//===--- NameBinding.cpp - Name Binding -----------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
//  This file implements name binding for Swift.
//
//===----------------------------------------------------------------------===//

#include "swift/Subsystems.h"
#include "NameLookup.h"
#include "swift/AST/AST.h"
#include "swift/AST/Component.h"
#include "swift/AST/Diagnostics.h"
#include "swift/AST/ASTWalker.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/system_error.h"
#include "llvm/Support/Path.h"
using namespace swift;

//===----------------------------------------------------------------------===//
// NameBinder
//===----------------------------------------------------------------------===//

typedef TranslationUnit::ImportedModule ImportedModule;
typedef llvm::PointerUnion<const ImportedModule*, OneOfType*> BoundScope;

namespace {  
  class NameBinder {
    llvm::error_code findModule(StringRef Module, 
                                SourceLoc ImportLoc,
                                llvm::OwningPtr<llvm::MemoryBuffer> &Buffer);
    
  public:
    TranslationUnit *TU;
    ASTContext &Context;
    llvm::StringMap<TranslationUnit*> LoadedModules;
    bool ImportedBuiltinModule;

    NameBinder(TranslationUnit *TU)
    : TU(TU), Context(TU->Ctx), ImportedBuiltinModule(false) {
    }
    ~NameBinder() {
    }
    
    template<typename ...ArgTypes>
    InFlightDiagnostic diagnose(ArgTypes... Args) {
      return Context.Diags.diagnose(Args...);
    }
    
    void addImport(ImportDecl *ID, SmallVectorImpl<ImportedModule> &Result);
    void addStandardLibraryImport(SmallVectorImpl<ImportedModule> &Result);

    /// resolveIdentifierType - Perform name binding for a IdentifierType,
    /// resolving it or diagnosing the error as appropriate and return true on
    /// failure.  On failure, this leaves IdentifierType alone, otherwise it
    /// fills in the Components.
    bool resolveIdentifierType(IdentifierType *DNT);
    
  private:
    /// getModule - Load a module referenced by an import statement,
    /// emitting an error at the specified location and returning null on
    /// failure.
    Module *getModule(std::pair<Identifier,SourceLoc> ModuleID);
  };
}

llvm::error_code NameBinder::findModule(StringRef Module, 
                                        SourceLoc ImportLoc,
                                llvm::OwningPtr<llvm::MemoryBuffer> &Buffer) {
  std::string ModuleFilename = Module.str() + std::string(".swift");
  
  llvm::SmallString<128> InputFilename;
  
  // First, search in the directory corresponding to the import location.
  // FIXME: This screams for a proper FileManager abstraction.
  llvm::SourceMgr &SourceMgr = Context.SourceMgr;
  int CurrentBufferID = SourceMgr.FindBufferContainingLoc(ImportLoc.Value);
  if (CurrentBufferID >= 0) {
    const llvm::MemoryBuffer *ImportingBuffer 
      = SourceMgr.getBufferInfo(CurrentBufferID).Buffer;
    StringRef CurrentDirectory 
      = llvm::sys::path::parent_path(ImportingBuffer->getBufferIdentifier());
    if (!CurrentDirectory.empty()) {
      InputFilename = CurrentDirectory;
      llvm::sys::path::append(InputFilename, ModuleFilename);
      llvm::error_code Err = llvm::MemoryBuffer::getFile(InputFilename, Buffer);
      if (!Err)
        return Err;
    }
  }
  
  // Second, search in the current directory.
  llvm::error_code Err = llvm::MemoryBuffer::getFile(ModuleFilename, Buffer);
  if (!Err)
    return Err;

  // If we fail, search each import search path.
  for (auto Path : Context.ImportSearchPaths) {
    InputFilename = Path;
    llvm::sys::path::append(InputFilename, ModuleFilename);
    Err = llvm::MemoryBuffer::getFile(InputFilename, Buffer);
    if (!Err)
      return Err;
  }

  return Err;
}

Module *NameBinder::getModule(std::pair<Identifier, SourceLoc> ModuleID) {
  // TODO: We currently just recursively parse referenced modules.  This works
  // fine for now since they are each a single file.  Ultimately we'll want a
  // compiled form of AST's like clang's that support lazy deserialization.

  // FIXME: We shouldn't really allow arbitrary modules to import Builtin.
  if (ModuleID.first.str() == "Builtin") {
    ImportedBuiltinModule = true;
    return TU->Ctx.TheBuiltinModule;
  }

  TranslationUnit *ImportedTU = LoadedModules.lookup(ModuleID.first.str());
  if (ImportedTU) return ImportedTU;

  // Open the input file.
  llvm::OwningPtr<llvm::MemoryBuffer> InputFile;
  if (llvm::error_code Err = findModule(ModuleID.first.str(), ModuleID.second,
                                        InputFile)) {
    diagnose(ModuleID.second, diag::sema_opening_import,
             ModuleID.first.str(), Err.message());
    return 0;
  }

  unsigned BufferID =
    Context.SourceMgr.AddNewSourceBuffer(InputFile.take(),
                                         ModuleID.second.Value);

  // For now, treat all separate modules as unique components.
  Component *Comp = new (Context.Allocate<Component>(1)) Component();

  // Parse the translation unit, but don't do name binding or type checking.
  // This can produce new errors etc if the input is erroneous.
  ImportedTU = parseTranslationUnit(BufferID, Comp, Context,
                                    /*IsMainModule*/false);
  if (ImportedTU == 0)
    return 0;
  LoadedModules[ModuleID.first.str()] = ImportedTU;

  // We have to do name binding on it to ensure that types are fully resolved.
  // This should eventually be eliminated by having actual fully resolved binary
  // dumps of the code instead of reparsing though.
  // FIXME: We also need to deal with circular imports!
  performNameBinding(ImportedTU);
  performTypeChecking(ImportedTU);
  
  return ImportedTU;
}


void NameBinder::addImport(ImportDecl *ID, 
                           SmallVectorImpl<ImportedModule> &Result) {
  ArrayRef<ImportDecl::AccessPathElement> Path = ID->getAccessPath();
  Module *M = getModule(Path[0]);
  if (M == 0) return;
  
  // FIXME: Validate the access path against the module.  Reject things like
  // import swift.aslkdfja
  if (Path.size() > 2) {
    diagnose(Path[2].second, diag::invalid_declaration_imported);
    return;
  }
  
  Result.push_back(std::make_pair(Path.slice(1), M));
}

void NameBinder::
addStandardLibraryImport(SmallVectorImpl<ImportedModule> &Result) {
  // FIXME: The current model is that if a module doesn't explicitly import
  // Builtin or swift, we implicitly import swift.  This isn't really ideal.
  if (ImportedBuiltinModule)
    return;
  if (LoadedModules.lookup("swift"))
    return;
  if (TU->Name.str() == "swift")
    return;

  Identifier SwiftID = Context.getIdentifier("swift");
  Module *M = getModule(std::make_pair(SwiftID, TU->Body->getStartLoc()));
  if (M == 0) return;
  Result.push_back(std::make_pair(Module::AccessPathTy(), M));
}

/// resolveIdentifierType - Perform name binding for a IdentifierType,
/// resolving it or diagnosing the error as appropriate and return true on
/// failure.  On failure, this leaves IdentifierType alone, otherwise it fills
/// in the Components.
bool NameBinder::resolveIdentifierType(IdentifierType *DNT) {
  const MutableArrayRef<IdentifierType::Component> &Components =DNT->Components;
  
  // If name lookup for the base of the type didn't get resolved in the
  // parsing phase, do a global lookup for it.
  if (Components[0].Value.isNull()) {
    Identifier Name = Components[0].Id;
    SourceLoc Loc = Components[0].Loc;
    
    // Perform an unqualified lookup.
    SmallVector<ValueDecl*, 4> Decls;
    TU->lookupGlobalValue(Name, NLKind::UnqualifiedLookup, Decls);
    
    // If we find multiple results, we have an ambiguity error.
    // FIXME: This should be reevaluated and probably turned into a new NLKind.
    // Certain matches (e.g. of a function) should just be filtered out/ignored.
    if (Decls.size() > 1) {
      diagnose(Loc, diag::abiguous_type_base, Name)
        << SourceRange(Loc, Components.back().Loc);
      for (ValueDecl *D : Decls)
        diagnose(D->getLocStart(), diag::found_candidate);
      return true;
    }
    
    if (!Decls.empty()) {
      Components[0].Value = Decls[0];
    } else {
      // If that fails, this may be the name of a module, try looking that up.
      for (const ImportedModule &ImpEntry : TU->getImportedModules())
        if (ImpEntry.second->Name == Name) {
          Components[0].Value = ImpEntry.second;
          break;
        }
    
      // If we still don't have anything, we fail.
      if (Components[0].Value.isNull()) {
        diagnose(Loc, Components.size() == 1 ? 
                   diag::use_undeclared_type : diag::unknown_name_in_type, Name)
          << SourceRange(Loc, Components.back().Loc);
        return true;
      }
    }
  }
  
  assert(!Components[0].Value.isNull() && "Failed to get a base");
  
  // Now that we have a base, iteratively resolve subsequent member entries.
  auto LastOne = Components[0];
  for (auto &C : Components.slice(1, Components.size()-1)) {
    // TODO: Only support digging into modules so far.
    if (auto M = LastOne.Value.dyn_cast<Module*>()) {
#if 0
      // FIXME: Why is this lookupType instead of lookupValue?  How are they
      // different?
#endif
      C.Value = M->lookupType(Module::AccessPathTy(), C.Id, 
                              NLKind::QualifiedLookup);
    } else {
      diagnose(C.Loc, diag::unknown_dotted_type_base, LastOne.Id)
        << SourceRange(Components[0].Loc, Components.back().Loc);
      return true;
    }
    
    if (C.Value.isNull()) {
      diagnose(C.Loc, diag::invalid_member_type, C.Id, LastOne.Id)
      << SourceRange(Components[0].Loc, Components.back().Loc);
      return true;
    }
    
    LastOne = C;
  }
  
  // Finally, sanity check that the last value is a type.
  if (ValueDecl *Last = Components.back().Value.dyn_cast<ValueDecl*>())
    if (auto TAD = dyn_cast<TypeAliasDecl>(Last)) {
      Components[Components.size()-1].Value = TAD->getAliasType();
      return false;
    }

  diagnose(Components.back().Loc,
           Components.size() == 1 ? diag::named_definition_isnt_type :
             diag::dotted_reference_not_type, Components.back().Id)
    << SourceRange(Components[0].Loc, Components.back().Loc);
  return true;
}


//===----------------------------------------------------------------------===//
// performNameBinding
//===----------------------------------------------------------------------===//

/// BindNameToIVar - We have an unresolved reference to an identifier in some
/// FuncDecl.  Check to see if this is a reference to an instance variable,
/// and return an AST for the reference if so.  If not, return null with no
/// error emitted.
static Expr *BindNameToIVar(UnresolvedDeclRefExpr *UDRE, FuncDecl *CurFD, 
                            NameBinder &Binder) {
  Type ExtendedType = CurFD->getExtensionType();
  if (ExtendedType.isNull()) return 0;

  // For a static method, we perform name lookup in the corresponding metatype.
  TypeAliasDecl *StaticAlias = 0;
  if (CurFD->isStatic()) {
    if (ProtocolType *Proto = ExtendedType->getAs<ProtocolType>())
      StaticAlias = Proto->TheDecl;
    else if (OneOfType *OneOf = ExtendedType->getAs<OneOfType>())
      StaticAlias = OneOf->getDecl();
    else
      return 0;
    
    ExtendedType = MetaTypeType::get(StaticAlias);
  }
  
  // Do a full "dot syntax" name lookup with the implicit 'this' base.
  MemberLookup Lookup(ExtendedType, UDRE->getName(), *Binder.TU);
  
  // On failure, this isn't an member reference.
  if (!Lookup.isSuccess()) return 0;
  
  // On success, this is a member reference. Build either a reference to the
  // implicit 'this' VarDecl (for instance methods) or to the metaclass
  // instance (for static methods).
  Expr *BaseExpr;
  if (StaticAlias) {
    BaseExpr = new (Binder.Context) DeclRefExpr(StaticAlias, SourceLoc(),
                                      StaticAlias->getTypeOfReference());
  } else {
    VarDecl *ThisDecl = CurFD->getImplicitThisDecl();
    assert(ThisDecl && "Couldn't find decl for 'this'");
    BaseExpr = new (Binder.Context) DeclRefExpr(ThisDecl, SourceLoc(),
                                                ThisDecl->getTypeOfReference());
  }
  
  return Lookup.createResultAST(BaseExpr, SourceLoc(), UDRE->getLoc(),
                                Binder.Context);
}

/// BindName - Bind an UnresolvedDeclRefExpr by performing name lookup and
/// returning the resultant expression.  If this reference is inside of a
/// FuncDecl (i.e. in a function body, not at global scope) then CurFD is the
/// innermost function, otherwise null.
static Expr *BindName(UnresolvedDeclRefExpr *UDRE, FuncDecl *CurFD, 
                      NameBinder &Binder) {
  
  // If we are inside of a method, check to see if there are any ivars in scope,
  // and if so, whether this is a reference to one of them.
  if (CurFD)
    if (Expr *E = BindNameToIVar(UDRE, CurFD, Binder))
      return E;

  // Process UnresolvedDeclRefExpr by doing an unqualified lookup.
  Identifier Name = UDRE->getName();
  SourceLoc Loc = UDRE->getLoc();
  SmallVector<ValueDecl*, 4> Decls;
  // Perform standard value name lookup.
  Binder.TU->lookupGlobalValue(Name, NLKind::UnqualifiedLookup, Decls);

  // If that fails, this may be the name of a module, try looking that up.
  if (Decls.empty()) {
    for (const ImportedModule &ImpEntry : Binder.TU->getImportedModules())
      if (ImpEntry.second->Name == Name) {
        ModuleType *MT = ModuleType::get(ImpEntry.second);
        return new (Binder.Context) ModuleExpr(Loc, MT);
      }
  }

  if (Decls.empty()) {
    Binder.diagnose(Loc, diag::use_unresolved_identifier, Name);
    return new (Binder.Context) ErrorExpr(Loc);
  }

  return OverloadedDeclRefExpr::createWithCopy(Decls, Loc);
}


/// performNameBinding - Once parsing is complete, this walks the AST to
/// resolve names and do other top-level validation.
///
/// At this parsing has been performed, but we still have UnresolvedDeclRefExpr
/// nodes for unresolved value names, and we may have unresolved type names as
/// well.  This handles import directives and forward references.
void swift::performNameBinding(TranslationUnit *TU) {
  NameBinder Binder(TU);

  SmallVector<ImportedModule, 8> ImportedModules;

  // Do a prepass over the declarations to find and load the imported modules.
  for (auto Elt : TU->Body->getElements())
    if (Decl *D = Elt.dyn_cast<Decl*>()) {
      if (ImportDecl *ID = dyn_cast<ImportDecl>(D))
        Binder.addImport(ID, ImportedModules);
    }

  Binder.addStandardLibraryImport(ImportedModules);

  TU->setImportedModules(TU->Ctx.AllocateCopy(ImportedModules));

  // Loop over all the unresolved dotted types in the translation unit,
  // resolving them if possible.
  for (IdentifierType *DNT : TU->getUnresolvedIdentifierTypes()) {
    if (Binder.resolveIdentifierType(DNT)) {
      TypeBase *Error = TU->Ctx.TheErrorType.getPointer();

      // This IdentifierType resolved to the error type.
      for (auto &C : DNT->Components)
        C.Value = Error;
    }
  }

  struct NameBindingWalker : public ASTWalker {
    NameBinder &Binder;
    NameBindingWalker(NameBinder &binder) : Binder(binder) {}
    
    /// CurFuncDecls - This is the stack of FuncDecls that we're nested in.
    SmallVector<FuncDecl*, 4> CurFuncDecls;
    
    virtual bool walkToDeclPre(Decl *D) {
      if (FuncDecl *FD = dyn_cast<FuncDecl>(D)) {
        CurFuncDecls.push_back(FD);
        
        // If this is an instance method with a body, set the type of it's
        // implicit 'this' variable.
        if (FD->getBody())
          if (Type ThisTy = FD->computeThisType()) {
            // References to the 'this' declaration will add back the lvalue
            // type as appropriate.
            if (LValueType *LValue = ThisTy->getAs<LValueType>())
              ThisTy = LValue->getObjectType();
            
            FD->getImplicitThisDecl()->setType(ThisTy);
          }
      }
      return true;
    }
    
    virtual bool walkToDeclPost(Decl *D) {
      if (isa<FuncDecl>(D)) {
        assert(CurFuncDecls.back() == D && "Decl misbalance");
        CurFuncDecls.pop_back();
      }
      return true;
    }
    
    Expr *walkToExprPost(Expr *E) {
      if (UnresolvedDeclRefExpr *UDRE = dyn_cast<UnresolvedDeclRefExpr>(E)) {
        return BindName(UDRE, CurFuncDecls.empty() ? 0 : CurFuncDecls.back(),
                        Binder);
      }
      return E;
    }
  };
  NameBindingWalker walker(Binder);
  
  // Now that we know the top-level value names, go through and resolve any
  // UnresolvedDeclRefExprs that exist.
  TU->Body = cast<BraceStmt>(TU->Body->walk(walker));

  TU->ASTStage = TranslationUnit::NameBound;
  verify(TU);
}