#include "Index/USR.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/AST/ODRHash.h"
#include "clang/Basic/SourceManager.h"

using namespace clang;

/// \returns true on error.
static bool printLoc(llvm::raw_ostream& OS,
                     SourceLocation Loc,
                     const SourceManager& SM,
                     bool IncludeOffset) {
    if(Loc.isInvalid()) {
        return true;
    }
    Loc = SM.getExpansionLoc(Loc);
    const std::pair<FileID, unsigned>& Decomposed = SM.getDecomposedLoc(Loc);
    OptionalFileEntryRef FE = SM.getFileEntryRefForID(Decomposed.first);
    if(FE) {
        OS << llvm::sys::path::filename(FE->getName());
    } else {
        // This case really isn't interesting.
        return true;
    }
    if(IncludeOffset) {
        // Use the offest into the FileID to represent the location.  Using
        // a line/column can cause us to look back at the original source file,
        // which is expensive.
        OS << '@' << Decomposed.second;
    }
    return false;
}

static StringRef GetExternalSourceContainer(const NamedDecl* D) {
    if(!D)
        return StringRef();
    if(auto* attr = D->getExternalSourceSymbolAttr()) {
        return attr->getDefinedIn();
    }
    return StringRef();
}

void AppendExprODRHash(const Expr* expr, llvm::raw_ostream& Out) {
    ODRHash Hash{};
    Hash.AddStmt(expr);
    Out << Hash.CalculateHash();
};

namespace {
class USRGenerator : public ConstDeclVisitor<USRGenerator> {
    SmallVectorImpl<char>& Buf;
    llvm::raw_svector_ostream Out;
    ASTContext* Context;
    const LangOptions& LangOpts;
    bool IgnoreResults = false;
    bool generatedLoc = false;

    llvm::DenseMap<const Type*, unsigned> TypeSubstitutions;

public:
    USRGenerator(ASTContext* Ctx, SmallVectorImpl<char>& Buf, const LangOptions& LangOpts) :
        Buf(Buf), Out(Buf), Context(Ctx), LangOpts(LangOpts) {
        // Add the USR space prefix.
        Out << "c:";
    }

    bool ignoreResults() const {
        return IgnoreResults;
    }

    // Visitation methods from generating USRs from AST elements.
    void VisitDeclContext(const DeclContext* D);
    void VisitFieldDecl(const FieldDecl* D);
    void VisitFunctionDecl(const FunctionDecl* D);
    void VisitNamedDecl(const NamedDecl* D);
    void VisitNamespaceDecl(const NamespaceDecl* D);
    void VisitNamespaceAliasDecl(const NamespaceAliasDecl* D);
    void VisitFunctionTemplateDecl(const FunctionTemplateDecl* D);
    void VisitClassTemplateDecl(const ClassTemplateDecl* D);
    void VisitTagDecl(const TagDecl* D);
    void VisitTypedefDecl(const TypedefDecl* D);
    void VisitTemplateTypeParmDecl(const TemplateTypeParmDecl* D);
    void VisitVarDecl(const VarDecl* D);
    void VisitBindingDecl(const BindingDecl* D);
    void VisitNonTypeTemplateParmDecl(const NonTypeTemplateParmDecl* D);
    void VisitTemplateTemplateParmDecl(const TemplateTemplateParmDecl* D);
    void VisitUnresolvedUsingValueDecl(const UnresolvedUsingValueDecl* D);
    void VisitUnresolvedUsingTypenameDecl(const UnresolvedUsingTypenameDecl* D);
    void VisitConceptDecl(const ConceptDecl* D);
    void VisitTemplateParamObjectDecl(const TemplateParamObjectDecl* D);

    void VisitLinkageSpecDecl(const LinkageSpecDecl* D) {
        IgnoreResults = true;  // No USRs for linkage specs themselves.
    }

    void VisitUsingDirectiveDecl(const UsingDirectiveDecl* D) {
        IgnoreResults = true;
    }

    void VisitUsingDecl(const UsingDecl* D) {
        VisitDeclContext(D->getDeclContext());
        Out << "@UD@";

        bool EmittedDeclName = !EmitDeclName(D);
        assert(EmittedDeclName && "EmitDeclName can not fail for UsingDecls");
        (void)EmittedDeclName;
    }

    bool ShouldGenerateLocation(const NamedDecl* D);

    bool isLocal(const NamedDecl* D) {
        return D->getParentFunctionOrMethod() != nullptr;
    }

    void GenExtSymbolContainer(const NamedDecl* D);

    /// Generate the string component containing the location of the
    ///  declaration.
    bool GenLoc(const Decl* D, bool IncludeOffset);

    /// String generation methods used both by the visitation methods
    /// and from other clients that want to directly generate USRs.  These
    /// methods do not construct complete USRs (which incorporate the parents
    /// of an AST element), but only the fragments concerning the AST element
    /// itself.

    void VisitType(QualType T);
    void VisitTemplateParameterList(const TemplateParameterList* Params);
    void VisitTemplateName(TemplateName Name);
    void VisitTemplateArgument(const TemplateArgument& Arg);

    void VisitMSGuidDecl(const MSGuidDecl* D);

    /// Emit a Decl's name using NamedDecl::printName() and return true if
    ///  the decl had no name.
    bool EmitDeclName(const NamedDecl* D);
};
}  // end anonymous namespace

//===----------------------------------------------------------------------===//
// Generating USRs from ASTS.
//===----------------------------------------------------------------------===//

bool USRGenerator::EmitDeclName(const NamedDecl* D) {
    DeclarationName N = D->getDeclName();
    if(N.isEmpty())
        return true;
    Out << N;
    return false;
}

bool USRGenerator::ShouldGenerateLocation(const NamedDecl* D) {
    if(D->isExternallyVisible())
        return false;
    if(D->getParentFunctionOrMethod())
        return true;
    SourceLocation Loc = D->getLocation();
    if(Loc.isInvalid())
        return false;
    const SourceManager& SM = Context->getSourceManager();
    return !SM.isInSystemHeader(Loc);
}

void USRGenerator::VisitDeclContext(const DeclContext* DC) {
    if(const NamedDecl* D = dyn_cast<NamedDecl>(DC))
        Visit(D);
    else if(isa<LinkageSpecDecl>(DC))  // Linkage specs are transparent in USRs.
        VisitDeclContext(DC->getParent());
}

void USRGenerator::VisitFieldDecl(const FieldDecl* D) {
    // The USR for an ivar declared in a class extension is based on the
    // ObjCInterfaceDecl, not the ObjCCategoryDecl.
    if(const ObjCInterfaceDecl* ID = Context->getObjContainingInterface(D))
        Visit(ID);
    else
        VisitDeclContext(D->getDeclContext());
    Out << (isa<ObjCIvarDecl>(D) ? "@" : "@FI@");
    if(EmitDeclName(D)) {
        // Bit fields can be anonymous.
        IgnoreResults = true;
        return;
    }
}

void USRGenerator::VisitFunctionDecl(const FunctionDecl* D) {
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;

    if(D->getType().isNull()) {
        IgnoreResults = true;
        return;
    }

    const unsigned StartSize = Buf.size();
    VisitDeclContext(D->getDeclContext());
    if(Buf.size() == StartSize)
        GenExtSymbolContainer(D);

    bool IsTemplate = false;
    if(FunctionTemplateDecl* FunTmpl = D->getDescribedFunctionTemplate()) {
        IsTemplate = true;
        Out << "@FT@";
        VisitTemplateParameterList(FunTmpl->getTemplateParameters());
        if(auto RC = D->getTrailingRequiresClause()) {
            Out << ":RC";
            AppendExprODRHash(RC, Out);
        }
    } else
        Out << "@F@";

    PrintingPolicy Policy(LangOpts);
    // Forward references can have different template argument names. Suppress the
    // template argument names in constructors to make their USR more stable.
    Policy.SuppressTemplateArgsInCXXConstructors = true;
    D->getDeclName().print(Out, Policy);

    if((!LangOpts.CPlusPlus || D->isExternC()) && !D->hasAttr<OverloadableAttr>())
        return;

    if(D->isFunctionTemplateSpecialization()) {
        Out << '<';
        if(const TemplateArgumentList* SpecArgs = D->getTemplateSpecializationArgs()) {
            for(const auto& Arg: SpecArgs->asArray()) {
                Out << '#';
                VisitTemplateArgument(Arg);
            }
        } else if(const ASTTemplateArgumentListInfo* SpecArgsWritten =
                      D->getTemplateSpecializationArgsAsWritten()) {
            for(const auto& ArgLoc: SpecArgsWritten->arguments()) {
                Out << '#';
                VisitTemplateArgument(ArgLoc.getArgument());
            }
        }
        Out << '>';
    }

    // Mangle in type information for the arguments.
    for(auto ParmVar: D->parameters()) {
        Out << '#';
        if(ParmVar->isExplicitObjectParameter()) {
            Out << "this";
        }
        VisitType(ParmVar->getType());
    }
    if(D->isVariadic())
        Out << '.';
    if(IsTemplate) {
        // Function templates can be overloaded by return type, for example:
        // \code
        //   template <class T> typename T::A foo() {}
        //   template <class T> typename T::B foo() {}
        // \endcode
        Out << '#';
        VisitType(D->getReturnType());
    }
    Out << '#';
    if(const CXXMethodDecl* MD = dyn_cast<CXXMethodDecl>(D)) {
        if(MD->isStatic())
            Out << 'S';
        // FIXME: OpenCL: Need to consider address spaces
        if(unsigned quals = MD->getMethodQualifiers().getCVRUQualifiers())
            Out << (char)('0' + quals);
        switch(MD->getRefQualifier()) {
            case RQ_None: break;
            case RQ_LValue: Out << '&'; break;
            case RQ_RValue: Out << "&&"; break;
        }
    }
}

void USRGenerator::VisitNamedDecl(const NamedDecl* D) {
    VisitDeclContext(D->getDeclContext());
    Out << "@";

    if(EmitDeclName(D)) {
        // The string can be empty if the declaration has no name; e.g., it is
        // the ParmDecl with no name for declaration of a function pointer type,
        // e.g.: void  (*f)(void *);
        // In this case, don't generate a USR.
        IgnoreResults = true;
    }
}

void USRGenerator::VisitVarDecl(const VarDecl* D) {
    // VarDecls can be declared 'extern' within a function or method body,
    // but their enclosing DeclContext is the function, not the TU.  We need
    // to check the storage class to correctly generate the USR.
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;

    VisitDeclContext(D->getDeclContext());

    if(VarTemplateDecl* VarTmpl = D->getDescribedVarTemplate()) {
        Out << "@VT";
        VisitTemplateParameterList(VarTmpl->getTemplateParameters());
    } else if(const VarTemplatePartialSpecializationDecl* PartialSpec =
                  dyn_cast<VarTemplatePartialSpecializationDecl>(D)) {
        Out << "@VP";
        VisitTemplateParameterList(PartialSpec->getTemplateParameters());
    }

    // Variables always have simple names.
    StringRef s = D->getName();

    // The string can be empty if the declaration has no name; e.g., it is
    // the ParmDecl with no name for declaration of a function pointer type, e.g.:
    //    void  (*f)(void *);
    // In this case, don't generate a USR.
    if(s.empty())
        IgnoreResults = true;
    else
        Out << '@' << s;

    // For a template specialization, mangle the template arguments.
    if(const VarTemplateSpecializationDecl* Spec = dyn_cast<VarTemplateSpecializationDecl>(D)) {
        const TemplateArgumentList& Args = Spec->getTemplateArgs();
        Out << '>';
        for(unsigned I = 0, N = Args.size(); I != N; ++I) {
            Out << '#';
            VisitTemplateArgument(Args.get(I));
        }
    }
}

void USRGenerator::VisitBindingDecl(const BindingDecl* D) {
    if(isLocal(D) && GenLoc(D, /*IncludeOffset=*/true))
        return;
    VisitNamedDecl(D);
}

void USRGenerator::VisitNonTypeTemplateParmDecl(const NonTypeTemplateParmDecl* D) {
    GenLoc(D, /*IncludeOffset=*/true);
}

void USRGenerator::VisitTemplateTemplateParmDecl(const TemplateTemplateParmDecl* D) {
    GenLoc(D, /*IncludeOffset=*/true);
}

void USRGenerator::VisitNamespaceDecl(const NamespaceDecl* D) {
    if(IgnoreResults)
        return;
    VisitDeclContext(D->getDeclContext());
    if(D->isAnonymousNamespace()) {
        Out << "@aN";
        return;
    }
    Out << "@N@" << D->getName();
}

void USRGenerator::VisitFunctionTemplateDecl(const FunctionTemplateDecl* D) {
    VisitFunctionDecl(D->getTemplatedDecl());
}

void USRGenerator::VisitClassTemplateDecl(const ClassTemplateDecl* D) {
    VisitTagDecl(D->getTemplatedDecl());
}

void USRGenerator::VisitNamespaceAliasDecl(const NamespaceAliasDecl* D) {
    VisitDeclContext(D->getDeclContext());
    if(!IgnoreResults)
        Out << "@NA@" << D->getName();
}

const static ObjCCategoryDecl* getCategoryContext(const NamedDecl* D) {
    if(auto* CD = dyn_cast<ObjCCategoryDecl>(D->getDeclContext()))
        return CD;
    if(auto* ICD = dyn_cast<ObjCCategoryImplDecl>(D->getDeclContext()))
        return ICD->getCategoryDecl();
    return nullptr;
}

void USRGenerator::VisitTagDecl(const TagDecl* D) {
    // Add the location of the tag decl to handle resolution across
    // translation units.
    if(!isa<EnumDecl>(D) && ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;

    GenExtSymbolContainer(D);

    D = D->getCanonicalDecl();
    VisitDeclContext(D->getDeclContext());

    bool AlreadyStarted = false;
    if(const CXXRecordDecl* CXXRecord = dyn_cast<CXXRecordDecl>(D)) {
        if(ClassTemplateDecl* ClassTmpl = CXXRecord->getDescribedClassTemplate()) {
            AlreadyStarted = true;

            switch(D->getTagKind()) {
                case TagTypeKind::Interface:
                case TagTypeKind::Class:
                case TagTypeKind::Struct: Out << "@ST"; break;
                case TagTypeKind::Union: Out << "@UT"; break;
                case TagTypeKind::Enum: llvm_unreachable("enum template");
            }
            VisitTemplateParameterList(ClassTmpl->getTemplateParameters());
        } else if(const ClassTemplatePartialSpecializationDecl* PartialSpec =
                      dyn_cast<ClassTemplatePartialSpecializationDecl>(CXXRecord)) {
            AlreadyStarted = true;

            switch(D->getTagKind()) {
                case TagTypeKind::Interface:
                case TagTypeKind::Class:
                case TagTypeKind::Struct: Out << "@SP"; break;
                case TagTypeKind::Union: Out << "@UP"; break;
                case TagTypeKind::Enum: llvm_unreachable("enum partial specialization");
            }
            VisitTemplateParameterList(PartialSpec->getTemplateParameters());
        }
    }

    if(!AlreadyStarted) {
        switch(D->getTagKind()) {
            case TagTypeKind::Interface:
            case TagTypeKind::Class:
            case TagTypeKind::Struct: Out << "@S"; break;
            case TagTypeKind::Union: Out << "@U"; break;
            case TagTypeKind::Enum: Out << "@E"; break;
        }
    }

    Out << '@';
    assert(Buf.size() > 0);
    const unsigned off = Buf.size() - 1;

    if(EmitDeclName(D)) {
        if(const TypedefNameDecl* TD = D->getTypedefNameForAnonDecl()) {
            Buf[off] = 'A';
            Out << '@' << *TD;
        } else {
            if(D->isEmbeddedInDeclarator() && !D->isFreeStanding()) {
                printLoc(Out, D->getLocation(), Context->getSourceManager(), true);
            } else {
                Buf[off] = 'a';
                if(auto* ED = dyn_cast<EnumDecl>(D)) {
                    // Distinguish USRs of anonymous enums by using their first
                    // enumerator.
                    auto enum_range = ED->enumerators();
                    if(enum_range.begin() != enum_range.end()) {
                        Out << '@' << **enum_range.begin();
                    }
                }
            }
        }
    }

    // For a class template specialization, mangle the template arguments.
    if(const ClassTemplateSpecializationDecl* Spec = dyn_cast<ClassTemplateSpecializationDecl>(D)) {
        const TemplateArgumentList& Args = Spec->getTemplateArgs();
        Out << '>';
        for(unsigned I = 0, N = Args.size(); I != N; ++I) {
            Out << '#';
            VisitTemplateArgument(Args.get(I));
        }
    }
}

void USRGenerator::VisitTypedefDecl(const TypedefDecl* D) {
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;
    const DeclContext* DC = D->getDeclContext();
    if(const NamedDecl* DCN = dyn_cast<NamedDecl>(DC))
        Visit(DCN);
    Out << "@T@";
    Out << D->getName();
}

void USRGenerator::VisitTemplateTypeParmDecl(const TemplateTypeParmDecl* D) {
    GenLoc(D, /*IncludeOffset=*/true);
}

void USRGenerator::GenExtSymbolContainer(const NamedDecl* D) {
    StringRef Container = GetExternalSourceContainer(D);
    if(!Container.empty())
        Out << "@M@" << Container;
}

bool USRGenerator::GenLoc(const Decl* D, bool IncludeOffset) {
    if(generatedLoc)
        return IgnoreResults;
    generatedLoc = true;

    // Guard against null declarations in invalid code.
    if(!D) {
        IgnoreResults = true;
        return true;
    }

    // Use the location of canonical decl.
    D = D->getCanonicalDecl();

    IgnoreResults = IgnoreResults ||
                    printLoc(Out, D->getBeginLoc(), Context->getSourceManager(), IncludeOffset);

    return IgnoreResults;
}

static void printQualifier(llvm::raw_ostream& Out,
                           const LangOptions& LangOpts,
                           NestedNameSpecifier* NNS) {
    // FIXME: Encode the qualifier, don't just print it.
    PrintingPolicy PO(LangOpts);
    PO.SuppressTagKeyword = true;
    PO.SuppressUnwrittenScope = true;
    PO.ConstantArraySizeAsWritten = false;
    PO.AnonymousTagLocations = false;
    NNS->print(Out, PO);
}

void USRGenerator::VisitType(QualType T) {
    // This method mangles in USR information for types.  It can possibly
    // just reuse the naming-mangling logic used by codegen, although the
    // requirements for USRs might not be the same.
    ASTContext& Ctx = *Context;

    do {
        T = Ctx.getCanonicalType(T);
        Qualifiers Q = T.getQualifiers();
        unsigned qVal = 0;
        if(Q.hasConst())
            qVal |= 0x1;
        if(Q.hasVolatile())
            qVal |= 0x2;
        if(Q.hasRestrict())
            qVal |= 0x4;
        if(qVal)
            Out << ((char)('0' + qVal));

        // Mangle in ObjC GC qualifiers?

        if(const PackExpansionType* Expansion = T->getAs<PackExpansionType>()) {
            Out << 'P';
            T = Expansion->getPattern();
        }

        if(const BuiltinType* BT = T->getAs<BuiltinType>()) {
            switch(BT->getKind()) {
                case BuiltinType::Void: Out << 'v'; break;
                case BuiltinType::Bool: Out << 'b'; break;
                case BuiltinType::UChar: Out << 'c'; break;
                case BuiltinType::Char8: Out << 'u'; break;
                case BuiltinType::Char16: Out << 'q'; break;
                case BuiltinType::Char32: Out << 'w'; break;
                case BuiltinType::UShort: Out << 's'; break;
                case BuiltinType::UInt: Out << 'i'; break;
                case BuiltinType::ULong: Out << 'l'; break;
                case BuiltinType::ULongLong: Out << 'k'; break;
                case BuiltinType::UInt128: Out << 'j'; break;
                case BuiltinType::Char_U:
                case BuiltinType::Char_S: Out << 'C'; break;
                case BuiltinType::SChar: Out << 'r'; break;
                case BuiltinType::WChar_S:
                case BuiltinType::WChar_U: Out << 'W'; break;
                case BuiltinType::Short: Out << 'S'; break;
                case BuiltinType::Int: Out << 'I'; break;
                case BuiltinType::Long: Out << 'L'; break;
                case BuiltinType::LongLong: Out << 'K'; break;
                case BuiltinType::Int128: Out << 'J'; break;
                case BuiltinType::Float16:
                case BuiltinType::Half: Out << 'h'; break;
                case BuiltinType::Float: Out << 'f'; break;
                case BuiltinType::Double: Out << 'd'; break;
                case BuiltinType::LongDouble: Out << 'D'; break;
                case BuiltinType::Float128: Out << 'Q'; break;
                case BuiltinType::NullPtr: Out << 'n'; break;
#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix)                                       \
    case BuiltinType::Id: Out << "@BT@" << #Suffix << "_" << #ImgType; break;
#include "clang/Basic/OpenCLImageTypes.def"
#define EXT_OPAQUE_TYPE(ExtType, Id, Ext)                                                          \
    case BuiltinType::Id: Out << "@BT@" << #ExtType; break;
#include "clang/Basic/OpenCLExtensionTypes.def"
                case BuiltinType::OCLEvent: Out << "@BT@OCLEvent"; break;
                case BuiltinType::OCLClkEvent: Out << "@BT@OCLClkEvent"; break;
                case BuiltinType::OCLQueue: Out << "@BT@OCLQueue"; break;
                case BuiltinType::OCLReserveID: Out << "@BT@OCLReserveID"; break;
                case BuiltinType::OCLSampler: Out << "@BT@OCLSampler"; break;
#define SVE_TYPE(Name, Id, SingletonId)                                                            \
    case BuiltinType::Id: Out << "@BT@" << #Name; break;
#include "clang/Basic/AArch64SVEACLETypes.def"
#define PPC_VECTOR_TYPE(Name, Id, Size)                                                            \
    case BuiltinType::Id: Out << "@BT@" << #Name; break;
#include "clang/Basic/PPCTypes.def"
#define RVV_TYPE(Name, Id, SingletonId)                                                            \
    case BuiltinType::Id: Out << "@BT@" << Name; break;
#include "clang/Basic/RISCVVTypes.def"
#define WASM_TYPE(Name, Id, SingletonId) case BuiltinType::Id:
#include "clang/Basic/WebAssemblyReferenceTypes.def"
#define AMDGPU_TYPE(Name, Id, SingletonId, Width, Align)                                           \
    case BuiltinType::Id: Out << "@BT@" << #Name; break;
#include "clang/Basic/AMDGPUTypes.def"
#define HLSL_INTANGIBLE_TYPE(Name, Id, SingletonId)                                                \
    case BuiltinType::Id: Out << "@BT@" << #Name; break;
#include "clang/Basic/HLSLIntangibleTypes.def"
                case BuiltinType::ShortAccum: Out << "@BT@ShortAccum"; break;
                case BuiltinType::Accum: Out << "@BT@Accum"; break;
                case BuiltinType::LongAccum: Out << "@BT@LongAccum"; break;
                case BuiltinType::UShortAccum: Out << "@BT@UShortAccum"; break;
                case BuiltinType::UAccum: Out << "@BT@UAccum"; break;
                case BuiltinType::ULongAccum: Out << "@BT@ULongAccum"; break;
                case BuiltinType::ShortFract: Out << "@BT@ShortFract"; break;
                case BuiltinType::Fract: Out << "@BT@Fract"; break;
                case BuiltinType::LongFract: Out << "@BT@LongFract"; break;
                case BuiltinType::UShortFract: Out << "@BT@UShortFract"; break;
                case BuiltinType::UFract: Out << "@BT@UFract"; break;
                case BuiltinType::ULongFract: Out << "@BT@ULongFract"; break;
                case BuiltinType::SatShortAccum: Out << "@BT@SatShortAccum"; break;
                case BuiltinType::SatAccum: Out << "@BT@SatAccum"; break;
                case BuiltinType::SatLongAccum: Out << "@BT@SatLongAccum"; break;
                case BuiltinType::SatUShortAccum: Out << "@BT@SatUShortAccum"; break;
                case BuiltinType::SatUAccum: Out << "@BT@SatUAccum"; break;
                case BuiltinType::SatULongAccum: Out << "@BT@SatULongAccum"; break;
                case BuiltinType::SatShortFract: Out << "@BT@SatShortFract"; break;
                case BuiltinType::SatFract: Out << "@BT@SatFract"; break;
                case BuiltinType::SatLongFract: Out << "@BT@SatLongFract"; break;
                case BuiltinType::SatUShortFract: Out << "@BT@SatUShortFract"; break;
                case BuiltinType::SatUFract: Out << "@BT@SatUFract"; break;
                case BuiltinType::SatULongFract: Out << "@BT@SatULongFract"; break;
                case BuiltinType::BFloat16: Out << "@BT@__bf16"; break;
                case BuiltinType::Ibm128: Out << "@BT@__ibm128"; break;
                case BuiltinType::ObjCId: Out << 'o'; break;
                case BuiltinType::ObjCClass: Out << 'O'; break;
                case BuiltinType::ObjCSel: Out << 'e'; break;
#define BUILTIN_TYPE(Id, SingletonId)
#define PLACEHOLDER_TYPE(Id, SingletonId) case BuiltinType::Id:
#include "clang/AST/BuiltinTypes.def"
                case BuiltinType::Dependent:
                    // If you're adding a new builtin type, please add its name prefixed
                    // with "@BT@" to `Out` (see cases above).
                    IgnoreResults = true;
                    break;
            }
            return;
        }

        // If we have already seen this (non-built-in) type, use a substitution
        // encoding.
        llvm::DenseMap<const Type*, unsigned>::iterator Substitution =
            TypeSubstitutions.find(T.getTypePtr());
        if(Substitution != TypeSubstitutions.end()) {
            Out << 'S' << Substitution->second << '_';
            return;
        } else {
            // Record this as a substitution.
            unsigned Number = TypeSubstitutions.size();
            TypeSubstitutions[T.getTypePtr()] = Number;
        }

        if(const PointerType* PT = T->getAs<PointerType>()) {
            Out << '*';
            T = PT->getPointeeType();
            continue;
        }
        if(const ObjCObjectPointerType* OPT = T->getAs<ObjCObjectPointerType>()) {
            Out << '*';
            T = OPT->getPointeeType();
            continue;
        }
        if(const RValueReferenceType* RT = T->getAs<RValueReferenceType>()) {
            Out << "&&";
            T = RT->getPointeeType();
            continue;
        }
        if(const ReferenceType* RT = T->getAs<ReferenceType>()) {
            Out << '&';
            T = RT->getPointeeType();
            continue;
        }
        if(const FunctionProtoType* FT = T->getAs<FunctionProtoType>()) {
            Out << 'F';
            VisitType(FT->getReturnType());
            Out << '(';
            for(const auto& I: FT->param_types()) {
                Out << '#';
                VisitType(I);
            }
            Out << ')';
            if(FT->isVariadic())
                Out << '.';
            return;
        }
        if(const BlockPointerType* BT = T->getAs<BlockPointerType>()) {
            Out << 'B';
            T = BT->getPointeeType();
            continue;
        }
        if(const ComplexType* CT = T->getAs<ComplexType>()) {
            Out << '<';
            T = CT->getElementType();
            continue;
        }
        if(const TagType* TT = T->getAs<TagType>()) {
            Out << '$';
            VisitTagDecl(TT->getDecl());
            return;
        }
        if(const ObjCInterfaceType* OIT = T->getAs<ObjCInterfaceType>()) {
            Out << '$';
            VisitObjCInterfaceDecl(OIT->getDecl());
            return;
        }
        if(const ObjCObjectType* OIT = T->getAs<ObjCObjectType>()) {
            Out << 'Q';
            VisitType(OIT->getBaseType());
            for(auto* Prot: OIT->getProtocols())
                VisitObjCProtocolDecl(Prot);
            return;
        }
        if(const TemplateTypeParmType* TTP = T->getAs<TemplateTypeParmType>()) {
            Out << 't' << TTP->getDepth() << '.' << TTP->getIndex();
            return;
        }
        if(const TemplateSpecializationType* Spec = T->getAs<TemplateSpecializationType>()) {
            Out << '>';
            VisitTemplateName(Spec->getTemplateName());
            Out << Spec->template_arguments().size();
            for(const auto& Arg: Spec->template_arguments())
                VisitTemplateArgument(Arg);
            return;
        }
        if(const auto* DeducedSpec = T->getAs<DeducedTemplateSpecializationType>()) {
            // TODO(sakria9): double check this
            Out << "D";
            VisitTemplateName(DeducedSpec->getTemplateName());
            if(!DeducedSpec->getDeducedType().isNull()) {
                VisitType(DeducedSpec->getDeducedType());
            }
            return;
        }
        if(const DependentNameType* DNT = T->getAs<DependentNameType>()) {
            Out << '^';
            printQualifier(Out, LangOpts, DNT->getQualifier());
            Out << ':' << DNT->getIdentifier()->getName();
            return;
        }
        if(const InjectedClassNameType* InjT = T->getAs<InjectedClassNameType>()) {
            T = InjT->getInjectedSpecializationType();
            continue;
        }
        if(const auto* VT = T->getAs<VectorType>()) {
            Out << (T->isExtVectorType() ? ']' : '[');
            Out << VT->getNumElements();
            T = VT->getElementType();
            continue;
        }
        if(const auto* const AT = dyn_cast<ArrayType>(T)) {
            Out << '{';
            switch(AT->getSizeModifier()) {
                case ArraySizeModifier::Static: Out << 's'; break;
                case ArraySizeModifier::Star: Out << '*'; break;
                case ArraySizeModifier::Normal: Out << 'n'; break;
            }
            if(const auto* const CAT = dyn_cast<ConstantArrayType>(T))
                Out << CAT->getSize();

            T = AT->getElementType();
            continue;
        }
        if(const auto* AT = dyn_cast<AutoType>(T)) {
            Out << 'a';
            return;
        }

        // Unhandled type.
        Out << ' ';
        break;
    } while(true);
}

void USRGenerator::VisitTemplateParameterList(const TemplateParameterList* Params) {
    if(!Params)
        return;

    Out << '>' << Params->size();
    for(TemplateParameterList::const_iterator P = Params->begin(), PEnd = Params->end(); P != PEnd;
        ++P) {
        Out << '#';
        if(auto p = dyn_cast<TemplateTypeParmDecl>(*P)) {
            if(p->isParameterPack())
                Out << 'p';
            Out << 'T';
            if(p->hasTypeConstraint()) {
                Out << ":TC";
                AppendExprODRHash(p->getTypeConstraint()->getImmediatelyDeclaredConstraint(), Out);
            }
            continue;
        }

        if(NonTypeTemplateParmDecl* NTTP = dyn_cast<NonTypeTemplateParmDecl>(*P)) {
            if(NTTP->isParameterPack())
                Out << 'p';
            Out << 'N';
            VisitType(NTTP->getType());
            if(auto constraint = NTTP->getPlaceholderTypeConstraint()) {
                Out << ":PTC";
                AppendExprODRHash(constraint, Out);
            }
            continue;
        }

        TemplateTemplateParmDecl* TTP = cast<TemplateTemplateParmDecl>(*P);
        if(TTP->isParameterPack())
            Out << 'p';
        Out << 't';
        VisitTemplateParameterList(TTP->getTemplateParameters());
    }

    if(auto requiresClause = Params->getRequiresClause()) {
        Out << ":RC";
        AppendExprODRHash(requiresClause, Out);
    }
}

void USRGenerator::VisitTemplateName(TemplateName Name) {
    if(TemplateDecl* Template = Name.getAsTemplateDecl()) {
        if(TemplateTemplateParmDecl* TTP = dyn_cast<TemplateTemplateParmDecl>(Template)) {
            Out << 't' << TTP->getDepth() << '.' << TTP->getIndex();
            return;
        }

        Visit(Template);
        return;
    }

    if(auto DT = Name.getAsDependentTemplateName()) {
        Out << '^';
        printQualifier(Out, LangOpts, DT->getQualifier());
        Out << ':' << DT->getIdentifier()->getName();
    }
}

void USRGenerator::VisitTemplateArgument(const TemplateArgument& Arg) {
    switch(Arg.getKind()) {
        case TemplateArgument::Null: break;

        case TemplateArgument::Declaration: Visit(Arg.getAsDecl()); break;

        case TemplateArgument::NullPtr: break;

        case TemplateArgument::TemplateExpansion:
            Out << 'P';  // pack expansion of...
            [[fallthrough]];
        case TemplateArgument::Template:
            VisitTemplateName(Arg.getAsTemplateOrTemplatePattern());
            break;

        case TemplateArgument::Expression: {
            Out << 'E';
            ODRHash Hash{};
            Hash.AddStmt(Arg.getAsExpr());
            Out << Hash.CalculateHash();
            break;
        }

        case TemplateArgument::Pack:
            Out << 'p' << Arg.pack_size();
            for(const auto& P: Arg.pack_elements())
                VisitTemplateArgument(P);
            break;

        case TemplateArgument::Type: VisitType(Arg.getAsType()); break;

        case TemplateArgument::Integral:
            Out << 'V';
            VisitType(Arg.getIntegralType());
            Out << Arg.getAsIntegral();
            break;

        case TemplateArgument::StructuralValue: {
            Out << 'S';
            VisitType(Arg.getStructuralValueType());
            ODRHash Hash{};
            Hash.AddStructuralValue(Arg.getAsStructuralValue());
            Out << Hash.CalculateHash();
            break;
        }
    }
}

void USRGenerator::VisitUnresolvedUsingValueDecl(const UnresolvedUsingValueDecl* D) {
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;
    VisitDeclContext(D->getDeclContext());
    Out << "@UUV@";
    printQualifier(Out, LangOpts, D->getQualifier());
    EmitDeclName(D);
}

void USRGenerator::VisitUnresolvedUsingTypenameDecl(const UnresolvedUsingTypenameDecl* D) {
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;
    VisitDeclContext(D->getDeclContext());
    Out << "@UUT@";
    printQualifier(Out, LangOpts, D->getQualifier());
    Out << D->getName();  // Simple name.
}

void USRGenerator::VisitConceptDecl(const ConceptDecl* D) {
    if(ShouldGenerateLocation(D) && GenLoc(D, /*IncludeOffset=*/isLocal(D)))
        return;
    VisitDeclContext(D->getDeclContext());
    Out << "@CT@";
    EmitDeclName(D);
}

void USRGenerator::VisitTemplateParamObjectDecl(const TemplateParamObjectDecl* D) {
    VisitType(D->getType());
    ODRHash Hash{};
    Hash.AddStructuralValue(D->getValue());
    Out << Hash.CalculateHash();
}

void USRGenerator::VisitMSGuidDecl(const MSGuidDecl* D) {
    VisitDeclContext(D->getDeclContext());
    Out << "@MG@";
    D->NamedDecl::printName(Out);
}

namespace clice::index {

bool generateUSRForDecl(const Decl* D, SmallVectorImpl<char>& Buf, const LangOptions& LangOpts) {
    if(!D)
        return true;
    // We don't ignore decls with invalid source locations. Implicit decls, like
    // C++'s operator new function, can have invalid locations but it is fine to
    // create USRs that can identify them.

    // Check if the declaration has explicit external USR specified.
    auto* CD = D->getCanonicalDecl();
    if(auto* ExternalSymAttr = CD->getAttr<ExternalSourceSymbolAttr>()) {
        if(!ExternalSymAttr->getUSR().empty()) {
            llvm::raw_svector_ostream Out(Buf);
            Out << ExternalSymAttr->getUSR();
            return false;
        }
    }
    USRGenerator UG(&D->getASTContext(), Buf, LangOpts);
    UG.Visit(D);
    return UG.ignoreResults();
}

bool generateUSRForDecl(const Decl* D, SmallVectorImpl<char>& Buf) {
    if(!D)
        return true;
    return generateUSRForDecl(D, Buf, D->getASTContext().getLangOpts());
}

bool generateUSRForMacro(StringRef MacroName,
                         SourceLocation Loc,
                         const SourceManager& SM,
                         SmallVectorImpl<char>& Buf) {
    if(MacroName.empty())
        return true;

    llvm::raw_svector_ostream Out(Buf);

    // Assume that system headers are sane.  Don't put source location
    // information into the USR if the macro comes from a system header.
    bool ShouldGenerateLocation = Loc.isValid() && !SM.isInSystemHeader(Loc);

    Out << "c:";
    if(ShouldGenerateLocation)
        printLoc(Out, Loc, SM, /*IncludeOffset=*/true);
    Out << "@macro@";
    Out << MacroName;
    return false;
}

}  // namespace clice::index
