[modules] Simplify and generalize the existing rule for finding hidden

declarations in redeclaration lookup. A declaration is now visible to
lookup if:

 * It is visible (not in a module, or in an imported module), or
 * We're doing redeclaration lookup and it's externally-visible, or
 * We're doing typo correction and looking for unimported decls.

We now support multiple modules having different internal-linkage or no-linkage
definitions of the same name for all entities, not just for functions,
variables, and some typedefs. As previously, if multiple such entities are
visible, any attempt to use them will result in an ambiguity error.

This patch fixes the linkage calculation for a number of entities where we
previously didn't need to get it right (using-declarations, namespace aliases,
and so on).  It also classifies enumerators as always having no linkage, which
is a slight deviation from the C++ standard's definition, but not an observable
change outside modules (this change is being discussed on the -core reflector
currently).

This also removes the prior special case for tag lookup, which made some cases
of this work, but also led to bizarre, bogus "must use 'struct' to refer to type
'Foo' in this scope" diagnostics in C++.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@252960 91177308-0d34-0410-b5e6-96231b3b80d8

15 files changed, 115 insertions, 72 deletions

diff --git a/include/clang/Sema/Lookup.h b/include/clang/Sema/Lookup.h
index 1162a1d65a..f291a8aef0 100644
--- a/include/clang/Sema/Lookup.h
+++ b/include/clang/Sema/Lookup.h
@@ -139,8 +139,7 @@ public:
       Redecl(Redecl != Sema::NotForRedeclaration),
       HideTags(true),
       Diagnose(Redecl == Sema::NotForRedeclaration),
-      AllowHidden(Redecl == Sema::ForRedeclaration),
-      AllowHiddenInternal(AllowHidden),
+      AllowHidden(false),
       Shadowed(false)
   {
     configure();
@@ -162,8 +161,7 @@ public:
       Redecl(Redecl != Sema::NotForRedeclaration),
       HideTags(true),
       Diagnose(Redecl == Sema::NotForRedeclaration),
-      AllowHidden(Redecl == Sema::ForRedeclaration),
-      AllowHiddenInternal(AllowHidden),
+      AllowHidden(false),
       Shadowed(false)
   {
     configure();
@@ -184,7 +182,6 @@ public:
       HideTags(Other.HideTags),
       Diagnose(false),
       AllowHidden(Other.AllowHidden),
-      AllowHiddenInternal(Other.AllowHiddenInternal),
       Shadowed(false)
   {}
 
@@ -226,27 +223,16 @@ public:
   /// \brief Specify whether hidden declarations are visible, e.g.,
   /// for recovery reasons.
   void setAllowHidden(bool AH) {
-    AllowHiddenInternal = AllowHidden = AH;
-  }
-
-  /// \brief Specify whether hidden internal declarations are visible.
-  void setAllowHiddenInternal(bool AHI) {
-    AllowHiddenInternal = AHI;
+    AllowHidden = AH;
   }
 
   /// \brief Determine whether this lookup is permitted to see hidden
   /// declarations, such as those in modules that have not yet been imported.
   bool isHiddenDeclarationVisible(NamedDecl *ND) const {
-    // If a using-shadow declaration is hidden, it's never visible, not
-    // even to redeclaration lookup.
-    // FIXME: Should this apply to typedefs and namespace aliases too?
-    if (isa<UsingShadowDecl>(ND) && LookupKind != Sema::LookupUsingDeclName)
-      return false;
-    return (AllowHidden &&
-            (AllowHiddenInternal || ND->isExternallyVisible())) ||
-           LookupKind == Sema::LookupTagName;
+    return AllowHidden ||
+           (isForRedeclaration() && ND->isExternallyVisible());
   }
-  
+
   /// Sets whether tag declarations should be hidden by non-tag
   /// declarations during resolution.  The default is true.
   void setHideTags(bool Hide) {
@@ -317,7 +303,8 @@ public:
     if (!D->isInIdentifierNamespace(IDNS))
       return nullptr;
 
-    if (isHiddenDeclarationVisible(D) || isVisible(getSema(), D))
+    if (!D->isHidden() || isHiddenDeclarationVisible(D) ||
+        isVisibleSlow(getSema(), D))
       return D;
 
     return getAcceptableDeclSlow(D);
@@ -526,7 +513,6 @@ public:
   /// \brief Change this lookup's redeclaration kind.
   void setRedeclarationKind(Sema::RedeclarationKind RK) {
     Redecl = RK;
-    AllowHiddenInternal = AllowHidden = (RK == Sema::ForRedeclaration);
     configure();
   }
 
@@ -698,9 +684,6 @@ private:
   /// \brief True if we should allow hidden declarations to be 'visible'.
   bool AllowHidden;
 
-  /// \brief True if we should allow hidden internal declarations to be visible.
-  bool AllowHiddenInternal;
-
   /// \brief True if the found declarations were shadowed by some other
   /// declaration that we skipped. This only happens when \c LookupKind
   /// is \c LookupRedeclarationWithLinkage.
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 0f6e8b0970..8c50af615c 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -635,6 +635,8 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D,
   if (D->isInAnonymousNamespace()) {
     const auto *Var = dyn_cast<VarDecl>(D);
     const auto *Func = dyn_cast<FunctionDecl>(D);
+    // FIXME: In C++11 onwards, anonymous namespaces should give decls
+    // within them internal linkage, not unique external linkage.
     if ((!Var || !isFirstInExternCContext(Var)) &&
         (!Func || !isFirstInExternCContext(Func)))
       return LinkageInfo::uniqueExternal();
@@ -821,10 +823,14 @@ static LinkageInfo getLVForNamespaceScopeDecl(const NamedDecl *D,
   } else if (isa<ObjCInterfaceDecl>(D)) {
     // fallout
 
+  } else if (auto *TD = dyn_cast<TypedefNameDecl>(D)) {
+    // A typedef declaration has linkage if it gives a type a name for
+    // linkage purposes.
+    if (!TD->getAnonDeclWithTypedefName(/*AnyRedecl*/true))
+      return LinkageInfo::none();
+
   // Everything not covered here has no linkage.
   } else {
-    // FIXME: A typedef declaration has linkage if it gives a type a name for
-    // linkage purposes.
     return LinkageInfo::none();
   }
 
@@ -1226,8 +1232,32 @@ static LinkageInfo computeLVForDecl(const NamedDecl *D,
   switch (D->getKind()) {
     default:
       break;
+
+    // Per C++ [basic.link]p2, only the names of objects, references,
+    // functions, types, templates, namespaces, and values ever have linkage.
+    //
+    // Note that the name of a typedef, namespace alias, using declaration,
+    // and so on are not the name of the corresponding type, namespace, or
+    // declaration, so they do *not* have linkage.
+    case Decl::EnumConstant: // FIXME: This has linkage, but that's dumb.
+    case Decl::ImplicitParam:
+    case Decl::Label:
+    case Decl::NamespaceAlias:
     case Decl::ParmVar:
+    case Decl::Using:
+    case Decl::UsingShadow:
+    case Decl::UsingDirective:
       return LinkageInfo::none();
+
+    case Decl::Typedef:
+    case Decl::TypeAlias:
+      // A typedef declaration has linkage if it gives a type a name for
+      // linkage purposes.
+      if (!cast<TypedefNameDecl>(D)
+               ->getAnonDeclWithTypedefName(/*AnyRedecl*/true))
+        return LinkageInfo::none();
+      break;
+
     case Decl::TemplateTemplateParm: // count these as external
     case Decl::NonTypeTemplateParm:
     case Decl::ObjCAtDefsField:
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 728697e78f..a23d9debb8 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -4819,12 +4819,6 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
   LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
                         ForRedeclaration);
 
-  // If we're hiding internal-linkage symbols in modules from redeclaration
-  // lookup, let name lookup know.
-  if ((getLangOpts().Modules || getLangOpts().ModulesLocalVisibility) &&
-      D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_typedef)
-    Previous.setAllowHiddenInternal(false);
-
   // See if this is a redefinition of a variable in the same scope.
   if (!D.getCXXScopeSpec().isSet()) {
     bool IsLinkageLookup = false;
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 74bffb2a04..910ebcf05d 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -7206,23 +7206,13 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
     //   treated as an original-namespace-name.
     //
     // Since namespace names are unique in their scope, and we don't
-    // look through using directives, just look for any ordinary names.
-    
-    const unsigned IDNS = Decl::IDNS_Ordinary | Decl::IDNS_Member | 
-    Decl::IDNS_Type | Decl::IDNS_Using | Decl::IDNS_Tag | 
-    Decl::IDNS_Namespace;
-    NamedDecl *PrevDecl = nullptr;
-    DeclContext::lookup_result R = CurContext->getRedeclContext()->lookup(II);
-    for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E;
-         ++I) {
-      if ((*I)->getIdentifierNamespace() & IDNS) {
-        PrevDecl = *I;
-        break;
-      }
-    }
-    
+    // look through using directives, just look for any ordinary names
+    // as if by qualified name lookup.
+    LookupResult R(*this, II, IdentLoc, LookupOrdinaryName, ForRedeclaration);
+    LookupQualifiedName(R, CurContext->getRedeclContext());
+    NamedDecl *PrevDecl = R.getAsSingle<NamedDecl>();
     PrevNS = dyn_cast_or_null<NamespaceDecl>(PrevDecl);
-    
+
     if (PrevNS) {
       // This is an extended namespace definition.
       if (IsInline != PrevNS->isInline())
diff --git a/test/Index/linkage.c b/test/Index/linkage.c
index ab006590b6..b0dcb30990 100644
--- a/test/Index/linkage.c
+++ b/test/Index/linkage.c
@@ -20,7 +20,7 @@ void f16(void) {
 
 
 // CHECK: EnumDecl=Baz:3:6 (Definition)linkage=External
-// CHECK: EnumConstantDecl=Qux:3:12 (Definition)linkage=External
+// CHECK: EnumConstantDecl=Qux:3:12 (Definition)linkage=NoLinkage
 // CHECK: VarDecl=x:4:5linkage=External
 // CHECK: FunctionDecl=foo:5:6linkage=External
 // CHECK: VarDecl=w:6:12linkage=Internal
diff --git a/test/Index/usrs.m b/test/Index/usrs.m
index fc3fbc9105..aa0c4a04fc 100644
--- a/test/Index/usrs.m
+++ b/test/Index/usrs.m
@@ -119,7 +119,7 @@ int test_multi_declaration(void) {
 // CHECK: usrs.m c:@SA@MyStruct Extent=[15:9 - 18:2]
 // CHECK: usrs.m c:@SA@MyStruct@FI@wa Extent=[16:3 - 16:9]
 // CHECK: usrs.m c:@SA@MyStruct@FI@moo Extent=[17:3 - 17:10]
-// CHECK: usrs.m c:usrs.m@T@MyStruct Extent=[15:1 - 18:11]
+// CHECK: usrs.m c:@T@MyStruct Extent=[15:1 - 18:11]
 // CHECK: usrs.m c:@E@Pizza Extent=[20:1 - 23:2]
 // CHECK: usrs.m c:@E@Pizza@CHEESE Extent=[21:3 - 21:9]
 // CHECK: usrs.m c:@E@Pizza@MUSHROOMS Extent=[22:3 - 22:12]
diff --git a/test/Modules/Inputs/no-linkage/decls.h b/test/Modules/Inputs/no-linkage/decls.h
new file mode 100644
index 0000000000..5c29044abf
--- /dev/null
+++ b/test/Modules/Inputs/no-linkage/decls.h
@@ -0,0 +1,6 @@
+namespace RealNS { int UsingDecl; }
+namespace NS = RealNS;
+typedef int Typedef;
+using AliasDecl = int;
+enum Enum { Enumerator };
+using RealNS::UsingDecl;
diff --git a/test/Modules/Inputs/no-linkage/empty.h b/test/Modules/Inputs/no-linkage/empty.h
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/Modules/Inputs/no-linkage/empty.h
diff --git a/test/Modules/Inputs/no-linkage/module.modulemap b/test/Modules/Inputs/no-linkage/module.modulemap
new file mode 100644
index 0000000000..3931b0fe8e
--- /dev/null
+++ b/test/Modules/Inputs/no-linkage/module.modulemap
@@ -0,0 +1 @@
+module M { module E { header "empty.h" } module D { header "decls.h" } }
diff --git a/test/Modules/decldef.m b/test/Modules/decldef.m
index 420c6774ec..784743ff6e 100644
--- a/test/Modules/decldef.m
+++ b/test/Modules/decldef.m
@@ -11,7 +11,13 @@ Def *def;
 #ifdef USE_EARLY
 A *a1; // expected-error{{declaration of 'A' must be imported from module 'decldef.Def' before it is required}}
 #endif
-B *b1; // expected-error{{must use 'struct' tag to refer to type 'B'}}
+B *b1;
+#ifdef USE_EARLY
+// expected-error@-2{{must use 'struct' tag to refer to type 'B'}}
+#else
+// expected-error@-4{{declaration of 'B' must be imported from module 'decldef.Decl' before it is required}}
+// expected-note@Inputs/decl.h:2 {{previous}}
+#endif
 @import decldef.Decl;
 
 A *a2;
diff --git a/test/Modules/merge-enumerators.cpp b/test/Modules/merge-enumerators.cpp
index 5267ac658b..10e1914bd7 100644
--- a/test/Modules/merge-enumerators.cpp
+++ b/test/Modules/merge-enumerators.cpp
@@ -16,11 +16,13 @@
 
 #ifdef MERGE_LATE
 namespace N {
-  // FIXME: Should we accept this and reject the usage below due to ambiguity instead?
-  enum { A } a; // expected-error {{redefinition of enumerator 'A'}}
-  // expected-note@a.h:1 {{here}} (from module B.b)
+  enum { A } a; // expected-note {{candidate}}
+  // expected-note@a.h:1 {{candidate}} (from module B.b)
 }
 #include "a.h"
 #endif
 
 N::E e = N::A;
+#ifdef MERGE_LATE
+// expected-error@-2 {{ambiguous}}
+#endif
diff --git a/test/Modules/module-private.cpp b/test/Modules/module-private.cpp
index 6e723c863c..42ab185760 100644
--- a/test/Modules/module-private.cpp
+++ b/test/Modules/module-private.cpp
@@ -12,11 +12,7 @@ void test() {
 }
 
 int test_broken() {
-  HiddenStruct hidden; // \
-  // expected-error{{must use 'struct' tag to refer to type 'HiddenStruct' in this scope}} \
-  // expected-error{{definition of 'HiddenStruct' must be imported}}
-  // expected-note@Inputs/module_private_left.h:3 {{previous definition is here}}
-
+  HiddenStruct hidden; // expected-error{{unknown type name 'HiddenStruct'}}
   Integer i; // expected-error{{unknown type name 'Integer'}}
 
   int *ip = 0;
diff --git a/test/Modules/no-linkage.cpp b/test/Modules/no-linkage.cpp
new file mode 100644
index 0000000000..508464e8db
--- /dev/null
+++ b/test/Modules/no-linkage.cpp
@@ -0,0 +1,35 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fmodules-local-submodule-visibility -I%S/Inputs/no-linkage -fmodule-map-file=%S/Inputs/no-linkage/module.modulemap %s -verify
+
+#include "empty.h"
+
+namespace NS { int n; } // expected-note {{candidate}}
+struct Typedef { int n; }; // expected-note {{candidate}}
+int AliasDecl; // expected-note {{candidate}}
+enum AlsoAnEnum { Enumerator }; // expected-note {{candidate}}
+int UsingDecl; // expected-note {{candidate}}
+
+// expected-note@decls.h:2 {{candidate}}
+// expected-note@decls.h:3 {{candidate}}
+// expected-note@decls.h:4 {{candidate}}
+// expected-note@decls.h:5 {{candidate}}
+// expected-note@decls.h:6 {{candidate}}
+
+void use(int);
+void use_things() {
+  use(Typedef().n);
+  use(NS::n);
+  use(AliasDecl);
+  use(Enumerator);
+  use(UsingDecl);
+}
+
+#include "decls.h"
+
+void use_things_again() {
+  use(Typedef().n); // expected-error {{ambiguous}}
+  use(NS::n); // expected-error {{ambiguous}} expected-error{{'NS' is not a class, namespace, or enumeration}}
+  use(AliasDecl); // expected-error {{ambiguous}}
+  use(Enumerator); // expected-error {{ambiguous}}
+  use(UsingDecl); // expected-error {{ambiguous}}
+}
diff --git a/test/Modules/submodule-visibility-cycles.cpp b/test/Modules/submodule-visibility-cycles.cpp
index f26f6f21ee..a01fe562b1 100644
--- a/test/Modules/submodule-visibility-cycles.cpp
+++ b/test/Modules/submodule-visibility-cycles.cpp
@@ -3,7 +3,7 @@
 
 #include "cycle1.h"
 C1 c1;
-C2 c2; // expected-error {{must be imported}} expected-error {{}}
+C2 c2; // expected-error {{must be imported}}
 // expected-note@cycle2.h:6 {{here}}
 
 #include "cycle2.h"
diff --git a/test/Modules/submodules-merge-defs.cpp b/test/Modules/submodules-merge-defs.cpp
index bb8e69367c..361f05b553 100644
--- a/test/Modules/submodules-merge-defs.cpp
+++ b/test/Modules/submodules-merge-defs.cpp
@@ -12,7 +12,7 @@
 #include "indirect.h"
 #endif
 
-A pre_a; // expected-error {{must use 'struct'}}
+A pre_a;
 #ifdef IMPORT_USE_2
 // expected-error-re@-2 {{must be imported from one of {{.*}}stuff.use{{.*}}stuff.use-2}}
 #elif EARLY_INDIRECT_INCLUDE
@@ -21,29 +21,28 @@ A pre_a; // expected-error {{must use 'struct'}}
 // expected-error@-6 {{must be imported from module 'stuff.use'}}
 #endif
 // expected-note@defs.h:1 +{{here}}
+extern class A pre_a2;
+int pre_use_a = use_a(pre_a2); // expected-error {{'A' must be imported}} expected-error {{'use_a' must be imported}}
 // expected-note@defs.h:2 +{{here}}
-int pre_use_a = use_a(pre_a); // expected-error {{'A' must be imported}} expected-error {{'use_a' must be imported}}
 
 B::Inner2 pre_bi; // expected-error +{{must be imported}}
 // expected-note@defs.h:4 +{{here}}
 // expected-note@defs.h:17 +{{here}}
-void pre_bfi(B b) { // expected-error {{must use 'class'}} expected-error +{{must be imported}}
-  b.f<int>(); // expected-error +{{must be imported}} expected-error +{{}}
-  // expected-note@defs.h:19 +{{here}}
+void pre_bfi(B b) { // expected-error +{{must be imported}}
+  b.f<int>(); // expected-error +{{}}
 }
 
 C_Base<1> pre_cb1; // expected-error +{{must be imported}}
 // expected-note@defs.h:23 +{{here}}
-C1 pre_c1; // expected-error +{{must be imported}} expected-error {{must use 'struct'}}
+C1 pre_c1; // expected-error +{{must be imported}}
 // expected-note@defs.h:25 +{{here}}
-C2 pre_c2; // expected-error +{{must be imported}} expected-error {{must use 'struct'}}
+C2 pre_c2; // expected-error +{{must be imported}}
 // expected-note@defs.h:26 +{{here}}
 
 D::X pre_dx; // expected-error +{{must be imported}}
 // expected-note@defs.h:28 +{{here}}
 // expected-note@defs.h:29 +{{here}}
-// FIXME: We should warn that use_dx is being used without being imported.
-int pre_use_dx = use_dx(pre_dx);
+int pre_use_dx = use_dx(pre_dx); // ignored; pre_dx is invalid
 
 int pre_e = E(0); // expected-error {{must be imported}}
 // expected-note@defs.h:32 +{{here}}
@@ -69,8 +68,9 @@ J<> pre_j; // expected-error {{declaration of 'J' must be imported}}
 #endif
 // expected-note@defs.h:58 +{{here}}
 
-ScopedEnum pre_scopedenum; // expected-error {{must be imported}} expected-error {{must use 'enum'}}
-// expected-note@defs.h:106 {{here}}
+ScopedEnum pre_scopedenum; // expected-error {{must be imported}}
+// expected-note@defs.h:105 0-1{{here}}
+// expected-note@defs.h:106 0-1{{here}}
 enum ScopedEnum : int;
 ScopedEnum pre_scopedenum_declared; // ok