1//===------- SemaTemplateVariadic.cpp - C++ Variadic Templates ------------===/
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//===----------------------------------------------------------------------===/
7//
8//  This file implements semantic analysis for C++0x variadic templates.
9//===----------------------------------------------------------------------===/
10
11#include "clang/Sema/Sema.h"
12#include "TypeLocBuilder.h"
13#include "clang/AST/Expr.h"
14#include "clang/AST/RecursiveASTVisitor.h"
15#include "clang/AST/TypeLoc.h"
16#include "clang/Sema/Lookup.h"
17#include "clang/Sema/ParsedTemplate.h"
18#include "clang/Sema/ScopeInfo.h"
19#include "clang/Sema/SemaInternal.h"
20#include "clang/Sema/Template.h"
21
22using namespace clang;
23
24//----------------------------------------------------------------------------
25// Visitor that collects unexpanded parameter packs
26//----------------------------------------------------------------------------
27
28namespace {
29  /// A class that collects unexpanded parameter packs.
30  class CollectUnexpandedParameterPacksVisitor :
31    public RecursiveASTVisitor<CollectUnexpandedParameterPacksVisitor>
32  {
33    typedef RecursiveASTVisitor<CollectUnexpandedParameterPacksVisitor>
34      inherited;
35
36    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded;
37
38    bool InLambda = false;
39    unsigned DepthLimit = (unsigned)-1;
40
41    void addUnexpanded(NamedDecl *ND, SourceLocation Loc = SourceLocation()) {
42      if (auto *VD = dyn_cast<VarDecl>(ND)) {
43        // For now, the only problematic case is a generic lambda's templated
44        // call operator, so we don't need to look for all the other ways we
45        // could have reached a dependent parameter pack.
46        auto *FD = dyn_cast<FunctionDecl>(VD->getDeclContext());
47        auto *FTD = FD ? FD->getDescribedFunctionTemplate() : nullptr;
48        if (FTD && FTD->getTemplateParameters()->getDepth() >= DepthLimit)
49          return;
50      } else if (getDepthAndIndex(ND).first >= DepthLimit)
51        return;
52
53      Unexpanded.push_back({ND, Loc});
54    }
55    void addUnexpanded(const TemplateTypeParmType *T,
56                       SourceLocation Loc = SourceLocation()) {
57      if (T->getDepth() < DepthLimit)
58        Unexpanded.push_back({T, Loc});
59    }
60
61  public:
62    explicit CollectUnexpandedParameterPacksVisitor(
63        SmallVectorImpl<UnexpandedParameterPack> &Unexpanded)
64        : Unexpanded(Unexpanded) {}
65
66    bool shouldWalkTypesOfTypeLocs() const { return false; }
67
68    //------------------------------------------------------------------------
69    // Recording occurrences of (unexpanded) parameter packs.
70    //------------------------------------------------------------------------
71
72    /// Record occurrences of template type parameter packs.
73    bool VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) {
74      if (TL.getTypePtr()->isParameterPack())
75        addUnexpanded(TL.getTypePtr(), TL.getNameLoc());
76      return true;
77    }
78
79    /// Record occurrences of template type parameter packs
80    /// when we don't have proper source-location information for
81    /// them.
82    ///
83    /// Ideally, this routine would never be used.
84    bool VisitTemplateTypeParmType(TemplateTypeParmType *T) {
85      if (T->isParameterPack())
86        addUnexpanded(T);
87
88      return true;
89    }
90
91    /// Record occurrences of function and non-type template
92    /// parameter packs in an expression.
93    bool VisitDeclRefExpr(DeclRefExpr *E) {
94      if (E->getDecl()->isParameterPack())
95        addUnexpanded(E->getDecl(), E->getLocation());
96
97      return true;
98    }
99
100    /// Record occurrences of template template parameter packs.
101    bool TraverseTemplateName(TemplateName Template) {
102      if (auto *TTP = dyn_cast_or_null<TemplateTemplateParmDecl>(
103              Template.getAsTemplateDecl())) {
104        if (TTP->isParameterPack())
105          addUnexpanded(TTP);
106      }
107
108      return inherited::TraverseTemplateName(Template);
109    }
110
111    /// Suppress traversal into Objective-C container literal
112    /// elements that are pack expansions.
113    bool TraverseObjCDictionaryLiteral(ObjCDictionaryLiteral *E) {
114      if (!E->containsUnexpandedParameterPack())
115        return true;
116
117      for (unsigned I = 0, N = E->getNumElements(); I != N; ++I) {
118        ObjCDictionaryElement Element = E->getKeyValueElement(I);
119        if (Element.isPackExpansion())
120          continue;
121
122        TraverseStmt(Element.Key);
123        TraverseStmt(Element.Value);
124      }
125      return true;
126    }
127    //------------------------------------------------------------------------
128    // Pruning the search for unexpanded parameter packs.
129    //------------------------------------------------------------------------
130
131    /// Suppress traversal into statements and expressions that
132    /// do not contain unexpanded parameter packs.
133    bool TraverseStmt(Stmt *S) {
134      Expr *E = dyn_cast_or_null<Expr>(S);
135      if ((E && E->containsUnexpandedParameterPack()) || InLambda)
136        return inherited::TraverseStmt(S);
137
138      return true;
139    }
140
141    /// Suppress traversal into types that do not contain
142    /// unexpanded parameter packs.
143    bool TraverseType(QualType T) {
144      if ((!T.isNull() && T->containsUnexpandedParameterPack()) || InLambda)
145        return inherited::TraverseType(T);
146
147      return true;
148    }
149
150    /// Suppress traversal into types with location information
151    /// that do not contain unexpanded parameter packs.
152    bool TraverseTypeLoc(TypeLoc TL) {
153      if ((!TL.getType().isNull() &&
154           TL.getType()->containsUnexpandedParameterPack()) ||
155          InLambda)
156        return inherited::TraverseTypeLoc(TL);
157
158      return true;
159    }
160
161    /// Suppress traversal of parameter packs.
162    bool TraverseDecl(Decl *D) {
163      // A function parameter pack is a pack expansion, so cannot contain
164      // an unexpanded parameter pack. Likewise for a template parameter
165      // pack that contains any references to other packs.
166      if (D && D->isParameterPack())
167        return true;
168
169      return inherited::TraverseDecl(D);
170    }
171
172    /// Suppress traversal of pack-expanded attributes.
173    bool TraverseAttr(Attr *A) {
174      if (A->isPackExpansion())
175        return true;
176
177      return inherited::TraverseAttr(A);
178    }
179
180    /// Suppress traversal of pack expansion expressions and types.
181    ///@{
182    bool TraversePackExpansionType(PackExpansionType *T) { return true; }
183    bool TraversePackExpansionTypeLoc(PackExpansionTypeLoc TL) { return true; }
184    bool TraversePackExpansionExpr(PackExpansionExpr *E) { return true; }
185    bool TraverseCXXFoldExpr(CXXFoldExpr *E) { return true; }
186
187    ///@}
188
189    /// Suppress traversal of using-declaration pack expansion.
190    bool TraverseUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D) {
191      if (D->isPackExpansion())
192        return true;
193
194      return inherited::TraverseUnresolvedUsingValueDecl(D);
195    }
196
197    /// Suppress traversal of using-declaration pack expansion.
198    bool TraverseUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D) {
199      if (D->isPackExpansion())
200        return true;
201
202      return inherited::TraverseUnresolvedUsingTypenameDecl(D);
203    }
204
205    /// Suppress traversal of template argument pack expansions.
206    bool TraverseTemplateArgument(const TemplateArgument &Arg) {
207      if (Arg.isPackExpansion())
208        return true;
209
210      return inherited::TraverseTemplateArgument(Arg);
211    }
212
213    /// Suppress traversal of template argument pack expansions.
214    bool TraverseTemplateArgumentLoc(const TemplateArgumentLoc &ArgLoc) {
215      if (ArgLoc.getArgument().isPackExpansion())
216        return true;
217
218      return inherited::TraverseTemplateArgumentLoc(ArgLoc);
219    }
220
221    /// Suppress traversal of base specifier pack expansions.
222    bool TraverseCXXBaseSpecifier(const CXXBaseSpecifier &Base) {
223      if (Base.isPackExpansion())
224        return true;
225
226      return inherited::TraverseCXXBaseSpecifier(Base);
227    }
228
229    /// Suppress traversal of mem-initializer pack expansions.
230    bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
231      if (Init->isPackExpansion())
232        return true;
233
234      return inherited::TraverseConstructorInitializer(Init);
235    }
236
237    /// Note whether we're traversing a lambda containing an unexpanded
238    /// parameter pack. In this case, the unexpanded pack can occur anywhere,
239    /// including all the places where we normally wouldn't look. Within a
240    /// lambda, we don't propagate the 'contains unexpanded parameter pack' bit
241    /// outside an expression.
242    bool TraverseLambdaExpr(LambdaExpr *Lambda) {
243      // The ContainsUnexpandedParameterPack bit on a lambda is always correct,
244      // even if it's contained within another lambda.
245      if (!Lambda->containsUnexpandedParameterPack())
246        return true;
247
248      bool WasInLambda = InLambda;
249      unsigned OldDepthLimit = DepthLimit;
250
251      InLambda = true;
252      if (auto *TPL = Lambda->getTemplateParameterList())
253        DepthLimit = TPL->getDepth();
254
255      inherited::TraverseLambdaExpr(Lambda);
256
257      InLambda = WasInLambda;
258      DepthLimit = OldDepthLimit;
259      return true;
260    }
261
262    /// Suppress traversal within pack expansions in lambda captures.
263    bool TraverseLambdaCapture(LambdaExpr *Lambda, const LambdaCapture *C,
264                               Expr *Init) {
265      if (C->isPackExpansion())
266        return true;
267
268      return inherited::TraverseLambdaCapture(Lambda, C, Init);
269    }
270  };
271}
272
273/// Determine whether it's possible for an unexpanded parameter pack to
274/// be valid in this location. This only happens when we're in a declaration
275/// that is nested within an expression that could be expanded, such as a
276/// lambda-expression within a function call.
277///
278/// This is conservatively correct, but may claim that some unexpanded packs are
279/// permitted when they are not.
280bool Sema::isUnexpandedParameterPackPermitted() {
281  for (auto *SI : FunctionScopes)
282    if (isa<sema::LambdaScopeInfo>(SI))
283      return true;
284  return false;
285}
286
287/// Diagnose all of the unexpanded parameter packs in the given
288/// vector.
289bool
290Sema::DiagnoseUnexpandedParameterPacks(SourceLocation Loc,
291                                       UnexpandedParameterPackContext UPPC,
292                                 ArrayRef<UnexpandedParameterPack> Unexpanded) {
293  if (Unexpanded.empty())
294    return false;
295
296  // If we are within a lambda expression and referencing a pack that is not
297  // declared within the lambda itself, that lambda contains an unexpanded
298  // parameter pack, and we are done.
299  // FIXME: Store 'Unexpanded' on the lambda so we don't need to recompute it
300  // later.
301  SmallVector<UnexpandedParameterPack, 4> LambdaParamPackReferences;
302  if (auto *LSI = getEnclosingLambda()) {
303    for (auto &Pack : Unexpanded) {
304      auto DeclaresThisPack = [&](NamedDecl *LocalPack) {
305        if (auto *TTPT = Pack.first.dyn_cast<const TemplateTypeParmType *>()) {
306          auto *TTPD = dyn_cast<TemplateTypeParmDecl>(LocalPack);
307          return TTPD && TTPD->getTypeForDecl() == TTPT;
308        }
309        return declaresSameEntity(Pack.first.get<NamedDecl *>(), LocalPack);
310      };
311      if (std::find_if(LSI->LocalPacks.begin(), LSI->LocalPacks.end(),
312                       DeclaresThisPack) != LSI->LocalPacks.end())
313        LambdaParamPackReferences.push_back(Pack);
314    }
315
316    if (LambdaParamPackReferences.empty()) {
317      // Construct in lambda only references packs declared outside the lambda.
318      // That's OK for now, but the lambda itself is considered to contain an
319      // unexpanded pack in this case, which will require expansion outside the
320      // lambda.
321
322      // We do not permit pack expansion that would duplicate a statement
323      // expression, not even within a lambda.
324      // FIXME: We could probably support this for statement expressions that
325      // do not contain labels.
326      // FIXME: This is insufficient to detect this problem; consider
327      //   f( ({ bad: 0; }) + pack ... );
328      bool EnclosingStmtExpr = false;
329      for (unsigned N = FunctionScopes.size(); N; --N) {
330        sema::FunctionScopeInfo *Func = FunctionScopes[N-1];
331        if (std::any_of(
332                Func->CompoundScopes.begin(), Func->CompoundScopes.end(),
333                [](sema::CompoundScopeInfo &CSI) { return CSI.IsStmtExpr; })) {
334          EnclosingStmtExpr = true;
335          break;
336        }
337        // Coumpound-statements outside the lambda are OK for now; we'll check
338        // for those when we finish handling the lambda.
339        if (Func == LSI)
340          break;
341      }
342
343      if (!EnclosingStmtExpr) {
344        LSI->ContainsUnexpandedParameterPack = true;
345        return false;
346      }
347    } else {
348      Unexpanded = LambdaParamPackReferences;
349    }
350  }
351
352  SmallVector<SourceLocation, 4> Locations;
353  SmallVector<IdentifierInfo *, 4> Names;
354  llvm::SmallPtrSet<IdentifierInfo *, 4> NamesKnown;
355
356  for (unsigned I = 0, N = Unexpanded.size(); I != N; ++I) {
357    IdentifierInfo *Name = nullptr;
358    if (const TemplateTypeParmType *TTP
359          = Unexpanded[I].first.dyn_cast<const TemplateTypeParmType *>())
360      Name = TTP->getIdentifier();
361    else
362      Name = Unexpanded[I].first.get<NamedDecl *>()->getIdentifier();
363
364    if (Name && NamesKnown.insert(Name).second)
365      Names.push_back(Name);
366
367    if (Unexpanded[I].second.isValid())
368      Locations.push_back(Unexpanded[I].second);
369  }
370
371  DiagnosticBuilder DB = Diag(Loc, diag::err_unexpanded_parameter_pack)
372                         << (int)UPPC << (int)Names.size();
373  for (size_t I = 0, E = std::min(Names.size(), (size_t)2); I != E; ++I)
374    DB << Names[I];
375
376  for (unsigned I = 0, N = Locations.size(); I != N; ++I)
377    DB << SourceRange(Locations[I]);
378  return true;
379}
380
381bool Sema::DiagnoseUnexpandedParameterPack(SourceLocation Loc,
382                                           TypeSourceInfo *T,
383                                         UnexpandedParameterPackContext UPPC) {
384  // C++0x [temp.variadic]p5:
385  //   An appearance of a name of a parameter pack that is not expanded is
386  //   ill-formed.
387  if (!T->getType()->containsUnexpandedParameterPack())
388    return false;
389
390  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
391  CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseTypeLoc(
392                                                              T->getTypeLoc());
393  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
394  return DiagnoseUnexpandedParameterPacks(Loc, UPPC, Unexpanded);
395}
396
397bool Sema::DiagnoseUnexpandedParameterPack(Expr *E,
398                                        UnexpandedParameterPackContext UPPC) {
399  // C++0x [temp.variadic]p5:
400  //   An appearance of a name of a parameter pack that is not expanded is
401  //   ill-formed.
402  if (!E->containsUnexpandedParameterPack())
403    return false;
404
405  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
406  CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseStmt(E);
407  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
408  return DiagnoseUnexpandedParameterPacks(E->getBeginLoc(), UPPC, Unexpanded);
409}
410
411bool Sema::DiagnoseUnexpandedParameterPack(const CXXScopeSpec &SS,
412                                        UnexpandedParameterPackContext UPPC) {
413  // C++0x [temp.variadic]p5:
414  //   An appearance of a name of a parameter pack that is not expanded is
415  //   ill-formed.
416  if (!SS.getScopeRep() ||
417      !SS.getScopeRep()->containsUnexpandedParameterPack())
418    return false;
419
420  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
421  CollectUnexpandedParameterPacksVisitor(Unexpanded)
422    .TraverseNestedNameSpecifier(SS.getScopeRep());
423  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
424  return DiagnoseUnexpandedParameterPacks(SS.getRange().getBegin(),
425                                          UPPC, Unexpanded);
426}
427
428bool Sema::DiagnoseUnexpandedParameterPack(const DeclarationNameInfo &NameInfo,
429                                         UnexpandedParameterPackContext UPPC) {
430  // C++0x [temp.variadic]p5:
431  //   An appearance of a name of a parameter pack that is not expanded is
432  //   ill-formed.
433  switch (NameInfo.getName().getNameKind()) {
434  case DeclarationName::Identifier:
435  case DeclarationName::ObjCZeroArgSelector:
436  case DeclarationName::ObjCOneArgSelector:
437  case DeclarationName::ObjCMultiArgSelector:
438  case DeclarationName::CXXOperatorName:
439  case DeclarationName::CXXLiteralOperatorName:
440  case DeclarationName::CXXUsingDirective:
441  case DeclarationName::CXXDeductionGuideName:
442    return false;
443
444  case DeclarationName::CXXConstructorName:
445  case DeclarationName::CXXDestructorName:
446  case DeclarationName::CXXConversionFunctionName:
447    // FIXME: We shouldn't need this null check!
448    if (TypeSourceInfo *TSInfo = NameInfo.getNamedTypeInfo())
449      return DiagnoseUnexpandedParameterPack(NameInfo.getLoc(), TSInfo, UPPC);
450
451    if (!NameInfo.getName().getCXXNameType()->containsUnexpandedParameterPack())
452      return false;
453
454    break;
455  }
456
457  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
458  CollectUnexpandedParameterPacksVisitor(Unexpanded)
459    .TraverseType(NameInfo.getName().getCXXNameType());
460  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
461  return DiagnoseUnexpandedParameterPacks(NameInfo.getLoc(), UPPC, Unexpanded);
462}
463
464bool Sema::DiagnoseUnexpandedParameterPack(SourceLocation Loc,
465                                           TemplateName Template,
466                                       UnexpandedParameterPackContext UPPC) {
467
468  if (Template.isNull() || !Template.containsUnexpandedParameterPack())
469    return false;
470
471  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
472  CollectUnexpandedParameterPacksVisitor(Unexpanded)
473    .TraverseTemplateName(Template);
474  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
475  return DiagnoseUnexpandedParameterPacks(Loc, UPPC, Unexpanded);
476}
477
478bool Sema::DiagnoseUnexpandedParameterPack(TemplateArgumentLoc Arg,
479                                         UnexpandedParameterPackContext UPPC) {
480  if (Arg.getArgument().isNull() ||
481      !Arg.getArgument().containsUnexpandedParameterPack())
482    return false;
483
484  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
485  CollectUnexpandedParameterPacksVisitor(Unexpanded)
486    .TraverseTemplateArgumentLoc(Arg);
487  assert(!Unexpanded.empty() && "Unable to find unexpanded parameter packs");
488  return DiagnoseUnexpandedParameterPacks(Arg.getLocation(), UPPC, Unexpanded);
489}
490
491void Sema::collectUnexpandedParameterPacks(TemplateArgument Arg,
492                   SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
493  CollectUnexpandedParameterPacksVisitor(Unexpanded)
494    .TraverseTemplateArgument(Arg);
495}
496
497void Sema::collectUnexpandedParameterPacks(TemplateArgumentLoc Arg,
498                   SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
499  CollectUnexpandedParameterPacksVisitor(Unexpanded)
500    .TraverseTemplateArgumentLoc(Arg);
501}
502
503void Sema::collectUnexpandedParameterPacks(QualType T,
504                   SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
505  CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseType(T);
506}
507
508void Sema::collectUnexpandedParameterPacks(TypeLoc TL,
509                   SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
510  CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseTypeLoc(TL);
511}
512
513void Sema::collectUnexpandedParameterPacks(
514    NestedNameSpecifierLoc NNS,
515    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
516  CollectUnexpandedParameterPacksVisitor(Unexpanded)
517      .TraverseNestedNameSpecifierLoc(NNS);
518}
519
520void Sema::collectUnexpandedParameterPacks(
521    const DeclarationNameInfo &NameInfo,
522    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
523  CollectUnexpandedParameterPacksVisitor(Unexpanded)
524    .TraverseDeclarationNameInfo(NameInfo);
525}
526
527
528ParsedTemplateArgument
529Sema::ActOnPackExpansion(const ParsedTemplateArgument &Arg,
530                         SourceLocation EllipsisLoc) {
531  if (Arg.isInvalid())
532    return Arg;
533
534  switch (Arg.getKind()) {
535  case ParsedTemplateArgument::Type: {
536    TypeResult Result = ActOnPackExpansion(Arg.getAsType(), EllipsisLoc);
537    if (Result.isInvalid())
538      return ParsedTemplateArgument();
539
540    return ParsedTemplateArgument(Arg.getKind(), Result.get().getAsOpaquePtr(),
541                                  Arg.getLocation());
542  }
543
544  case ParsedTemplateArgument::NonType: {
545    ExprResult Result = ActOnPackExpansion(Arg.getAsExpr(), EllipsisLoc);
546    if (Result.isInvalid())
547      return ParsedTemplateArgument();
548
549    return ParsedTemplateArgument(Arg.getKind(), Result.get(),
550                                  Arg.getLocation());
551  }
552
553  case ParsedTemplateArgument::Template:
554    if (!Arg.getAsTemplate().get().containsUnexpandedParameterPack()) {
555      SourceRange R(Arg.getLocation());
556      if (Arg.getScopeSpec().isValid())
557        R.setBegin(Arg.getScopeSpec().getBeginLoc());
558      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
559        << R;
560      return ParsedTemplateArgument();
561    }
562
563    return Arg.getTemplatePackExpansion(EllipsisLoc);
564  }
565  llvm_unreachable("Unhandled template argument kind?");
566}
567
568TypeResult Sema::ActOnPackExpansion(ParsedType Type,
569                                    SourceLocation EllipsisLoc) {
570  TypeSourceInfo *TSInfo;
571  GetTypeFromParser(Type, &TSInfo);
572  if (!TSInfo)
573    return true;
574
575  TypeSourceInfo *TSResult = CheckPackExpansion(TSInfo, EllipsisLoc, None);
576  if (!TSResult)
577    return true;
578
579  return CreateParsedType(TSResult->getType(), TSResult);
580}
581
582TypeSourceInfo *
583Sema::CheckPackExpansion(TypeSourceInfo *Pattern, SourceLocation EllipsisLoc,
584                         Optional<unsigned> NumExpansions) {
585  // Create the pack expansion type and source-location information.
586  QualType Result = CheckPackExpansion(Pattern->getType(),
587                                       Pattern->getTypeLoc().getSourceRange(),
588                                       EllipsisLoc, NumExpansions);
589  if (Result.isNull())
590    return nullptr;
591
592  TypeLocBuilder TLB;
593  TLB.pushFullCopy(Pattern->getTypeLoc());
594  PackExpansionTypeLoc TL = TLB.push<PackExpansionTypeLoc>(Result);
595  TL.setEllipsisLoc(EllipsisLoc);
596
597  return TLB.getTypeSourceInfo(Context, Result);
598}
599
600QualType Sema::CheckPackExpansion(QualType Pattern, SourceRange PatternRange,
601                                  SourceLocation EllipsisLoc,
602                                  Optional<unsigned> NumExpansions) {
603  // C++11 [temp.variadic]p5:
604  //   The pattern of a pack expansion shall name one or more
605  //   parameter packs that are not expanded by a nested pack
606  //   expansion.
607  //
608  // A pattern containing a deduced type can't occur "naturally" but arises in
609  // the desugaring of an init-capture pack.
610  if (!Pattern->containsUnexpandedParameterPack() &&
611      !Pattern->getContainedDeducedType()) {
612    Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
613      << PatternRange;
614    return QualType();
615  }
616
617  return Context.getPackExpansionType(Pattern, NumExpansions);
618}
619
620ExprResult Sema::ActOnPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc) {
621  return CheckPackExpansion(Pattern, EllipsisLoc, None);
622}
623
624ExprResult Sema::CheckPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc,
625                                    Optional<unsigned> NumExpansions) {
626  if (!Pattern)
627    return ExprError();
628
629  // C++0x [temp.variadic]p5:
630  //   The pattern of a pack expansion shall name one or more
631  //   parameter packs that are not expanded by a nested pack
632  //   expansion.
633  if (!Pattern->containsUnexpandedParameterPack()) {
634    Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
635    << Pattern->getSourceRange();
636    CorrectDelayedTyposInExpr(Pattern);
637    return ExprError();
638  }
639
640  // Create the pack expansion expression and source-location information.
641  return new (Context)
642    PackExpansionExpr(Context.DependentTy, Pattern, EllipsisLoc, NumExpansions);
643}
644
645bool Sema::CheckParameterPacksForExpansion(
646    SourceLocation EllipsisLoc, SourceRange PatternRange,
647    ArrayRef<UnexpandedParameterPack> Unexpanded,
648    const MultiLevelTemplateArgumentList &TemplateArgs, bool &ShouldExpand,
649    bool &RetainExpansion, Optional<unsigned> &NumExpansions) {
650  ShouldExpand = true;
651  RetainExpansion = false;
652  std::pair<IdentifierInfo *, SourceLocation> FirstPack;
653  bool HaveFirstPack = false;
654  Optional<unsigned> NumPartialExpansions;
655  SourceLocation PartiallySubstitutedPackLoc;
656
657  for (ArrayRef<UnexpandedParameterPack>::iterator i = Unexpanded.begin(),
658                                                 end = Unexpanded.end();
659                                                  i != end; ++i) {
660    // Compute the depth and index for this parameter pack.
661    unsigned Depth = 0, Index = 0;
662    IdentifierInfo *Name;
663    bool IsVarDeclPack = false;
664
665    if (const TemplateTypeParmType *TTP
666        = i->first.dyn_cast<const TemplateTypeParmType *>()) {
667      Depth = TTP->getDepth();
668      Index = TTP->getIndex();
669      Name = TTP->getIdentifier();
670    } else {
671      NamedDecl *ND = i->first.get<NamedDecl *>();
672      if (isa<VarDecl>(ND))
673        IsVarDeclPack = true;
674      else
675        std::tie(Depth, Index) = getDepthAndIndex(ND);
676
677      Name = ND->getIdentifier();
678    }
679
680    // Determine the size of this argument pack.
681    unsigned NewPackSize;
682    if (IsVarDeclPack) {
683      // Figure out whether we're instantiating to an argument pack or not.
684      typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
685
686      llvm::PointerUnion<Decl *, DeclArgumentPack *> *Instantiation
687        = CurrentInstantiationScope->findInstantiationOf(
688                                        i->first.get<NamedDecl *>());
689      if (Instantiation->is<DeclArgumentPack *>()) {
690        // We could expand this function parameter pack.
691        NewPackSize = Instantiation->get<DeclArgumentPack *>()->size();
692      } else {
693        // We can't expand this function parameter pack, so we can't expand
694        // the pack expansion.
695        ShouldExpand = false;
696        continue;
697      }
698    } else {
699      // If we don't have a template argument at this depth/index, then we
700      // cannot expand the pack expansion. Make a note of this, but we still
701      // want to check any parameter packs we *do* have arguments for.
702      if (Depth >= TemplateArgs.getNumLevels() ||
703          !TemplateArgs.hasTemplateArgument(Depth, Index)) {
704        ShouldExpand = false;
705        continue;
706      }
707
708      // Determine the size of the argument pack.
709      NewPackSize = TemplateArgs(Depth, Index).pack_size();
710    }
711
712    // C++0x [temp.arg.explicit]p9:
713    //   Template argument deduction can extend the sequence of template
714    //   arguments corresponding to a template parameter pack, even when the
715    //   sequence contains explicitly specified template arguments.
716    if (!IsVarDeclPack && CurrentInstantiationScope) {
717      if (NamedDecl *PartialPack
718                    = CurrentInstantiationScope->getPartiallySubstitutedPack()){
719        unsigned PartialDepth, PartialIndex;
720        std::tie(PartialDepth, PartialIndex) = getDepthAndIndex(PartialPack);
721        if (PartialDepth == Depth && PartialIndex == Index) {
722          RetainExpansion = true;
723          // We don't actually know the new pack size yet.
724          NumPartialExpansions = NewPackSize;
725          PartiallySubstitutedPackLoc = i->second;
726          continue;
727        }
728      }
729    }
730
731    if (!NumExpansions) {
732      // The is the first pack we've seen for which we have an argument.
733      // Record it.
734      NumExpansions = NewPackSize;
735      FirstPack.first = Name;
736      FirstPack.second = i->second;
737      HaveFirstPack = true;
738      continue;
739    }
740
741    if (NewPackSize != *NumExpansions) {
742      // C++0x [temp.variadic]p5:
743      //   All of the parameter packs expanded by a pack expansion shall have
744      //   the same number of arguments specified.
745      if (HaveFirstPack)
746        Diag(EllipsisLoc, diag::err_pack_expansion_length_conflict)
747          << FirstPack.first << Name << *NumExpansions << NewPackSize
748          << SourceRange(FirstPack.second) << SourceRange(i->second);
749      else
750        Diag(EllipsisLoc, diag::err_pack_expansion_length_conflict_multilevel)
751          << Name << *NumExpansions << NewPackSize
752          << SourceRange(i->second);
753      return true;
754    }
755  }
756
757  // If we're performing a partial expansion but we also have a full expansion,
758  // expand to the number of common arguments. For example, given:
759  //
760  //   template<typename ...T> struct A {
761  //     template<typename ...U> void f(pair<T, U>...);
762  //   };
763  //
764  // ... a call to 'A<int, int>().f<int>' should expand the pack once and
765  // retain an expansion.
766  if (NumPartialExpansions) {
767    if (NumExpansions && *NumExpansions < *NumPartialExpansions) {
768      NamedDecl *PartialPack =
769          CurrentInstantiationScope->getPartiallySubstitutedPack();
770      Diag(EllipsisLoc, diag::err_pack_expansion_length_conflict_partial)
771        << PartialPack << *NumPartialExpansions << *NumExpansions
772        << SourceRange(PartiallySubstitutedPackLoc);
773      return true;
774    }
775
776    NumExpansions = NumPartialExpansions;
777  }
778
779  return false;
780}
781
782Optional<unsigned> Sema::getNumArgumentsInExpansion(QualType T,
783                          const MultiLevelTemplateArgumentList &TemplateArgs) {
784  QualType Pattern = cast<PackExpansionType>(T)->getPattern();
785  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
786  CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseType(Pattern);
787
788  Optional<unsigned> Result;
789  for (unsigned I = 0, N = Unexpanded.size(); I != N; ++I) {
790    // Compute the depth and index for this parameter pack.
791    unsigned Depth;
792    unsigned Index;
793
794    if (const TemplateTypeParmType *TTP
795          = Unexpanded[I].first.dyn_cast<const TemplateTypeParmType *>()) {
796      Depth = TTP->getDepth();
797      Index = TTP->getIndex();
798    } else {
799      NamedDecl *ND = Unexpanded[I].first.get<NamedDecl *>();
800      if (isa<VarDecl>(ND)) {
801        // Function parameter pack or init-capture pack.
802        typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
803
804        llvm::PointerUnion<Decl *, DeclArgumentPack *> *Instantiation
805          = CurrentInstantiationScope->findInstantiationOf(
806                                        Unexpanded[I].first.get<NamedDecl *>());
807        if (Instantiation->is<Decl*>())
808          // The pattern refers to an unexpanded pack. We're not ready to expand
809          // this pack yet.
810          return None;
811
812        unsigned Size = Instantiation->get<DeclArgumentPack *>()->size();
813        assert((!Result || *Result == Size) && "inconsistent pack sizes");
814        Result = Size;
815        continue;
816      }
817
818      std::tie(Depth, Index) = getDepthAndIndex(ND);
819    }
820    if (Depth >= TemplateArgs.getNumLevels() ||
821        !TemplateArgs.hasTemplateArgument(Depth, Index))
822      // The pattern refers to an unknown template argument. We're not ready to
823      // expand this pack yet.
824      return None;
825
826    // Determine the size of the argument pack.
827    unsigned Size = TemplateArgs(Depth, Index).pack_size();
828    assert((!Result || *Result == Size) && "inconsistent pack sizes");
829    Result = Size;
830  }
831
832  return Result;
833}
834
835bool Sema::containsUnexpandedParameterPacks(Declarator &D) {
836  const DeclSpec &DS = D.getDeclSpec();
837  switch (DS.getTypeSpecType()) {
838  case TST_typename:
839  case TST_typeofType:
840  case TST_underlyingType:
841  case TST_atomic: {
842    QualType T = DS.getRepAsType().get();
843    if (!T.isNull() && T->containsUnexpandedParameterPack())
844      return true;
845    break;
846  }
847
848  case TST_typeofExpr:
849  case TST_decltype:
850    if (DS.getRepAsExpr() &&
851        DS.getRepAsExpr()->containsUnexpandedParameterPack())
852      return true;
853    break;
854
855  case TST_unspecified:
856  case TST_void:
857  case TST_char:
858  case TST_wchar:
859  case TST_char8:
860  case TST_char16:
861  case TST_char32:
862  case TST_int:
863  case TST_int128:
864  case TST_half:
865  case TST_float:
866  case TST_double:
867  case TST_Accum:
868  case TST_Fract:
869  case TST_Float16:
870  case TST_float128:
871  case TST_bool:
872  case TST_decimal32:
873  case TST_decimal64:
874  case TST_decimal128:
875  case TST_enum:
876  case TST_union:
877  case TST_struct:
878  case TST_interface:
879  case TST_class:
880  case TST_auto:
881  case TST_auto_type:
882  case TST_decltype_auto:
883#define GENERIC_IMAGE_TYPE(ImgType, Id) case TST_##ImgType##_t:
884#include "clang/Basic/OpenCLImageTypes.def"
885  case TST_unknown_anytype:
886  case TST_error:
887    break;
888  }
889
890  for (unsigned I = 0, N = D.getNumTypeObjects(); I != N; ++I) {
891    const DeclaratorChunk &Chunk = D.getTypeObject(I);
892    switch (Chunk.Kind) {
893    case DeclaratorChunk::Pointer:
894    case DeclaratorChunk::Reference:
895    case DeclaratorChunk::Paren:
896    case DeclaratorChunk::Pipe:
897    case DeclaratorChunk::BlockPointer:
898      // These declarator chunks cannot contain any parameter packs.
899      break;
900
901    case DeclaratorChunk::Array:
902      if (Chunk.Arr.NumElts &&
903          Chunk.Arr.NumElts->containsUnexpandedParameterPack())
904        return true;
905      break;
906    case DeclaratorChunk::Function:
907      for (unsigned i = 0, e = Chunk.Fun.NumParams; i != e; ++i) {
908        ParmVarDecl *Param = cast<ParmVarDecl>(Chunk.Fun.Params[i].Param);
909        QualType ParamTy = Param->getType();
910        assert(!ParamTy.isNull() && "Couldn't parse type?");
911        if (ParamTy->containsUnexpandedParameterPack()) return true;
912      }
913
914      if (Chunk.Fun.getExceptionSpecType() == EST_Dynamic) {
915        for (unsigned i = 0; i != Chunk.Fun.getNumExceptions(); ++i) {
916          if (Chunk.Fun.Exceptions[i]
917                  .Ty.get()
918                  ->containsUnexpandedParameterPack())
919            return true;
920        }
921      } else if (isComputedNoexcept(Chunk.Fun.getExceptionSpecType()) &&
922                 Chunk.Fun.NoexceptExpr->containsUnexpandedParameterPack())
923        return true;
924
925      if (Chunk.Fun.hasTrailingReturnType()) {
926        QualType T = Chunk.Fun.getTrailingReturnType().get();
927        if (!T.isNull() && T->containsUnexpandedParameterPack())
928          return true;
929      }
930      break;
931
932    case DeclaratorChunk::MemberPointer:
933      if (Chunk.Mem.Scope().getScopeRep() &&
934          Chunk.Mem.Scope().getScopeRep()->containsUnexpandedParameterPack())
935        return true;
936      break;
937    }
938  }
939
940  if (Expr *TRC = D.getTrailingRequiresClause())
941    if (TRC->containsUnexpandedParameterPack())
942      return true;
943
944  return false;
945}
946
947namespace {
948
949// Callback to only accept typo corrections that refer to parameter packs.
950class ParameterPackValidatorCCC final : public CorrectionCandidateCallback {
951 public:
952  bool ValidateCandidate(const TypoCorrection &candidate) override {
953    NamedDecl *ND = candidate.getCorrectionDecl();
954    return ND && ND->isParameterPack();
955  }
956
957  std::unique_ptr<CorrectionCandidateCallback> clone() override {
958    return std::make_unique<ParameterPackValidatorCCC>(*this);
959  }
960};
961
962}
963
964/// Called when an expression computing the size of a parameter pack
965/// is parsed.
966///
967/// \code
968/// template<typename ...Types> struct count {
969///   static const unsigned value = sizeof...(Types);
970/// };
971/// \endcode
972///
973//
974/// \param OpLoc The location of the "sizeof" keyword.
975/// \param Name The name of the parameter pack whose size will be determined.
976/// \param NameLoc The source location of the name of the parameter pack.
977/// \param RParenLoc The location of the closing parentheses.
978ExprResult Sema::ActOnSizeofParameterPackExpr(Scope *S,
979                                              SourceLocation OpLoc,
980                                              IdentifierInfo &Name,
981                                              SourceLocation NameLoc,
982                                              SourceLocation RParenLoc) {
983  // C++0x [expr.sizeof]p5:
984  //   The identifier in a sizeof... expression shall name a parameter pack.
985  LookupResult R(*this, &Name, NameLoc, LookupOrdinaryName);
986  LookupName(R, S);
987
988  NamedDecl *ParameterPack = nullptr;
989  switch (R.getResultKind()) {
990  case LookupResult::Found:
991    ParameterPack = R.getFoundDecl();
992    break;
993
994  case LookupResult::NotFound:
995  case LookupResult::NotFoundInCurrentInstantiation: {
996    ParameterPackValidatorCCC CCC{};
997    if (TypoCorrection Corrected =
998            CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, nullptr,
999                        CCC, CTK_ErrorRecovery)) {
1000      diagnoseTypo(Corrected,
1001                   PDiag(diag::err_sizeof_pack_no_pack_name_suggest) << &Name,
1002                   PDiag(diag::note_parameter_pack_here));
1003      ParameterPack = Corrected.getCorrectionDecl();
1004    }
1005    break;
1006  }
1007  case LookupResult::FoundOverloaded:
1008  case LookupResult::FoundUnresolvedValue:
1009    break;
1010
1011  case LookupResult::Ambiguous:
1012    DiagnoseAmbiguousLookup(R);
1013    return ExprError();
1014  }
1015
1016  if (!ParameterPack || !ParameterPack->isParameterPack()) {
1017    Diag(NameLoc, diag::err_sizeof_pack_no_pack_name)
1018      << &Name;
1019    return ExprError();
1020  }
1021
1022  MarkAnyDeclReferenced(OpLoc, ParameterPack, true);
1023
1024  return SizeOfPackExpr::Create(Context, OpLoc, ParameterPack, NameLoc,
1025                                RParenLoc);
1026}
1027
1028TemplateArgumentLoc
1029Sema::getTemplateArgumentPackExpansionPattern(
1030      TemplateArgumentLoc OrigLoc,
1031      SourceLocation &Ellipsis, Optional<unsigned> &NumExpansions) const {
1032  const TemplateArgument &Argument = OrigLoc.getArgument();
1033  assert(Argument.isPackExpansion());
1034  switch (Argument.getKind()) {
1035  case TemplateArgument::Type: {
1036    // FIXME: We shouldn't ever have to worry about missing
1037    // type-source info!
1038    TypeSourceInfo *ExpansionTSInfo = OrigLoc.getTypeSourceInfo();
1039    if (!ExpansionTSInfo)
1040      ExpansionTSInfo = Context.getTrivialTypeSourceInfo(Argument.getAsType(),
1041                                                         Ellipsis);
1042    PackExpansionTypeLoc Expansion =
1043        ExpansionTSInfo->getTypeLoc().castAs<PackExpansionTypeLoc>();
1044    Ellipsis = Expansion.getEllipsisLoc();
1045
1046    TypeLoc Pattern = Expansion.getPatternLoc();
1047    NumExpansions = Expansion.getTypePtr()->getNumExpansions();
1048
1049    // We need to copy the TypeLoc because TemplateArgumentLocs store a
1050    // TypeSourceInfo.
1051    // FIXME: Find some way to avoid the copy?
1052    TypeLocBuilder TLB;
1053    TLB.pushFullCopy(Pattern);
1054    TypeSourceInfo *PatternTSInfo =
1055        TLB.getTypeSourceInfo(Context, Pattern.getType());
1056    return TemplateArgumentLoc(TemplateArgument(Pattern.getType()),
1057                               PatternTSInfo);
1058  }
1059
1060  case TemplateArgument::Expression: {
1061    PackExpansionExpr *Expansion
1062      = cast<PackExpansionExpr>(Argument.getAsExpr());
1063    Expr *Pattern = Expansion->getPattern();
1064    Ellipsis = Expansion->getEllipsisLoc();
1065    NumExpansions = Expansion->getNumExpansions();
1066    return TemplateArgumentLoc(Pattern, Pattern);
1067  }
1068
1069  case TemplateArgument::TemplateExpansion:
1070    Ellipsis = OrigLoc.getTemplateEllipsisLoc();
1071    NumExpansions = Argument.getNumTemplateExpansions();
1072    return TemplateArgumentLoc(Argument.getPackExpansionPattern(),
1073                               OrigLoc.getTemplateQualifierLoc(),
1074                               OrigLoc.getTemplateNameLoc());
1075
1076  case TemplateArgument::Declaration:
1077  case TemplateArgument::NullPtr:
1078  case TemplateArgument::Template:
1079  case TemplateArgument::Integral:
1080  case TemplateArgument::Pack:
1081  case TemplateArgument::Null:
1082    return TemplateArgumentLoc();
1083  }
1084
1085  llvm_unreachable("Invalid TemplateArgument Kind!");
1086}
1087
1088Optional<unsigned> Sema::getFullyPackExpandedSize(TemplateArgument Arg) {
1089  assert(Arg.containsUnexpandedParameterPack());
1090
1091  // If this is a substituted pack, grab that pack. If not, we don't know
1092  // the size yet.
1093  // FIXME: We could find a size in more cases by looking for a substituted
1094  // pack anywhere within this argument, but that's not necessary in the common
1095  // case for 'sizeof...(A)' handling.
1096  TemplateArgument Pack;
1097  switch (Arg.getKind()) {
1098  case TemplateArgument::Type:
1099    if (auto *Subst = Arg.getAsType()->getAs<SubstTemplateTypeParmPackType>())
1100      Pack = Subst->getArgumentPack();
1101    else
1102      return None;
1103    break;
1104
1105  case TemplateArgument::Expression:
1106    if (auto *Subst =
1107            dyn_cast<SubstNonTypeTemplateParmPackExpr>(Arg.getAsExpr()))
1108      Pack = Subst->getArgumentPack();
1109    else if (auto *Subst = dyn_cast<FunctionParmPackExpr>(Arg.getAsExpr()))  {
1110      for (VarDecl *PD : *Subst)
1111        if (PD->isParameterPack())
1112          return None;
1113      return Subst->getNumExpansions();
1114    } else
1115      return None;
1116    break;
1117
1118  case TemplateArgument::Template:
1119    if (SubstTemplateTemplateParmPackStorage *Subst =
1120            Arg.getAsTemplate().getAsSubstTemplateTemplateParmPack())
1121      Pack = Subst->getArgumentPack();
1122    else
1123      return None;
1124    break;
1125
1126  case TemplateArgument::Declaration:
1127  case TemplateArgument::NullPtr:
1128  case TemplateArgument::TemplateExpansion:
1129  case TemplateArgument::Integral:
1130  case TemplateArgument::Pack:
1131  case TemplateArgument::Null:
1132    return None;
1133  }
1134
1135  // Check that no argument in the pack is itself a pack expansion.
1136  for (TemplateArgument Elem : Pack.pack_elements()) {
1137    // There's no point recursing in this case; we would have already
1138    // expanded this pack expansion into the enclosing pack if we could.
1139    if (Elem.isPackExpansion())
1140      return None;
1141  }
1142  return Pack.pack_size();
1143}
1144
1145static void CheckFoldOperand(Sema &S, Expr *E) {
1146  if (!E)
1147    return;
1148
1149  E = E->IgnoreImpCasts();
1150  auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
1151  if ((OCE && OCE->isInfixBinaryOp()) || isa<BinaryOperator>(E) ||
1152      isa<AbstractConditionalOperator>(E)) {
1153    S.Diag(E->getExprLoc(), diag::err_fold_expression_bad_operand)
1154        << E->getSourceRange()
1155        << FixItHint::CreateInsertion(E->getBeginLoc(), "(")
1156        << FixItHint::CreateInsertion(E->getEndLoc(), ")");
1157  }
1158}
1159
1160ExprResult Sema::ActOnCXXFoldExpr(SourceLocation LParenLoc, Expr *LHS,
1161                                  tok::TokenKind Operator,
1162                                  SourceLocation EllipsisLoc, Expr *RHS,
1163                                  SourceLocation RParenLoc) {
1164  // LHS and RHS must be cast-expressions. We allow an arbitrary expression
1165  // in the parser and reduce down to just cast-expressions here.
1166  CheckFoldOperand(*this, LHS);
1167  CheckFoldOperand(*this, RHS);
1168
1169  auto DiscardOperands = [&] {
1170    CorrectDelayedTyposInExpr(LHS);
1171    CorrectDelayedTyposInExpr(RHS);
1172  };
1173
1174  // [expr.prim.fold]p3:
1175  //   In a binary fold, op1 and op2 shall be the same fold-operator, and
1176  //   either e1 shall contain an unexpanded parameter pack or e2 shall contain
1177  //   an unexpanded parameter pack, but not both.
1178  if (LHS && RHS &&
1179      LHS->containsUnexpandedParameterPack() ==
1180          RHS->containsUnexpandedParameterPack()) {
1181    DiscardOperands();
1182    return Diag(EllipsisLoc,
1183                LHS->containsUnexpandedParameterPack()
1184                    ? diag::err_fold_expression_packs_both_sides
1185                    : diag::err_pack_expansion_without_parameter_packs)
1186        << LHS->getSourceRange() << RHS->getSourceRange();
1187  }
1188
1189  // [expr.prim.fold]p2:
1190  //   In a unary fold, the cast-expression shall contain an unexpanded
1191  //   parameter pack.
1192  if (!LHS || !RHS) {
1193    Expr *Pack = LHS ? LHS : RHS;
1194    assert(Pack && "fold expression with neither LHS nor RHS");
1195    DiscardOperands();
1196    if (!Pack->containsUnexpandedParameterPack())
1197      return Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
1198             << Pack->getSourceRange();
1199  }
1200
1201  BinaryOperatorKind Opc = ConvertTokenKindToBinaryOpcode(Operator);
1202  return BuildCXXFoldExpr(LParenLoc, LHS, Opc, EllipsisLoc, RHS, RParenLoc,
1203                          None);
1204}
1205
1206ExprResult Sema::BuildCXXFoldExpr(SourceLocation LParenLoc, Expr *LHS,
1207                                  BinaryOperatorKind Operator,
1208                                  SourceLocation EllipsisLoc, Expr *RHS,
1209                                  SourceLocation RParenLoc,
1210                                  Optional<unsigned> NumExpansions) {
1211  return new (Context) CXXFoldExpr(Context.DependentTy, LParenLoc, LHS,
1212                                   Operator, EllipsisLoc, RHS, RParenLoc,
1213                                   NumExpansions);
1214}
1215
1216ExprResult Sema::BuildEmptyCXXFoldExpr(SourceLocation EllipsisLoc,
1217                                       BinaryOperatorKind Operator) {
1218  // [temp.variadic]p9:
1219  //   If N is zero for a unary fold-expression, the value of the expression is
1220  //       &&  ->  true
1221  //       ||  ->  false
1222  //       ,   ->  void()
1223  //   if the operator is not listed [above], the instantiation is ill-formed.
1224  //
1225  // Note that we need to use something like int() here, not merely 0, to
1226  // prevent the result from being a null pointer constant.
1227  QualType ScalarType;
1228  switch (Operator) {
1229  case BO_LOr:
1230    return ActOnCXXBoolLiteral(EllipsisLoc, tok::kw_false);
1231  case BO_LAnd:
1232    return ActOnCXXBoolLiteral(EllipsisLoc, tok::kw_true);
1233  case BO_Comma:
1234    ScalarType = Context.VoidTy;
1235    break;
1236
1237  default:
1238    return Diag(EllipsisLoc, diag::err_fold_expression_empty)
1239        << BinaryOperator::getOpcodeStr(Operator);
1240  }
1241
1242  return new (Context) CXXScalarValueInitExpr(
1243      ScalarType, Context.getTrivialTypeSourceInfo(ScalarType, EllipsisLoc),
1244      EllipsisLoc);
1245}
1246