//===-- ldmd.cpp - Drop-in DMD replacement wrapper for LDC ----------------===//
//
//                         LDC – the LLVM D compiler
//
// This file is distributed under the BSD-style LDC license, except for the
// command line handling code, which originated from DMD. See the LICENSE
// file for details.
//
//===----------------------------------------------------------------------===//
//
// Wrapper allowing use of LDC as drop-in replacement for DMD.
//
// The reason why full command line parsing is required instead of just
// rewriting the names of a few switches is an annoying impedance mismatch
// between the way how DMD handles arguments and the LLVM command line library:
// DMD allows all switches to be specified multiple times – in case of
// conflicts, the last one takes precedence. There is no easy way to replicate
// this behavior with LLVM, save parsing the switches and re-emitting a cleaned
// up string.
//
// DMD also reads switches from the DFLAGS enviroment variable, if present. This
// is contrary to what C compilers do, where CFLAGS is usually handled by the
// build system. Thus, conflicts like mentioned above occur quite frequently in
// practice in makefiles written for DMD, as DFLAGS is also a natural name for
// handling flags there.
//
// In order to maintain backwards compatibility with earlier versions of LDMD,
// unknown switches are passed through verbatim to LDC. Finding a better
// solution for this is tricky, as some of the LLVM arguments can be
// intentionally specified multiple times to get a certain effect (e.g. pass,
// linker options).
//
// Just as with the old LDMD script, arguments can be passed through unmodified
// to LDC by using -Csomearg.
//
// If maintaining this wrapper is deemed too messy at some point, an alternative
// would be to either extend the LLVM command line library to support the DMD
// semantics (unlikely to happen), or to abandon it altogether (except for
// passing the LLVM-defined flags to the various passes).
//
// Note: This program inherited ugly C-style string handling and memory leaks
// from DMD, but this should not be a problem due to the short-livedness of
// the process.
//
//===----------------------------------------------------------------------===//

#ifndef LDC_EXE_NAME
#error "Please define LDC_EXE_NAME to the name of the LDC executable to use."
#endif

#include "driver/exe_path.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Program.h"
#include "llvm/Support/SystemUtils.h"
#include "llvm/Support/raw_ostream.h"
#if _WIN32
#include "Windows.h"
#else
#include <sys/stat.h>
#endif
#include <cassert>
#include <cerrno>
#include <climits>
#include <cstdarg>
#include <cstdio>
#include <cstdlib>
#include <numeric>
#include <vector>

#ifdef HAVE_SC_ARG_MAX
#include <unistd.h>
#endif

namespace ls = llvm::sys;

// We reuse DMD's response file parsing routine for maximum compatibilty - it
// handles quotes in a very peculiar way.
int response_expand(size_t *pargc, char ***pargv);
void browse(const char *url);

/**
 * Prints a formatted error message to stderr and exits the program.
 */
void error(const char *fmt, ...) {
  va_list argp;
  va_start(argp, fmt);
  fprintf(stderr, "Error: ");
  vfprintf(stderr, fmt, argp);
  fprintf(stderr, "\n");
  exit(EXIT_FAILURE);
  va_end(argp);
}

/**
 * Prints a formatted warning message to stderr.
 */
void warning(const char *fmt, ...) {
  va_list argp;
  va_start(argp, fmt);
  fprintf(stderr, "Warning: ");
  vfprintf(stderr, fmt, argp);
  fprintf(stderr, "\n");
  va_end(argp);
}

char *concat(const char *a, const char *b) {
  size_t na = strlen(a);
  size_t nb = strlen(b);
  char *result = static_cast<char *>(malloc(na + nb + 1));
  assert(result);
  memcpy(result, a, na);
  memcpy(result + na, b, nb + 1);
  return result;
}

char *concat(const char *a, int b) {
  char bStr[14];
#if defined(_MSC_VER)
  _snprintf_s(bStr, _countof(bStr), sizeof(bStr), "%d", b);
#else
  snprintf(bStr, sizeof(bStr), "%d", b);
#endif
  return concat(a, bStr);
}

/**
 * Runs the given executable, returning its error code.
 */
int execute(const std::string &exePath, const char **args) {
  std::string errorMsg;
  int rc = ls::ExecuteAndWait(exePath, args, nullptr, nullptr, 0, 0, &errorMsg);
  if (!errorMsg.empty()) {
    error("Error executing %s: %s", exePath.c_str(), errorMsg.c_str());
  }
  return rc;
}

/**
 * Prints usage information to stdout.
 */
void printUsage(const char *argv0, const std::string &ldcPath) {
  // Print version information by actually invoking ldc -version.
  const char *args[] = {ldcPath.c_str(), "-version", nullptr};
  execute(ldcPath, args);

  printf(
      "\n\
Usage:\n\
  %s files.d ... { -switch }\n\
\n\
  files.d        D source files\n\
  @cmdfile       read arguments from cmdfile\n\
  -allinst       generate code for all template instantiations\n\
  -c             do not link\n\
  -color[=on|off]   force colored console output on or off\n\
  -conf=path     use config file at path\n\
  -cov           do code coverage analysis\n\
  -cov=nnn       require at least nnn%% code coverage\n\
  -D             generate documentation\n\
  -Dddocdir      write documentation file to docdir directory\n\
  -Dffilename    write documentation file to filename\n\
  -d             silently allow deprecated features\n\
  -dw            show use of deprecated features as warnings (default)\n\
  -de            show use of deprecated features as errors (halt compilation)\n\
  -debug         compile in debug code\n\
  -debug=level   compile in debug code <= level\n\
  -debug=ident   compile in debug code identified by ident\n\
  -debuglib=name    set symbolic debug library to name\n\
  -defaultlib=name  set default library to name\n\
  -deps          print module dependencies (imports/file/version/debug/lib)\n\
  -deps=filename write module dependencies to filename (only imports)\n\
  -dip25         implement http://wiki.dlang.org/DIP25 (experimental)\n\
  -fPIC          generate position independent code\n\
  -g             add symbolic debug info\n\
  -gc            add symbolic debug info, pretend to be C\n\
  -gs            always emit stack frame\n\
  -H             generate 'header' file\n\
  -Hddirectory   write 'header' file to directory\n\
  -Hffilename    write 'header' file to filename\n\
  --help         print help\n\
  -Ipath         where to look for imports\n\
  -ignore        ignore unsupported pragmas\n\
  -inline        do function inlining\n\
  -Jpath         where to look for string imports\n\
  -Llinkerflag   pass linkerflag to link\n\
  -lib           generate library rather than object files\n\
  -m32           generate 32 bit code\n\
  -m64           generate 64 bit code\n\
  -man           open web browser on manual page\n"
#if 0
"  -map           generate linker .map file\n"
#endif
"  -boundscheck=[on|safeonly|off]   bounds checks on, in @safe only, or off\n\
  -noboundscheck no array bounds checking (deprecated, use -boundscheck=off)\n\
  -O             optimize\n\
  -o-            do not write object file\n\
  -odobjdir      write object & library files to directory objdir\n\
  -offilename    name output file to filename\n\
  -op            do not strip paths from source file\n"
#if 0
"  -profile       profile runtime performance of generated code\n"
#endif
"  -property      enforce property syntax (deprecated, no effect)\n\
  -quiet         suppress unnecessary messages\n\
  -release       compile release version\n\
  -run srcfile args...   run resulting program, passing args\n\
  -shared        generate shared library\n\
  -transition=id show additional info about language change identified by 'id'\n\
  -transition=?  list all language changes\n\
  -unittest      compile in unit tests\n\
  -v             verbose\n\
  -vcolumns      print character (column) numbers in diagnostics\n\
  -vdmd          print the command used to invoke the underlying compiler\n\
  --version      print compiler version and exit\n\
  -version=level compile in version code >= level\n\
  -version=ident compile in version code identified by ident\n\
  -vtls          list all variables going into thread local storage\n\
  -vgc           list all gc allocations including hidden ones\n\
  -verrors=num   limit the number of error messages (0 means unlimited)\n\
  -w             enable warnings\n\
  -wi            enable informational warnings\n\
  -X             generate JSON file\n\
  -Xffilename    write JSON file to filename\n\n",
      argv0);
}

/**
 * Parses an enviroment variable for flags and appends them to given list of
 * arguments.
 *
 * This corresponds to getenv_setargv() in DMD, but we need to duplicate it
 * here since it is defined in mars.c.
 */
void appendEnvVar(const char *envVarName, std::vector<char *> &args) {
  char *env = getenv(envVarName);
  if (!env) {
    return;
  }

  env = strdup(env); // create our own writable copy

  size_t j = 1; // leave argv[0] alone
  while (1) {
    switch (*env) {
    case ' ':
    case '\t':
      env++;
      break;

    case 0:
      return;

    default:
      args.push_back(env); // append
      j++;
      char *p = env;
      int slash = 0;
      int instring = 0;
      char c = 0;

      while (1) {
        c = *env++;
        switch (c) {
        case '"':
          p -= (slash >> 1);
          if (slash & 1) {
            p--;
            goto Laddc;
          }
          instring ^= 1;
          slash = 0;
          continue;

        case ' ':
        case '\t':
          if (instring) {
            goto Laddc;
          }
          *p = 0;
          break;

        case '\\':
          slash++;
          *p++ = c;
          continue;

        case 0:
          *p = 0;
          return;

        default:
        Laddc:
          slash = 0;
          *p++ = c;
          continue;
        }
        break;
      }
    }
  }
}

struct BoundsCheck {
  enum Type { defaultVal, off, safeOnly, on };
};

struct Color {
  enum Type { automatic, on, off };
};

struct Debug {
  enum Type { none, normal, pretendC };
};

struct Deprecated {
  enum Type { allow, warn, error };
};

struct Model {
  enum Type { automatic, m32, m64 };
};

struct Warnings {
  enum Type { none, asErrors, informational };
};

struct Params {
  bool allinst = false;
  Deprecated::Type useDeprecated = Deprecated::warn;
  bool compileOnly = false;
  bool coverage = false;
  bool emitSharedLib = false;
  bool pic = false;
  bool emitMap = false;
  bool multiObj = false;
  Debug::Type debugInfo = Debug::none;
  bool alwaysStackFrame = false;
  Model::Type targetModel = Model::automatic;
  bool profile = false;
  bool verbose = false;
  bool vcolumns = false;
  bool vdmd = false;
  bool vgc = false;
  bool logTlsUse = false;
  unsigned errorLimit = 0;
  bool errorLimitSet = false;
  Warnings::Type warnings = Warnings::none;
  bool optimize = false;
  bool noObj = false;
  char *objDir = nullptr;
  char *objName = nullptr;
  bool preservePaths = false;
  bool generateDocs = false;
  char *docDir = nullptr;
  char *docName = nullptr;
  bool generateHeaders = false;
  char *headerDir = nullptr;
  char *headerName = nullptr;
  bool generateJson = false;
  char *jsonName = nullptr;
  bool ignoreUnsupportedPragmas = false;
  bool enforcePropertySyntax = false;
  bool enableInline = false;
  bool emitStaticLib = false;
  bool quiet = false;
  bool release = false;
  BoundsCheck::Type boundsChecks = BoundsCheck::defaultVal;
  bool emitUnitTests = false;
  std::vector<char *> modulePaths;
  std::vector<char *> importPaths;
  bool debugFlag = false;
  unsigned debugLevel = 0;
  std::vector<char *> debugIdentifiers;
  unsigned versionLevel = 0;
  std::vector<char *> versionIdentifiers;
  std::vector<char *> linkerSwitches;
  std::vector<char *> transitions;
  char *defaultLibName = nullptr;
  char *debugLibName = nullptr;
  char *moduleDepsFile = nullptr;
  Color::Type color = Color::automatic;
  bool useDIP25 = false;
  char *conf = nullptr;

  bool hiddenDebugB = false;
  bool hiddenDebugC = false;
  bool hiddenDebugF = false;
  bool hiddenDebugR = false;
  bool hiddenDebugX = false;
  bool hiddenDebugY = false;

  std::vector<char *> unknownSwitches;

  bool run = false;
  std::vector<char *> files;
  std::vector<char *> runArgs;
};

/**
 * Parses the flags from the given command line and the DFLAGS environment
 * variable into a Params struct.
 */
Params parseArgs(size_t originalArgc, char **originalArgv,
                 const std::string &ldcPath) {
  // Expand any response files present into the list of arguments.
  size_t argc = originalArgc;
  char **argv = originalArgv;
  if (response_expand(&argc, &argv)) {
    error("Could not read response file.");
  }

  std::vector<char *> args(argv, argv + argc);

  appendEnvVar("DFLAGS", args);

  Params result = Params();
  for (size_t i = 1; i < args.size(); i++) {
    char *p = args[i];
    if (*p == '-') {
      if (strcmp(p + 1, "allinst") == 0) {
        result.allinst = true;
      } else if (strcmp(p + 1, "de") == 0) {
        result.useDeprecated = Deprecated::error;
      } else if (strcmp(p + 1, "d") == 0) {
        result.useDeprecated = Deprecated::allow;
      } else if (strcmp(p + 1, "dw") == 0) {
        result.useDeprecated = Deprecated::warn;
      } else if (strcmp(p + 1, "c") == 0) {
        result.compileOnly = true;
      } else if (strncmp(p + 1, "color", 5) == 0) {
        result.color = Color::on;
        // Parse:
        //      -color
        //      -color=on|off
        if (p[6] == '=') {
          if (strcmp(p + 7, "off") == 0) {
            result.color = Color::off;
          } else if (strcmp(p + 7, "on") != 0) {
            goto Lerror;
          }
        } else if (p[6]) {
          goto Lerror;
        }
      } else if (strncmp(p + 1, "conf=", 5) == 0) {
        result.conf = p + 1 + 5;
      } else if (strcmp(p + 1, "cov") == 0) {
        // For "-cov=...", the whole cmdline switch is forwarded to LDC.
        // For plain "-cov", the cmdline switch must be explicitly forwarded
        // and result.coverage must be set to true to that effect.
        result.coverage = (p[4] != '=');
      } else if (strcmp(p + 1, "dip25") == 0) {
        result.useDIP25 = true;
      } else if (strcmp(p + 1, "shared") == 0
                 // backwards compatibility with old switch
                 || strcmp(p + 1, "dylib") == 0) {
        result.emitSharedLib = true;
      } else if (strcmp(p + 1, "fPIC") == 0) {
        result.pic = true;
      } else if (strcmp(p + 1, "map") == 0) {
        result.emitMap = true;
      } else if (strcmp(p + 1, "multiobj") == 0) {
        result.multiObj = true;
      } else if (strcmp(p + 1, "g") == 0) {
        result.debugInfo = Debug::normal;
      } else if (strcmp(p + 1, "gc") == 0) {
        result.debugInfo = Debug::pretendC;
      } else if (strcmp(p + 1, "gs") == 0) {
        result.alwaysStackFrame = true;
      } else if (strcmp(p + 1, "gt") == 0) {
        error("use -profile instead of -gt\n");
      } else if (strcmp(p + 1, "m32") == 0) {
        result.targetModel = Model::m32;
      } else if (strcmp(p + 1, "m64") == 0) {
        result.targetModel = Model::m64;
      } else if (strcmp(p + 1, "profile") == 0) {
        result.profile = true;
      } else if (memcmp(p + 1, "transition=", 11) == 0) {
        result.transitions.push_back(p + 1 + 11);
      } else if (strcmp(p + 1, "v") == 0) {
        result.verbose = true;
      } else if (strcmp(p + 1, "vcolumns") == 0) {
        result.vcolumns = true;
      } else if (strcmp(p + 1, "vdmd") == 0) {
        result.vdmd = true;
      } else if (strcmp(p + 1, "vgc") == 0) {
        result.vgc = true;
      } else if (strcmp(p + 1, "vtls") == 0) {
        result.logTlsUse = true;
      } else if (strcmp(p + 1, "v1") == 0) {
        error("use DMD 1.0 series compilers for -v1 switch");
        break;
      } else if (memcmp(p + 1, "verrors", 7) == 0) {
        if (p[8] == '=' && isdigit(static_cast<unsigned char>(p[9]))) {
          long num;
          char *endp;
          errno = 0;
          num = strtol(p + 9, &endp, 10);
          if (*endp || errno || num > INT_MAX) {
            goto Lerror;
          }
          // Bugzilla issue number
          result.errorLimit = static_cast<unsigned>(num);
          result.errorLimitSet = true;
        } else {
          goto Lerror;
        }
      } else if (strcmp(p + 1, "w") == 0) {
        result.warnings = Warnings::asErrors;
      } else if (strcmp(p + 1, "wi") == 0) {
        result.warnings = Warnings::informational;
      } else if (strcmp(p + 1, "O") == 0) {
        result.optimize = true;
      } else if (p[1] == 'o') {
        switch (p[2]) {
        case '-':
          result.noObj = true;
          break;

        case 'd':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.objDir = p + 3;
          break;

        case 'f':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.objName = p + 3;
          break;

        case 'p':
          if (p[3]) {
            goto Lerror;
          }
          result.preservePaths = 1;
          break;

        case 0:
          error("-o no longer supported, use -of or -od");
          break;

        default:
          goto Lerror;
        }
      } else if (p[1] == 'D') {
        result.generateDocs = true;
        switch (p[2]) {
        case 'd':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.docDir = p + 3;
          break;
        case 'f':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.docName = p + 3;
          break;

        case 0:
          break;

        default:
          goto Lerror;
        }
      } else if (p[1] == 'H') {
        result.generateHeaders = true;
        switch (p[2]) {
        case 'd':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.headerDir = p + 3;
          break;

        case 'f':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.headerName = p + 3;
          break;

        case 0:
          break;

        default:
          goto Lerror;
        }
      } else if (p[1] == 'X') {
        result.generateJson = true;
        switch (p[2]) {
        case 'f':
          if (!p[3]) {
            goto Lnoarg;
          }
          result.jsonName = p + 3;
          break;

        case 0:
          break;

        default:
          goto Lerror;
        }
      } else if (strcmp(p + 1, "ignore") == 0) {
        result.ignoreUnsupportedPragmas = true;
      } else if (strcmp(p + 1, "property") == 0) {
        result.enforcePropertySyntax = true;
      } else if (strcmp(p + 1, "inline") == 0) {
        result.enableInline = true;
      } else if (strcmp(p + 1, "lib") == 0) {
        result.emitStaticLib = true;
      } else if (strcmp(p + 1, "quiet") == 0) {
        result.quiet = 1;
      } else if (strcmp(p + 1, "release") == 0) {
        result.release = 1;
      } else if (strcmp(p + 1, "noboundscheck") == 0) {
        warning("The -noboundscheck switch is deprecated, use -boundscheck=off "
                "instead.");
        result.boundsChecks = BoundsCheck::off;
      } else if (memcmp(p + 1, "boundscheck", 11) == 0) {
        if (p[12] == '=') {
          if (strcmp(p + 13, "on") == 0) {
            result.boundsChecks = BoundsCheck::on;
          } else if (strcmp(p + 13, "safeonly") == 0) {
            result.boundsChecks = BoundsCheck::safeOnly;
          } else if (strcmp(p + 13, "off") == 0) {
            result.boundsChecks = BoundsCheck::off;
          } else {
            goto Lerror;
          }
        }
      } else if (strcmp(p + 1, "unittest") == 0) {
        result.emitUnitTests = 1;
      } else if (p[1] == 'I') {
        result.modulePaths.push_back(p + 2);
      } else if (p[1] == 'J') {
        result.importPaths.push_back(p + 2);
      } else if (memcmp(p + 1, "debug", 5) == 0 && p[6] != 'l') {
        // Parse:
        //      -debug
        //      -debug=number
        //      -debug=identifier
        if (p[6] == '=') {
          if (isdigit(static_cast<unsigned char>(p[7]))) {
            long level;

            errno = 0;
            level = strtol(p + 7, &p, 10);
            if (*p || errno || level > INT_MAX) {
              goto Lerror;
            }
            result.debugLevel = static_cast<int>(level);
          } else {
            result.debugIdentifiers.push_back(p + 7);
          }
        } else if (p[6]) {
          goto Lerror;
        } else {
          result.debugFlag = true;
        }
      } else if (memcmp(p + 1, "version", 5) == 0) {
        // Parse:
        //      -version=number
        //      -version=identifier
        if (p[8] == '=') {
          if (isdigit(static_cast<unsigned char>(p[9]))) {
            long level;

            errno = 0;
            level = strtol(p + 9, &p, 10);
            if (*p || errno || level > INT_MAX) {
              goto Lerror;
            }
            result.versionLevel = static_cast<int>(level);
          } else {
            result.versionIdentifiers.push_back(p + 9);
          }
        } else {
          goto Lerror;
        }
      } else if (strcmp(p + 1, "-b") == 0) {
        result.hiddenDebugB = 1;
      } else if (strcmp(p + 1, "-c") == 0) {
        result.hiddenDebugC = 1;
      } else if (strcmp(p + 1, "-f") == 0) {
        result.hiddenDebugF = 1;
      } else if (strcmp(p + 1, "-help") == 0) {
        printUsage(originalArgv[0], ldcPath);
        exit(EXIT_SUCCESS);
      } else if (strcmp(p + 1, "-version") == 0) {
        // Print version information by actually invoking ldc -version.
        const char *versionargs[] = {ldcPath.c_str(), "-version", nullptr};
        execute(ldcPath, versionargs);
        exit(EXIT_SUCCESS);
      } else if (strcmp(p + 1, "-r") == 0) {
        result.hiddenDebugR = 1;
      } else if (strcmp(p + 1, "-x") == 0) {
        result.hiddenDebugX = 1;
      } else if (strcmp(p + 1, "-y") == 0) {
        result.hiddenDebugY = 1;
      } else if (p[1] == 'L') {
        result.linkerSwitches.push_back(p + 2);
      } else if (memcmp(p + 1, "defaultlib=", 11) == 0) {
        result.defaultLibName = p + 1 + 11;
      } else if (memcmp(p + 1, "debuglib=", 9) == 0) {
        result.debugLibName = p + 1 + 9;
      } else if (memcmp(p + 1, "deps", 4) == 0) {
        result.moduleDepsFile = p + 1 + (p[1 + 4] == '=' ? 5 : 4);
      } else if (memcmp(p + 1, "man", 3) == 0) {
        browse("http://wiki.dlang.org/LDC");
        exit(EXIT_SUCCESS);
      } else if (strcmp(p + 1, "run") == 0) {
        result.run = true;
        int runargCount = ((i >= originalArgc) ? argc : originalArgc) - i - 1;
        if (runargCount) {
          result.files.push_back(argv[i + 1]);
          result.runArgs =
              std::vector<char *>(argv + i + 2, argv + i + runargCount + 1);
          i += runargCount;
        } else {
          result.run = false;
          goto Lnoarg;
        }
      } else if (p[1] == 'C') {
        result.unknownSwitches.push_back(concat("-", p + 2));
      } else {
      Lerror:
        result.unknownSwitches.push_back(p);
        continue;

      Lnoarg:
        error("argument expected for switch '%s'", p);
        continue;
      }
    } else {
      // FIXME: #if TARGET_WINDOS
      llvm::StringRef ext = ls::path::extension(p);
      if (ext.equals_lower("exe")) {
        result.objName = p;
        continue;
      }
      // #endif
      result.files.push_back(p);
    }
  }
  if (result.files.empty()) {
    printUsage(originalArgv[0], ldcPath);
    error("No source file specified.");
  }
  return result;
}

void pushSwitches(const char *prefix, const std::vector<char *> &vals,
                  std::vector<const char *> &r) {
  for (auto v : vals) {
    r.push_back(concat(prefix, v));
  }
}

/**
 * Appends the LDC command line parameters corresponding to the given set of
 * parameters to r.
 */
void buildCommandLine(std::vector<const char *> &r, const Params &p) {
  if (p.allinst) {
    r.push_back("-allinst");
  }
  if (p.useDeprecated == Deprecated::allow) {
    r.push_back("-d");
  }
  if (p.useDeprecated == Deprecated::error) {
    r.push_back("-de");
  }
  if (p.compileOnly) {
    r.push_back("-c");
  }
  if (p.coverage) {
    r.push_back("-cov");
  }
  if (p.emitSharedLib) {
    r.push_back("-shared");
  }
  if (p.pic) {
    r.push_back("-relocation-model=pic");
  }
  if (p.emitMap) {
    warning("Map file generation not yet supported by LDC.");
  }
  if (!p.emitStaticLib && ((!p.multiObj && !p.compileOnly) || p.objName)) {
    r.push_back("-singleobj");
  }
  if (p.debugInfo == Debug::normal) {
    r.push_back("-g");
  } else if (p.debugInfo == Debug::pretendC) {
    r.push_back("-gc");
  }
  if (p.alwaysStackFrame) {
    r.push_back("-disable-fp-elim");
  }
  if (p.targetModel == Model::m32) {
    r.push_back("-m32");
  } else if (p.targetModel == Model::m64) {
    r.push_back("-m64");
  }
  if (p.profile) {
    warning("CPU profile generation not yet supported by LDC.");
  }
  if (p.verbose) {
    r.push_back("-v");
  }
  if (p.vcolumns) {
    r.push_back("-vcolumns");
  }
  if (p.vgc) {
    r.push_back("-vgc");
  }
  if (p.logTlsUse) {
    r.push_back("-transition=tls");
  }
  if (p.errorLimitSet) {
    r.push_back(concat("-verrors=", p.errorLimit));
  }
  if (p.warnings == Warnings::asErrors) {
    r.push_back("-w");
  } else if (p.warnings == Warnings::informational) {
    r.push_back("-wi");
  }
  if (p.optimize) {
    r.push_back("-O3");
  }
  if (p.noObj) {
    r.push_back("-o-");
  }
  if (p.objDir) {
    r.push_back(concat("-od=", p.objDir));
  }
  if (p.objName) {
    r.push_back(concat("-of=", p.objName));
  }
  if (p.preservePaths) {
    r.push_back("-op");
  }
  if (p.generateDocs) {
    r.push_back("-D");
  }
  if (p.docDir) {
    r.push_back(concat("-Dd=", p.docDir));
  }
  if (p.docName) {
    r.push_back(concat("-Df=", p.docName));
  }
  if (p.generateHeaders) {
    r.push_back("-H");
  }
  if (p.headerDir) {
    r.push_back(concat("-Hd=", p.headerDir));
  }
  if (p.headerName) {
    r.push_back(concat("-Hf=", p.headerName));
  }
  if (p.generateJson) {
    r.push_back("-X");
  }
  if (p.jsonName) {
    r.push_back(concat("-Xf=", p.jsonName));
  }
  if (p.ignoreUnsupportedPragmas) {
    r.push_back("-ignore");
  }
  if (p.enforcePropertySyntax) {
    r.push_back("-property");
  }
  if (p.enableInline) {
    // -inline also influences .di generation with DMD.
    r.push_back("-enable-inlining");
    r.push_back("-Hkeep-all-bodies");
  }
  if (p.emitStaticLib) {
    r.push_back("-lib");
  }
  // -quiet is the default in (newer?) frontend versions, just ignore it.
  if (p.release) {
    r.push_back("-release"); // Also disables boundscheck.
  }
  if (p.boundsChecks == BoundsCheck::on) {
    r.push_back("-boundscheck=on");
  }
  if (p.boundsChecks == BoundsCheck::safeOnly) {
    r.push_back("-boundscheck=safeonly");
  }
  if (p.boundsChecks == BoundsCheck::off) {
    r.push_back("-boundscheck=off");
  }
  if (p.emitUnitTests) {
    r.push_back("-unittest");
  }
  pushSwitches("-I=", p.modulePaths, r);
  pushSwitches("-J=", p.importPaths, r);
  if (p.debugFlag) {
    r.push_back("-d-debug");
  }
  if (p.debugLevel) {
    r.push_back(concat("-d-debug=", p.debugLevel));
  }
  pushSwitches("-d-debug=", p.debugIdentifiers, r);
  if (p.versionLevel) {
    r.push_back(concat("-d-version=", p.versionLevel));
  }
  pushSwitches("-d-version=", p.versionIdentifiers, r);
  pushSwitches("-L=", p.linkerSwitches, r);
  pushSwitches("-transition=", p.transitions, r);
  if (p.defaultLibName) {
    r.push_back(concat("-defaultlib=", p.defaultLibName));
  }
  if (p.debugLibName) {
    r.push_back(concat("-debuglib=", p.debugLibName));
  }
  if (p.moduleDepsFile) {
    r.push_back(p.moduleDepsFile[0] == 0 ? "-deps"
                                         : concat("-deps=", p.moduleDepsFile));
  }
  if (p.color == Color::on) {
    r.push_back("-enable-color");
  }
  if (p.color == Color::off) {
    r.push_back("-disable-color");
  }
  if (p.useDIP25) {
    r.push_back("-dip25");
  }
  if (p.conf) {
    r.push_back(concat("-conf=", p.conf));
  }
  if (p.hiddenDebugB) {
    r.push_back("-hidden-debug-b");
  }
  if (p.hiddenDebugC) {
    r.push_back("-hidden-debug-c");
  }
  if (p.hiddenDebugF) {
    r.push_back("-hidden-debug-f");
  }
  if (p.hiddenDebugR) {
    r.push_back("-hidden-debug-r");
  }
  if (p.hiddenDebugX) {
    r.push_back("-hidden-debug-x");
  }
  if (p.hiddenDebugY) {
    r.push_back("-hidden-debug-y");
  }
  r.insert(r.end(), p.unknownSwitches.begin(), p.unknownSwitches.end());
  if (p.run) {
    r.push_back("-run");
  }
  r.insert(r.end(), p.files.begin(), p.files.end());
  r.insert(r.end(), p.runArgs.begin(), p.runArgs.end());
}

/**
 * Returns the OS-dependent length limit for the command line when invoking
 * subprocesses.
 */
size_t maxCommandLineLen() {
#if defined(HAVE_SC_ARG_MAX)
  // http://www.in-ulm.de/~mascheck/various/argmax – the factor 2 is just
  // a wild guess to account for the enviroment.
  return sysconf(_SC_ARG_MAX) / 2;
#elif defined(_WIN32)
  // http://blogs.msdn.com/b/oldnewthing/archive/2003/12/10/56028.aspx
  return 32767;
#else
#error "Do not know how to determine maximum command line length."
#endif
}

/**
 * Tries to locate an executable with the given name, or an invalid path if
 * nothing was found. Search paths: 1. Directory where this binary resides.
 * 2. System PATH.
 */
std::string locateBinary(std::string exeName) {
  std::string path = exe_path::prependBinDir(exeName.c_str());
  if (ls::fs::can_execute(path)) {
    return path;
  }

#if LDC_LLVM_VER >= 306
  llvm::ErrorOr<std::string> res = ls::findProgramByName(exeName);
  path = res ? res.get() : std::string();
#else
  path = ls::FindProgramByName(exeName);
#endif
  if (ls::fs::can_execute(path)) {
    return path;
  }

  return "";
}

/**
 * Makes sure the given directory (absolute or relative) exists on disk.
 */
static void createOutputDir(const char *dir) {
  if (ls::fs::create_directories(dir)) {
    error("Could not create output directory '%s'.", dir);
  }
}

static size_t addStrlen(size_t acc, const char *str) {
  if (!str) {
    return acc;
  }
  return acc + strlen(str);
}

// In driver/main.d
int main(int argc, char **argv);

int cppmain(int argc, char **argv) {
  exe_path::initialize(argv[0]);

  std::string ldcExeName = LDC_EXE_NAME;
#ifdef _WIN32
  ldcExeName += ".exe";
#endif
  std::string ldcPath = locateBinary(ldcExeName);
  if (ldcPath.empty()) {
    error("Could not locate " LDC_EXE_NAME " executable.");
  }

  // We need to manually set up argv[0] and the terminating NULL.
  std::vector<const char *> args;
  args.push_back(ldcPath.c_str());

  Params p = parseArgs(argc, argv, ldcPath);
  buildCommandLine(args, p);
  if (p.vdmd) {
    printf(" -- Invoking:");
    for (auto &arg : args) {
      printf(" %s", arg);
    }
    puts("");
  }

  args.push_back(nullptr);

  // On Linux, DMD creates output directores that don't already exist, while
  // LDC does not (and neither does GDC). Do this here for rdmd compatibility.
  if (p.objName) {
    llvm::SmallString<256> outputPath(p.objName);
    ls::path::remove_filename(outputPath);
    if (!outputPath.empty()) {
      createOutputDir(outputPath.c_str());
    }
  }

  if (p.objDir) {
    createOutputDir(p.objDir);
  }

  // Check if we need to write out a response file.
  size_t totalLen = std::accumulate(args.begin(), args.end(), 0, addStrlen);
  if (totalLen > maxCommandLineLen()) {
    int rspFd;
    llvm::SmallString<128> rspPath;
    if (ls::fs::createUniqueFile("ldmd-%%-%%-%%-%%.rsp", rspFd, rspPath)) {
      error("Could not open temporary response file.");
    }

    {
      llvm::raw_fd_ostream rspOut(rspFd, /*shouldClose=*/true);
      for (auto arg : args) {
        rspOut << arg << '\n';
      }
    }

    std::string rspArg = "@";
    rspArg += rspPath.str();

    std::vector<const char *> newArgs;
    newArgs.push_back(argv[0]);
    newArgs.push_back(rspArg.c_str());
    newArgs.push_back(nullptr);

    int rc = execute(ldcPath, &newArgs[0]);

    if (ls::fs::remove(rspPath.str())) {
      warning("Could not remove response file.");
    }

    return rc;
  }
  return execute(ldcPath, &args[0]);
}