StmtCXX.h

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//===--- StmtCXX.h - Classes for representing C++ statements ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the C++ statement AST node classes.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CLANG_AST_STMTCXX_H
#define LLVM_CLANG_AST_STMTCXX_H
 
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/AST/Stmt.h"
#include "llvm/Support/Compiler.h"
 
namespace clang {
 
class VarDecl;
class CXXExpansionStmtDecl;
 
/// CXXCatchStmt - This represents a C++ catch block.
///
class CXXCatchStmt : public Stmt {
  SourceLocation CatchLoc;
  /// The exception-declaration of the type.
  VarDecl *ExceptionDecl;
  /// The handler block.
  Stmt *HandlerBlock;
 
public:
  CXXCatchStmt(SourceLocation catchLoc, VarDecl *exDecl, Stmt *handlerBlock)
  : Stmt(CXXCatchStmtClass), CatchLoc(catchLoc), ExceptionDecl(exDecl),
    HandlerBlock(handlerBlock) {}
 
  CXXCatchStmt(EmptyShell Empty)
  : Stmt(CXXCatchStmtClass), ExceptionDecl(nullptr), HandlerBlock(nullptr) {}
 
  SourceLocation getBeginLoc() const LLVM_READONLY { return CatchLoc; }
  SourceLocation getEndLoc() const LLVM_READONLY {
    return HandlerBlock->getEndLoc();
  }
 
  SourceLocation getCatchLoc() const { return CatchLoc; }
  VarDecl *getExceptionDecl() const { return ExceptionDecl; }
  QualType getCaughtType() const;
  Stmt *getHandlerBlock() const { return HandlerBlock; }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CXXCatchStmtClass;
  }
 
  child_range children() { return child_range(&HandlerBlock, &HandlerBlock+1); }
 
  const_child_range children() const {
    return const_child_range(&HandlerBlock, &HandlerBlock + 1);
  }
 
  friend class ASTStmtReader;
};
 
/// CXXTryStmt - A C++ try block, including all handlers.
///
class CXXTryStmt final : public Stmt,
                         private llvm::TrailingObjects<CXXTryStmt, Stmt *> {
 
  friend TrailingObjects;
  friend class ASTStmtReader;
 
  SourceLocation TryLoc;
  unsigned NumHandlers;
  size_t numTrailingObjects(OverloadToken<Stmt *>) const { return NumHandlers; }
 
  CXXTryStmt(SourceLocation tryLoc, CompoundStmt *tryBlock,
             ArrayRef<Stmt *> handlers);
  CXXTryStmt(EmptyShell Empty, unsigned numHandlers)
    : Stmt(CXXTryStmtClass), NumHandlers(numHandlers) { }
 
  Stmt *const *getStmts() const { return getTrailingObjects(); }
  Stmt **getStmts() { return getTrailingObjects(); }
 
public:
  static CXXTryStmt *Create(const ASTContext &C, SourceLocation tryLoc,
                            CompoundStmt *tryBlock, ArrayRef<Stmt *> handlers);
 
  static CXXTryStmt *Create(const ASTContext &C, EmptyShell Empty,
                            unsigned numHandlers);
 
  SourceLocation getBeginLoc() const LLVM_READONLY { return getTryLoc(); }
 
  SourceLocation getTryLoc() const { return TryLoc; }
  SourceLocation getEndLoc() const {
    return getStmts()[NumHandlers]->getEndLoc();
  }
 
  CompoundStmt *getTryBlock() {
    return cast<CompoundStmt>(getStmts()[0]);
  }
  const CompoundStmt *getTryBlock() const {
    return cast<CompoundStmt>(getStmts()[0]);
  }
 
  unsigned getNumHandlers() const { return NumHandlers; }
  CXXCatchStmt *getHandler(unsigned i) {
    return cast<CXXCatchStmt>(getStmts()[i + 1]);
  }
  const CXXCatchStmt *getHandler(unsigned i) const {
    return cast<CXXCatchStmt>(getStmts()[i + 1]);
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CXXTryStmtClass;
  }
 
  child_range children() {
    return child_range(getStmts(), getStmts() + getNumHandlers() + 1);
  }
 
  const_child_range children() const {
    return const_child_range(getStmts(), getStmts() + getNumHandlers() + 1);
  }
};
 
/// CXXForRangeStmt - This represents C++0x [stmt.ranged]'s ranged for
/// statement, represented as 'for (range-declarator : range-expression)'
/// or 'for (init-statement range-declarator : range-expression)'.
///
/// This is stored in a partially-desugared form to allow full semantic
/// analysis of the constituent components. The original syntactic components
/// can be extracted using getLoopVariable and getRangeInit.
class CXXForRangeStmt : public Stmt {
  enum { INIT, RANGE, BEGINSTMT, ENDSTMT, COND, INC, LOOPVAR, BODY, END };
  // SubExprs[RANGE] is an expression or declstmt.
  // SubExprs[COND] and SubExprs[INC] are expressions.
  Stmt *SubExprs[END];
  SourceLocation ForLoc;
  SourceLocation CoawaitLoc;
  SourceLocation ColonLoc;
  SourceLocation RParenLoc;
 
  friend class ASTStmtReader;
public:
  CXXForRangeStmt(Stmt *InitStmt, DeclStmt *Range, DeclStmt *Begin,
                  DeclStmt *End, Expr *Cond, Expr *Inc, DeclStmt *LoopVar,
                  Stmt *Body, SourceLocation FL, SourceLocation CAL,
                  SourceLocation CL, SourceLocation RPL);
  CXXForRangeStmt(EmptyShell Empty) : Stmt(CXXForRangeStmtClass, Empty) { }
 
  Stmt *getInit() { return SubExprs[INIT]; }
  VarDecl *getLoopVariable();
  Expr *getRangeInit();
 
  const Stmt *getInit() const { return SubExprs[INIT]; }
  const VarDecl *getLoopVariable() const;
  const Expr *getRangeInit() const;
 
 
  DeclStmt *getRangeStmt() { return cast<DeclStmt>(SubExprs[RANGE]); }
  DeclStmt *getBeginStmt() {
    return cast_or_null<DeclStmt>(SubExprs[BEGINSTMT]);
  }
  DeclStmt *getEndStmt() { return cast_or_null<DeclStmt>(SubExprs[ENDSTMT]); }
  Expr *getCond() { return cast_or_null<Expr>(SubExprs[COND]); }
  Expr *getInc() { return cast_or_null<Expr>(SubExprs[INC]); }
  DeclStmt *getLoopVarStmt() { return cast<DeclStmt>(SubExprs[LOOPVAR]); }
  Stmt *getBody() { return SubExprs[BODY]; }
 
  const DeclStmt *getRangeStmt() const {
    return cast<DeclStmt>(SubExprs[RANGE]);
  }
  const DeclStmt *getBeginStmt() const {
    return cast_or_null<DeclStmt>(SubExprs[BEGINSTMT]);
  }
  const DeclStmt *getEndStmt() const {
    return cast_or_null<DeclStmt>(SubExprs[ENDSTMT]);
  }
  const Expr *getCond() const {
    return cast_or_null<Expr>(SubExprs[COND]);
  }
  const Expr *getInc() const {
    return cast_or_null<Expr>(SubExprs[INC]);
  }
  const DeclStmt *getLoopVarStmt() const {
    return cast<DeclStmt>(SubExprs[LOOPVAR]);
  }
  const Stmt *getBody() const { return SubExprs[BODY]; }
 
  void setInit(Stmt *S) { SubExprs[INIT] = S; }
  void setRangeInit(Expr *E) { SubExprs[RANGE] = reinterpret_cast<Stmt*>(E); }
  void setRangeStmt(Stmt *S) { SubExprs[RANGE] = S; }
  void setBeginStmt(Stmt *S) { SubExprs[BEGINSTMT] = S; }
  void setEndStmt(Stmt *S) { SubExprs[ENDSTMT] = S; }
  void setCond(Expr *E) { SubExprs[COND] = reinterpret_cast<Stmt*>(E); }
  void setInc(Expr *E) { SubExprs[INC] = reinterpret_cast<Stmt*>(E); }
  void setLoopVarStmt(Stmt *S) { SubExprs[LOOPVAR] = S; }
  void setBody(Stmt *S) { SubExprs[BODY] = S; }
 
  SourceLocation getForLoc() const { return ForLoc; }
  SourceLocation getCoawaitLoc() const { return CoawaitLoc; }
  SourceLocation getColonLoc() const { return ColonLoc; }
  SourceLocation getRParenLoc() const { return RParenLoc; }
 
  SourceLocation getBeginLoc() const LLVM_READONLY { return ForLoc; }
  SourceLocation getEndLoc() const LLVM_READONLY {
    return SubExprs[BODY]->getEndLoc();
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CXXForRangeStmtClass;
  }
 
  // Iterators
  child_range children() {
    return child_range(&SubExprs[0], &SubExprs[END]);
  }
 
  const_child_range children() const {
    return const_child_range(&SubExprs[0], &SubExprs[END]);
  }
};
 
/// Representation of a Microsoft __if_exists or __if_not_exists
/// statement with a dependent name.
///
/// The __if_exists statement can be used to include a sequence of statements
/// in the program only when a particular dependent name does not exist. For
/// example:
///
/// \code
/// template<typename T>
/// void call_foo(T &t) {
///   __if_exists (T::foo) {
///     t.foo(); // okay: only called when T::foo exists.
///   }
/// }
/// \endcode
///
/// Similarly, the __if_not_exists statement can be used to include the
/// statements when a particular name does not exist.
///
/// Note that this statement only captures __if_exists and __if_not_exists
/// statements whose name is dependent. All non-dependent cases are handled
/// directly in the parser, so that they don't introduce a new scope. Clang
/// introduces scopes in the dependent case to keep names inside the compound
/// statement from leaking out into the surround statements, which would
/// compromise the template instantiation model. This behavior differs from
/// Visual C++ (which never introduces a scope), but is a fairly reasonable
/// approximation of the VC++ behavior.
class MSDependentExistsStmt : public Stmt {
  SourceLocation KeywordLoc;
  bool IsIfExists;
  NestedNameSpecifierLoc QualifierLoc;
  DeclarationNameInfo NameInfo;
  Stmt *SubStmt;
 
  friend class ASTReader;
  friend class ASTStmtReader;
 
public:
  MSDependentExistsStmt(SourceLocation KeywordLoc, bool IsIfExists,
                        NestedNameSpecifierLoc QualifierLoc,
                        DeclarationNameInfo NameInfo,
                        CompoundStmt *SubStmt)
  : Stmt(MSDependentExistsStmtClass),
    KeywordLoc(KeywordLoc), IsIfExists(IsIfExists),
    QualifierLoc(QualifierLoc), NameInfo(NameInfo),
    SubStmt(reinterpret_cast<Stmt *>(SubStmt)) { }
 
  /// Retrieve the location of the __if_exists or __if_not_exists
  /// keyword.
  SourceLocation getKeywordLoc() const { return KeywordLoc; }
 
  /// Determine whether this is an __if_exists statement.
  bool isIfExists() const { return IsIfExists; }
 
  /// Determine whether this is an __if_exists statement.
  bool isIfNotExists() const { return !IsIfExists; }
 
  /// Retrieve the nested-name-specifier that qualifies this name, if
  /// any.
  NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
  /// Retrieve the name of the entity we're testing for, along with
  /// location information
  DeclarationNameInfo getNameInfo() const { return NameInfo; }
 
  /// Retrieve the compound statement that will be included in the
  /// program only if the existence of the symbol matches the initial keyword.
  CompoundStmt *getSubStmt() const {
    return reinterpret_cast<CompoundStmt *>(SubStmt);
  }
 
  SourceLocation getBeginLoc() const LLVM_READONLY { return KeywordLoc; }
  SourceLocation getEndLoc() const LLVM_READONLY {
    return SubStmt->getEndLoc();
  }
 
  child_range children() {
    return child_range(&SubStmt, &SubStmt+1);
  }
 
  const_child_range children() const {
    return const_child_range(&SubStmt, &SubStmt + 1);
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == MSDependentExistsStmtClass;
  }
};
 
/// Represents the body of a coroutine. This wraps the normal function
/// body and holds the additional semantic context required to set up and tear
/// down the coroutine frame.
class CoroutineBodyStmt final
    : public Stmt,
      private llvm::TrailingObjects<CoroutineBodyStmt, Stmt *> {
  enum SubStmt {
    Body,          ///< The body of the coroutine.
    Promise,       ///< The promise statement.
    InitSuspend,   ///< The initial suspend statement, run before the body.
    FinalSuspend,  ///< The final suspend statement, run after the body.
    OnException,   ///< Handler for exceptions thrown in the body.
    OnFallthrough, ///< Handler for control flow falling off the body.
    Allocate,      ///< Coroutine frame memory allocation.
    Deallocate,    ///< Coroutine frame memory deallocation.
    ResultDecl,    ///< Declaration holding the result of get_return_object.
    ReturnValue,   ///< Return value for thunk function: p.get_return_object().
    ReturnStmt,    ///< Return statement for the thunk function.
    ReturnStmtOnAllocFailure, ///< Return statement if allocation failed.
    FirstParamMove ///< First offset for move construction of parameter copies.
  };
  unsigned NumParams;
 
  friend class ASTStmtReader;
  friend class ASTReader;
  friend TrailingObjects;
 
  Stmt **getStoredStmts() { return getTrailingObjects(); }
 
  Stmt *const *getStoredStmts() const { return getTrailingObjects(); }
 
public:
 
  struct CtorArgs {
    Stmt *Body = nullptr;
    Stmt *Promise = nullptr;
    Expr *InitialSuspend = nullptr;
    Expr *FinalSuspend = nullptr;
    Stmt *OnException = nullptr;
    Stmt *OnFallthrough = nullptr;
    Expr *Allocate = nullptr;
    Expr *Deallocate = nullptr;
    Stmt *ResultDecl = nullptr;
    Expr *ReturnValue = nullptr;
    Stmt *ReturnStmt = nullptr;
    Stmt *ReturnStmtOnAllocFailure = nullptr;
    ArrayRef<Stmt *> ParamMoves;
  };
 
private:
 
  CoroutineBodyStmt(CtorArgs const& Args);
 
public:
  static CoroutineBodyStmt *Create(const ASTContext &C, CtorArgs const &Args);
  static CoroutineBodyStmt *Create(const ASTContext &C, EmptyShell,
                                   unsigned NumParams);
 
  bool hasDependentPromiseType() const {
    return getPromiseDecl()->getType()->isDependentType();
  }
 
  /// Retrieve the body of the coroutine as written. This will be either
  /// a CompoundStmt. If the coroutine is in function-try-block, we will
  /// wrap the CXXTryStmt into a CompoundStmt to keep consistency.
  CompoundStmt *getBody() const {
    return cast<CompoundStmt>(getStoredStmts()[SubStmt::Body]);
  }
 
  Stmt *getPromiseDeclStmt() const {
    return getStoredStmts()[SubStmt::Promise];
  }
  VarDecl *getPromiseDecl() const {
    return cast<VarDecl>(cast<DeclStmt>(getPromiseDeclStmt())->getSingleDecl());
  }
 
  Stmt *getInitSuspendStmt() const {
    return getStoredStmts()[SubStmt::InitSuspend];
  }
  Stmt *getFinalSuspendStmt() const {
    return getStoredStmts()[SubStmt::FinalSuspend];
  }
 
  Stmt *getExceptionHandler() const {
    return getStoredStmts()[SubStmt::OnException];
  }
  Stmt *getFallthroughHandler() const {
    return getStoredStmts()[SubStmt::OnFallthrough];
  }
 
  Expr *getAllocate() const {
    return cast_or_null<Expr>(getStoredStmts()[SubStmt::Allocate]);
  }
  Expr *getDeallocate() const {
    return cast_or_null<Expr>(getStoredStmts()[SubStmt::Deallocate]);
  }
  Stmt *getResultDecl() const { return getStoredStmts()[SubStmt::ResultDecl]; }
  Expr *getReturnValueInit() const {
    return cast<Expr>(getStoredStmts()[SubStmt::ReturnValue]);
  }
  Expr *getReturnValue() const {
    auto *RS = dyn_cast_or_null<clang::ReturnStmt>(getReturnStmt());
    return RS ? RS->getRetValue() : nullptr;
  }
  Stmt *getReturnStmt() const { return getStoredStmts()[SubStmt::ReturnStmt]; }
  Stmt *getReturnStmtOnAllocFailure() const {
    return getStoredStmts()[SubStmt::ReturnStmtOnAllocFailure];
  }
  ArrayRef<Stmt const *> getParamMoves() const {
    return {getStoredStmts() + SubStmt::FirstParamMove, NumParams};
  }
 
  SourceLocation getBeginLoc() const LLVM_READONLY {
    return getBody() ? getBody()->getBeginLoc()
                     : getPromiseDecl()->getBeginLoc();
  }
  SourceLocation getEndLoc() const LLVM_READONLY {
    return getBody() ? getBody()->getEndLoc() : getPromiseDecl()->getEndLoc();
  }
 
  child_range children() {
    return child_range(getStoredStmts(),
                       getStoredStmts() + SubStmt::FirstParamMove + NumParams);
  }
 
  const_child_range children() const {
    return const_child_range(getStoredStmts(), getStoredStmts() +
                                                   SubStmt::FirstParamMove +
                                                   NumParams);
  }
 
  child_range childrenExclBody() {
    return child_range(getStoredStmts() + SubStmt::Body + 1,
                       getStoredStmts() + SubStmt::FirstParamMove + NumParams);
  }
 
  const_child_range childrenExclBody() const {
    return const_child_range(getStoredStmts() + SubStmt::Body + 1,
                             getStoredStmts() + SubStmt::FirstParamMove +
                                 NumParams);
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CoroutineBodyStmtClass;
  }
};
 
/// Represents a 'co_return' statement in the C++ Coroutines TS.
///
/// This statament models the initialization of the coroutine promise
/// (encapsulating the eventual notional return value) from an expression
/// (or braced-init-list), followed by termination of the coroutine.
///
/// This initialization is modeled by the evaluation of the operand
/// followed by a call to one of:
///   <promise>.return_value(<operand>)
///   <promise>.return_void()
/// which we name the "promise call".
class CoreturnStmt : public Stmt {
  SourceLocation CoreturnLoc;
 
  enum SubStmt { Operand, PromiseCall, Count };
  Stmt *SubStmts[SubStmt::Count];
 
  bool IsImplicit : 1;
 
  friend class ASTStmtReader;
public:
  CoreturnStmt(SourceLocation CoreturnLoc, Stmt *Operand, Stmt *PromiseCall,
               bool IsImplicit = false)
      : Stmt(CoreturnStmtClass), CoreturnLoc(CoreturnLoc),
        IsImplicit(IsImplicit) {
    SubStmts[SubStmt::Operand] = Operand;
    SubStmts[SubStmt::PromiseCall] = PromiseCall;
  }
 
  CoreturnStmt(EmptyShell) : CoreturnStmt({}, {}, {}) {}
 
  SourceLocation getKeywordLoc() const { return CoreturnLoc; }
 
  /// Retrieve the operand of the 'co_return' statement. Will be nullptr
  /// if none was specified.
  Expr *getOperand() const { return static_cast<Expr*>(SubStmts[Operand]); }
 
  /// Retrieve the promise call that results from this 'co_return'
  /// statement. Will be nullptr if either the coroutine has not yet been
  /// finalized or the coroutine has no eventual return type.
  Expr *getPromiseCall() const {
    return static_cast<Expr*>(SubStmts[PromiseCall]);
  }
 
  bool isImplicit() const { return IsImplicit; }
  void setIsImplicit(bool value = true) { IsImplicit = value; }
 
  SourceLocation getBeginLoc() const LLVM_READONLY { return CoreturnLoc; }
  SourceLocation getEndLoc() const LLVM_READONLY {
    return getOperand() ? getOperand()->getEndLoc() : getBeginLoc();
  }
 
  child_range children() {
    return child_range(SubStmts, SubStmts + SubStmt::Count);
  }
 
  const_child_range children() const {
    return const_child_range(SubStmts, SubStmts + SubStmt::Count);
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CoreturnStmtClass;
  }
};
 
/// CXXExpansionStmtPattern - Represents an unexpanded C++ expansion statement.
///
/// There are four kinds of expansion statements.
///
/// 1. Enumerating expansion statements.
/// 2. Iterating expansion statements.
/// 3. Destructuring expansion statements.
/// 4. Dependent expansion statements.
///
/// 1. An 'enumerating' expansion statement is one whose expansion-initializer
/// is a brace-enclosed expression-list; this list is syntactically similar to
/// an initializer list, but it isn't actually an expression in and of itself
/// (in that it is never evaluated or emitted) and instead is just treated as
/// a group of expressions. The expansion initializer of this is always a
/// syntactic-form 'InitListExpr'.
///
/// Example:
/// \verbatim
///   template for (auto x : { 1, 2, 3 }) {
///     // ...
///   }
/// \endverbatim
///
/// Note that the expression-list may also contain pack expansions, e.g.
/// '{ 1, xs... }', in which case the expansion size is dependent.
///
/// Here, the '{ 1, 2, 3 }' is parsed as an 'InitListExpr'. This node
/// handles storing (and pack-expanding) the individual expressions.
///
/// Sema then wraps this with a 'CXXExpansionSelectExpr', which also
/// contains a reference to an integral NTTP that is used as the expansion
/// index; this index is either dependent (if the expansion-size is dependent),
/// or set to a value of I in the I-th expansion during the expansion process.
///
/// The actual expansion is done by 'BuildCXXExpansionSelectExpr()': for
/// example, during the 2nd expansion of '{ a, b, c }', I is equal to 1, and
/// BuildCXXExpansionSelectExpr(), when called via TreeTransform,
/// 'instantiates' the expression '{ a, b, c }' to just 'b'.
///
/// 2. Represents an unexpanded iterating expansion statement.
///
/// An 'iterating' expansion statement is one whose expansion-initializer is a
/// a range, i.e. it has a corresponding 'begin()'/'end()' pair that is
/// determined based on a number of conditions as stated in [stmt.expand] and
/// [stmt.ranged].
///
/// Specifically, let E denote the expansion-initializer; the expansion
/// statement is iterating if the type of E is not an array type, and either
///
///   2a. 'E.begin' and 'E.end' *exist* (irrespective of whether they're
///        accessible, deleted, or even callable), or
///
///   2b. ADL for 'begin(E)' and 'end(E)' finds at least one viable function.
///
/// If neither A nor B apply to E (or if E is an array type), we treat this as
/// a destructuring expansion statement instead (see case 3 below).
///
/// Notably, case 2a only checks whether the 'begin' and 'end' members exist and
/// does *not* perform proper overload resolution; this is because if there is
/// a begin/end function, but it for some reason is not usable (e.g. because it
/// is non-const but E is const), then we'd rather error and tell the user that
/// their begin/end function is wrong rather than falling back to destructuring.
///
/// Conversely, case 2b *does* perform overload resolution, simply because ADL
/// may find quite a few begin/end overloads for unrelated types that happen to
/// be in the same namespace. E.g. if the type of E is 'std::tuple', then there
/// are quite a few begin/end pairs in the namespace 'std', but non of them can
/// actually be used for a 'std::tuple', and we definitely want to destructure a
/// tuple rather than error about it not being iterable.
///
/// In either case, once we've decided that the expansion statement is indeed
/// iterating, we *do* make sure that the expression 'E.begin()'/'begin(E)' is
/// well-formed, but any error at that point is a hard error and does not make
/// us switch to destructuring instead.
///
/// The result of this expression is stored in a variable 'begin', which is then
/// used to compute another variable 'iter' (which is just 'begin' + the
/// expansion index) during expansion. During the N-th expansion, the expansion
/// variable is then set to '*iter'. See [stmt.expand] for more information.
///
/// The expression used to compute the size of the expansion is not stored and
/// is only created at the moment of expansion. See Sema::ComputeExpansionSize()
/// for more information about this.
///
/// Example:
/// \verbatim
///   static constexpr std::string_view foo = "abcd";
///   template for (auto x : foo) {
///     // ...
///   }
/// \endverbatim
///
/// Here, 'begin' is 'foo.begin()', and during e.g. the 0-th expansion, 'iter'
/// is 'begin + 0', and thus '*iter' yields 'a', which results in 'x' being
/// a variable of type 'char' with value 'a'.
///
/// 3. Represents an unexpanded destructuring expansion statement.
///
/// A 'destructuring' expansion statement is any expansion statement that is
/// not enumerating or iterating (i.e. destructuring is the last thing we try,
/// and if it doesn't work, the program is ill-formed).
///
/// This essentially involves treating the expansion-initializer as the
/// initializer of a structured-binding declaration, with the number of
/// bindings and expansion size determined by the usual means (array size,
/// std::tuple_size, etc.).
///
/// During the N-th expansion, the expansion variable is then initialized with
/// the N-th binding of the structured-binding declaration. This is implemented
/// by wrapping the initializer with a CXXExpansionSelectExpr, which selects a
/// binding based on the current expansion index when called from TreeTransform.
///
/// Example:
/// \verbatim
///   std::tuple<int, long, unsigned> a {1, 2l, 3u};
///   template for (auto x : a) {
///     // ...
///   }
/// \endverbatim
///
/// Here, we build 'auto [_U0, _U1, _U2] = a', and during e.g. the 0-th
/// expansion, 'x' is initialized with '_U0'.
///
/// 4. Represents an expansion statement whose expansion-initializer is
/// type-dependent.
///
/// This will eventually become an iterating or destructuring expansion
/// statement once the expansion-initializer is no longer dependent.
///
/// Dependent expansion statements can never be enumerating: even if the
/// expansion size of an enumerating expansion statement is dependent (which
/// is possible if the expression-list contains a pack), we still don't build
/// an 'Enumerating' 'CXXExpansionStmtPattern' for it.
///
/// Example:
/// \verbatim
///   template <typename T>
///   void f() {
///     template for (auto x : T()) {
///       // ...
///     }
///   }
/// \endverbatim
///
/// \see CXXExpansionStmtDecl for more documentation on expansion statements.
class CXXExpansionStmtPattern final
    : public Stmt,
      llvm::TrailingObjects<CXXExpansionStmtPattern, Stmt *> {
  friend class ASTStmtReader;
  friend TrailingObjects;
 
public:
  enum class ExpansionStmtKind : uint8_t {
    Enumerating,
    Iterating,
    Destructuring,
    Dependent,
  };
 
private:
  ExpansionStmtKind PatternKind;
  SourceLocation LParenLoc;
  SourceLocation ColonLoc;
  SourceLocation RParenLoc;
  CXXExpansionStmtDecl *ParentDecl;
 
  /// Substatements of an unexpanded expansion statement.
  ///
  /// 'INIT', 'VAR', and 'BODY' are common to all kinds of expansion statements;
  /// the former may be null if there is no init-statement.
  ///
  /// Depending on the kind of expansion statement, we may have to store
  /// additional sub-statements, the first of which is denoted by
  /// 'FIRST_CHILD_STATEMENT'.
  ///
  /// All of the sub-statements are allocated as 'TrailingObjects' so we can
  /// return a single contiguous range from 'children()'.
  enum SubStmt {
    INIT,
    VAR,
    BODY,
    FIRST_CHILD_STMT,
 
    // Enumerating expansion statement (no additional sub-statements).
    COUNT_Enumerating = FIRST_CHILD_STMT,
 
    // Dependent expansion statement (1 additional sub-statement).
    EXPANSION_INITIALIZER = FIRST_CHILD_STMT,
    COUNT_Dependent,
 
    // Destructuring expansion statement (1 additional sub-statement).
    DECOMP_DECL = FIRST_CHILD_STMT,
    COUNT_Destructuring,
 
    // Iterating expansion statement (3 additional sub-statements).
    RANGE = FIRST_CHILD_STMT,
    BEGIN,
    ITER,
    COUNT_Iterating,
  };
 
  CXXExpansionStmtPattern(ExpansionStmtKind PatternKind, EmptyShell Empty);
  CXXExpansionStmtPattern(ExpansionStmtKind PatternKind,
                          CXXExpansionStmtDecl *ESD, Stmt *Init,
                          DeclStmt *ExpansionVar, SourceLocation LParenLoc,
                          SourceLocation ColonLoc, SourceLocation RParenLoc);
 
public:
  static CXXExpansionStmtPattern *
  CreateEmpty(ASTContext &Context, EmptyShell Empty, ExpansionStmtKind Kind);
 
  /// Create a dependent expansion statement pattern.
  static CXXExpansionStmtPattern *
  CreateDependent(ASTContext &Context, CXXExpansionStmtDecl *ESD, Stmt *Init,
                  DeclStmt *ExpansionVar, Expr *ExpansionInitializer,
                  SourceLocation LParenLoc, SourceLocation ColonLoc,
                  SourceLocation RParenLoc);
 
  /// Create a destructuring expansion statement pattern.
  static CXXExpansionStmtPattern *
  CreateDestructuring(ASTContext &Context, CXXExpansionStmtDecl *ESD,
                      Stmt *Init, DeclStmt *ExpansionVar,
                      Stmt *DecompositionDeclStmt, SourceLocation LParenLoc,
                      SourceLocation ColonLoc, SourceLocation RParenLoc);
 
  /// Create an enumerating expansion statement pattern.
  static CXXExpansionStmtPattern *
  CreateEnumerating(ASTContext &Context, CXXExpansionStmtDecl *ESD, Stmt *Init,
                    DeclStmt *ExpansionVar, SourceLocation LParenLoc,
                    SourceLocation ColonLoc, SourceLocation RParenLoc);
 
  /// Create an iterating expansion statement pattern.
  static CXXExpansionStmtPattern *
  CreateIterating(ASTContext &Context, CXXExpansionStmtDecl *ESD, Stmt *Init,
                  DeclStmt *ExpansionVar, DeclStmt *Range, DeclStmt *Begin,
                  DeclStmt *Iter, SourceLocation LParenLoc,
                  SourceLocation ColonLoc, SourceLocation RParenLoc);
 
  SourceLocation getLParenLoc() const { return LParenLoc; }
  SourceLocation getColonLoc() const { return ColonLoc; }
  SourceLocation getRParenLoc() const { return RParenLoc; }
  SourceLocation getBeginLoc() const;
  SourceLocation getEndLoc() const {
    return getBody() ? getBody()->getEndLoc() : RParenLoc;
  }
 
  ExpansionStmtKind getKind() const { return PatternKind; }
  bool isDependent() const {
    return PatternKind == ExpansionStmtKind::Dependent;
  }
  bool isEnumerating() const {
    return PatternKind == ExpansionStmtKind::Enumerating;
  }
  bool isIterating() const {
    return PatternKind == ExpansionStmtKind::Iterating;
  }
  bool isDestructuring() const {
    return PatternKind == ExpansionStmtKind::Destructuring;
  }
 
  unsigned getNumSubStmts() const { return getNumSubStmts(PatternKind); }
 
  // Accessors for subcomponents common to all expansion statements.
  CXXExpansionStmtDecl *getDecl() { return ParentDecl; }
  const CXXExpansionStmtDecl *getDecl() const { return ParentDecl; }
 
  Stmt *getInit() { return getSubStmt(INIT); }
  const Stmt *getInit() const { return getSubStmt(INIT); }
  void setInit(Stmt *S) { getSubStmt(INIT) = S; }
 
  VarDecl *getExpansionVariable();
  const VarDecl *getExpansionVariable() const {
    return const_cast<CXXExpansionStmtPattern *>(this)->getExpansionVariable();
  }
 
  DeclStmt *getExpansionVarStmt() { return cast<DeclStmt>(getSubStmt(VAR)); }
  const DeclStmt *getExpansionVarStmt() const {
    return cast<DeclStmt>(getSubStmt(VAR));
  }
 
  void setExpansionVarStmt(Stmt *S) { getSubStmt(VAR) = S; }
 
  Stmt *getBody() { return getSubStmt(BODY); }
  const Stmt *getBody() const { return getSubStmt(BODY); }
  void setBody(Stmt *S) { getSubStmt(BODY) = S; }
 
  // Accessors for iterating statements.
  const DeclStmt *getRangeVarStmt() const {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(RANGE));
  }
 
  DeclStmt *getRangeVarStmt() {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(RANGE));
  }
 
  void setRangeVarStmt(DeclStmt *S) {
    assert(isIterating());
    getSubStmt(RANGE) = S;
  }
 
  const VarDecl *getRangeVar() const {
    assert(isIterating());
    return cast<VarDecl>(getRangeVarStmt()->getSingleDecl());
  }
 
  VarDecl *getRangeVar() {
    assert(isIterating());
    return cast<VarDecl>(getRangeVarStmt()->getSingleDecl());
  }
 
  const DeclStmt *getBeginVarStmt() const {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(BEGIN));
  }
 
  DeclStmt *getBeginVarStmt() {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(BEGIN));
  }
 
  void setBeginVarStmt(DeclStmt *S) {
    assert(isIterating());
    getSubStmt(BEGIN) = S;
  }
 
  const VarDecl *getBeginVar() const {
    assert(isIterating());
    return cast<VarDecl>(getBeginVarStmt()->getSingleDecl());
  }
 
  VarDecl *getBeginVar() {
    assert(isIterating());
    return cast<VarDecl>(getBeginVarStmt()->getSingleDecl());
  }
 
  const DeclStmt *getIterVarStmt() const {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(ITER));
  }
 
  DeclStmt *getIterVarStmt() {
    assert(isIterating());
    return cast<DeclStmt>(getSubStmt(ITER));
  }
 
  void setIterVarStmt(DeclStmt *S) {
    assert(isIterating());
    getSubStmt(ITER) = S;
  }
 
  const VarDecl *getIterVar() const {
    assert(isIterating());
    return cast<VarDecl>(getIterVarStmt()->getSingleDecl());
  }
 
  VarDecl *getIterVar() {
    assert(isIterating());
    return cast<VarDecl>(getIterVarStmt()->getSingleDecl());
  }
 
  // Accessors for destructuring statements.
  Stmt *getDecompositionDeclStmt() {
    assert(isDestructuring());
    return getSubStmt(DECOMP_DECL);
  }
 
  const Stmt *getDecompositionDeclStmt() const {
    assert(isDestructuring());
    return getSubStmt(DECOMP_DECL);
  }
 
  void setDecompositionDeclStmt(Stmt *S) {
    assert(isDestructuring());
    getSubStmt(DECOMP_DECL) = S;
  }
 
  DecompositionDecl *getDecompositionDecl();
  const DecompositionDecl *getDecompositionDecl() const {
    return const_cast<CXXExpansionStmtPattern *>(this)->getDecompositionDecl();
  }
 
  // Accessors for dependent statements.
  Expr *getExpansionInitializer() {
    assert(isDependent());
    return cast<Expr>(getSubStmt(EXPANSION_INITIALIZER));
  }
 
  const Expr *getExpansionInitializer() const {
    assert(isDependent());
    return cast<Expr>(getSubStmt(EXPANSION_INITIALIZER));
  }
 
  void setExpansionInitializer(Expr *S) {
    assert(isDependent());
    getSubStmt(EXPANSION_INITIALIZER) = S;
  }
 
  child_range children() {
    return child_range(getTrailingObjects(),
                       getTrailingObjects() + getNumSubStmts());
  }
 
  const_child_range children() const {
    return const_child_range(getTrailingObjects(),
                             getTrailingObjects() + getNumSubStmts());
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CXXExpansionStmtPatternClass;
  }
 
private:
  template <typename... Args>
  static CXXExpansionStmtPattern *AllocateAndConstruct(ASTContext &Context,
                                                       ExpansionStmtKind Kind,
                                                       Args &&...Arguments);
 
  static unsigned getNumSubStmts(ExpansionStmtKind Kind);
  Stmt *getSubStmt(unsigned Idx) const {
    assert(Idx < getNumSubStmts());
    return getTrailingObjects()[Idx];
  }
 
  Stmt *&getSubStmt(unsigned Idx) {
    assert(Idx < getNumSubStmts());
    return getTrailingObjects()[Idx];
  }
};
 
/// Represents the code generated for an expanded expansion statement.
///
/// This holds 'preamble statements' and 'instantiations'; these encode the
/// general underlying pattern that all expansion statements desugar to. Note
/// that only the inner '{}' (i.e. those marked as 'Actual "CompoundStmt"'
/// below) are actually present as 'CompoundStmt's in the AST; the outer braces
/// that wrap everything do *not* correspond to an actual 'CompoundStmt' and are
/// implicit in the sense that we simply push a scope when evaluating or
/// emitting IR for a 'CXXExpansionStmtInstantiation'.
///
/// The 'instantiations' are precisely these inner compound statements.
///
/// \verbatim
/// { // Not actually present in the AST.
///   <preamble statements>
///   { // Actual 'CompoundStmt'.
///     <1st instantiation>
///   }
///   ...
///   { // Actual 'CompoundStmt'.
///     <n-th instantiation>
///   }
/// }
/// \endverbatim
///
/// For example, the CXXExpansionStmtInstantiation that corresponds to the
/// following expansion statement
///
/// \verbatim
///   std::tuple<int, int, int> a{1, 2, 3};
///   template for (auto x : a) {
///     // ...
///   }
/// \endverbatim
///
/// would be
///
/// \verbatim
/// {
///   auto [__u0, __u1, __u2] = a;
///   {
///     auto x = __u0;
///     // ...
///   }
///   {
///     auto x = __u1;
///     // ...
///   }
///   {
///     auto x = __u2;
///     // ...
///   }
/// }
/// \endverbatim
///
/// There are two reasons why this needs to exist and why we don't just store a
/// list of instantiations in some other node:
///
///   1. We need custom codegen to handle break/continue in expansion statements
///      properly, so it can't just be a compound statement.
///
///   2. The expansions are created after both the pattern and the
///      'CXXExpansionStmtDecl', so we can't just store them as trailing data in
///      either of those nodes (because we don't know how many expansions there
///      will be when those notes are allocated).
///
/// \see CXXExpansionStmtDecl
class CXXExpansionStmtInstantiation final
    : public Stmt,
      llvm::TrailingObjects<CXXExpansionStmtInstantiation, Stmt *> {
  friend class ASTStmtReader;
  friend TrailingObjects;
 
  CXXExpansionStmtDecl *Parent;
 
  // Instantiations are stored first, then preamble statements.
  const unsigned NumInstantiations : 20;
  const unsigned NumPreambleStmts : 3;
  unsigned ShouldApplyLifetimeExtensionToPreamble : 1;
 
  CXXExpansionStmtInstantiation(EmptyShell Empty, unsigned NumInstantiations,
                                unsigned NumPreambleStmts);
  CXXExpansionStmtInstantiation(CXXExpansionStmtDecl *Parent,
                                ArrayRef<Stmt *> Instantiations,
                                ArrayRef<Stmt *> PreambleStmts,
                                bool ShouldApplyLifetimeExtensionToPreamble);
 
public:
  static CXXExpansionStmtInstantiation *
  Create(ASTContext &C, CXXExpansionStmtDecl *Parent,
         ArrayRef<Stmt *> Instantiations, ArrayRef<Stmt *> PreambleStmts,
         bool ShouldApplyLifetimeExtensionToPreamble);
 
  static CXXExpansionStmtInstantiation *CreateEmpty(ASTContext &C,
                                                    EmptyShell Empty,
                                                    unsigned NumInstantiations,
                                                    unsigned NumPreambleStmts);
 
  ArrayRef<Stmt *> getAllSubStmts() const {
    return getTrailingObjects(getNumSubStmts());
  }
 
  MutableArrayRef<Stmt *> getAllSubStmts() {
    return getTrailingObjects(getNumSubStmts());
  }
 
  unsigned getNumSubStmts() const {
    return NumInstantiations + NumPreambleStmts;
  }
 
  ArrayRef<Stmt *> getInstantiations() const {
    return getTrailingObjects(NumInstantiations);
  }
 
  ArrayRef<Stmt *> getPreambleStmts() const {
    return getAllSubStmts().drop_front(NumInstantiations);
  }
 
  bool shouldApplyLifetimeExtensionToPreamble() const {
    return ShouldApplyLifetimeExtensionToPreamble;
  }
 
  void setShouldApplyLifetimeExtensionToPreamble(bool Apply) {
    ShouldApplyLifetimeExtensionToPreamble = Apply;
  }
 
  SourceLocation getBeginLoc() const;
  SourceLocation getEndLoc() const;
 
  CXXExpansionStmtDecl *getParent() { return Parent; }
  const CXXExpansionStmtDecl *getParent() const { return Parent; }
 
  child_range children() {
    Stmt **S = getTrailingObjects();
    return child_range(S, S + getNumSubStmts());
  }
 
  const_child_range children() const {
    Stmt *const *S = getTrailingObjects();
    return const_child_range(S, S + getNumSubStmts());
  }
 
  static bool classof(const Stmt *T) {
    return T->getStmtClass() == CXXExpansionStmtInstantiationClass;
  }
};
 
}  // end namespace clang
 
#endif