 // selected in the AST. (Returning a selection forest is unreasonably difficult
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69 // for callers to handle correctly.)
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150
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70 //
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71 // Comments, directives and whitespace are completely ignored.
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72 // Semicolons are also ignored, as the AST generally does not model them well.
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73 //
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74 // The SelectionTree owns the Node structures, but the ASTNode attributes
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75 // point back into the AST it was constructed with.
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76 class SelectionTree {
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77 public:
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173
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78 // Create selection trees for the given range, and pass them to Func.
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79 //
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80 // There may be multiple possible selection trees:
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81 // - if the range is empty and borders two tokens, a tree for the right token
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82 // and a tree for the left token will be yielded.
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83 // - Func should return true on success (stop) and false on failure (continue)
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84 //
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85 // Always yields at least one tree. If no tokens are touched, it is empty.
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86 static bool createEach(ASTContext &AST, const syntax::TokenBuffer &Tokens,
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87 unsigned Begin, unsigned End,
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88 llvm::function_ref<bool(SelectionTree)> Func);
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89
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90 // Create a selection tree for the given range.
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91 //
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92 // Where ambiguous (range is empty and borders two tokens), prefer the token
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93 // on the right.
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94 static SelectionTree createRight(ASTContext &AST,
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95 const syntax::TokenBuffer &Tokens,
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96 unsigned Begin, unsigned End);
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97
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98 // Copies are no good - contain pointers to other nodes.
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99 SelectionTree(const SelectionTree &) = delete;
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100 SelectionTree &operator=(const SelectionTree &) = delete;
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101 // Moves are OK though - internal storage is pointer-stable when moved.
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102 SelectionTree(SelectionTree &&) = default;
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103 SelectionTree &operator=(SelectionTree &&) = default;
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150
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104
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105 // Describes to what extent an AST node is covered by the selection.
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106 enum Selection : unsigned char {
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107 // The AST node owns no characters covered by the selection.
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108 // Note that characters owned by children don't count:
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109 // if (x == 0) scream();
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110 // ^^^^^^
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111 // The IfStmt would be Unselected because all the selected characters are
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112 // associated with its children.
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113 // (Invisible nodes like ImplicitCastExpr are always unselected).
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114 Unselected,
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115 // The AST node owns selected characters, but is not completely covered.
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116 Partial,
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117 // The AST node owns characters, and is covered by the selection.
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118 Complete,
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119 };
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120 // An AST node that is implicated in the selection.
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121 // (Either selected directly, or some descendant is selected).
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122 struct Node {
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123 // The parent within the selection tree. nullptr for TranslationUnitDecl.
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124 Node *Parent;
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125 // Direct children within the selection tree.
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126 llvm::SmallVector<const Node *, 8> Children;
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127 // The corresponding node from the full AST.
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128 ast_type_traits::DynTypedNode ASTNode;
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129 // The extent to which this node is covered by the selection.
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130 Selection Selected;
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131 // Walk up the AST to get the DeclContext of this Node,
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132 // which is not the node itself.
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173
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133 const DeclContext &getDeclContext() const;
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150
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134 // Printable node kind, like "CXXRecordDecl" or "AutoTypeLoc".
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135 std::string kind() const;
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136 // If this node is a wrapper with no syntax (e.g. implicit cast), return
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137 // its contents. (If multiple wrappers are present, unwraps all of them).
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173
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138 const Node &ignoreImplicit() const;
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150
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139 // If this node is inside a wrapper with no syntax (e.g. implicit cast),
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140 // return that wrapper. (If multiple are present, unwraps all of them).
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173
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141 const Node &outerImplicit() const;
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150
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142 };
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143 // The most specific common ancestor of all the selected nodes.
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144 // Returns nullptr if the common ancestor is the root.
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145 // (This is to avoid accidentally traversing the TUDecl and thus preamble).
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146 const Node *commonAncestor() const;
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147 // The selection node corresponding to TranslationUnitDecl.
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148 const Node &root() const { return *Root; }
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149
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150 private:
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173
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151 // Creates a selection tree for the given range in the main file.
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152 // The range includes bytes [Start, End).
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153 SelectionTree(ASTContext &AST, const syntax::TokenBuffer &Tokens,
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154 unsigned Start, unsigned End);
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155
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150
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156 std::deque<Node> Nodes; // Stable-pointer storage.
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157 const Node *Root;
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158 clang::PrintingPolicy PrintPolicy;
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159
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160 void print(llvm::raw_ostream &OS, const Node &N, int Indent) const;
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161 friend llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
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162 const SelectionTree &T) {
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163 T.print(OS, T.root(), 1);
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164 return OS;
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165 }
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166 };
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167
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168 } // namespace clangd
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169 } // namespace clang
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170 #endif
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