SemaDecl.cpp

//===--- SemaDecl.cpp - Semantic Analysis for Declarations ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file implements semantic analysis for declarations.
//
//===----------------------------------------------------------------------===//

#include "Sema.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/ExprCXX.h"
#include "clang/Parse/DeclSpec.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/SourceManager.h"
// FIXME: layering (ideally, Sema shouldn't be dependent on Lex API's)
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/HeaderSearch.h" 
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <functional>
using namespace clang;

/// getDeclName - Return a pretty name for the specified decl if possible, or
/// an empty string if not.  This is used for pretty crash reporting. 
std::string Sema::getDeclName(DeclPtrTy d) {
  Decl *D = d.getAs<Decl>();
  if (NamedDecl *DN = dyn_cast_or_null<NamedDecl>(D))
    return DN->getQualifiedNameAsString();
  return "";
}

Sema::DeclGroupPtrTy Sema::ConvertDeclToDeclGroup(DeclPtrTy Ptr) {
  return DeclGroupPtrTy::make(DeclGroupRef(Ptr.getAs<Decl>()));
}

/// \brief If the identifier refers to a type name within this scope,
/// return the declaration of that type.
///
/// This routine performs ordinary name lookup of the identifier II
/// within the given scope, with optional C++ scope specifier SS, to
/// determine whether the name refers to a type. If so, returns an
/// opaque pointer (actually a QualType) corresponding to that
/// type. Otherwise, returns NULL.
///
/// If name lookup results in an ambiguity, this routine will complain
/// and then return NULL.
Sema::TypeTy *Sema::getTypeName(IdentifierInfo &II, SourceLocation NameLoc,
                                Scope *S, const CXXScopeSpec *SS) {
  // C++ [temp.res]p3:
  //   A qualified-id that refers to a type and in which the
  //   nested-name-specifier depends on a template-parameter (14.6.2)
  //   shall be prefixed by the keyword typename to indicate that the
  //   qualified-id denotes a type, forming an
  //   elaborated-type-specifier (7.1.5.3).
  //
  // We therefore do not perform any name lookup up SS is a dependent
  // scope name. FIXME: we will need to perform a special kind of
  // lookup if the scope specifier names a member of the current
  // instantiation.
  if (SS && isDependentScopeSpecifier(*SS))
    return 0;

  NamedDecl *IIDecl = 0;
  LookupResult Result = LookupParsedName(S, SS, &II, LookupOrdinaryName, 
                                         false, false);
  switch (Result.getKind()) {
  case LookupResult::NotFound:
  case LookupResult::FoundOverloaded:
    return 0;

  case LookupResult::AmbiguousBaseSubobjectTypes:
  case LookupResult::AmbiguousBaseSubobjects:
  case LookupResult::AmbiguousReference: {
    // Look to see if we have a type anywhere in the list of results.
    for (LookupResult::iterator Res = Result.begin(), ResEnd = Result.end();
         Res != ResEnd; ++Res) {
      if (isa<TypeDecl>(*Res) || isa<ObjCInterfaceDecl>(*Res)) {
        if (!IIDecl || 
            (*Res)->getLocation().getRawEncoding() < 
              IIDecl->getLocation().getRawEncoding())
          IIDecl = *Res;
      }
    }

    if (!IIDecl) {
      // None of the entities we found is a type, so there is no way
      // to even assume that the result is a type. In this case, don't
      // complain about the ambiguity. The parser will either try to
      // perform this lookup again (e.g., as an object name), which
      // will produce the ambiguity, or will complain that it expected
      // a type name.
      Result.Destroy();
      return 0;
    }

    // We found a type within the ambiguous lookup; diagnose the
    // ambiguity and then return that type. This might be the right
    // answer, or it might not be, but it suppresses any attempt to
    // perform the name lookup again.
    DiagnoseAmbiguousLookup(Result, DeclarationName(&II), NameLoc);
    break;
  }

  case LookupResult::Found:
    IIDecl = Result.getAsDecl();
    break;
  }

  if (IIDecl) {
    QualType T;
  
    if (TypeDecl *TD = dyn_cast<TypeDecl>(IIDecl)) {
      // Check whether we can use this type
      (void)DiagnoseUseOfDecl(IIDecl, NameLoc);
      
      T = Context.getTypeDeclType(TD);
    } else if (ObjCInterfaceDecl *IDecl = dyn_cast<ObjCInterfaceDecl>(IIDecl)) {
      // Check whether we can use this interface.
      (void)DiagnoseUseOfDecl(IIDecl, NameLoc);
      
      T = Context.getObjCInterfaceType(IDecl);
    } else
      return 0;

    if (SS)
      T = getQualifiedNameType(*SS, T);

    return T.getAsOpaquePtr();
  }

  return 0;
}

/// isTagName() - This method is called *for error recovery purposes only*
/// to determine if the specified name is a valid tag name ("struct foo").  If
/// so, this returns the TST for the tag corresponding to it (TST_enum,
/// TST_union, TST_struct, TST_class).  This is used to diagnose cases in C
/// where the user forgot to specify the tag.
DeclSpec::TST Sema::isTagName(IdentifierInfo &II, Scope *S) {
  // Do a tag name lookup in this scope.
  LookupResult R = LookupName(S, &II, LookupTagName, false, false);
  if (R.getKind() == LookupResult::Found)
    if (const TagDecl *TD = dyn_cast<TagDecl>(R.getAsDecl())) {
      switch (TD->getTagKind()) {
      case TagDecl::TK_struct: return DeclSpec::TST_struct;
      case TagDecl::TK_union:  return DeclSpec::TST_union;
      case TagDecl::TK_class:  return DeclSpec::TST_class;
      case TagDecl::TK_enum:   return DeclSpec::TST_enum;
      }
    }
  
  return DeclSpec::TST_unspecified;
}



DeclContext *Sema::getContainingDC(DeclContext *DC) {
  if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(DC)) {
    // A C++ out-of-line method will return to the file declaration context.
    if (MD->isOutOfLineDefinition())
      return MD->getLexicalDeclContext();

    // A C++ inline method is parsed *after* the topmost class it was declared
    // in is fully parsed (it's "complete").
    // The parsing of a C++ inline method happens at the declaration context of
    // the topmost (non-nested) class it is lexically declared in.
    assert(isa<CXXRecordDecl>(MD->getParent()) && "C++ method not in Record.");
    DC = MD->getParent();
    while (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(DC->getLexicalParent()))
      DC = RD;

    // Return the declaration context of the topmost class the inline method is
    // declared in.
    return DC;
  }

  if (isa<ObjCMethodDecl>(DC))
    return Context.getTranslationUnitDecl();

  return DC->getLexicalParent();
}

void Sema::PushDeclContext(Scope *S, DeclContext *DC) {
  assert(getContainingDC(DC) == CurContext &&
      "The next DeclContext should be lexically contained in the current one.");
  CurContext = DC;
  S->setEntity(DC);
}

void Sema::PopDeclContext() {
  assert(CurContext && "DeclContext imbalance!");

  CurContext = getContainingDC(CurContext);
}

/// \brief Determine whether we allow overloading of the function
/// PrevDecl with another declaration.
///
/// This routine determines whether overloading is possible, not
/// whether some new function is actually an overload. It will return
/// true in C++ (where we can always provide overloads) or, as an
/// extension, in C when the previous function is already an
/// overloaded function declaration or has the "overloadable"
/// attribute.
static bool AllowOverloadingOfFunction(Decl *PrevDecl, ASTContext &Context) {
  if (Context.getLangOptions().CPlusPlus)
    return true;

  if (isa<OverloadedFunctionDecl>(PrevDecl))
    return true;

  return PrevDecl->getAttr<OverloadableAttr>() != 0;
}

/// Add this decl to the scope shadowed decl chains.
void Sema::PushOnScopeChains(NamedDecl *D, Scope *S) {
  // Move up the scope chain until we find the nearest enclosing
  // non-transparent context. The declaration will be introduced into this
  // scope.
  while (S->getEntity() && 
         ((DeclContext *)S->getEntity())->isTransparentContext())
    S = S->getParent();

  S->AddDecl(DeclPtrTy::make(D));

  // Add scoped declarations into their context, so that they can be
  // found later. Declarations without a context won't be inserted
  // into any context.
  CurContext->addDecl(Context, D);

  // C++ [basic.scope]p4:
  //   -- exactly one declaration shall declare a class name or
  //   enumeration name that is not a typedef name and the other
  //   declarations shall all refer to the same object or
  //   enumerator, or all refer to functions and function templates;
  //   in this case the class name or enumeration name is hidden.
  if (TagDecl *TD = dyn_cast<TagDecl>(D)) {
    // We are pushing the name of a tag (enum or class).
    if (CurContext->getLookupContext() 
          == TD->getDeclContext()->getLookupContext()) {
      // We're pushing the tag into the current context, which might
      // require some reshuffling in the identifier resolver.
      IdentifierResolver::iterator
        I = IdResolver.begin(TD->getDeclName()),
        IEnd = IdResolver.end();
      if (I != IEnd && isDeclInScope(*I, CurContext, S)) {
        NamedDecl *PrevDecl = *I;
        for (; I != IEnd && isDeclInScope(*I, CurContext, S); 
             PrevDecl = *I, ++I) {
          if (TD->declarationReplaces(*I)) {
            // This is a redeclaration. Remove it from the chain and
            // break out, so that we'll add in the shadowed
            // declaration.
            S->RemoveDecl(DeclPtrTy::make(*I));
            if (PrevDecl == *I) {
              IdResolver.RemoveDecl(*I);
              IdResolver.AddDecl(TD);
              return;
            } else {
              IdResolver.RemoveDecl(*I);
              break;
            }
          }
        }

        // There is already a declaration with the same name in the same
        // scope, which is not a tag declaration. It must be found
        // before we find the new declaration, so insert the new
        // declaration at the end of the chain.
        IdResolver.AddShadowedDecl(TD, PrevDecl);
        
        return;
      }
    }
  } else if (isa<FunctionDecl>(D) &&
             AllowOverloadingOfFunction(D, Context)) {
    // We are pushing the name of a function, which might be an
    // overloaded name.
    FunctionDecl *FD = cast<FunctionDecl>(D);
    IdentifierResolver::iterator Redecl
      = std::find_if(IdResolver.begin(FD->getDeclName()),
                     IdResolver.end(),
                     std::bind1st(std::mem_fun(&NamedDecl::declarationReplaces),
                                  FD));
    if (Redecl != IdResolver.end() &&
        S->isDeclScope(DeclPtrTy::make(*Redecl))) {
      // There is already a declaration of a function on our
      // IdResolver chain. Replace it with this declaration.
      S->RemoveDecl(DeclPtrTy::make(*Redecl));
      IdResolver.RemoveDecl(*Redecl);
    }
  }

  IdResolver.AddDecl(D);
}

void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
  if (S->decl_empty()) return;
  assert((S->getFlags() & (Scope::DeclScope | Scope::TemplateParamScope)) &&
	 "Scope shouldn't contain decls!");

  for (Scope::decl_iterator I = S->decl_begin(), E = S->decl_end();
       I != E; ++I) {
    Decl *TmpD = (*I).getAs<Decl>();
    assert(TmpD && "This decl didn't get pushed??");

    assert(isa<NamedDecl>(TmpD) && "Decl isn't NamedDecl?");
    NamedDecl *D = cast<NamedDecl>(TmpD);

    if (!D->getDeclName()) continue;

    // Remove this name from our lexical scope.
    IdResolver.RemoveDecl(D);
  }
}

/// getObjCInterfaceDecl - Look up a for a class declaration in the scope.
/// return 0 if one not found.
ObjCInterfaceDecl *Sema::getObjCInterfaceDecl(IdentifierInfo *Id) {
  // The third "scope" argument is 0 since we aren't enabling lazy built-in
  // creation from this context.
  NamedDecl *IDecl = LookupName(TUScope, Id, LookupOrdinaryName);
  
  return dyn_cast_or_null<ObjCInterfaceDecl>(IDecl);
}

/// getNonFieldDeclScope - Retrieves the innermost scope, starting
/// from S, where a non-field would be declared. This routine copes
/// with the difference between C and C++ scoping rules in structs and
/// unions. For example, the following code is well-formed in C but
/// ill-formed in C++:
/// @code
/// struct S6 {
///   enum { BAR } e;
/// };
/// 
/// void test_S6() {
///   struct S6 a;
///   a.e = BAR;
/// }
/// @endcode
/// For the declaration of BAR, this routine will return a different
/// scope. The scope S will be the scope of the unnamed enumeration
/// within S6. In C++, this routine will return the scope associated
/// with S6, because the enumeration's scope is a transparent
/// context but structures can contain non-field names. In C, this
/// routine will return the translation unit scope, since the
/// enumeration's scope is a transparent context and structures cannot
/// contain non-field names.
Scope *Sema::getNonFieldDeclScope(Scope *S) {
  while (((S->getFlags() & Scope::DeclScope) == 0) ||
         (S->getEntity() && 
          ((DeclContext *)S->getEntity())->isTransparentContext()) ||
         (S->isClassScope() && !getLangOptions().CPlusPlus))
    S = S->getParent();
  return S;
}

void Sema::InitBuiltinVaListType() {
  if (!Context.getBuiltinVaListType().isNull())
    return;
  
  IdentifierInfo *VaIdent = &Context.Idents.get("__builtin_va_list");
  NamedDecl *VaDecl = LookupName(TUScope, VaIdent, LookupOrdinaryName);
  TypedefDecl *VaTypedef = cast<TypedefDecl>(VaDecl);
  Context.setBuiltinVaListType(Context.getTypedefType(VaTypedef));
}

/// LazilyCreateBuiltin - The specified Builtin-ID was first used at
/// file scope.  lazily create a decl for it. ForRedeclaration is true
/// if we're creating this built-in in anticipation of redeclaring the
/// built-in.
NamedDecl *Sema::LazilyCreateBuiltin(IdentifierInfo *II, unsigned bid,
                                     Scope *S, bool ForRedeclaration,
                                     SourceLocation Loc) {
  Builtin::ID BID = (Builtin::ID)bid;

  if (Context.BuiltinInfo.hasVAListUse(BID))
    InitBuiltinVaListType();

  Builtin::Context::GetBuiltinTypeError Error;
  QualType R = Context.BuiltinInfo.GetBuiltinType(BID, Context, Error);  
  switch (Error) {
  case Builtin::Context::GE_None:
    // Okay
    break;

  case Builtin::Context::GE_Missing_FILE:
    if (ForRedeclaration)
      Diag(Loc, diag::err_implicit_decl_requires_stdio)
        << Context.BuiltinInfo.GetName(BID);
    return 0;
  }

  if (!ForRedeclaration && Context.BuiltinInfo.isPredefinedLibFunction(BID)) {
    Diag(Loc, diag::ext_implicit_lib_function_decl)
      << Context.BuiltinInfo.GetName(BID)
      << R;
    if (Context.BuiltinInfo.getHeaderName(BID) &&
        Diags.getDiagnosticMapping(diag::ext_implicit_lib_function_decl)
          != diag::MAP_IGNORE)
      Diag(Loc, diag::note_please_include_header)
        << Context.BuiltinInfo.getHeaderName(BID)
        << Context.BuiltinInfo.GetName(BID);
  }

  FunctionDecl *New = FunctionDecl::Create(Context,
                                           Context.getTranslationUnitDecl(),
                                           Loc, II, R,
                                           FunctionDecl::Extern, false,
                                           /*hasPrototype=*/true);
  New->setImplicit();

  // Create Decl objects for each parameter, adding them to the
  // FunctionDecl.
  if (FunctionProtoType *FT = dyn_cast<FunctionProtoType>(R)) {
    llvm::SmallVector<ParmVarDecl*, 16> Params;
    for (unsigned i = 0, e = FT->getNumArgs(); i != e; ++i)
      Params.push_back(ParmVarDecl::Create(Context, New, SourceLocation(), 0,
                                           FT->getArgType(i), VarDecl::None, 0));
    New->setParams(Context, &Params[0], Params.size());
  }
  
  AddKnownFunctionAttributes(New);  
  
  // TUScope is the translation-unit scope to insert this function into.
  // FIXME: This is hideous. We need to teach PushOnScopeChains to
  // relate Scopes to DeclContexts, and probably eliminate CurContext
  // entirely, but we're not there yet.
  DeclContext *SavedContext = CurContext;
  CurContext = Context.getTranslationUnitDecl();
  PushOnScopeChains(New, TUScope);
  CurContext = SavedContext;
  return New;
}

/// GetStdNamespace - This method gets the C++ "std" namespace. This is where
/// everything from the standard library is defined.
NamespaceDecl *Sema::GetStdNamespace() {
  if (!StdNamespace) {
    IdentifierInfo *StdIdent = &PP.getIdentifierTable().get("std");
    DeclContext *Global = Context.getTranslationUnitDecl();
    Decl *Std = LookupQualifiedName(Global, StdIdent, LookupNamespaceName);
    StdNamespace = dyn_cast_or_null<NamespaceDecl>(Std);
  }
  return StdNamespace;
}

/// MergeTypeDefDecl - We just parsed a typedef 'New' which has the
/// same name and scope as a previous declaration 'Old'.  Figure out
/// how to resolve this situation, merging decls or emitting
/// diagnostics as appropriate. Returns true if there was an error,
/// false otherwise.
///
bool Sema::MergeTypeDefDecl(TypedefDecl *New, Decl *OldD) {
  bool objc_types = false;
  // Allow multiple definitions for ObjC built-in typedefs.
  // FIXME: Verify the underlying types are equivalent!
  if (getLangOptions().ObjC1) {
    const IdentifierInfo *TypeID = New->getIdentifier();
    switch (TypeID->getLength()) {
    default: break;
    case 2: 
      if (!TypeID->isStr("id"))
        break;
      Context.setObjCIdType(New);
      objc_types = true;
      break;
    case 5:
      if (!TypeID->isStr("Class"))
        break;
      Context.setObjCClassType(New);
      objc_types = true;
      return false;
    case 3:
      if (!TypeID->isStr("SEL"))
        break;
      Context.setObjCSelType(New);
      objc_types = true;
      return false;
    case 8:
      if (!TypeID->isStr("Protocol"))
        break;
      Context.setObjCProtoType(New->getUnderlyingType());
      objc_types = true;
      return false;
    }
    // Fall through - the typedef name was not a builtin type.
  }
  // Verify the old decl was also a type.
  TypeDecl *Old = dyn_cast<TypeDecl>(OldD);
  if (!Old) {
    Diag(New->getLocation(), diag::err_redefinition_different_kind) 
      << New->getDeclName();
    if (!objc_types)
      Diag(OldD->getLocation(), diag::note_previous_definition);
    return true;
  }

  // Determine the "old" type we'll use for checking and diagnostics.  
  QualType OldType;
  if (TypedefDecl *OldTypedef = dyn_cast<TypedefDecl>(Old))
    OldType = OldTypedef->getUnderlyingType();
  else
    OldType = Context.getTypeDeclType(Old);

  // If the typedef types are not identical, reject them in all languages and
  // with any extensions enabled.

  if (OldType != New->getUnderlyingType() && 
      Context.getCanonicalType(OldType) != 
      Context.getCanonicalType(New->getUnderlyingType())) {
    Diag(New->getLocation(), diag::err_redefinition_different_typedef)
      << New->getUnderlyingType() << OldType;
    if (!objc_types)
      Diag(Old->getLocation(), diag::note_previous_definition);
    return true;
  }
  if (objc_types) return false;
  if (getLangOptions().Microsoft) return false;

  // C++ [dcl.typedef]p2:
  //   In a given non-class scope, a typedef specifier can be used to
  //   redefine the name of any type declared in that scope to refer
  //   to the type to which it already refers.
  if (getLangOptions().CPlusPlus && !isa<CXXRecordDecl>(CurContext))
    return false;

  // In C, redeclaration of a type is a constraint violation (6.7.2.3p1).
  // Apparently GCC, Intel, and Sun all silently ignore the redeclaration if
  // *either* declaration is in a system header. The code below implements
  // this adhoc compatibility rule. FIXME: The following code will not
  // work properly when compiling ".i" files (containing preprocessed output).
  if (PP.getDiagnostics().getSuppressSystemWarnings()) {
    SourceManager &SrcMgr = Context.getSourceManager();
    if (SrcMgr.isInSystemHeader(Old->getLocation()))
      return false;
    if (SrcMgr.isInSystemHeader(New->getLocation()))
      return false;
  }

  Diag(New->getLocation(), diag::err_redefinition) << New->getDeclName();
  Diag(Old->getLocation(), diag::note_previous_definition);
  return true;
}

/// DeclhasAttr - returns true if decl Declaration already has the target
/// attribute.
static bool DeclHasAttr(const Decl *decl, const Attr *target) {
  for (const Attr *attr = decl->getAttrs(); attr; attr = attr->getNext())
    if (attr->getKind() == target->getKind())
      return true;

  return false;
}

/// MergeAttributes - append attributes from the Old decl to the New one.
static void MergeAttributes(Decl *New, Decl *Old, ASTContext &C) {
  Attr *attr = const_cast<Attr*>(Old->getAttrs());

  while (attr) {
    Attr *tmp = attr;
    attr = attr->getNext();

    if (!DeclHasAttr(New, tmp) && tmp->isMerged()) {
      tmp->setInherited(true);
      New->addAttr(tmp);
    } else {
      tmp->setNext(0);
      tmp->Destroy(C);
    }
  }

  Old->invalidateAttrs();
}

/// Used in MergeFunctionDecl to keep track of function parameters in
/// C.
struct GNUCompatibleParamWarning {
  ParmVarDecl *OldParm;
  ParmVarDecl *NewParm;
  QualType PromotedType;
};

/// MergeFunctionDecl - We just parsed a function 'New' from
/// declarator D which has the same name and scope as a previous
/// declaration 'Old'.  Figure out how to resolve this situation,
/// merging decls or emitting diagnostics as appropriate.
///
/// In C++, New and Old must be declarations that are not
/// overloaded. Use IsOverload to determine whether New and Old are
/// overloaded, and to select the Old declaration that New should be
/// merged with.
///
/// Returns true if there was an error, false otherwise.
bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD) {
  assert(!isa<OverloadedFunctionDecl>(OldD) && 
         "Cannot merge with an overloaded function declaration");

  // Verify the old decl was also a function.
  FunctionDecl *Old = dyn_cast<FunctionDecl>(OldD);
  if (!Old) {
    Diag(New->getLocation(), diag::err_redefinition_different_kind)
      << New->getDeclName();
    Diag(OldD->getLocation(), diag::note_previous_definition);
    return true;
  }

  // Determine whether the previous declaration was a definition,
  // implicit declaration, or a declaration.
  diag::kind PrevDiag;
  if (Old->isThisDeclarationADefinition())
    PrevDiag = diag::note_previous_definition;
  else if (Old->isImplicit())
    PrevDiag = diag::note_previous_implicit_declaration;
  else 
    PrevDiag = diag::note_previous_declaration;
  
  QualType OldQType = Context.getCanonicalType(Old->getType());
  QualType NewQType = Context.getCanonicalType(New->getType());
  
  if (!isa<CXXMethodDecl>(New) && !isa<CXXMethodDecl>(Old) &&
      New->getStorageClass() == FunctionDecl::Static &&
      Old->getStorageClass() != FunctionDecl::Static) {
    Diag(New->getLocation(), diag::err_static_non_static)
      << New;
    Diag(Old->getLocation(), PrevDiag);
    return true;
  }

  if (getLangOptions().CPlusPlus) {
    // (C++98 13.1p2):
    //   Certain function declarations cannot be overloaded:
    //     -- Function declarations that differ only in the return type 
    //        cannot be overloaded.
    QualType OldReturnType 
      = cast<FunctionType>(OldQType.getTypePtr())->getResultType();
    QualType NewReturnType 
      = cast<FunctionType>(NewQType.getTypePtr())->getResultType();
    if (OldReturnType != NewReturnType) {
      Diag(New->getLocation(), diag::err_ovl_diff_return_type);
      Diag(Old->getLocation(), PrevDiag) << Old << Old->getType();
      return true;
    }

    const CXXMethodDecl* OldMethod = dyn_cast<CXXMethodDecl>(Old);
    const CXXMethodDecl* NewMethod = dyn_cast<CXXMethodDecl>(New);
    if (OldMethod && NewMethod && 
        OldMethod->getLexicalDeclContext() == 
          NewMethod->getLexicalDeclContext()) {
      //    -- Member function declarations with the same name and the 
      //       same parameter types cannot be overloaded if any of them 
      //       is a static member function declaration.
      if (OldMethod->isStatic() || NewMethod->isStatic()) {
        Diag(New->getLocation(), diag::err_ovl_static_nonstatic_member);
        Diag(Old->getLocation(), PrevDiag) << Old << Old->getType();
        return true;
      }

      // C++ [class.mem]p1:
      //   [...] A member shall not be declared twice in the
      //   member-specification, except that a nested class or member
      //   class template can be declared and then later defined.
      unsigned NewDiag;
      if (isa<CXXConstructorDecl>(OldMethod))
        NewDiag = diag::err_constructor_redeclared;
      else if (isa<CXXDestructorDecl>(NewMethod))
        NewDiag = diag::err_destructor_redeclared;
      else if (isa<CXXConversionDecl>(NewMethod))
        NewDiag = diag::err_conv_function_redeclared;
      else
        NewDiag = diag::err_member_redeclared;
      
      Diag(New->getLocation(), NewDiag);
      Diag(Old->getLocation(), PrevDiag) << Old << Old->getType();
    }

    // (C++98 8.3.5p3):
    //   All declarations for a function shall agree exactly in both the
    //   return type and the parameter-type-list.
    if (OldQType == NewQType)
      return MergeCompatibleFunctionDecls(New, Old);

    // Fall through for conflicting redeclarations and redefinitions.
  }

  // C: Function types need to be compatible, not identical. This handles
  // duplicate function decls like "void f(int); void f(enum X);" properly.
  if (!getLangOptions().CPlusPlus &&
      Context.typesAreCompatible(OldQType, NewQType)) {
    const FunctionType *OldFuncType = OldQType->getAsFunctionType();
    const FunctionType *NewFuncType = NewQType->getAsFunctionType();
    const FunctionProtoType *OldProto = 0;
    if (isa<FunctionNoProtoType>(NewFuncType) &&
        (OldProto = dyn_cast<FunctionProtoType>(OldFuncType))) {
      // The old declaration provided a function prototype, but the
      // new declaration does not. Merge in the prototype.
      llvm::SmallVector<QualType, 16> ParamTypes(OldProto->arg_type_begin(),
                                                 OldProto->arg_type_end());
      NewQType = Context.getFunctionType(NewFuncType->getResultType(),
                                         &ParamTypes[0], ParamTypes.size(),
                                         OldProto->isVariadic(),
                                         OldProto->getTypeQuals());
      New->setType(NewQType);
      New->setInheritedPrototype();

      // Synthesize a parameter for each argument type.
      llvm::SmallVector<ParmVarDecl*, 16> Params;
      for (FunctionProtoType::arg_type_iterator 
             ParamType = OldProto->arg_type_begin(), 
             ParamEnd = OldProto->arg_type_end();
           ParamType != ParamEnd; ++ParamType) {
        ParmVarDecl *Param = ParmVarDecl::Create(Context, New,
                                                 SourceLocation(), 0,
                                                 *ParamType, VarDecl::None,
                                                 0);
        Param->setImplicit();
        Params.push_back(Param);
      }

      New->setParams(Context, &Params[0], Params.size());
    } 

    return MergeCompatibleFunctionDecls(New, Old);
  }

  // GNU C permits a K&R definition to follow a prototype declaration
  // if the declared types of the parameters in the K&R definition
  // match the types in the prototype declaration, even when the
  // promoted types of the parameters from the K&R definition differ
  // from the types in the prototype. GCC then keeps the types from
  // the prototype.
  if (!getLangOptions().CPlusPlus &&
      !getLangOptions().NoExtensions &&
      Old->hasPrototype() && !New->hasPrototype() &&
      New->getType()->getAsFunctionProtoType() &&
      Old->getNumParams() == New->getNumParams()) {
    llvm::SmallVector<QualType, 16> ArgTypes;
    llvm::SmallVector<GNUCompatibleParamWarning, 16> Warnings;
    const FunctionProtoType *OldProto 
      = Old->getType()->getAsFunctionProtoType();
    const FunctionProtoType *NewProto 
      = New->getType()->getAsFunctionProtoType();
    
    // Determine whether this is the GNU C extension.
    bool GNUCompatible = 
      Context.typesAreCompatible(OldProto->getResultType(),
                                 NewProto->getResultType()) &&
      (OldProto->isVariadic() == NewProto->isVariadic());
    for (unsigned Idx = 0, End = Old->getNumParams(); 
         GNUCompatible && Idx != End; ++Idx) {
      ParmVarDecl *OldParm = Old->getParamDecl(Idx);
      ParmVarDecl *NewParm = New->getParamDecl(Idx);
      if (Context.typesAreCompatible(OldParm->getType(), 
                                     NewProto->getArgType(Idx))) {
        ArgTypes.push_back(NewParm->getType());
      } else if (Context.typesAreCompatible(OldParm->getType(),
                                            NewParm->getType())) {
        GNUCompatibleParamWarning Warn 
          = { OldParm, NewParm, NewProto->getArgType(Idx) };
        Warnings.push_back(Warn);
        ArgTypes.push_back(NewParm->getType());
      } else
        GNUCompatible = false;
    }

    if (GNUCompatible) {
      for (unsigned Warn = 0; Warn < Warnings.size(); ++Warn) {
        Diag(Warnings[Warn].NewParm->getLocation(),
             diag::ext_param_promoted_not_compatible_with_prototype)
          << Warnings[Warn].PromotedType
          << Warnings[Warn].OldParm->getType();
        Diag(Warnings[Warn].OldParm->getLocation(), 
             diag::note_previous_declaration);
      }

      New->setType(Context.getFunctionType(NewProto->getResultType(),
                                           &ArgTypes[0], ArgTypes.size(),
                                           NewProto->isVariadic(),
                                           NewProto->getTypeQuals()));
      return MergeCompatibleFunctionDecls(New, Old);
    }

    // Fall through to diagnose conflicting types.
  }

  // A function that has already been declared has been redeclared or defined
  // with a different type- show appropriate diagnostic
  if (unsigned BuiltinID = Old->getBuiltinID(Context)) {
    // The user has declared a builtin function with an incompatible
    // signature.
    if (Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID)) {
      // The function the user is redeclaring is a library-defined
      // function like 'malloc' or 'printf'. Warn about the
      // redeclaration, then pretend that we don't know about this
      // library built-in.
      Diag(New->getLocation(), diag::warn_redecl_library_builtin) << New;
      Diag(Old->getLocation(), diag::note_previous_builtin_declaration)
        << Old << Old->getType();
      New->getIdentifier()->setBuiltinID(Builtin::NotBuiltin);
      Old->setInvalidDecl();
      return false;
    }

    PrevDiag = diag::note_previous_builtin_declaration;
  }

  Diag(New->getLocation(), diag::err_conflicting_types) << New->getDeclName();
  Diag(Old->getLocation(), PrevDiag) << Old << Old->getType();
  return true;
}

/// \brief Completes the merge of two function declarations that are
/// known to be compatible. 
///
/// This routine handles the merging of attributes and other
/// properties of function declarations form the old declaration to
/// the new declaration, once we know that New is in fact a
/// redeclaration of Old.
///
/// \returns false
bool Sema::MergeCompatibleFunctionDecls(FunctionDecl *New, FunctionDecl *Old) {
  // Merge the attributes
  MergeAttributes(New, Old, Context);

  // Merge the storage class.
  New->setStorageClass(Old->getStorageClass());

  // FIXME: need to implement inline semantics

  // Merge "pure" flag.
  if (Old->isPure())
    New->setPure();

  // Merge the "deleted" flag.
  if (Old->isDeleted())
    New->setDeleted();
  
  if (getLangOptions().CPlusPlus)
    return MergeCXXFunctionDecl(New, Old);

  return false;
}

/// MergeVarDecl - We just parsed a variable 'New' which has the same name
/// and scope as a previous declaration 'Old'.  Figure out how to resolve this
/// situation, merging decls or emitting diagnostics as appropriate.
///
/// Tentative definition rules (C99 6.9.2p2) are checked by 
/// FinalizeDeclaratorGroup. Unfortunately, we can't analyze tentative 
/// definitions here, since the initializer hasn't been attached.
/// 
bool Sema::MergeVarDecl(VarDecl *New, Decl *OldD) {
  // Verify the old decl was also a variable.
  VarDecl *Old = dyn_cast<VarDecl>(OldD);
  if (!Old) {
    Diag(New->getLocation(), diag::err_redefinition_different_kind)
      << New->getDeclName();
    Diag(OldD->getLocation(), diag::note_previous_definition);
    return true;
  }

  MergeAttributes(New, Old, Context);

  // Merge the types
  QualType MergedT = Context.mergeTypes(New->getType(), Old->getType());
  if (MergedT.isNull()) {
    Diag(New->getLocation(), diag::err_redefinition_different_type) 
      << New->getDeclName();
    Diag(Old->getLocation(), diag::note_previous_definition);
    return true;
  }
  New->setType(MergedT);

  // C99 6.2.2p4: Check if we have a static decl followed by a non-static.
  if (New->getStorageClass() == VarDecl::Static &&
      (Old->getStorageClass() == VarDecl::None ||
       Old->getStorageClass() == VarDecl::Extern)) {
    Diag(New->getLocation(), diag::err_static_non_static) << New->getDeclName();
    Diag(Old->getLocation(), diag::note_previous_definition);
    return true;
  }
  // C99 6.2.2p4: 
  //   For an identifier declared with the storage-class specifier
  //   extern in a scope in which a prior declaration of that
  //   identifier is visible,23) if the prior declaration specifies
  //   internal or external linkage, the linkage of the identifier at
  //   the later declaration is the same as the linkage specified at
  //   the prior declaration. If no prior declaration is visible, or
  //   if the prior declaration specifies no linkage, then the
  //   identifier has external linkage.
  if (New->hasExternalStorage() && Old->hasLinkage())
    /* Okay */;
  else if (New->getStorageClass() != VarDecl::Static &&
           Old->getStorageClass() == VarDecl::Static) {
    Diag(New->getLocation(), diag::err_non_static_static) << New->getDeclName();
    Diag(Old->getLocation(), diag::note_previous_definition);
    return true;
  }
  // Variables with external linkage are analyzed in FinalizeDeclaratorGroup.
  if (New->getStorageClass() != VarDecl::Extern && !New->isFileVarDecl() &&
      // Don't complain about out-of-line definitions of static members.
      !(Old->getLexicalDeclContext()->isRecord() &&
        !New->getLexicalDeclContext()->isRecord())) {
    Diag(New->getLocation(), diag::err_redefinition) << New->getDeclName();
    Diag(Old->getLocation(), diag::note_previous_definition);
    return true;
  }

  // Keep a chain of previous declarations.
  New->setPreviousDeclaration(Old);

  return false;
}

/// CheckParmsForFunctionDef - Check that the parameters of the given
/// function are appropriate for the definition of a function. This
/// takes care of any checks that cannot be performed on the
/// declaration itself, e.g., that the types of each of the function
/// parameters are complete.
bool Sema::CheckParmsForFunctionDef(FunctionDecl *FD) {
  bool HasInvalidParm = false;
  for (unsigned p = 0, NumParams = FD->getNumParams(); p < NumParams; ++p) {
    ParmVarDecl *Param = FD->getParamDecl(p);

    // C99 6.7.5.3p4: the parameters in a parameter type list in a
    // function declarator that is part of a function definition of
    // that function shall not have incomplete type.
    //
    // This is also C++ [dcl.fct]p6.
    if (!Param->isInvalidDecl() &&
        RequireCompleteType(Param->getLocation(), Param->getType(),
                               diag::err_typecheck_decl_incomplete_type)) {
      Param->setInvalidDecl();
      HasInvalidParm = true;
    }
    
    // C99 6.9.1p5: If the declarator includes a parameter type list, the
    // declaration of each parameter shall include an identifier.
    if (Param->getIdentifier() == 0 && 
        !Param->isImplicit() &&
        !getLangOptions().CPlusPlus)
      Diag(Param->getLocation(), diag::err_parameter_name_omitted);
  }

  return HasInvalidParm;
}

/// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
/// no declarator (e.g. "struct foo;") is parsed.
Sema::DeclPtrTy Sema::ParsedFreeStandingDeclSpec(Scope *S, DeclSpec &DS) {
  // FIXME: Error on auto/register at file scope
  // FIXME: Error on inline/virtual/explicit
  // FIXME: Error on invalid restrict
  // FIXME: Warn on useless const/volatile
  // FIXME: Warn on useless static/extern/typedef/private_extern/mutable
  // FIXME: Warn on useless attributes

  TagDecl *Tag = 0;
  if (DS.getTypeSpecType() == DeclSpec::TST_class ||
      DS.getTypeSpecType() == DeclSpec::TST_struct ||
      DS.getTypeSpecType() == DeclSpec::TST_union ||
      DS.getTypeSpecType() == DeclSpec::TST_enum)
    Tag = dyn_cast<TagDecl>(static_cast<Decl *>(DS.getTypeRep()));

  if (RecordDecl *Record = dyn_cast_or_null<RecordDecl>(Tag)) {
    if (!Record->getDeclName() && Record->isDefinition() &&
        DS.getStorageClassSpec() != DeclSpec::SCS_typedef) {
      if (getLangOptions().CPlusPlus ||
          Record->getDeclContext()->isRecord())
        return BuildAnonymousStructOrUnion(S, DS, Record);

      Diag(DS.getSourceRange().getBegin(), diag::err_no_declarators)
        << DS.getSourceRange();
    }

    // Microsoft allows unnamed struct/union fields. Don't complain
    // about them.
    // FIXME: Should we support Microsoft's extensions in this area?
    if (Record->getDeclName() && getLangOptions().Microsoft)
      return DeclPtrTy::make(Tag);
  }

  if (!DS.isMissingDeclaratorOk() && 
      DS.getTypeSpecType() != DeclSpec::TST_error) {
    // Warn about typedefs of enums without names, since this is an
    // extension in both Microsoft an GNU.
    if (DS.getStorageClassSpec() == DeclSpec::SCS_typedef &&
        Tag && isa<EnumDecl>(Tag)) {
      Diag(DS.getSourceRange().getBegin(), diag::ext_typedef_without_a_name)