[Modules TS] Module ownership semantics for redeclarations.

When declaring an entity in the "purview" of a module, it's never a
redeclaration of an entity in the purview of a default module or in no module
("in the global module"). Don't consider those other declarations as possible
redeclaration targets if they're not visible, and reject any cases where we
pick a prior visible declaration that violates this rule.

This reinstates r315251 and r315256, reverted in r315309 and r315308
respectively, tweaked to avoid triggering a linkage calculation when declaring
implicit special members (this exposed our pre-existing issue with typedef
names for linkage changing the linkage of types whose linkage has already been
computed and cached in more cases). A testcase for that regression has been
added in r315366.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315379 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 3 deletions

diff --git a/include/clang/Sema/Lookup.h b/include/clang/Sema/Lookup.h
index ea32997d40..546df8842a 100644
--- a/include/clang/Sema/Lookup.h
+++ b/include/clang/Sema/Lookup.h
@@ -139,6 +139,7 @@ public:
       LookupKind(LookupKind),
       IDNS(0),
       Redecl(Redecl != Sema::NotForRedeclaration),
+      ExternalRedecl(Redecl == Sema::ForExternalRedeclaration),
       HideTags(true),
       Diagnose(Redecl == Sema::NotForRedeclaration),
       AllowHidden(false),
@@ -161,6 +162,7 @@ public:
       LookupKind(LookupKind),
       IDNS(0),
       Redecl(Redecl != Sema::NotForRedeclaration),
+      ExternalRedecl(Redecl == Sema::ForExternalRedeclaration),
       HideTags(true),
       Diagnose(Redecl == Sema::NotForRedeclaration),
       AllowHidden(false),
@@ -181,6 +183,7 @@ public:
       LookupKind(Other.LookupKind),
       IDNS(Other.IDNS),
       Redecl(Other.Redecl),
+      ExternalRedecl(Other.ExternalRedecl),
       HideTags(Other.HideTags),
       Diagnose(false),
       AllowHidden(Other.AllowHidden),
@@ -201,7 +204,9 @@ public:
         SemaPtr(std::move(Other.SemaPtr)), NameInfo(std::move(Other.NameInfo)),
         NameContextRange(std::move(Other.NameContextRange)),
         LookupKind(std::move(Other.LookupKind)), IDNS(std::move(Other.IDNS)),
-        Redecl(std::move(Other.Redecl)), HideTags(std::move(Other.HideTags)),
+        Redecl(std::move(Other.Redecl)),
+        ExternalRedecl(std::move(Other.ExternalRedecl)),
+        HideTags(std::move(Other.HideTags)),
         Diagnose(std::move(Other.Diagnose)),
         AllowHidden(std::move(Other.AllowHidden)),
         Shadowed(std::move(Other.Shadowed)) {
@@ -221,6 +226,7 @@ public:
     LookupKind = std::move(Other.LookupKind);
     IDNS = std::move(Other.IDNS);
     Redecl = std::move(Other.Redecl);
+    ExternalRedecl = std::move(Other.ExternalRedecl);
     HideTags = std::move(Other.HideTags);
     Diagnose = std::move(Other.Diagnose);
     AllowHidden = std::move(Other.AllowHidden);
@@ -265,6 +271,17 @@ public:
     return Redecl;
   }
 
+  /// True if this lookup is just looking for an existing declaration to link
+  /// against a declaration with external linkage.
+  bool isForExternalRedeclaration() const {
+    return ExternalRedecl;
+  }
+
+  Sema::RedeclarationKind redeclarationKind() const {
+    return ExternalRedecl ? Sema::ForExternalRedeclaration :
+           Redecl ? Sema::ForVisibleRedeclaration : Sema::NotForRedeclaration;
+  }
+
   /// \brief Specify whether hidden declarations are visible, e.g.,
   /// for recovery reasons.
   void setAllowHidden(bool AH) {
@@ -275,7 +292,7 @@ public:
   /// declarations, such as those in modules that have not yet been imported.
   bool isHiddenDeclarationVisible(NamedDecl *ND) const {
     return AllowHidden ||
-           (isForRedeclaration() && ND->hasExternalFormalLinkage());
+           (isForExternalRedeclaration() && ND->isExternallyDeclarable());
   }
 
   /// Sets whether tag declarations should be hidden by non-tag
@@ -556,7 +573,8 @@ public:
 
   /// \brief Change this lookup's redeclaration kind.
   void setRedeclarationKind(Sema::RedeclarationKind RK) {
-    Redecl = RK;
+    Redecl = (RK != Sema::NotForRedeclaration);
+    ExternalRedecl = (RK == Sema::ForExternalRedeclaration);
     configure();
   }
 
@@ -719,6 +737,7 @@ private:
   unsigned IDNS; // set by configure()
 
   bool Redecl;
+  bool ExternalRedecl;
 
   /// \brief True if tag declarations should be hidden if non-tags
   ///   are present