lix/nix-repl.cc

#include <iostream>
#include <cstdlib>

#include <setjmp.h>

#include <readline/readline.h>
#include <readline/history.h>

#include "shared.hh"
#include "eval.hh"
#include "eval-inline.hh"
#include "store-api.hh"
#include "common-opts.hh"
#include "get-drvs.hh"
#include "derivations.hh"
#include "affinity.hh"

using namespace std;
using namespace nix;


string programId = "nix-repl";


struct NixRepl
{
    string curDir;
    EvalState state;

    Strings loadedFiles;

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

    StringSet completions;
    StringSet::iterator curCompletion;

    NixRepl(const Strings & searchPath);
    void mainLoop(const Strings & files);
    void completePrefix(string prefix);
    bool getLine(string & line);
    bool processLine(string line);
    void loadFile(const Path & path);
    void initEnv();
    void reloadFiles();
    void addAttrsToScope(Value & attrs);
    void addVarToScope(const Symbol & name, Value & v);
    Expr * parseString(string s);
    void evalString(string s, Value & v);

    typedef set<Value *> ValuesSeen;
    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()
{
    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"
         << flush;
}


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


NixRepl::NixRepl(const Strings & searchPath)
    : state(searchPath)
    , staticEnv(false, &state.staticBaseEnv)
{
    curDir = absPath(".");

    store = openStore();
}


void NixRepl::mainLoop(const Strings & files)
{
    std::cout << "Welcome to Nix version " << NIX_VERSION << ". Type :? for help." << std::endl << std::endl;

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

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

    using_history();
    read_history(0);

    while (true) {
        string line;
        if (!getLine(line)) {
            std::cout << std::endl;
            break;
        }

        try {
            if (!processLine(removeWhitespace(line))) return;
        } catch (Error & e) {
            printMsg(lvlError, "error: " + e.msg());
        } catch (Interrupted & e) {
            printMsg(lvlError, "error: " + e.msg());
        }

        std::cout << std::endl;
    }
}


/* Apparently, the only way to get readline() to return on Ctrl-C
   (SIGINT) is to use siglongjmp().  That's fucked up... */
static sigjmp_buf sigintJmpBuf;


static void sigintHandler(int signo)
{
    siglongjmp(sigintJmpBuf, 1);
}


/* Oh, if only g++ had nested functions... */
NixRepl * curRepl;

char * completerThunk(const char * s, int state)
{
    string prefix(s);

    /* If the prefix has a slash in it, use readline's builtin filename
       completer. */
    if (prefix.find('/') != string::npos)
        return rl_filename_completion_function(s, state);

    /* Otherwise, return all symbols that start with the prefix. */
    if (state == 0) {
        curRepl->completePrefix(s);
        curRepl->curCompletion = curRepl->completions.begin();
    }
    if (curRepl->curCompletion == curRepl->completions.end()) return 0;
    return strdup((curRepl->curCompletion++)->c_str());
}


bool NixRepl::getLine(string & line)
{
    struct sigaction act, old;
    act.sa_handler = sigintHandler;
    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
    if (sigaction(SIGINT, &act, &old))
        throw SysError("installing handler for SIGINT");

    if (sigsetjmp(sigintJmpBuf, 1))
        line = "";
    else {
        curRepl = this;
        rl_completion_entry_function = completerThunk;

        char * s = readline("nix-repl> ");
        if (!s) return false;
        line = chomp(string(s));
        free(s);
        if (line != "") {
            add_history(line.c_str());
            append_history(1, 0);
        }
    }

    _isInterrupted = 0;

    if (sigaction(SIGINT, &old, 0))
        throw SysError("restoring handler for SIGINT");

    return true;
}


void NixRepl::completePrefix(string prefix)
{
    completions.clear();

    size_t dot = prefix.rfind('.');

    if (dot == string::npos) {
        /* This is a variable name; look it up in the current scope. */
        StringSet::iterator i = varNames.lower_bound(prefix);
        while (i != varNames.end()) {
            if (string(*i, 0, prefix.size()) != prefix) break;
            completions.insert(*i);
            i++;
        }
    } else {
        try {
            /* This is an expression that should evaluate to an
               attribute set.  Evaluate it to get the names of the
               attributes. */
            string expr(prefix, 0, dot);
            string prefix2 = string(prefix, dot + 1);

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

            for (auto & i : *v.attrs) {
                string name = i.name;
                if (string(name, 0, prefix2.size()) != prefix2) continue;
                completions.insert(expr + "." + name);
            }

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


static int runProgram(const string & program, const Strings & args)
{
    std::vector<const char *> cargs; /* careful with c_str()! */
    cargs.push_back(program.c_str());
    for (Strings::const_iterator i = args.begin(); i != args.end(); ++i)
        cargs.push_back(i->c_str());
    cargs.push_back(0);

    Pid pid;
    pid = fork();
    if (pid == -1) throw SysError("forking");
    if (pid == 0) {
        restoreAffinity();
        execvp(program.c_str(), (char * *) &cargs[0]);
        _exit(1);
    }

    return pid.wait(true);
}


bool isVarName(const string & s)
{
    if (s.size() == 0) 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;
}


bool NixRepl::processLine(string line)
{
    if (line == "") return true;

    string command, arg;

    if (line[0] == ':') {
        size_t p = line.find(' ');
        command = string(line, 0, p);
        if (p != string::npos) arg = removeWhitespace(string(line, p));
    } else {
        arg = line;
    }

    if (command == ":?" || command == ":help") {
        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"
             << "  :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";
    }

    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 == ":b" || command == ":s") {
        Value v;
        evalString(arg, v);
        DrvInfo drvInfo(state);
        if (!getDerivation(state, v, drvInfo, false))
            throw Error("expression does not evaluation to a derivation, so I can't build it");
        Path drvPath = drvInfo.queryDrvPath();
        if (drvPath == "" || !store->isValidPath(drvPath))
            throw Error("expression did not evaluate to a valid derivation");

        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("nix-store", Strings{"-r", 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
            runProgram("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 != "")
        throw Error(format("unknown command ‘%1%’") % command);

    else {
        size_t p = line.find('=');
        string name;
        if (p != string::npos &&
            p < line.size() &&
            line[p + 1] != '=' &&
            isVarName(name = removeWhitespace(string(line, 0, p))))
        {
            Expr * e = parseString(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, v2;
    state.evalFile(lookupFileArg(state, path), v);
    Bindings & bindings(*state.allocBindings(0));
    state.autoCallFunction(bindings, 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.name, *i.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((string) name);
}


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


void NixRepl::evalString(string s, Value & v)
{
    Expr * e = parseString(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);
}


// 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 << v.integer;
        break;

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

    case tString:
        str << "\"";
        for (const char * i = v.string.s; *i; 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 << "\"";
        break;

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

    case tNull:
        str << "null";
        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->pos, *i->value, context) : "???";
            str << drvPath << "»";
        }

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

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

            /* If this is a derivation, then don't show the
               self-references ("all", "out", etc.). */
            StringSet hidden;
            if (isDrv) {
                hidden.insert("all");
                Bindings::iterator i = v.attrs->find(state.sOutputs);
                if (i == v.attrs->end())
                    hidden.insert("out");
                else {
                    state.forceList(*i->value);
                    for (unsigned int j = 0; j < i->value->listSize(); ++j)
                        hidden.insert(state.forceStringNoCtx(*i->value->listElems()[j]));
                }
            }

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

    case tLambda:
        str << "«lambda»";
        break;

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

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

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

    return str;
}


int main(int argc, char * * argv)
{
    return handleExceptions(argv[0], [&]() {
        initNix();
        initGC();

        Strings files, searchPath;

        parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
            if (*arg == "--version")
                printVersion("nix-repl");
            else if (*arg == "--help") {
                printHelp();
                // exit with 0 since user asked for help
                _exit(0);
            }
            else if (parseSearchPathArg(arg, end, searchPath))
                ;
            else if (*arg != "" && arg->at(0) == '-')
                return false;
            else
                files.push_back(*arg);
            return true;
        });

        NixRepl repl(searchPath);
        repl.mainLoop(files);
    });
}