//===--- GenClangDecl.cpp - Swift IRGen for imported Clang declarations ---===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "IRGenModule.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclGroup.h"
#include "clang/AST/GlobalDecl.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/CodeGen/ModuleBuilder.h"
#include "llvm/ADT/SmallPtrSet.h"

using namespace swift;
using namespace irgen;

namespace {
class ClangDeclRefFinder
    : public clang::RecursiveASTVisitor<ClangDeclRefFinder> {
  std::function<void(const clang::DeclRefExpr *)> callback;
public:
  template <typename Fn>
  explicit ClangDeclRefFinder(Fn fn) : callback(fn) {}

  bool VisitDeclRefExpr(clang::DeclRefExpr *DRE) {
    callback(DRE);
    return true;
  }
};

// If any (re)declaration of `decl` contains executable code, returns that
// redeclaration; otherwise, returns nullptr.
// In the case of a function, executable code is contained in the function
// definition. In the case of a variable, executable code can be contained in
// the initializer of the variable.
clang::Decl *getDeclWithExecutableCode(clang::Decl *decl) {
  if (auto fd = dyn_cast<clang::FunctionDecl>(decl)) {
    const clang::FunctionDecl *definition;
    if (fd->hasBody(definition)) {
      return const_cast<clang::FunctionDecl *>(definition);
    }
  } else if (auto vd = dyn_cast<clang::VarDecl>(decl)) {
    clang::VarDecl *initializingDecl = vd->getInitializingDeclaration();
    if (initializingDecl) {
      return initializingDecl;
    }
  }

  return nullptr;
}

} // end anonymous namespace

void IRGenModule::emitClangDecl(const clang::Decl *decl) {
  // Ignore this decl if we've seen it before.
  if (!GlobalClangDecls.insert(decl->getCanonicalDecl()).second)
    return;

  // Fast path for the case where `decl` doesn't contain executable code, so it
  // can't reference any other declarations that we would need to emit.
  if (getDeclWithExecutableCode(const_cast<clang::Decl *>(decl)) == nullptr) {
    ClangCodeGen->HandleTopLevelDecl(
                          clang::DeclGroupRef(const_cast<clang::Decl*>(decl)));
    return;
  }

  SmallVector<const clang::Decl *, 8> stack;
  stack.push_back(decl);

  ClangDeclRefFinder refFinder([&](const clang::DeclRefExpr *DRE) {
    const clang::Decl *D = DRE->getDecl();
    // Check that this is a file-level declaration and not inside a function.
    // If it's a member of a file-level decl, like a C++ static member variable,
    // we want to add the entire file-level declaration because Clang doesn't
    // expect to see members directly here.
    for (auto *DC = D->getDeclContext();; DC = DC->getParent()) {
      if (DC->isFunctionOrMethod())
        return;
      if (DC->isFileContext())
        break;
      D = cast<const clang::Decl>(DC);
    }
    if (!GlobalClangDecls.insert(D->getCanonicalDecl()).second)
      return;
    stack.push_back(D);
  });

  while (!stack.empty()) {
    auto *next = const_cast<clang::Decl *>(stack.pop_back_val());
    if (clang::Decl *executableDecl = getDeclWithExecutableCode(next)) {
        refFinder.TraverseDecl(executableDecl);
        next = executableDecl;
    }
    ClangCodeGen->HandleTopLevelDecl(clang::DeclGroupRef(next));
  }
}

llvm::Constant *
IRGenModule::getAddrOfClangGlobalDecl(clang::GlobalDecl global,
                                      ForDefinition_t forDefinition) {
  // Register the decl with the clang code generator.
  if (auto decl = global.getDecl())
    emitClangDecl(decl);

  return ClangCodeGen->GetAddrOfGlobal(global, (bool) forDefinition);
}

void IRGenModule::finalizeClangCodeGen() {
  // Ensure that code is emitted for any `PragmaCommentDecl`s. (These are
  // always guaranteed to be directly below the TranslationUnitDecl.)
  // In Clang, this happens automatically during the Sema phase, but here we
  // need to take care of it manually because our Clang CodeGenerator is not
  // attached to Clang Sema as an ASTConsumer.
  for (const auto *D : ClangASTContext->getTranslationUnitDecl()->decls()) {
    if (const auto *PCD = dyn_cast<clang::PragmaCommentDecl>(D)) {
      emitClangDecl(PCD);
    }
  }

  ClangCodeGen->HandleTranslationUnit(
      *const_cast<clang::ASTContext *>(ClangASTContext));
}