aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/clang14/lib/Sema/SemaModule.cpp
blob: 747734f2d0ff0a0d4caf58e608e59670fb634299 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
//===--- SemaModule.cpp - Semantic Analysis for Modules -------------------===//
//
// 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 implements semantic analysis for modules (C++ modules syntax,
//  Objective-C modules syntax, and Clang header modules).
//
//===----------------------------------------------------------------------===//

#include "clang/AST/ASTConsumer.h"
#include "clang/Lex/HeaderSearch.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/SemaInternal.h"

using namespace clang;
using namespace sema;

static void checkModuleImportContext(Sema &S, Module *M,
                                     SourceLocation ImportLoc, DeclContext *DC,
                                     bool FromInclude = false) {
  SourceLocation ExternCLoc;

  if (auto *LSD = dyn_cast<LinkageSpecDecl>(DC)) {
    switch (LSD->getLanguage()) {
    case LinkageSpecDecl::lang_c:
      if (ExternCLoc.isInvalid())
        ExternCLoc = LSD->getBeginLoc();
      break;
    case LinkageSpecDecl::lang_cxx:
      break;
    }
    DC = LSD->getParent();
  }

  while (isa<LinkageSpecDecl>(DC) || isa<ExportDecl>(DC))
    DC = DC->getParent();

  if (!isa<TranslationUnitDecl>(DC)) {
    S.Diag(ImportLoc, (FromInclude && S.isModuleVisible(M))
                          ? diag::ext_module_import_not_at_top_level_noop
                          : diag::err_module_import_not_at_top_level_fatal)
        << M->getFullModuleName() << DC;
    S.Diag(cast<Decl>(DC)->getBeginLoc(),
           diag::note_module_import_not_at_top_level)
        << DC;
  } else if (!M->IsExternC && ExternCLoc.isValid()) {
    S.Diag(ImportLoc, diag::ext_module_import_in_extern_c)
      << M->getFullModuleName();
    S.Diag(ExternCLoc, diag::note_extern_c_begins_here);
  }
}

Sema::DeclGroupPtrTy
Sema::ActOnGlobalModuleFragmentDecl(SourceLocation ModuleLoc) {
  if (!ModuleScopes.empty() &&
      ModuleScopes.back().Module->Kind == Module::GlobalModuleFragment) {
    // Under -std=c++2a -fmodules-ts, we can find an explicit 'module;' after
    // already implicitly entering the global module fragment. That's OK.
    assert(getLangOpts().CPlusPlusModules && getLangOpts().ModulesTS &&
           "unexpectedly encountered multiple global module fragment decls");
    ModuleScopes.back().BeginLoc = ModuleLoc;
    return nullptr;
  }

  // We start in the global module; all those declarations are implicitly
  // module-private (though they do not have module linkage).
  Module *GlobalModule =
      PushGlobalModuleFragment(ModuleLoc, /*IsImplicit=*/false);

  // All declarations created from now on are owned by the global module.
  auto *TU = Context.getTranslationUnitDecl();
  TU->setModuleOwnershipKind(Decl::ModuleOwnershipKind::Visible);
  TU->setLocalOwningModule(GlobalModule);

  // FIXME: Consider creating an explicit representation of this declaration.
  return nullptr;
}

Sema::DeclGroupPtrTy
Sema::ActOnModuleDecl(SourceLocation StartLoc, SourceLocation ModuleLoc,
                      ModuleDeclKind MDK, ModuleIdPath Path, bool IsFirstDecl) {
  assert((getLangOpts().ModulesTS || getLangOpts().CPlusPlusModules) &&
         "should only have module decl in Modules TS or C++20");

  // A module implementation unit requires that we are not compiling a module
  // of any kind. A module interface unit requires that we are not compiling a
  // module map.
  switch (getLangOpts().getCompilingModule()) {
  case LangOptions::CMK_None:
    // It's OK to compile a module interface as a normal translation unit.
    break;

  case LangOptions::CMK_ModuleInterface:
    if (MDK != ModuleDeclKind::Implementation)
      break;

    // We were asked to compile a module interface unit but this is a module
    // implementation unit. That indicates the 'export' is missing.
    Diag(ModuleLoc, diag::err_module_interface_implementation_mismatch)
      << FixItHint::CreateInsertion(ModuleLoc, "export ");
    MDK = ModuleDeclKind::Interface;
    break;

  case LangOptions::CMK_ModuleMap:
    Diag(ModuleLoc, diag::err_module_decl_in_module_map_module);
    return nullptr;

  case LangOptions::CMK_HeaderModule:
    Diag(ModuleLoc, diag::err_module_decl_in_header_module);
    return nullptr;
  }

  assert(ModuleScopes.size() <= 1 && "expected to be at global module scope");

  // FIXME: Most of this work should be done by the preprocessor rather than
  // here, in order to support macro import.

  // Only one module-declaration is permitted per source file.
  if (!ModuleScopes.empty() &&
      ModuleScopes.back().Module->isModulePurview()) {
    Diag(ModuleLoc, diag::err_module_redeclaration);
    Diag(VisibleModules.getImportLoc(ModuleScopes.back().Module),
         diag::note_prev_module_declaration);
    return nullptr;
  }

  // Find the global module fragment we're adopting into this module, if any.
  Module *GlobalModuleFragment = nullptr;
  if (!ModuleScopes.empty() &&
      ModuleScopes.back().Module->Kind == Module::GlobalModuleFragment)
    GlobalModuleFragment = ModuleScopes.back().Module;

  // In C++20, the module-declaration must be the first declaration if there
  // is no global module fragment.
  if (getLangOpts().CPlusPlusModules && !IsFirstDecl && !GlobalModuleFragment) {
    Diag(ModuleLoc, diag::err_module_decl_not_at_start);
    SourceLocation BeginLoc =
        ModuleScopes.empty()
            ? SourceMgr.getLocForStartOfFile(SourceMgr.getMainFileID())
            : ModuleScopes.back().BeginLoc;
    if (BeginLoc.isValid()) {
      Diag(BeginLoc, diag::note_global_module_introducer_missing)
          << FixItHint::CreateInsertion(BeginLoc, "module;\n");
    }
  }

  // Flatten the dots in a module name. Unlike Clang's hierarchical module map
  // modules, the dots here are just another character that can appear in a
  // module name.
  std::string ModuleName;
  for (auto &Piece : Path) {
    if (!ModuleName.empty())
      ModuleName += ".";
    ModuleName += Piece.first->getName();
  }

  // If a module name was explicitly specified on the command line, it must be
  // correct.
  if (!getLangOpts().CurrentModule.empty() &&
      getLangOpts().CurrentModule != ModuleName) {
    Diag(Path.front().second, diag::err_current_module_name_mismatch)
        << SourceRange(Path.front().second, Path.back().second)
        << getLangOpts().CurrentModule;
    return nullptr;
  }
  const_cast<LangOptions&>(getLangOpts()).CurrentModule = ModuleName;

  auto &Map = PP.getHeaderSearchInfo().getModuleMap();
  Module *Mod;

  switch (MDK) {
  case ModuleDeclKind::Interface: {
    // We can't have parsed or imported a definition of this module or parsed a
    // module map defining it already.
    if (auto *M = Map.findModule(ModuleName)) {
      Diag(Path[0].second, diag::err_module_redefinition) << ModuleName;
      if (M->DefinitionLoc.isValid())
        Diag(M->DefinitionLoc, diag::note_prev_module_definition);
      else if (Optional<FileEntryRef> FE = M->getASTFile())
        Diag(M->DefinitionLoc, diag::note_prev_module_definition_from_ast_file)
            << FE->getName();
      Mod = M;
      break;
    }

    // Create a Module for the module that we're defining.
    Mod = Map.createModuleForInterfaceUnit(ModuleLoc, ModuleName,
                                           GlobalModuleFragment);
    assert(Mod && "module creation should not fail");
    break;
  }

  case ModuleDeclKind::Implementation:
    std::pair<IdentifierInfo *, SourceLocation> ModuleNameLoc(
        PP.getIdentifierInfo(ModuleName), Path[0].second);
    Mod = getModuleLoader().loadModule(ModuleLoc, {ModuleNameLoc},
                                       Module::AllVisible,
                                       /*IsInclusionDirective=*/false);
    if (!Mod) {
      Diag(ModuleLoc, diag::err_module_not_defined) << ModuleName;
      // Create an empty module interface unit for error recovery.
      Mod = Map.createModuleForInterfaceUnit(ModuleLoc, ModuleName,
                                             GlobalModuleFragment);
    }
    break;
  }

  if (!GlobalModuleFragment) {
    ModuleScopes.push_back({});
    if (getLangOpts().ModulesLocalVisibility)
      ModuleScopes.back().OuterVisibleModules = std::move(VisibleModules);
  } else {
    // We're done with the global module fragment now.
    ActOnEndOfTranslationUnitFragment(TUFragmentKind::Global);
  }

  // Switch from the global module fragment (if any) to the named module.
  ModuleScopes.back().BeginLoc = StartLoc;
  ModuleScopes.back().Module = Mod;
  ModuleScopes.back().ModuleInterface = MDK != ModuleDeclKind::Implementation;
  VisibleModules.setVisible(Mod, ModuleLoc);

  // From now on, we have an owning module for all declarations we see.
  // However, those declarations are module-private unless explicitly
  // exported.
  auto *TU = Context.getTranslationUnitDecl();
  TU->setModuleOwnershipKind(Decl::ModuleOwnershipKind::ModulePrivate);
  TU->setLocalOwningModule(Mod);

  // FIXME: Create a ModuleDecl.
  return nullptr;
}

Sema::DeclGroupPtrTy
Sema::ActOnPrivateModuleFragmentDecl(SourceLocation ModuleLoc,
                                     SourceLocation PrivateLoc) {
  // C++20 [basic.link]/2:
  //   A private-module-fragment shall appear only in a primary module
  //   interface unit.
  switch (ModuleScopes.empty() ? Module::GlobalModuleFragment
                               : ModuleScopes.back().Module->Kind) {
  case Module::ModuleMapModule:
  case Module::GlobalModuleFragment:
    Diag(PrivateLoc, diag::err_private_module_fragment_not_module);
    return nullptr;

  case Module::PrivateModuleFragment:
    Diag(PrivateLoc, diag::err_private_module_fragment_redefined);
    Diag(ModuleScopes.back().BeginLoc, diag::note_previous_definition);
    return nullptr;

  case Module::ModuleInterfaceUnit:
    break;
  }

  if (!ModuleScopes.back().ModuleInterface) {
    Diag(PrivateLoc, diag::err_private_module_fragment_not_module_interface);
    Diag(ModuleScopes.back().BeginLoc,
         diag::note_not_module_interface_add_export)
        << FixItHint::CreateInsertion(ModuleScopes.back().BeginLoc, "export ");
    return nullptr;
  }

  // FIXME: Check this isn't a module interface partition.
  // FIXME: Check that this translation unit does not import any partitions;
  // such imports would violate [basic.link]/2's "shall be the only module unit"
  // restriction.

  // We've finished the public fragment of the translation unit.
  ActOnEndOfTranslationUnitFragment(TUFragmentKind::Normal);

  auto &Map = PP.getHeaderSearchInfo().getModuleMap();
  Module *PrivateModuleFragment =
      Map.createPrivateModuleFragmentForInterfaceUnit(
          ModuleScopes.back().Module, PrivateLoc);
  assert(PrivateModuleFragment && "module creation should not fail");

  // Enter the scope of the private module fragment.
  ModuleScopes.push_back({});
  ModuleScopes.back().BeginLoc = ModuleLoc;
  ModuleScopes.back().Module = PrivateModuleFragment;
  ModuleScopes.back().ModuleInterface = true;
  VisibleModules.setVisible(PrivateModuleFragment, ModuleLoc);

  // All declarations created from now on are scoped to the private module
  // fragment (and are neither visible nor reachable in importers of the module
  // interface).
  auto *TU = Context.getTranslationUnitDecl();
  TU->setModuleOwnershipKind(Decl::ModuleOwnershipKind::ModulePrivate);
  TU->setLocalOwningModule(PrivateModuleFragment);

  // FIXME: Consider creating an explicit representation of this declaration.
  return nullptr;
}

DeclResult Sema::ActOnModuleImport(SourceLocation StartLoc,
                                   SourceLocation ExportLoc,
                                   SourceLocation ImportLoc,
                                   ModuleIdPath Path) {
  // Flatten the module path for a Modules TS module name.
  std::pair<IdentifierInfo *, SourceLocation> ModuleNameLoc;
  if (getLangOpts().ModulesTS) {
    std::string ModuleName;
    for (auto &Piece : Path) {
      if (!ModuleName.empty())
        ModuleName += ".";
      ModuleName += Piece.first->getName();
    }
    ModuleNameLoc = {PP.getIdentifierInfo(ModuleName), Path[0].second};
    Path = ModuleIdPath(ModuleNameLoc);
  }

  Module *Mod =
      getModuleLoader().loadModule(ImportLoc, Path, Module::AllVisible,
                                   /*IsInclusionDirective=*/false);
  if (!Mod)
    return true;

  return ActOnModuleImport(StartLoc, ExportLoc, ImportLoc, Mod, Path);
}

/// Determine whether \p D is lexically within an export-declaration.
static const ExportDecl *getEnclosingExportDecl(const Decl *D) {
  for (auto *DC = D->getLexicalDeclContext(); DC; DC = DC->getLexicalParent())
    if (auto *ED = dyn_cast<ExportDecl>(DC))
      return ED;
  return nullptr;
}

DeclResult Sema::ActOnModuleImport(SourceLocation StartLoc,
                                   SourceLocation ExportLoc,
                                   SourceLocation ImportLoc,
                                   Module *Mod, ModuleIdPath Path) {
  VisibleModules.setVisible(Mod, ImportLoc);

  checkModuleImportContext(*this, Mod, ImportLoc, CurContext);

  // FIXME: we should support importing a submodule within a different submodule
  // of the same top-level module. Until we do, make it an error rather than
  // silently ignoring the import.
  // Import-from-implementation is valid in the Modules TS. FIXME: Should we
  // warn on a redundant import of the current module?
  // FIXME: Import of a module from an implementation partition of the same
  // module is permitted.
  if (Mod->getTopLevelModuleName() == getLangOpts().CurrentModule &&
      (getLangOpts().isCompilingModule() || !getLangOpts().ModulesTS)) {
    Diag(ImportLoc, getLangOpts().isCompilingModule()
                        ? diag::err_module_self_import
                        : diag::err_module_import_in_implementation)
        << Mod->getFullModuleName() << getLangOpts().CurrentModule;
  }

  SmallVector<SourceLocation, 2> IdentifierLocs;
  Module *ModCheck = Mod;
  for (unsigned I = 0, N = Path.size(); I != N; ++I) {
    // If we've run out of module parents, just drop the remaining identifiers.
    // We need the length to be consistent.
    if (!ModCheck)
      break;
    ModCheck = ModCheck->Parent;

    IdentifierLocs.push_back(Path[I].second);
  }

  // If this was a header import, pad out with dummy locations.
  // FIXME: Pass in and use the location of the header-name token in this case.
  if (Path.empty()) {
    for (; ModCheck; ModCheck = ModCheck->Parent) {
      IdentifierLocs.push_back(SourceLocation());
    }
  }

  ImportDecl *Import = ImportDecl::Create(Context, CurContext, StartLoc,
                                          Mod, IdentifierLocs);
  CurContext->addDecl(Import);

  // Sequence initialization of the imported module before that of the current
  // module, if any.
  if (!ModuleScopes.empty())
    Context.addModuleInitializer(ModuleScopes.back().Module, Import);

  if (!ModuleScopes.empty() && ModuleScopes.back().ModuleInterface) {
    // Re-export the module if the imported module is exported.
    // Note that we don't need to add re-exported module to Imports field
    // since `Exports` implies the module is imported already.
    if (ExportLoc.isValid() || getEnclosingExportDecl(Import))
      getCurrentModule()->Exports.emplace_back(Mod, false);
    else
      getCurrentModule()->Imports.insert(Mod);
  } else if (ExportLoc.isValid()) {
    // [module.interface]p1:
    // An export-declaration shall inhabit a namespace scope and appear in the
    // purview of a module interface unit.
    Diag(ExportLoc, diag::err_export_not_in_module_interface) << 0;
  }

  return Import;
}

void Sema::ActOnModuleInclude(SourceLocation DirectiveLoc, Module *Mod) {
  checkModuleImportContext(*this, Mod, DirectiveLoc, CurContext, true);
  BuildModuleInclude(DirectiveLoc, Mod);
}

void Sema::BuildModuleInclude(SourceLocation DirectiveLoc, Module *Mod) {
  // Determine whether we're in the #include buffer for a module. The #includes
  // in that buffer do not qualify as module imports; they're just an
  // implementation detail of us building the module.
  //
  // FIXME: Should we even get ActOnModuleInclude calls for those?
  bool IsInModuleIncludes =
      TUKind == TU_Module &&
      getSourceManager().isWrittenInMainFile(DirectiveLoc);

  bool ShouldAddImport = !IsInModuleIncludes;

  // If this module import was due to an inclusion directive, create an
  // implicit import declaration to capture it in the AST.
  if (ShouldAddImport) {
    TranslationUnitDecl *TU = getASTContext().getTranslationUnitDecl();
    ImportDecl *ImportD = ImportDecl::CreateImplicit(getASTContext(), TU,
                                                     DirectiveLoc, Mod,
                                                     DirectiveLoc);
    if (!ModuleScopes.empty())
      Context.addModuleInitializer(ModuleScopes.back().Module, ImportD);
    TU->addDecl(ImportD);
    Consumer.HandleImplicitImportDecl(ImportD);
  }

  getModuleLoader().makeModuleVisible(Mod, Module::AllVisible, DirectiveLoc);
  VisibleModules.setVisible(Mod, DirectiveLoc);
}

void Sema::ActOnModuleBegin(SourceLocation DirectiveLoc, Module *Mod) {
  checkModuleImportContext(*this, Mod, DirectiveLoc, CurContext, true);

  ModuleScopes.push_back({});
  ModuleScopes.back().Module = Mod;
  if (getLangOpts().ModulesLocalVisibility)
    ModuleScopes.back().OuterVisibleModules = std::move(VisibleModules);

  VisibleModules.setVisible(Mod, DirectiveLoc);

  // The enclosing context is now part of this module.
  // FIXME: Consider creating a child DeclContext to hold the entities
  // lexically within the module.
  if (getLangOpts().trackLocalOwningModule()) {
    for (auto *DC = CurContext; DC; DC = DC->getLexicalParent()) {
      cast<Decl>(DC)->setModuleOwnershipKind(
          getLangOpts().ModulesLocalVisibility
              ? Decl::ModuleOwnershipKind::VisibleWhenImported
              : Decl::ModuleOwnershipKind::Visible);
      cast<Decl>(DC)->setLocalOwningModule(Mod);
    }
  }
}

void Sema::ActOnModuleEnd(SourceLocation EomLoc, Module *Mod) {
  if (getLangOpts().ModulesLocalVisibility) {
    VisibleModules = std::move(ModuleScopes.back().OuterVisibleModules);
    // Leaving a module hides namespace names, so our visible namespace cache
    // is now out of date.
    VisibleNamespaceCache.clear();
  }

  assert(!ModuleScopes.empty() && ModuleScopes.back().Module == Mod &&
         "left the wrong module scope");
  ModuleScopes.pop_back();

  // We got to the end of processing a local module. Create an
  // ImportDecl as we would for an imported module.
  FileID File = getSourceManager().getFileID(EomLoc);
  SourceLocation DirectiveLoc;
  if (EomLoc == getSourceManager().getLocForEndOfFile(File)) {
    // We reached the end of a #included module header. Use the #include loc.
    assert(File != getSourceManager().getMainFileID() &&
           "end of submodule in main source file");
    DirectiveLoc = getSourceManager().getIncludeLoc(File);
  } else {
    // We reached an EOM pragma. Use the pragma location.
    DirectiveLoc = EomLoc;
  }
  BuildModuleInclude(DirectiveLoc, Mod);

  // Any further declarations are in whatever module we returned to.
  if (getLangOpts().trackLocalOwningModule()) {
    // The parser guarantees that this is the same context that we entered
    // the module within.
    for (auto *DC = CurContext; DC; DC = DC->getLexicalParent()) {
      cast<Decl>(DC)->setLocalOwningModule(getCurrentModule());
      if (!getCurrentModule())
        cast<Decl>(DC)->setModuleOwnershipKind(
            Decl::ModuleOwnershipKind::Unowned);
    }
  }
}

void Sema::createImplicitModuleImportForErrorRecovery(SourceLocation Loc,
                                                      Module *Mod) {
  // Bail if we're not allowed to implicitly import a module here.
  if (isSFINAEContext() || !getLangOpts().ModulesErrorRecovery ||
      VisibleModules.isVisible(Mod))
    return;

  // Create the implicit import declaration.
  TranslationUnitDecl *TU = getASTContext().getTranslationUnitDecl();
  ImportDecl *ImportD = ImportDecl::CreateImplicit(getASTContext(), TU,
                                                   Loc, Mod, Loc);
  TU->addDecl(ImportD);
  Consumer.HandleImplicitImportDecl(ImportD);

  // Make the module visible.
  getModuleLoader().makeModuleVisible(Mod, Module::AllVisible, Loc);
  VisibleModules.setVisible(Mod, Loc);
}

/// We have parsed the start of an export declaration, including the '{'
/// (if present).
Decl *Sema::ActOnStartExportDecl(Scope *S, SourceLocation ExportLoc,
                                 SourceLocation LBraceLoc) {
  ExportDecl *D = ExportDecl::Create(Context, CurContext, ExportLoc);

  // Set this temporarily so we know the export-declaration was braced.
  D->setRBraceLoc(LBraceLoc);

  CurContext->addDecl(D);
  PushDeclContext(S, D);

  // C++2a [module.interface]p1:
  //   An export-declaration shall appear only [...] in the purview of a module
  //   interface unit. An export-declaration shall not appear directly or
  //   indirectly within [...] a private-module-fragment.
  if (ModuleScopes.empty() || !ModuleScopes.back().Module->isModulePurview()) {
    Diag(ExportLoc, diag::err_export_not_in_module_interface) << 0;
    D->setInvalidDecl();
    return D;
  } else if (!ModuleScopes.back().ModuleInterface) {
    Diag(ExportLoc, diag::err_export_not_in_module_interface) << 1;
    Diag(ModuleScopes.back().BeginLoc,
         diag::note_not_module_interface_add_export)
        << FixItHint::CreateInsertion(ModuleScopes.back().BeginLoc, "export ");
    D->setInvalidDecl();
    return D;
  } else if (ModuleScopes.back().Module->Kind ==
             Module::PrivateModuleFragment) {
    Diag(ExportLoc, diag::err_export_in_private_module_fragment);
    Diag(ModuleScopes.back().BeginLoc, diag::note_private_module_fragment);
    D->setInvalidDecl();
    return D;
  }

  for (const DeclContext *DC = CurContext; DC; DC = DC->getLexicalParent()) {
    if (const auto *ND = dyn_cast<NamespaceDecl>(DC)) {
      //   An export-declaration shall not appear directly or indirectly within
      //   an unnamed namespace [...]
      if (ND->isAnonymousNamespace()) {
        Diag(ExportLoc, diag::err_export_within_anonymous_namespace);
        Diag(ND->getLocation(), diag::note_anonymous_namespace);
        // Don't diagnose internal-linkage declarations in this region.
        D->setInvalidDecl();
        return D;
      }

      //   A declaration is exported if it is [...] a namespace-definition
      //   that contains an exported declaration.
      //
      // Defer exporting the namespace until after we leave it, in order to
      // avoid marking all subsequent declarations in the namespace as exported.
      if (!DeferredExportedNamespaces.insert(ND).second)
        break;
    }
  }

  //   [...] its declaration or declaration-seq shall not contain an
  //   export-declaration.
  if (auto *ED = getEnclosingExportDecl(D)) {
    Diag(ExportLoc, diag::err_export_within_export);
    if (ED->hasBraces())
      Diag(ED->getLocation(), diag::note_export);
    D->setInvalidDecl();
    return D;
  }

  D->setModuleOwnershipKind(Decl::ModuleOwnershipKind::VisibleWhenImported);
  return D;
}

static bool checkExportedDeclContext(Sema &S, DeclContext *DC,
                                     SourceLocation BlockStart);

namespace {
enum class UnnamedDeclKind {
  Empty,
  StaticAssert,
  Asm,
  UsingDirective,
  Context
};
}

static llvm::Optional<UnnamedDeclKind> getUnnamedDeclKind(Decl *D) {
  if (isa<EmptyDecl>(D))
    return UnnamedDeclKind::Empty;
  if (isa<StaticAssertDecl>(D))
    return UnnamedDeclKind::StaticAssert;
  if (isa<FileScopeAsmDecl>(D))
    return UnnamedDeclKind::Asm;
  if (isa<UsingDirectiveDecl>(D))
    return UnnamedDeclKind::UsingDirective;
  // Everything else either introduces one or more names or is ill-formed.
  return llvm::None;
}

unsigned getUnnamedDeclDiag(UnnamedDeclKind UDK, bool InBlock) {
  switch (UDK) {
  case UnnamedDeclKind::Empty:
  case UnnamedDeclKind::StaticAssert:
    // Allow empty-declarations and static_asserts in an export block as an
    // extension.
    return InBlock ? diag::ext_export_no_name_block : diag::err_export_no_name;

  case UnnamedDeclKind::UsingDirective:
    // Allow exporting using-directives as an extension.
    return diag::ext_export_using_directive;

  case UnnamedDeclKind::Context:
    // Allow exporting DeclContexts that transitively contain no declarations
    // as an extension.
    return diag::ext_export_no_names;

  case UnnamedDeclKind::Asm:
    return diag::err_export_no_name;
  }
  llvm_unreachable("unknown kind");
}

static void diagExportedUnnamedDecl(Sema &S, UnnamedDeclKind UDK, Decl *D,
                                    SourceLocation BlockStart) {
  S.Diag(D->getLocation(), getUnnamedDeclDiag(UDK, BlockStart.isValid()))
      << (unsigned)UDK;
  if (BlockStart.isValid())
    S.Diag(BlockStart, diag::note_export);
}

/// Check that it's valid to export \p D.
static bool checkExportedDecl(Sema &S, Decl *D, SourceLocation BlockStart) {
  // C++2a [module.interface]p3:
  //   An exported declaration shall declare at least one name
  if (auto UDK = getUnnamedDeclKind(D))
    diagExportedUnnamedDecl(S, *UDK, D, BlockStart);

  //   [...] shall not declare a name with internal linkage.
  if (auto *ND = dyn_cast<NamedDecl>(D)) {
    // Don't diagnose anonymous union objects; we'll diagnose their members
    // instead.
    if (ND->getDeclName() && ND->getFormalLinkage() == InternalLinkage) {
      S.Diag(ND->getLocation(), diag::err_export_internal) << ND;
      if (BlockStart.isValid())
        S.Diag(BlockStart, diag::note_export);
    }
  }

  // C++2a [module.interface]p5:
  //   all entities to which all of the using-declarators ultimately refer
  //   shall have been introduced with a name having external linkage
  if (auto *USD = dyn_cast<UsingShadowDecl>(D)) {
    NamedDecl *Target = USD->getUnderlyingDecl();
    if (Target->getFormalLinkage() == InternalLinkage) {
      S.Diag(USD->getLocation(), diag::err_export_using_internal) << Target;
      S.Diag(Target->getLocation(), diag::note_using_decl_target);
      if (BlockStart.isValid())
        S.Diag(BlockStart, diag::note_export);
    }
  }

  // Recurse into namespace-scope DeclContexts. (Only namespace-scope
  // declarations are exported.)
  if (auto *DC = dyn_cast<DeclContext>(D))
    if (DC->getRedeclContext()->isFileContext() && !isa<EnumDecl>(D))
      return checkExportedDeclContext(S, DC, BlockStart);
  return false;
}

/// Check that it's valid to export all the declarations in \p DC.
static bool checkExportedDeclContext(Sema &S, DeclContext *DC,
                                     SourceLocation BlockStart) {
  bool AllUnnamed = true;
  for (auto *D : DC->decls())
    AllUnnamed &= checkExportedDecl(S, D, BlockStart);
  return AllUnnamed;
}

/// Complete the definition of an export declaration.
Decl *Sema::ActOnFinishExportDecl(Scope *S, Decl *D, SourceLocation RBraceLoc) {
  auto *ED = cast<ExportDecl>(D);
  if (RBraceLoc.isValid())
    ED->setRBraceLoc(RBraceLoc);

  PopDeclContext();

  if (!D->isInvalidDecl()) {
    SourceLocation BlockStart =
        ED->hasBraces() ? ED->getBeginLoc() : SourceLocation();
    for (auto *Child : ED->decls()) {
      if (checkExportedDecl(*this, Child, BlockStart)) {
        // If a top-level child is a linkage-spec declaration, it might contain
        // no declarations (transitively), in which case it's ill-formed.
        diagExportedUnnamedDecl(*this, UnnamedDeclKind::Context, Child,
                                BlockStart);
      }
    }
  }

  return D;
}

Module *Sema::PushGlobalModuleFragment(SourceLocation BeginLoc,
                                       bool IsImplicit) {
  ModuleMap &Map = PP.getHeaderSearchInfo().getModuleMap();
  Module *GlobalModule =
      Map.createGlobalModuleFragmentForModuleUnit(BeginLoc, getCurrentModule());
  assert(GlobalModule && "module creation should not fail");

  // Enter the scope of the global module.
  ModuleScopes.push_back({BeginLoc, GlobalModule,
                          /*ModuleInterface=*/false,
                          /*ImplicitGlobalModuleFragment=*/IsImplicit,
                          /*VisibleModuleSet*/{}});
  VisibleModules.setVisible(GlobalModule, BeginLoc);

  return GlobalModule;
}

void Sema::PopGlobalModuleFragment() {
  assert(!ModuleScopes.empty() && getCurrentModule()->isGlobalModule() &&
         "left the wrong module scope, which is not global module fragment");
  ModuleScopes.pop_back();
}