path: root/third_party/nix/src/nix/repl.cc

#include <climits>
#include <csetjmp>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <utility>

#include <absl/strings/ascii.h>
#include <absl/strings/match.h>
#include <glog/logging.h>

#ifdef READLINE
#include <readline/history.h>
#include <readline/readline.h>
#else
// editline < 1.15.2 don't wrap their API for C++ usage
// (added in
// https://github.com/troglobit/editline/commit/91398ceb3427b730995357e9d120539fb9bb7461).
// This results in linker errors due to to name-mangling of editline C symbols.
// For compatibility with these versions, we wrap the API here
// (wrapping multiple times on newer versions is no problem).
extern "C" {
#include <editline.h>
}
#endif

#include "libexpr/common-eval-args.hh"
#include "libexpr/eval-inline.hh"
#include "libexpr/eval.hh"
#include "libexpr/get-drvs.hh"
#include "libmain/shared.hh"
#include "libstore/derivations.hh"
#include "libstore/globals.hh"
#include "libstore/store-api.hh"
#include "libutil/affinity.hh"
#include "libutil/finally.hh"
#include "nix/command.hh"

namespace nix {

#define ESC_RED "\033[31m"
#define ESC_GRE "\033[32m"
#define ESC_YEL "\033[33m"
#define ESC_BLU "\033[34;1m"
#define ESC_MAG "\033[35m"
#define ESC_CYA "\033[36m"
#define ESC_END "\033[0m"

struct NixRepl {
  std::string curDir;
  EvalState state;
  Bindings* autoArgs;

  Strings loadedFiles;

  const static int envSize = 32768;
  StaticEnv staticEnv;
  Env* env;
  int displ;
  StringSet varNames;

  const Path historyFile;

  NixRepl(const Strings& searchPath, const nix::ref<Store>& store);
  ~NixRepl();
  void mainLoop(const std::vector<std::string>& files);
  StringSet completePrefix(const std::string& prefix);
  static bool getLine(std::string& input, const std::string& prompt);
  Path getDerivationPath(Value& v);
  bool processLine(std::string line);
  void loadFile(const Path& path);
  void initEnv();
  void reloadFiles();
  void addAttrsToScope(Value& attrs);
  void addVarToScope(const Symbol& name, Value& v);
  Expr* parseString(const std::string& s);
  void evalString(std::string s, Value& v);

  using ValuesSeen = std::set<Value*>;
  std::ostream& printValue(std::ostream& str, Value& v, unsigned int maxDepth);
  std::ostream& printValue(std::ostream& str, Value& v, unsigned int maxDepth,
                           ValuesSeen& seen);
};

void printHelp() {
  std::cout << "Usage: nix-repl [--help] [--version] [-I path] paths...\n"
            << "\n"
            << "nix-repl is a simple read-eval-print loop (REPL) for the Nix "
               "package manager.\n"
            << "\n"
            << "Options:\n"
            << "    --help\n"
            << "        Prints out a summary of the command syntax and exits.\n"
            << "\n"
            << "    --version\n"
            << "        Prints out the Nix version number on standard output "
               "and exits.\n"
            << "\n"
            << "    -I path\n"
            << "        Add a path to the Nix expression search path. This "
               "option may be given\n"
            << "        multiple times. See the NIX_PATH environment variable "
               "for information on\n"
            << "        the semantics of the Nix search path. Paths added "
               "through -I take\n"
            << "        precedence over NIX_PATH.\n"
            << "\n"
            << "    paths...\n"
            << "        A list of paths to files containing Nix expressions "
               "which nix-repl will\n"
            << "        load and add to its scope.\n"
            << "\n"
            << "        A path surrounded in < and > will be looked up in the "
               "Nix expression search\n"
            << "        path, as in the Nix language itself.\n"
            << "\n"
            << "        If an element of paths starts with http:// or "
               "https://, it is interpreted\n"
            << "        as the URL of a tarball that will be downloaded and "
               "unpacked to a temporary\n"
            << "        location. The tarball must include a single top-level "
               "directory containing\n"
            << "        at least a file named default.nix.\n";
}

std::string removeWhitespace(std::string s) {
  s = absl::StripTrailingAsciiWhitespace(s);
  size_t n = s.find_first_not_of(" \n\r\t");
  if (n != std::string::npos) {
    s = std::string(s, n);
  }
  return s;
}

NixRepl::NixRepl(const Strings& searchPath, const nix::ref<Store>& store)
    : state(searchPath, store),
      staticEnv(false, &state.staticBaseEnv),
      historyFile(getDataDir() + "/nix/repl-history") {
  curDir = absPath(".");
}

NixRepl::~NixRepl() { write_history(historyFile.c_str()); }

static NixRepl* curRepl;  // ugly

static char* completionCallback(char* s, int* match) {
  auto possible = curRepl->completePrefix(s);
  if (possible.size() == 1) {
    *match = 1;
    auto* res = strdup(possible.begin()->c_str() + strlen(s));
    if (res == nullptr) {
      throw Error("allocation failure");
    }
    return res;
  }
  if (possible.size() > 1) {
    auto checkAllHaveSameAt = [&](size_t pos) {
      auto& first = *possible.begin();
      for (auto& p : possible) {
        if (p.size() <= pos || p[pos] != first[pos]) {
          return false;
        }
      }
      return true;
    };
    size_t start = strlen(s);
    size_t len = 0;
    while (checkAllHaveSameAt(start + len)) {
      ++len;
    }
    if (len > 0) {
      *match = 1;
      auto* res = strdup(std::string(*possible.begin(), start, len).c_str());
      if (res == nullptr) {
        throw Error("allocation failure");
      }
      return res;
    }
  }

  *match = 0;
  return nullptr;
}

static int listPossibleCallback(char* s, char*** avp) {
  auto possible = curRepl->completePrefix(s);

  if (possible.size() > (INT_MAX / sizeof(char*))) {
    throw Error("too many completions");
  }

  int ac = 0;
  char** vp = nullptr;

  auto check = [&](auto* p) {
    if (!p) {
      if (vp) {
        while (--ac >= 0) {
          free(vp[ac]);
        }
        free(vp);
      }
      throw Error("allocation failure");
    }
    return p;
  };

  vp = check((char**)malloc(possible.size() * sizeof(char*)));

  for (auto& p : possible) {
    vp[ac++] = check(strdup(p.c_str()));
  }

  *avp = vp;

  return ac;
}

namespace {
// Used to communicate to NixRepl::getLine whether a signal occurred in
// ::readline.
volatile sig_atomic_t g_signal_received = 0;

void sigintHandler(int signo) { g_signal_received = signo; }
}  // namespace

void NixRepl::mainLoop(const std::vector<std::string>& files) {
  std::string error = ANSI_RED "error:" ANSI_NORMAL " ";
  std::cout << "Welcome to Nix version " << nixVersion << ". Type :? for help."
            << std::endl
            << std::endl;

  for (auto& i : files) {
    loadedFiles.push_back(i);
  }

  reloadFiles();
  if (!loadedFiles.empty()) {
    std::cout << std::endl;
  }

  // Allow nix-repl specific settings in .inputrc
  rl_readline_name = "nix-repl";
  createDirs(dirOf(historyFile));
#ifndef READLINE
  el_hist_size = 1000;
#endif
  read_history(historyFile.c_str());
  curRepl = this;
#ifndef READLINE
  rl_set_complete_func(completionCallback);
  rl_set_list_possib_func(listPossibleCallback);
#endif

  std::string input;

  while (true) {
    // When continuing input from previous lines, don't print a prompt, just
    // align to the same number of chars as the prompt.
    if (!getLine(input, input.empty() ? "nix-repl> " : "          ")) {
      break;
    }

    try {
      if (!removeWhitespace(input).empty() && !processLine(input)) {
        return;
      }
    } catch (ParseError& e) {
      if (e.msg().find("unexpected $end") != std::string::npos) {
        // For parse errors on incomplete input, we continue waiting for the
        // next line of input without clearing the input so far.
        continue;
      }
      LOG(ERROR) << error << (settings.showTrace ? e.prefix() : "") << e.msg();

    } catch (Error& e) {
      LOG(ERROR) << error << (settings.showTrace ? e.prefix() : "") << e.msg();
    } catch (Interrupted& e) {
      LOG(ERROR) << error << (settings.showTrace ? e.prefix() : "") << e.msg();
    }

    // We handled the current input fully, so we should clear it
    // and read brand new input.
    input.clear();
    std::cout << std::endl;
  }
}

bool NixRepl::getLine(std::string& input, const std::string& prompt) {
  struct sigaction act;
  struct sigaction old;
  sigset_t savedSignalMask;
  sigset_t set;

  auto setupSignals = [&]() {
    act.sa_handler = sigintHandler;
    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
    if (sigaction(SIGINT, &act, &old) != 0) {
      throw SysError("installing handler for SIGINT");
    }

    sigemptyset(&set);
    sigaddset(&set, SIGINT);
    if (sigprocmask(SIG_UNBLOCK, &set, &savedSignalMask) != 0) {
      throw SysError("unblocking SIGINT");
    }
  };
  auto restoreSignals = [&]() {
    if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr) != 0) {
      throw SysError("restoring signals");
    }

    if (sigaction(SIGINT, &old, nullptr) != 0) {
      throw SysError("restoring handler for SIGINT");
    }
  };

  setupSignals();
  char* s = readline(prompt.c_str());
  Finally doFree([&]() { free(s); });
  restoreSignals();

  if (g_signal_received != 0) {
    g_signal_received = 0;
    input.clear();
    return true;
  }

  if (s == nullptr) {
    return false;
  }
  input += s;
  input += '\n';
  return true;
}

StringSet NixRepl::completePrefix(const std::string& prefix) {
  StringSet completions;

  size_t start = prefix.find_last_of(" \n\r\t(){}[]");
  std::string prev;
  std::string cur;
  if (start == std::string::npos) {
    prev = "";
    cur = prefix;
  } else {
    prev = std::string(prefix, 0, start + 1);
    cur = std::string(prefix, start + 1);
  }

  size_t slash;
  size_t dot;

  if ((slash = cur.rfind('/')) != std::string::npos) {
    try {
      auto dir = std::string(cur, 0, slash);
      auto prefix2 = std::string(cur, slash + 1);
      for (auto& entry : readDirectory(dir.empty() ? "/" : dir)) {
        if (entry.name[0] != '.' && absl::StartsWith(entry.name, prefix2)) {
          completions.insert(prev + dir + "/" + entry.name);
        }
      }
    } catch (Error&) {
    }
  } else if ((dot = cur.rfind('.')) == std::string::npos) {
    /* This is a variable name; look it up in the current scope. */
    auto i = varNames.lower_bound(cur);
    while (i != varNames.end()) {
      if (std::string(*i, 0, cur.size()) != cur) {
        break;
      }
      completions.insert(prev + *i);
      i++;
    }
  } else {
    try {
      /* This is an expression that should evaluate to an
         attribute set.  Evaluate it to get the names of the
         attributes. */
      std::string expr(cur, 0, dot);
      std::string cur2 = std::string(cur, dot + 1);

      Expr* e = parseString(expr);
      Value v;
      e->eval(state, *env, v);
      state.forceAttrs(v);

      for (auto& i : *v.attrs) {
        std::string name = i.second.name;
        if (std::string(name, 0, cur2.size()) != cur2) {
          continue;
        }
        completions.insert(prev + expr + "." + name);
      }

    } catch (ParseError& e) {
      // Quietly ignore parse errors.
    } catch (EvalError& e) {
      // Quietly ignore evaluation errors.
    } catch (UndefinedVarError& e) {
      // Quietly ignore undefined variable errors.
    }
  }

  return completions;
}

static int runProgram(const std::string& program, const Strings& args) {
  Strings args2(args);
  args2.push_front(program);

  Pid pid;
  pid = fork();
  if (pid == -1) {
    throw SysError("forking");
  }
  if (pid == 0) {
    restoreAffinity();
    execvp(program.c_str(), stringsToCharPtrs(args2).data());
    _exit(1);
  }

  return pid.wait();
}

bool isVarName(const std::string& s) {
  if (s.empty()) {
    return false;
  }
  char c = s[0];
  if ((c >= '0' && c <= '9') || c == '-' || c == '\'') {
    return false;
  }
  for (auto& i : s) {
    if (!((i >= 'a' && i <= 'z') || (i >= 'A' && i <= 'Z') ||
          (i >= '0' && i <= '9') || i == '_' || i == '-' || i == '\'')) {
      return false;
    }
  }
  return true;
}

Path NixRepl::getDerivationPath(Value& v) {
  auto drvInfo = getDerivation(state, v, false);
  if (!drvInfo) {
    throw Error(
        "expression does not evaluate to a derivation, so I can't build it");
  }
  Path drvPath = drvInfo->queryDrvPath();
  if (drvPath.empty() || !state.store->isValidPath(drvPath)) {
    throw Error("expression did not evaluate to a valid derivation");
  }
  return drvPath;
}

bool NixRepl::processLine(std::string line) {
  if (line.empty()) {
    return true;
  }

  std::string command;
  std::string arg;

  if (line[0] == ':') {
    size_t p = line.find_first_of(" \n\r\t");
    command = std::string(line, 0, p);
    if (p != std::string::npos) {
      arg = removeWhitespace(std::string(line, p));
    }
  } else {
    arg = line;
  }

  if (command == ":?" || command == ":help") {
    std::cout << "The following commands are available:\n"
              << "\n"
              << "  <expr>        Evaluate and print expression\n"
              << "  <x> = <expr>  Bind expression to variable\n"
              << "  :a <expr>     Add attributes from resulting set to scope\n"
              << "  :b <expr>     Build derivation\n"
              << "  :i <expr>     Build derivation, then install result into "
                 "current profile\n"
              << "  :l <path>     Load Nix expression and add it to scope\n"
              << "  :p <expr>     Evaluate and print expression recursively\n"
              << "  :q            Exit nix-repl\n"
              << "  :r            Reload all files\n"
              << "  :s <expr>     Build dependencies of derivation, then start "
                 "nix-shell\n"
              << "  :t <expr>     Describe result of evaluation\n"
              << "  :u <expr>     Build derivation, then start nix-shell\n";
  }

  else if (command == ":a" || command == ":add") {
    Value v;
    evalString(arg, v);
    addAttrsToScope(v);
  }

  else if (command == ":l" || command == ":load") {
    state.resetFileCache();
    loadFile(arg);
  }

  else if (command == ":r" || command == ":reload") {
    state.resetFileCache();
    reloadFiles();
  }

  else if (command == ":t") {
    Value v;
    evalString(arg, v);
    std::cout << showType(v) << std::endl;

  } else if (command == ":u") {
    Value v;
    Value f;
    Value result;
    evalString(arg, v);
    evalString(
        "drv: (import <nixpkgs> {}).runCommand \"shell\" { buildInputs = [ drv "
        "]; } \"\"",
        f);
    state.callFunction(f, v, result, Pos());

    Path drvPath = getDerivationPath(result);
    runProgram(settings.nixBinDir + "/nix-shell", Strings{drvPath});
  }

  else if (command == ":b" || command == ":i" || command == ":s") {
    Value v;
    evalString(arg, v);
    Path drvPath = getDerivationPath(v);

    if (command == ":b") {
      /* We could do the build in this process using buildPaths(),
         but doing it in a child makes it easier to recover from
         problems / SIGINT. */
      if (runProgram(settings.nixBinDir + "/nix",
                     Strings{"build", "--no-link", drvPath}) == 0) {
        Derivation drv = readDerivation(drvPath);
        std::cout << std::endl
                  << "this derivation produced the following outputs:"
                  << std::endl;
        for (auto& i : drv.outputs) {
          std::cout << format("  %1% -> %2%") % i.first % i.second.path
                    << std::endl;
        }
      }
    } else if (command == ":i") {
      runProgram(settings.nixBinDir + "/nix-env", Strings{"-i", drvPath});
    } else {
      runProgram(settings.nixBinDir + "/nix-shell", Strings{drvPath});
    }
  }

  else if (command == ":p" || command == ":print") {
    Value v;
    evalString(arg, v);
    printValue(std::cout, v, 1000000000) << std::endl;
  }

  else if (command == ":q" || command == ":quit") {
    return false;

  } else if (!command.empty()) {
    throw Error(format("unknown command '%1%'") % command);

  } else {
    size_t p = line.find('=');
    std::string name;
    if (p != std::string::npos && p < line.size() && line[p + 1] != '=' &&
        isVarName(name = removeWhitespace(std::string(line, 0, p)))) {
      Expr* e = parseString(std::string(line, p + 1));
      Value& v(*state.allocValue());
      v.type = tThunk;
      v.thunk.env = env;
      v.thunk.expr = e;
      addVarToScope(state.symbols.Create(name), v);
    } else {
      Value v;
      evalString(line, v);
      printValue(std::cout, v, 1) << std::endl;
    }
  }

  return true;
}

void NixRepl::loadFile(const Path& path) {
  loadedFiles.remove(path);
  loadedFiles.push_back(path);
  Value v;
  Value v2;
  state.evalFile(lookupFileArg(state, path), v);
  state.autoCallFunction(*autoArgs, v, v2);
  addAttrsToScope(v2);
}

void NixRepl::initEnv() {
  env = &state.allocEnv(envSize);
  env->up = &state.baseEnv;
  displ = 0;
  staticEnv.vars.clear();

  varNames.clear();
  for (auto& i : state.staticBaseEnv.vars) {
    varNames.insert(i.first);
  }
}

void NixRepl::reloadFiles() {
  initEnv();

  Strings old = loadedFiles;
  loadedFiles.clear();

  bool first = true;
  for (auto& i : old) {
    if (!first) {
      std::cout << std::endl;
    }
    first = false;
    std::cout << format("Loading '%1%'...") % i << std::endl;
    loadFile(i);
  }
}

void NixRepl::addAttrsToScope(Value& attrs) {
  state.forceAttrs(attrs);
  for (auto& i : *attrs.attrs) {
    addVarToScope(i.second.name, *i.second.value);
  }
  std::cout << format("Added %1% variables.") % attrs.attrs->size()
            << std::endl;
}

void NixRepl::addVarToScope(const Symbol& name, Value& v) {
  if (displ >= envSize) {
    throw Error("environment full; cannot add more variables");
  }
  staticEnv.vars[name] = displ;
  env->values[displ++] = &v;
  varNames.insert((std::string)name);
}

Expr* NixRepl::parseString(const std::string& s) {
  Expr* e = state.parseExprFromString(s, curDir, staticEnv);
  return e;
}

void NixRepl::evalString(std::string s, Value& v) {
  Expr* e = parseString(std::move(s));
  e->eval(state, *env, v);
  state.forceValue(v);
}

std::ostream& NixRepl::printValue(std::ostream& str, Value& v,
                                  unsigned int maxDepth) {
  ValuesSeen seen;
  return printValue(str, v, maxDepth, seen);
}

std::ostream& printStringValue(std::ostream& str, const char* string) {
  str << "\"";
  for (const char* i = string; *i != 0; i++) {
    if (*i == '\"' || *i == '\\') {
      str << "\\" << *i;
    } else if (*i == '\n') {
      str << "\\n";
    } else if (*i == '\r') {
      str << "\\r";
    } else if (*i == '\t') {
      str << "\\t";
    } else {
      str << *i;
    }
  }
  str << "\"";
  return str;
}

// FIXME: lot of cut&paste from Nix's eval.cc.
std::ostream& NixRepl::printValue(std::ostream& str, Value& v,
                                  unsigned int maxDepth, ValuesSeen& seen) {
  str.flush();
  checkInterrupt();

  state.forceValue(v);

  switch (v.type) {
    case tInt:
      str << ESC_CYA << v.integer << ESC_END;
      break;

    case tBool:
      str << ESC_CYA << (v.boolean ? "true" : "false") << ESC_END;
      break;

    case tString:
      str << ESC_YEL;
      printStringValue(str, v.string.s);
      str << ESC_END;
      break;

    case tPath:
      str << ESC_GRE << v.path << ESC_END;  // !!! escaping?
      break;

    case tNull:
      str << ESC_CYA "null" ESC_END;
      break;

    case tAttrs: {
      seen.insert(&v);

      bool isDrv = state.isDerivation(v);

      if (isDrv) {
        str << "«derivation ";
        Bindings::iterator i = v.attrs->find(state.sDrvPath);
        PathSet context;
        Path drvPath =
            i != v.attrs->end()
                ? state.coerceToPath(*i->second.pos, *i->second.value, context)
                : "???";
        str << drvPath << "»";
      }

      else if (maxDepth > 0) {
        str << "{ ";

        typedef std::map<std::string, Value*> Sorted;
        Sorted sorted;
        for (auto& i : *v.attrs) {
          sorted[i.second.name] = i.second.value;
        }

        for (auto& i : sorted) {
          if (isVarName(i.first)) {
            str << i.first;
          } else {
            printStringValue(str, i.first.c_str());
          }
          str << " = ";
          if (seen.find(i.second) != seen.end()) {
            str << "«repeated»";
          } else {
            try {
              printValue(str, *i.second, maxDepth - 1, seen);
            } catch (AssertionError& e) {
              str << ESC_RED "«error: " << e.msg() << "»" ESC_END;
            }
          }
          str << "; ";
        }

        str << "}";
      } else {
        str << "{ ... }";
      }

      break;
    }

    case tList1:
    case tList2:
    case tListN:
      seen.insert(&v);

      str << "[ ";
      if (maxDepth > 0) {
        for (unsigned int n = 0; n < v.listSize(); ++n) {
          if (seen.find(v.listElems()[n]) != seen.end()) {
            str << "«repeated»";
          } else {
            try {
              printValue(str, *v.listElems()[n], maxDepth - 1, seen);
            } catch (AssertionError& e) {
              str << ESC_RED "«error: " << e.msg() << "»" ESC_END;
            }
          }
          str << " ";
        }
      } else {
        str << "... ";
      }

      str << "]";
      break;

    case tLambda: {
      std::ostringstream s;
      s << v.lambda.fun->pos;
      str << ESC_BLU "«lambda @ " << filterANSIEscapes(s.str()) << "»" ESC_END;
      break;
    }

    case tPrimOp:
      str << ESC_MAG "«primop»" ESC_END;
      break;

    case tPrimOpApp:
      str << ESC_BLU "«primop-app»" ESC_END;
      break;

    case tFloat:
      str << v.fpoint;
      break;

    default:
      str << ESC_RED "«unknown»" ESC_END;
      break;
  }

  return str;
}

struct CmdRepl : StoreCommand, MixEvalArgs {
  std::vector<std::string> files;

  CmdRepl() { expectArgs("files", &files); }

  std::string name() override { return "repl"; }

  std::string description() override {
    return "start an interactive environment for evaluating Nix expressions";
  }

  void run(ref<Store> store) override {
    auto repl = std::make_unique<NixRepl>(searchPath, openStore());
    repl->autoArgs = getAutoArgs(repl->state);
    repl->mainLoop(files);
  }
};

static RegisterCommand r1(make_ref<CmdRepl>());

}  // namespace nix