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1 //===--- InlayHints.cpp ------------------------------------------*- 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 #include "InlayHints.h"
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9 #include "HeuristicResolver.h"
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10 #include "ParsedAST.h"
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11 #include "support/Logger.h"
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12 #include "clang/AST/DeclarationName.h"
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13 #include "clang/AST/ExprCXX.h"
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14 #include "clang/AST/RecursiveASTVisitor.h"
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15 #include "clang/Basic/SourceManager.h"
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16
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17 namespace clang {
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18 namespace clangd {
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19
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20 class InlayHintVisitor : public RecursiveASTVisitor<InlayHintVisitor> {
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21 public:
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22 InlayHintVisitor(std::vector<InlayHint> &Results, ParsedAST &AST)
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23 : Results(Results), AST(AST.getASTContext()),
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24 MainFileID(AST.getSourceManager().getMainFileID()),
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25 Resolver(AST.getHeuristicResolver()),
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26 TypeHintPolicy(this->AST.getPrintingPolicy()) {
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27 bool Invalid = false;
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28 llvm::StringRef Buf =
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29 AST.getSourceManager().getBufferData(MainFileID, &Invalid);
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30 MainFileBuf = Invalid ? StringRef{} : Buf;
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31
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32 TypeHintPolicy.SuppressScope = true; // keep type names short
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33 TypeHintPolicy.AnonymousTagLocations =
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34 false; // do not print lambda locations
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35 }
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36
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37 bool VisitCXXConstructExpr(CXXConstructExpr *E) {
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38 // Weed out constructor calls that don't look like a function call with
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39 // an argument list, by checking the validity of getParenOrBraceRange().
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40 // Also weed out std::initializer_list constructors as there are no names
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41 // for the individual arguments.
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42 if (!E->getParenOrBraceRange().isValid() ||
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43 E->isStdInitListInitialization()) {
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44 return true;
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45 }
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46
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47 processCall(E->getParenOrBraceRange().getBegin(), E->getConstructor(),
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48 {E->getArgs(), E->getNumArgs()});
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49 return true;
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50 }
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51
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52 bool VisitCallExpr(CallExpr *E) {
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53 // Do not show parameter hints for operator calls written using operator
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54 // syntax or user-defined literals. (Among other reasons, the resulting
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55 // hints can look awkard, e.g. the expression can itself be a function
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56 // argument and then we'd get two hints side by side).
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57 if (isa<CXXOperatorCallExpr>(E) || isa<UserDefinedLiteral>(E))
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58 return true;
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59
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60 auto CalleeDecls = Resolver->resolveCalleeOfCallExpr(E);
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61 if (CalleeDecls.size() != 1)
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62 return true;
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63 const FunctionDecl *Callee = nullptr;
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64 if (const auto *FD = dyn_cast<FunctionDecl>(CalleeDecls[0]))
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65 Callee = FD;
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66 else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(CalleeDecls[0]))
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67 Callee = FTD->getTemplatedDecl();
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68 if (!Callee)
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69 return true;
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70
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71 processCall(E->getRParenLoc(), Callee, {E->getArgs(), E->getNumArgs()});
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72 return true;
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73 }
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74
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75 bool VisitVarDecl(VarDecl *D) {
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76 // Do not show hints for the aggregate in a structured binding.
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77 // In the future, we may show hints for the individual bindings.
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78 if (isa<DecompositionDecl>(D))
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79 return true;
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80
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81 if (D->getType()->getContainedAutoType()) {
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82 if (!D->getType()->isDependentType()) {
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83 // Our current approach is to place the hint on the variable
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84 // and accordingly print the full type
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85 // (e.g. for `const auto& x = 42`, print `const int&`).
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86 // Alternatively, we could place the hint on the `auto`
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87 // (and then just print the type deduced for the `auto`).
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88 addInlayHint(D->getLocation(), InlayHintKind::TypeHint,
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89 ": " + D->getType().getAsString(TypeHintPolicy));
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90 }
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91 }
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92 return true;
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93 }
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94
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95 // FIXME: Handle RecoveryExpr to try to hint some invalid calls.
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96
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97 private:
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98 using NameVec = SmallVector<StringRef, 8>;
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99
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100 // The purpose of Anchor is to deal with macros. It should be the call's
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101 // opening or closing parenthesis or brace. (Always using the opening would
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102 // make more sense but CallExpr only exposes the closing.) We heuristically
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103 // assume that if this location does not come from a macro definition, then
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104 // the entire argument list likely appears in the main file and can be hinted.
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105 void processCall(SourceLocation Anchor, const FunctionDecl *Callee,
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106 llvm::ArrayRef<const Expr *const> Args) {
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107 if (Args.size() == 0 || !Callee)
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108 return;
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109
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110 // If the anchor location comes from a macro defintion, there's nowhere to
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111 // put hints.
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112 if (!AST.getSourceManager().getTopMacroCallerLoc(Anchor).isFileID())
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113 return;
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114
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115 // The parameter name of a move or copy constructor is not very interesting.
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116 if (auto *Ctor = dyn_cast<CXXConstructorDecl>(Callee))
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117 if (Ctor->isCopyOrMoveConstructor())
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118 return;
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119
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120 // Don't show hints for variadic parameters.
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121 size_t FixedParamCount = getFixedParamCount(Callee);
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122 size_t ArgCount = std::min(FixedParamCount, Args.size());
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123
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124 NameVec ParameterNames = chooseParameterNames(Callee, ArgCount);
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125
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126 // Exclude setters (i.e. functions with one argument whose name begins with
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127 // "set"), as their parameter name is also not likely to be interesting.
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128 if (isSetter(Callee, ParameterNames))
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129 return;
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130
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131 for (size_t I = 0; I < ArgCount; ++I) {
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132 StringRef Name = ParameterNames[I];
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133 if (!shouldHint(Args[I], Name))
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134 continue;
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135
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136 addInlayHint(Args[I]->getSourceRange(), InlayHintKind::ParameterHint,
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137 Name.str() + ": ");
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138 }
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139 }
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140
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141 static bool isSetter(const FunctionDecl *Callee, const NameVec &ParamNames) {
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142 if (ParamNames.size() != 1)
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143 return false;
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144
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145 StringRef Name = getSimpleName(*Callee);
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146 if (!Name.startswith_lower("set"))
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147 return false;
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148
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149 // In addition to checking that the function has one parameter and its
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150 // name starts with "set", also check that the part after "set" matches
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151 // the name of the parameter (ignoring case). The idea here is that if
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152 // the parameter name differs, it may contain extra information that
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153 // may be useful to show in a hint, as in:
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154 // void setTimeout(int timeoutMillis);
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155 // This currently doesn't handle cases where params use snake_case
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156 // and functions don't, e.g.
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157 // void setExceptionHandler(EHFunc exception_handler);
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158 // We could improve this by replacing `equals_lower` with some
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159 // `sloppy_equals` which ignores case and also skips underscores.
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160 StringRef WhatItIsSetting = Name.substr(3).ltrim("_");
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161 return WhatItIsSetting.equals_lower(ParamNames[0]);
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162 }
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163
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164 bool shouldHint(const Expr *Arg, StringRef ParamName) {
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165 if (ParamName.empty())
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166 return false;
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167
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168 // If the argument expression is a single name and it matches the
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169 // parameter name exactly, omit the hint.
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170 if (ParamName == getSpelledIdentifier(Arg))
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171 return false;
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172
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173 // Exclude argument expressions preceded by a /*paramName*/.
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174 if (isPrecededByParamNameComment(Arg, ParamName))
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175 return false;
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176
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177 return true;
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178 }
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179
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180 // Checks if "E" is spelled in the main file and preceded by a C-style comment
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181 // whose contents match ParamName (allowing for whitespace and an optional "="
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182 // at the end.
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183 bool isPrecededByParamNameComment(const Expr *E, StringRef ParamName) {
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184 auto &SM = AST.getSourceManager();
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185 auto ExprStartLoc = SM.getTopMacroCallerLoc(E->getBeginLoc());
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186 auto Decomposed = SM.getDecomposedLoc(ExprStartLoc);
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187 if (Decomposed.first != MainFileID)
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188 return false;
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189
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190 StringRef SourcePrefix = MainFileBuf.substr(0, Decomposed.second);
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191 // Allow whitespace between comment and expression.
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192 SourcePrefix = SourcePrefix.rtrim();
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193 // Check for comment ending.
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194 if (!SourcePrefix.consume_back("*/"))
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195 return false;
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196 // Allow whitespace and "=" at end of comment.
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197 SourcePrefix = SourcePrefix.rtrim().rtrim('=').rtrim();
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198 // Other than that, the comment must contain exactly ParamName.
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199 if (!SourcePrefix.consume_back(ParamName))
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200 return false;
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201 return SourcePrefix.rtrim().endswith("/*");
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202 }
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203
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204 // If "E" spells a single unqualified identifier, return that name.
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205 // Otherwise, return an empty string.
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206 static StringRef getSpelledIdentifier(const Expr *E) {
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207 E = E->IgnoreUnlessSpelledInSource();
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208
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209 if (auto *DRE = dyn_cast<DeclRefExpr>(E))
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210 if (!DRE->getQualifier())
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211 return getSimpleName(*DRE->getDecl());
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212
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213 if (auto *ME = dyn_cast<MemberExpr>(E))
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214 if (!ME->getQualifier() && ME->isImplicitAccess())
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215 return getSimpleName(*ME->getMemberDecl());
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216
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217 return {};
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218 }
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219
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220 NameVec chooseParameterNames(const FunctionDecl *Callee, size_t ArgCount) {
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221 // The current strategy here is to use all the parameter names from the
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222 // canonical declaration, unless they're all empty, in which case we
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223 // use all the parameter names from the definition (in present in the
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224 // translation unit).
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225 // We could try a bit harder, e.g.:
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226 // - try all re-declarations, not just canonical + definition
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227 // - fall back arg-by-arg rather than wholesale
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228
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229 NameVec ParameterNames = getParameterNamesForDecl(Callee, ArgCount);
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230
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231 if (llvm::all_of(ParameterNames, std::mem_fn(&StringRef::empty))) {
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232 if (const FunctionDecl *Def = Callee->getDefinition()) {
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233 ParameterNames = getParameterNamesForDecl(Def, ArgCount);
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234 }
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235 }
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236 assert(ParameterNames.size() == ArgCount);
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237
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238 // Standard library functions often have parameter names that start
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239 // with underscores, which makes the hints noisy, so strip them out.
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240 for (auto &Name : ParameterNames)
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241 stripLeadingUnderscores(Name);
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242
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243 return ParameterNames;
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244 }
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245
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246 static void stripLeadingUnderscores(StringRef &Name) {
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247 Name = Name.ltrim('_');
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248 }
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249
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250 // Return the number of fixed parameters Function has, that is, not counting
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251 // parameters that are variadic (instantiated from a parameter pack) or
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252 // C-style varargs.
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253 static size_t getFixedParamCount(const FunctionDecl *Function) {
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254 if (FunctionTemplateDecl *Template = Function->getPrimaryTemplate()) {
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255 FunctionDecl *F = Template->getTemplatedDecl();
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256 size_t Result = 0;
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257 for (ParmVarDecl *Parm : F->parameters()) {
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258 if (Parm->isParameterPack()) {
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259 break;
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260 }
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261 ++Result;
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262 }
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263 return Result;
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264 }
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265 // C-style varargs don't need special handling, they're already
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266 // not included in getNumParams().
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267 return Function->getNumParams();
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268 }
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269
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270 static StringRef getSimpleName(const NamedDecl &D) {
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271 if (IdentifierInfo *Ident = D.getDeclName().getAsIdentifierInfo()) {
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272 return Ident->getName();
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273 }
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274
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275 return StringRef();
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276 }
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277
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278 NameVec getParameterNamesForDecl(const FunctionDecl *Function,
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279 size_t ArgCount) {
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280 NameVec Result;
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281 for (size_t I = 0; I < ArgCount; ++I) {
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282 const ParmVarDecl *Parm = Function->getParamDecl(I);
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283 assert(Parm);
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284 Result.emplace_back(getSimpleName(*Parm));
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285 }
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286 return Result;
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287 }
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288
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289 void addInlayHint(SourceRange R, InlayHintKind Kind, llvm::StringRef Label) {
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290 auto FileRange =
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291 toHalfOpenFileRange(AST.getSourceManager(), AST.getLangOpts(), R);
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292 if (!FileRange)
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293 return;
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294 Results.push_back(InlayHint{
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295 Range{
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296 sourceLocToPosition(AST.getSourceManager(), FileRange->getBegin()),
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297 sourceLocToPosition(AST.getSourceManager(), FileRange->getEnd())},
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298 Kind, Label.str()});
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299 }
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300
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301 std::vector<InlayHint> &Results;
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302 ASTContext &AST;
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303 FileID MainFileID;
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304 StringRef MainFileBuf;
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305 const HeuristicResolver *Resolver;
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306 PrintingPolicy TypeHintPolicy;
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307 };
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308
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309 std::vector<InlayHint> inlayHints(ParsedAST &AST) {
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310 std::vector<InlayHint> Results;
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311 InlayHintVisitor Visitor(Results, AST);
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312 Visitor.TraverseAST(AST.getASTContext());
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313 return Results;
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314 }
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315
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316 } // namespace clangd
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317 } // namespace clang
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