clang的AST源码分析

clang的AST源码分析

QualType类
重点关注函数：

/// Return true if this QualType doesn't point to a type yet.
  bool isNull() const {
    return Value.getPointer().isNull();
  }

被RecursiveASTVisitor调用

template <typename Derived>
bool RecursiveASTVisitor<Derived>::TraverseType(QualType T) {
  if (T.isNull())
    return true;

  switch (T->getTypeClass()) {
#define ABSTRACT_TYPE(CLASS, BASE)
#define TYPE(CLASS, BASE)                                                      \
  case Type::CLASS:                                                            \
    return getDerived().Traverse##CLASS##Type(                                 \
        static_cast<CLASS##Type *>(const_cast<Type *>(T.getTypePtr())));
#include "clang/AST/TypeNodes.inc"
  }

  return true;
} 

RecursiveASTVisitor的模版类DeducedTypeVisitor

namespace {
/// Computes the deduced type at a given location by visiting the relevant
/// nodes. We use this to display the actual type when hovering over an "auto"
/// keyword or "decltype()" expression.
/// FIXME: This could have been a lot simpler by visiting AutoTypeLocs but it
/// seems that the AutoTypeLocs that can be visited along with their AutoType do
/// not have the deduced type set. Instead, we have to go to the appropriate
/// DeclaratorDecl/FunctionDecl and work our back to the AutoType that does have
/// a deduced type set. The AST should be improved to simplify this scenario.
class DeducedTypeVisitor : public RecursiveASTVisitor<DeducedTypeVisitor> {
  SourceLocation SearchedLocation;

public:
  DeducedTypeVisitor(SourceLocation SearchedLocation)
      : SearchedLocation(SearchedLocation) {}

  // Handle auto initializers:
  //- auto i = 1;
  //- decltype(auto) i = 1;
  //- auto& i = 1;
  //- auto* i = &a;
  bool VisitDeclaratorDecl(DeclaratorDecl *D) {
    if (!D->getTypeSourceInfo() ||
        D->getTypeSourceInfo()->getTypeLoc().getBeginLoc() != SearchedLocation)
      return true;

    if (auto *AT = D->getType()->getContainedAutoType()) {
      DeducedType = AT->desugar();
    }
    return true;
  }

  // Handle auto return types:
  //- auto foo() {}
  //- auto& foo() {}
  //- auto foo() -> int {}
  //- auto foo() -> decltype(1+1) {}
  //- operator auto() const { return 10; }
  bool VisitFunctionDecl(FunctionDecl *D) {
    if (!D->getTypeSourceInfo())
      return true;
    // Loc of auto in return type (c++14).
    auto CurLoc = D->getReturnTypeSourceRange().getBegin();
    // Loc of "auto" in operator auto()
    if (CurLoc.isInvalid() && isa<CXXConversionDecl>(D))
      CurLoc = D->getTypeSourceInfo()->getTypeLoc().getBeginLoc();
    // Loc of "auto" in function with trailing return type (c++11).
    if (CurLoc.isInvalid())
      CurLoc = D->getSourceRange().getBegin();
    if (CurLoc != SearchedLocation)
      return true;

    const AutoType *AT = D->getReturnType()->getContainedAutoType();
    if (AT && !AT->getDeducedType().isNull()) {
      DeducedType = AT->getDeducedType();
    } else if (auto *DT = dyn_cast<DecltypeType>(D->getReturnType())) {
      // auto in a trailing return type just points to a DecltypeType and
      // getContainedAutoType does not unwrap it.
      if (!DT->getUnderlyingType().isNull())
        DeducedType = DT->getUnderlyingType();
    } else if (!D->getReturnType().isNull()) {
      DeducedType = D->getReturnType();
    }
    return true;
  }

  // Handle non-auto decltype, e.g.:
  // - auto foo() -> decltype(expr) {}
  // - decltype(expr);
  bool VisitDecltypeTypeLoc(DecltypeTypeLoc TL) {
    if (TL.getBeginLoc() != SearchedLocation)
      return true;

    // A DecltypeType's underlying type can be another DecltypeType! E.g.
    //  int I = 0;
    //  decltype(I) J = I;
    //  decltype(J) K = J;
    const DecltypeType *DT = dyn_cast<DecltypeType>(TL.getTypePtr());
    while (DT && !DT->getUnderlyingType().isNull()) {
      DeducedType = DT->getUnderlyingType();
      DT = dyn_cast<DecltypeType>(DeducedType.getTypePtr());
    }
    return true;
  }

  QualType DeducedType;
};
} // namespace

注意getDeducedType

llvm::Optional<QualType> getDeducedType(ASTContext &ASTCtx,
                                        SourceLocation Loc) {
  if (!Loc.isValid())
    return {};
  DeducedTypeVisitor V(Loc);
  V.TraverseAST(ASTCtx);
  if (V.DeducedType.isNull())
    return llvm::None;
  return V.DeducedType;
}

MatchASTVisitor

bool MatchASTVisitor::TraverseType(QualType TypeNode) {
  match(TypeNode);
  return RecursiveASTVisitor<MatchASTVisitor>::TraverseType(TypeNode);
}