Implement redeclaration checking and hiding semantics for using declarations. There

are a couple of O(n^2) operations in this, some analogous to the usual O(n^2)
redeclaration problem and some not.  In particular, retroactively removing
shadow declarations when they're hidden by later decls is pretty unfortunate.
I'm not yet convinced it's worse than the alternative, though.

llvm-svn: 91045

1 files changed, 268 insertions, 38 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index d977ad6000d..f97b7637451 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -2925,12 +2925,146 @@ Sema::DeclPtrTy Sema::ActOnUsingDeclaration(Scope *S,
   return DeclPtrTy::make(UD);
 }
 
+/// Determines whether to create a using shadow decl for a particular
+/// decl, given the set of decls existing prior to this using lookup.
+bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
+                                const LookupResult &Previous) {
+  // Diagnose finding a decl which is not from a base class of the
+  // current class.  We do this now because there are cases where this
+  // function will silently decide not to build a shadow decl, which
+  // will pre-empt further diagnostics.
+  //
+  // We don't need to do this in C++0x because we do the check once on
+  // the qualifier.
+  //
+  // FIXME: diagnose the following if we care enough:
+  //   struct A { int foo; };
+  //   struct B : A { using A::foo; };
+  //   template <class T> struct C : A {};
+  //   template <class T> struct D : C<T> { using B::foo; } // <---
+  // This is invalid (during instantiation) in C++03 because B::foo
+  // resolves to the using decl in B, which is not a base class of D<T>.
+  // We can't diagnose it immediately because C<T> is an unknown
+  // specialization.  The UsingShadowDecl in D<T> then points directly
+  // to A::foo, which will look well-formed when we instantiate.
+  // The right solution is to not collapse the shadow-decl chain.
+  if (!getLangOptions().CPlusPlus0x && CurContext->isRecord()) {
+    DeclContext *OrigDC = Orig->getDeclContext();
+
+    // Handle enums and anonymous structs.
+    if (isa<EnumDecl>(OrigDC)) OrigDC = OrigDC->getParent();
+    CXXRecordDecl *OrigRec = cast<CXXRecordDecl>(OrigDC);
+    while (OrigRec->isAnonymousStructOrUnion())
+      OrigRec = cast<CXXRecordDecl>(OrigRec->getDeclContext());
+
+    if (cast<CXXRecordDecl>(CurContext)->isProvablyNotDerivedFrom(OrigRec)) {
+      if (OrigDC == CurContext) {
+        Diag(Using->getLocation(),
+             diag::err_using_decl_nested_name_specifier_is_current_class)
+          << Using->getNestedNameRange();
+        Diag(Orig->getLocation(), diag::note_using_decl_target);
+        return true;
+      }
+
+      Diag(Using->getNestedNameRange().getBegin(),
+           diag::err_using_decl_nested_name_specifier_is_not_base_class)
+        << Using->getTargetNestedNameDecl()
+        << cast<CXXRecordDecl>(CurContext)
+        << Using->getNestedNameRange();
+      Diag(Orig->getLocation(), diag::note_using_decl_target);
+      return true;
+    }
+  }
+
+  if (Previous.empty()) return false;
+
+  NamedDecl *Target = Orig;
+  if (isa<UsingShadowDecl>(Target))
+    Target = cast<UsingShadowDecl>(Target)->getTargetDecl();
+
+  if (Target->isFunctionOrFunctionTemplate()) {
+    FunctionDecl *FD;
+    if (isa<FunctionTemplateDecl>(Target))
+      FD = cast<FunctionTemplateDecl>(Target)->getTemplatedDecl();
+    else
+      FD = cast<FunctionDecl>(Target);
+
+    NamedDecl *OldDecl = 0;
+    switch (CheckOverload(FD, Previous, OldDecl)) {
+    case Ovl_Overload:
+      return false;
+
+    case Ovl_NonFunction:
+      Diag(Using->getLocation(), diag::err_using_decl_conflict)
+        << 0  // target decl is a function
+        << 1; // other decl is not a function
+      break;
+      
+    // We found a decl with the exact signature.
+    case Ovl_Match:
+      if (isa<UsingShadowDecl>(OldDecl)) {
+        // Silently ignore the possible conflict.
+        return false;
+      }
+
+      // If we're in a record, we want to hide the target, so we
+      // return true (without a diagnostic) to tell the caller not to
+      // build a shadow decl.
+      if (CurContext->isRecord())
+        return true;
+
+      // If we're not in a record, this is an error.
+      Diag(Using->getLocation(), diag::err_using_decl_conflict)
+        << 0  // target decl is a function
+        << 0; // other decl is a function
+      break;
+    }
+
+    Diag(Target->getLocation(), diag::note_using_decl_target);
+    Diag(OldDecl->getLocation(), diag::note_using_decl_conflict);
+    return true;
+  }
+
+  // Target is not a function.
+
+  // If the target happens to be one of the previous declarations, we
+  // don't have a conflict.
+  NamedDecl *NonTag = 0, *Tag = 0;
+  for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
+         I != E; ++I) {
+    NamedDecl *D = (*I)->getUnderlyingDecl();
+    if (D->getCanonicalDecl() == Target->getCanonicalDecl())
+      return false;
+
+    (isa<TagDecl>(D) ? Tag : NonTag) = D;
+  }
+
+  if (isa<TagDecl>(Target)) {
+    // No conflict between a tag and a non-tag.
+    if (!Tag) return false;
+
+    Diag(Using->getLocation(), diag::err_using_decl_conflict)
+      << 1 << 1; // both non-functions
+    Diag(Target->getLocation(), diag::note_using_decl_target);
+    Diag(Tag->getLocation(), diag::note_using_decl_conflict);
+    return true;
+  }
+
+  // No conflict between a tag and a non-tag.
+  if (!NonTag) return false;
+
+  Diag(Using->getLocation(), diag::err_using_decl_conflict)
+    << 1  // target not a function
+    << int(NonTag->isFunctionOrFunctionTemplate());
+  Diag(Target->getLocation(), diag::note_using_decl_target);
+  Diag(NonTag->getLocation(), diag::note_using_decl_conflict);
+  return true;
+}
+
 /// Builds a shadow declaration corresponding to a 'using' declaration.
 UsingShadowDecl *Sema::BuildUsingShadowDecl(Scope *S,
-                                            AccessSpecifier AS,
                                             UsingDecl *UD,
                                             NamedDecl *Orig) {
-  // FIXME: diagnose hiding, collisions
 
   // If we resolved to another shadow declaration, just coalesce them.
   NamedDecl *Target = Orig;
@@ -2948,47 +3082,58 @@ UsingShadowDecl *Sema::BuildUsingShadowDecl(Scope *S,
     PushOnScopeChains(Shadow, S);
   else
     CurContext->addDecl(Shadow);
-  Shadow->setAccess(AS);
+  Shadow->setAccess(UD->getAccess());
 
   if (Orig->isInvalidDecl() || UD->isInvalidDecl())
     Shadow->setInvalidDecl();
 
-  // If we haven't already declared the shadow decl invalid, check
-  // whether the decl comes from a base class of the current class.
-  // We don't have to do this in C++0x because we do the check once on
-  // the qualifier.
-  else if (!getLangOptions().CPlusPlus0x && CurContext->isRecord()) {
-    DeclContext *OrigDC = Orig->getDeclContext();
-
-    // Handle enums and anonymous structs.
-    if (isa<EnumDecl>(OrigDC)) OrigDC = OrigDC->getParent();
-    CXXRecordDecl *OrigRec = cast<CXXRecordDecl>(OrigDC);
-    while (OrigRec->isAnonymousStructOrUnion())
-      OrigRec = cast<CXXRecordDecl>(OrigRec->getDeclContext());
-
-    if (cast<CXXRecordDecl>(CurContext)->isProvablyNotDerivedFrom(OrigRec)) {
-      if (OrigDC == CurContext) {
-        Diag(UD->getLocation(),
-             diag::err_using_decl_nested_name_specifier_is_current_class)
-          << UD->getNestedNameRange();
-        Diag(Orig->getLocation(), diag::note_using_decl_target);
-        Shadow->setInvalidDecl();
-        return Shadow;
-      }
-
-      Diag(UD->getNestedNameRange().getBegin(),
-           diag::err_using_decl_nested_name_specifier_is_not_base_class)
-        << UD->getTargetNestedNameDecl()
-        << cast<CXXRecordDecl>(CurContext)
-        << UD->getNestedNameRange();
-      Diag(Orig->getLocation(), diag::note_using_decl_target);
-      return Shadow;
-    }
-  }
-
   return Shadow;
 }
 
+/// Hides a using shadow declaration.  This is required by the current
+/// using-decl implementation when a resolvable using declaration in a
+/// class is followed by a declaration which would hide or override
+/// one or more of the using decl's targets; for example:
+///
+///   struct Base { void foo(int); };
+///   struct Derived : Base {
+///     using Base::foo;
+///     void foo(int);
+///   };
+///
+/// The governing language is C++03 [namespace.udecl]p12:
+///
+///   When a using-declaration brings names from a base class into a
+///   derived class scope, member functions in the derived class
+///   override and/or hide member functions with the same name and
+///   parameter types in a base class (rather than conflicting).
+///
+/// There are two ways to implement this:
+///   (1) optimistically create shadow decls when they're not hidden
+///       by existing declarations, or
+///   (2) don't create any shadow decls (or at least don't make them
+///       visible) until we've fully parsed/instantiated the class.
+/// The problem with (1) is that we might have to retroactively remove
+/// a shadow decl, which requires several O(n) operations because the
+/// decl structures are (very reasonably) not designed for removal.
+/// (2) avoids this but is very fiddly and phase-dependent.
+void Sema::HideUsingShadowDecl(Scope *S, UsingShadowDecl *Shadow) {
+  // Remove it from the DeclContext...
+  Shadow->getDeclContext()->removeDecl(Shadow);
+
+  // ...and the scope, if applicable...
+  if (S) {
+    S->RemoveDecl(DeclPtrTy::make(static_cast<Decl*>(Shadow)));
+    IdResolver.RemoveDecl(Shadow);
+  }
+
+  // ...and the using decl.
+  Shadow->getUsingDecl()->removeShadowDecl(Shadow);
+
+  // TODO: complain somehow if Shadow was used.  It shouldn't
+  // be possible for this to happen, because 
+}
+
 /// Builds a using declaration.
 ///
 /// \param IsInstantiation - Whether this call arises from an
@@ -3014,9 +3159,35 @@ NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
     return 0;
   }
 
+  // Do the redeclaration lookup in the current scope.
+  LookupResult Previous(*this, Name, IdentLoc, LookupUsingDeclName,
+                        ForRedeclaration);
+  Previous.setHideTags(false);
+  if (S) {
+    LookupName(Previous, S);
+
+    // It is really dumb that we have to do this.
+    LookupResult::Filter F = Previous.makeFilter();
+    while (F.hasNext()) {
+      NamedDecl *D = F.next();
+      if (!isDeclInScope(D, CurContext, S))
+        F.erase();
+    }
+    F.done();
+  } else {
+    assert(IsInstantiation && "no scope in non-instantiation");
+    assert(CurContext->isRecord() && "scope not record in instantiation");
+    LookupQualifiedName(Previous, CurContext);
+  }
+
   NestedNameSpecifier *NNS =
     static_cast<NestedNameSpecifier *>(SS.getScopeRep());
 
+  // Check for invalid redeclarations.
+  if (CheckUsingDeclRedeclaration(UsingLoc, IsTypeName, SS, IdentLoc, Previous))
+    return 0;
+
+  // Check for bad qualifiers.
   if (CheckUsingDeclQualifier(UsingLoc, SS, IdentLoc))
     return 0;
 
@@ -3106,12 +3277,71 @@ NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
     return UD;
   }
 
-  for (LookupResult::iterator I = R.begin(), E = R.end(); I != E; ++I)
-    BuildUsingShadowDecl(S, AS, UD, *I);
+  for (LookupResult::iterator I = R.begin(), E = R.end(); I != E; ++I) {
+    if (!CheckUsingShadowDecl(UD, *I, Previous))
+      BuildUsingShadowDecl(S, UD, *I);
+  }
 
   return UD;
 }
 
+/// Checks that the given using declaration is not an invalid
+/// redeclaration.  Note that this is checking only for the using decl
+/// itself, not for any ill-formedness among the UsingShadowDecls.
+bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
+                                       bool isTypeName,
+                                       const CXXScopeSpec &SS,
+                                       SourceLocation NameLoc,
+                                       const LookupResult &Prev) {
+  // C++03 [namespace.udecl]p8:
+  // C++0x [namespace.udecl]p10:
+  //   A using-declaration is a declaration and can therefore be used
+  //   repeatedly where (and only where) multiple declarations are
+  //   allowed.
+  // That's only in file contexts.
+  if (CurContext->getLookupContext()->isFileContext())
+    return false;
+
+  NestedNameSpecifier *Qual
+    = static_cast<NestedNameSpecifier*>(SS.getScopeRep());
+
+  for (LookupResult::iterator I = Prev.begin(), E = Prev.end(); I != E; ++I) {
+    NamedDecl *D = *I;
+
+    bool DTypename;
+    NestedNameSpecifier *DQual;
+    if (UsingDecl *UD = dyn_cast<UsingDecl>(D)) {
+      DTypename = UD->isTypeName();
+      DQual = UD->getTargetNestedNameDecl();
+    } else if (UnresolvedUsingValueDecl *UD
+                 = dyn_cast<UnresolvedUsingValueDecl>(D)) {
+      DTypename = false;
+      DQual = UD->getTargetNestedNameSpecifier();
+    } else if (UnresolvedUsingTypenameDecl *UD
+                 = dyn_cast<UnresolvedUsingTypenameDecl>(D)) {
+      DTypename = true;
+      DQual = UD->getTargetNestedNameSpecifier();
+    } else continue;
+
+    // using decls differ if one says 'typename' and the other doesn't.
+    // FIXME: non-dependent using decls?
+    if (isTypeName != DTypename) continue;
+
+    // using decls differ if they name different scopes (but note that
+    // template instantiation can cause this check to trigger when it
+    // didn't before instantiation).
+    if (Context.getCanonicalNestedNameSpecifier(Qual) !=
+        Context.getCanonicalNestedNameSpecifier(DQual))
+      continue;
+
+    Diag(NameLoc, diag::err_using_decl_redeclaration) << SS.getRange();
+    Diag(D->getLocation(), diag::note_previous_using_decl);
+    return true;
+  }
+
+  return false;
+}
+
 
 /// Checks that the given nested-name qualifier used in a using decl
 /// in the current context is appropriately related to the current