nix-build/nix-shell: Eliminate call to nix-instantiate / nix-store

Note that this removes the need for a derivation symlink, so the
--drv-path and --add-drv-link flags now do nothing.

1 files changed, 378 insertions, 452 deletions

diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 72f89003d0..8a3c8a0250 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -5,8 +5,6 @@
 #include <sstream>
 #include <vector>
 
-#include <unistd.h>
-
 #include "store-api.hh"
 #include "globals.hh"
 #include "derivations.hh"
@@ -14,7 +12,10 @@
 #include "util.hh"
 #include "shared.hh"
 #include "eval.hh"
+#include "eval-inline.hh"
 #include "get-drvs.hh"
+#include "common-opts.hh"
+#include "attr-path.hh"
 
 using namespace nix;
 using namespace std::string_literals;
@@ -65,510 +66,435 @@ std::vector<string> shellwords(const string & s)
     return res;
 }
 
-static void maybePrintExecError(ExecError & e)
+void mainWrapped(int argc, char * * argv)
 {
-    if (WIFEXITED(e.status))
-        throw Exit(WEXITSTATUS(e.status));
-    else
-        throw e;
-}
-
-int main(int argc, char ** argv)
-{
-    return handleExceptions(argv[0], [&]() {
-        initNix();
-        initGC();
-
-        auto store = openStore();
-        auto dryRun = false;
-        auto verbose = false;
-        auto runEnv = std::regex_search(argv[0], std::regex("nix-shell$"));
-        auto pure = false;
-        auto fromArgs = false;
-        auto packages = false;
-        // Same condition as bash uses for interactive shells
-        auto interactive = isatty(STDIN_FILENO) && isatty(STDERR_FILENO);
-
-        Strings instArgs;
-        Strings buildArgs;
-        Strings exprs;
-        Strings searchPath;
-
-        auto shell = getEnv("SHELL", "/bin/sh");
-        std::string envCommand; // interactive shell
-        Strings envExclude;
-
-        auto myName = runEnv ? "nix-shell" : "nix-build";
-
-        auto inShebang = false;
-        std::string script;
-        std::vector<string> savedArgs;
-
-        AutoDelete tmpDir(createTempDir("", myName));
-
-        std::string outLink = "./result";
-        auto drvLink = (Path) tmpDir + "/derivation";
-
-        std::vector<string> args;
-        for (int i = 1; i < argc; ++i)
-            args.push_back(argv[i]);
-
-        // Heuristic to see if we're invoked as a shebang script, namely, if we
-        // have a single argument, it's the name of an executable file, and it
-        // starts with "#!".
-        if (runEnv && argc > 1 && !std::regex_search(argv[1], std::regex("nix-shell"))) {
-            script = argv[1];
-            if (access(script.c_str(), F_OK) == 0 && access(script.c_str(), X_OK) == 0) {
-                auto lines = tokenizeString<Strings>(readFile(script), "\n");
-                if (std::regex_search(lines.front(), std::regex("^#!"))) {
-                    lines.pop_front();
-                    inShebang = true;
-                    for (int i = 2; i < argc; ++i)
-                        savedArgs.push_back(argv[i]);
-                    args.clear();
-                    for (auto line : lines) {
-                        line = chomp(line);
-                        std::smatch match;
-                        if (std::regex_match(line, match, std::regex("^#!\\s*nix-shell (.*)$")))
-                            for (const auto & word : shellwords(match[1].str()))
-                                args.push_back(word);
-                    }
+    initNix();
+    initGC();
+
+    auto dryRun = false;
+    auto runEnv = std::regex_search(argv[0], std::regex("nix-shell$"));
+    auto pure = false;
+    auto fromArgs = false;
+    auto packages = false;
+    // Same condition as bash uses for interactive shells
+    auto interactive = isatty(STDIN_FILENO) && isatty(STDERR_FILENO);
+    Strings attrPaths;
+    Strings left;
+    Strings searchPath;
+    std::map<string, string> autoArgs_;
+    RepairFlag repair = NoRepair;
+    Path gcRoot;
+    BuildMode buildMode = bmNormal;
+    bool readStdin = false;
+
+    auto shell = getEnv("SHELL", "/bin/sh");
+    std::string envCommand; // interactive shell
+    Strings envExclude;
+
+    auto myName = runEnv ? "nix-shell" : "nix-build";
+
+    auto inShebang = false;
+    std::string script;
+    std::vector<string> savedArgs;
+
+    AutoDelete tmpDir(createTempDir("", myName));
+
+    std::string outLink = "./result";
+
+    Strings args;
+    for (int i = 1; i < argc; ++i)
+        args.push_back(argv[i]);
+
+    // Heuristic to see if we're invoked as a shebang script, namely, if we
+    // have a single argument, it's the name of an executable file, and it
+    // starts with "#!".
+    if (runEnv && argc > 1 && !std::regex_search(argv[1], std::regex("nix-shell"))) {
+        script = argv[1];
+        if (access(script.c_str(), F_OK) == 0 && access(script.c_str(), X_OK) == 0) {
+            auto lines = tokenizeString<Strings>(readFile(script), "\n");
+            if (std::regex_search(lines.front(), std::regex("^#!"))) {
+                lines.pop_front();
+                inShebang = true;
+                for (int i = 2; i < argc; ++i)
+                    savedArgs.push_back(argv[i]);
+                args.clear();
+                for (auto line : lines) {
+                    line = chomp(line);
+                    std::smatch match;
+                    if (std::regex_match(line, match, std::regex("^#!\\s*nix-shell (.*)$")))
+                        for (const auto & word : shellwords(match[1].str()))
+                            args.push_back(word);
                 }
             }
         }
+    }
 
-        for (size_t n = 0; n < args.size(); ++n) {
-            auto arg = args[n];
+    parseCmdLine(myName, args, [&](Strings::iterator & arg, const Strings::iterator & end) {
+        if (*arg == "--help") {
+            deletePath(tmpDir);
+            showManPage(myName);
+        }
 
-            if (arg == "--help") {
-                deletePath(tmpDir);
-                showManPage(myName);
-            }
+        else if (*arg == "--version")
+            printVersion(myName);
 
-            else if (arg == "--version")
-                printVersion(myName);
+        else if (*arg == "--add-drv-link")
+            ; // obsolete
 
-            else if (arg == "--add-drv-link") {
-                drvLink = "./derivation";
-            }
+        else if (*arg == "--no-out-link" || *arg == "--no-link")
+            outLink = (Path) tmpDir + "/result";
 
-            else if (arg == "--no-out-link" || arg == "--no-link") {
-                outLink = (Path) tmpDir + "/result";
-            }
+        else if (*arg == "--attr" || *arg == "-A")
+            attrPaths.push_back(getArg(*arg, arg, end));
 
-            else if (arg == "--drv-link") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError("--drv-link requires an argument");
-                }
-                drvLink = args[n];
-            }
+        else if (*arg == "--drv-link")
+            getArg(*arg, arg, end); // obsolete
 
-            else if (arg == "--out-link" || arg == "-o") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                outLink = args[n];
-            }
+        else if (*arg == "--out-link" || *arg == "-o")
+            outLink = getArg(*arg, arg, end);
 
-            else if (arg == "--attr" || arg == "-A" || arg == "-I") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                instArgs.push_back(arg);
-                instArgs.push_back(args[n]);
-            }
+        else if (parseAutoArgs(arg, end, autoArgs_))
+            ;
 
-            else if (arg == "--arg" || arg == "--argstr") {
-                if (n + 2 >= args.size()) {
-                    throw UsageError(format("%1% requires two arguments") % arg);
-                }
-                instArgs.push_back(arg);
-                instArgs.push_back(args[n + 1]);
-                instArgs.push_back(args[n + 2]);
-                n += 2;
-            }
+        else if (parseSearchPathArg(arg, end, searchPath))
+            ;
 
-            else if (arg == "--option") {
-                if (n + 2 >= args.size()) {
-                    throw UsageError(format("%1% requires two arguments") % arg);
-                }
-                instArgs.push_back(arg);
-                instArgs.push_back(args[n + 1]);
-                instArgs.push_back(args[n + 2]);
-                buildArgs.push_back(arg);
-                buildArgs.push_back(args[n + 1]);
-                buildArgs.push_back(args[n + 2]);
-                settings.set(args[n + 1], args[n + 2]);
-                n += 2;
-            }
+        else if (*arg == "--add-root")
+            gcRoot = getArg(*arg, arg, end);
 
-            else if (arg == "--max-jobs" || arg == "-j" || arg == "--max-silent-time" || arg == "--cores" || arg == "--timeout" || arg == "--add-root") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                buildArgs.push_back(arg);
-                buildArgs.push_back(args[n]);
-            }
+        else if (*arg == "--dry-run")
+            dryRun = true;
 
-            else if (arg == "--dry-run") {
-                buildArgs.push_back("--dry-run");
-                dryRun = true;
-            }
+        else if (*arg == "--repair") {
+            repair = Repair;
+            buildMode = bmRepair;
+        }
 
-            else if (arg == "--show-trace") {
-                instArgs.push_back(arg);
-            }
+        else if (*arg == "--run-env") // obsolete
+            runEnv = true;
 
-            else if (arg == "-") {
-                exprs = Strings{"-"};
-            }
+        else if (*arg == "--command" || *arg == "--run") {
+            if (*arg == "--run")
+                interactive = false;
+            envCommand = getArg(*arg, arg, end) + "\nexit";
+        }
 
-            else if (arg == "--verbose" || (arg.size() >= 2 && arg.substr(0, 2) == "-v")) {
-                buildArgs.push_back(arg);
-                instArgs.push_back(arg);
-                verbose = true;
-            }
+        else if (*arg == "--check")
+            buildMode = bmCheck;
 
-            else if (arg == "--quiet" || arg == "--repair") {
-                buildArgs.push_back(arg);
-                instArgs.push_back(arg);
-            }
+        else if (*arg == "--exclude")
+            envExclude.push_back(getArg(*arg, arg, end));
 
-            else if (arg == "--check") {
-                buildArgs.push_back(arg);
-            }
+        else if (*arg == "--expr" || *arg == "-E")
+            fromArgs = true;
 
-            else if (arg == "--run-env") { // obsolete
-                runEnv = true;
-            }
+        else if (*arg == "--pure") pure = true;
+        else if (*arg == "--impure") pure = false;
 
-            else if (arg == "--command" || arg == "--run") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                envCommand = args[n] + "\nexit";
-                if (arg == "--run")
-                    interactive = false;
-            }
+        else if (*arg == "--packages" || *arg == "-p")
+            packages = true;
 
-            else if (arg == "--exclude") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                envExclude.push_back(args[n]);
-            }
+        else if (inShebang && *arg == "-i") {
+            auto interpreter = getArg(*arg, arg, end);
+            interactive = false;
+            auto execArgs = "";
 
-            else if (arg == "--pure") { pure = true; }
-            else if (arg == "--impure") { pure = false; }
+            auto shellEscape = [](const string & s) {
+                return "'" + std::regex_replace(s, std::regex("'"), "'\\''") + "'";
+            };
 
-            else if (arg == "--expr" || arg == "-E") {
-                fromArgs = true;
-                instArgs.push_back("--expr");
-            }
+            // Überhack to support Perl. Perl examines the shebang and
+            // executes it unless it contains the string "perl" or "indir",
+            // or (undocumented) argv[0] does not contain "perl". Exploit
+            // the latter by doing "exec -a".
+            if (std::regex_search(interpreter, std::regex("perl")))
+                execArgs = "-a PERL";
 
-            else if (arg == "--packages" || arg == "-p") {
-                packages = true;
+            std::ostringstream joined;
+            for (const auto & i : savedArgs)
+                joined << shellEscape(i) << ' ';
+
+            if (std::regex_search(interpreter, std::regex("ruby"))) {
+                // Hack for Ruby. Ruby also examines the shebang. It tries to
+                // read the shebang to understand which packages to read from. Since
+                // this is handled via nix-shell -p, we wrap our ruby script execution
+                // in ruby -e 'load' which ignores the shebangs.
+                envCommand = (format("exec %1% %2% -e 'load(\"%3%\") -- %4%") % execArgs % interpreter % script % joined.str()).str();
+            } else {
+                envCommand = (format("exec %1% %2% %3% %4%") % execArgs % interpreter % script % joined.str()).str();
             }
+        }
 
-            else if (inShebang && arg == "-i") {
-                n++;
-                if (n >= args.size()) {
-                    throw UsageError(format("%1% requires an argument") % arg);
-                }
-                interactive = false;
-                auto interpreter = args[n];
-                auto execArgs = "";
-
-                auto shellEscape = [](const string & s) {
-                    return "'" + std::regex_replace(s, std::regex("'"), "'\\''") + "'";
-                };
-
-                // Überhack to support Perl. Perl examines the shebang and
-                // executes it unless it contains the string "perl" or "indir",
-                // or (undocumented) argv[0] does not contain "perl". Exploit
-                // the latter by doing "exec -a".
-                if (std::regex_search(interpreter, std::regex("perl")))
-                    execArgs = "-a PERL";
-
-                std::ostringstream joined;
-                for (const auto & i : savedArgs)
-                    joined << shellEscape(i) << ' ';
-
-                if (std::regex_search(interpreter, std::regex("ruby"))) {
-                    // Hack for Ruby. Ruby also examines the shebang. It tries to
-                    // read the shebang to understand which packages to read from. Since
-                    // this is handled via nix-shell -p, we wrap our ruby script execution
-                    // in ruby -e 'load' which ignores the shebangs.
-                    envCommand = (format("exec %1% %2% -e 'load(\"%3%\") -- %4%") % execArgs % interpreter % script % joined.str()).str();
-                } else {
-                    envCommand = (format("exec %1% %2% %3% %4%") % execArgs % interpreter % script % joined.str()).str();
-                }
-            }
+        else if (*arg == "-")
+            readStdin = true;
 
-            else if (!arg.empty() && arg[0] == '-') {
-                buildArgs.push_back(arg);
-            }
+        else if (*arg != "" && arg->at(0) == '-')
+            return false;
 
-            else if (arg == "-Q" || arg == "--no-build-output") {
-                buildArgs.push_back(arg);
-                instArgs.push_back(arg);
-            }
+        else
+            left.push_back(*arg);
 
-            else {
-                exprs.push_back(arg);
-            }
-        }
+        return true;
+    });
 
-        EvalState state(searchPath, store);
+    if (packages && fromArgs)
+        throw UsageError("‘-p’ and ‘-E’ are mutually exclusive");
+
+    auto store = openStore();
+
+    EvalState state(searchPath, store);
+    state.repair = repair;
+
+    Bindings & autoArgs(*evalAutoArgs(state, autoArgs_));
+
+    if (packages) {
+        std::ostringstream joined;
+        joined << "with import <nixpkgs> { }; (pkgs.runCommandCC or pkgs.runCommand) \"shell\" { buildInputs = [ ";
+        for (const auto & i : left)
+            joined << '(' << i << ") ";
+        joined << "]; } \"\"";
+        fromArgs = true;
+        left = {joined.str()};
+    } else if (!fromArgs) {
+        if (left.empty() && runEnv && pathExists("shell.nix"))
+            left = {"shell.nix"};
+        if (left.empty())
+            left = {"default.nix"};
+    }
 
-        if (packages && fromArgs) {
-            throw UsageError("‘-p’ and ‘-E’ are mutually exclusive");
-        }
+    if (runEnv)
+        setenv("IN_NIX_SHELL", pure ? "pure" : "impure", 1);
 
-        if (packages) {
-            instArgs.push_back("--expr");
-            std::ostringstream joined;
-            joined << "with import <nixpkgs> { }; (pkgs.runCommandCC or pkgs.runCommand) \"shell\" { buildInputs = [ ";
-            for (const auto & i : exprs)
-                joined << '(' << i << ") ";
-            joined << "]; } \"\"";
-            exprs = Strings{joined.str()};
-        } else if (!fromArgs) {
-            if (exprs.empty() && runEnv && access("shell.nix", F_OK) == 0)
-                exprs.push_back("shell.nix");
-            if (exprs.empty())
-                exprs.push_back("default.nix");
+    /* Parse the expressions. */
+    std::vector<Expr *> exprs;
+
+    if (readStdin)
+        exprs = {state.parseStdin()};
+    else
+        for (auto i : left) {
+            if (fromArgs)
+                exprs.push_back(state.parseExprFromString(i, absPath(".")));
+            else
+                /* If we're in a #! script, interpret filenames
+                   relative to the script. */
+                exprs.push_back(state.parseExprFromFile(resolveExprPath(lookupFileArg(state,
+                    inShebang && !packages ? absPath(i, dirOf(script)) : i))));
         }
 
-        if (runEnv)
-            setenv("IN_NIX_SHELL", pure ? "pure" : "impure", 1);
-
-        for (auto & expr : exprs) {
-            // Instantiate.
-            std::vector<string> drvPaths;
-            if (!std::regex_match(expr, std::regex("^/.*\\.drv$"))) {
-                // If we're in a #! script, interpret filenames relative to the
-                // script.
-                if (inShebang && !packages)
-                    expr = absPath(expr, dirOf(script));
-
-                Strings instantiateArgs{"--add-root", drvLink, "--indirect"};
-                for (const auto & arg : instArgs)
-                    instantiateArgs.push_back(arg);
-                instantiateArgs.push_back(expr);
-                try {
-                    auto instOutput = runProgram(settings.nixBinDir + "/nix-instantiate", false, instantiateArgs);
-                    drvPaths = tokenizeString<std::vector<string>>(instOutput);
-                } catch (ExecError & e) {
-                    maybePrintExecError(e);
-                }
-            } else {
-                drvPaths.push_back(expr);
-            }
+    /* Evaluate them into derivations. */
+    DrvInfos drvs;
 
-            if (runEnv) {
-                if (drvPaths.size() != 1)
-                    throw UsageError("a single derivation is required");
-                auto drvPath = drvPaths[0];
-                drvPath = drvPath.substr(0, drvPath.find_first_of('!'));
-                if (isLink(drvPath))
-                    drvPath = readLink(drvPath);
-                auto drv = store->derivationFromPath(drvPath);
-
-                // Build or fetch all dependencies of the derivation.
-                Strings nixStoreArgs{"-r", "--no-output", "--no-gc-warning"};
-                for (const auto & arg : buildArgs)
-                    nixStoreArgs.push_back(arg);
-                for (const auto & input : drv.inputDrvs)
-                    if (std::all_of(envExclude.cbegin(), envExclude.cend(), [&](const string & exclude) { return !std::regex_search(input.first, std::regex(exclude)); }))
-                        nixStoreArgs.push_back(input.first);
-                for (const auto & src : drv.inputSrcs)
-                    nixStoreArgs.push_back(src);
-
-                try {
-                    runProgram(settings.nixBinDir + "/nix-store", false, nixStoreArgs);
-                } catch (ExecError & e) {
-                    maybePrintExecError(e);
-                }
+    if (attrPaths.empty()) attrPaths = {""};
 
-                if (dryRun) return;
+    for (auto e : exprs) {
+        Value vRoot;
+        state.eval(e, vRoot);
 
-                // Set the environment.
-                auto env = getEnv();
+        for (auto & i : attrPaths) {
+            Value & v(*findAlongAttrPath(state, i, autoArgs, vRoot));
+            state.forceValue(v);
+            getDerivations(state, v, "", autoArgs, drvs, false);
+        }
+    }
 
-                auto tmp = getEnv("TMPDIR", getEnv("XDG_RUNTIME_DIR", "/tmp"));
+    auto buildPaths = [&](const PathSet & paths) {
+        /* Note: we do this even when !printMissing to efficiently
+           fetch binary cache data. */
+        unsigned long long downloadSize, narSize;
+        PathSet willBuild, willSubstitute, unknown;
+        store->queryMissing(paths,
+            willBuild, willSubstitute, unknown, downloadSize, narSize);
 
-                if (pure) {
-                    std::set<string> keepVars{"HOME", "USER", "LOGNAME", "DISPLAY", "PATH", "TERM", "IN_NIX_SHELL", "TZ", "PAGER", "NIX_BUILD_SHELL", "SHLVL"};
-                    decltype(env) newEnv;
-                    for (auto & i : env)
-                        if (keepVars.count(i.first))
-                            newEnv.emplace(i);
-                    env = newEnv;
-                    // NixOS hack: prevent /etc/bashrc from sourcing /etc/profile.
-                    env["__ETC_PROFILE_SOURCED"] = "1";
-                }
+        if (settings.printMissing)
+            printMissing(ref<Store>(store), willBuild, willSubstitute, unknown, downloadSize, narSize);
 
-                env["NIX_BUILD_TOP"] = env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] = tmp;
-                env["NIX_STORE"] = store->storeDir;
-                env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
-
-                auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile", ""));
-
-                bool keepTmp = false;
-                int fileNr = 0;
-
-                for (auto & var : drv.env)
-                    if (passAsFile.count(var.first)) {
-                        keepTmp = true;
-                        string fn = ".attr-" + std::to_string(fileNr++);
-                        Path p = (Path) tmpDir + "/" + fn;
-                        writeFile(p, var.second);
-                        env[var.first + "Path"] = p;
-                    } else
-                        env[var.first] = var.second;
-
-                restoreAffinity();
-
-                // Run a shell using the derivation's environment.  For
-                // convenience, source $stdenv/setup to setup additional
-                // environment variables and shell functions.  Also don't lose
-                // the current $PATH directories.
-                auto rcfile = (Path) tmpDir + "/rc";
-                writeFile(rcfile, fmt(
-                        (keepTmp ? "" : "rm -rf '%1%'; "s) +
-                        "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc; "
-                        "%2%"
-                        "dontAddDisableDepTrack=1; "
-                        "[ -e $stdenv/setup ] && source $stdenv/setup; "
-                        "%3%"
-                        "set +e; "
-                        R"s([ -n "$PS1" ] && PS1='\n\[\033[1;32m\][nix-shell:\w]\$\[\033[0m\] '; )s"
-                        "if [ \"$(type -t runHook)\" = function ]; then runHook shellHook; fi; "
-                        "unset NIX_ENFORCE_PURITY; "
-                        "unset NIX_INDENT_MAKE; "
-                        "shopt -u nullglob; "
-                        "unset TZ; %4%"
-                        "%5%",
-                        (Path) tmpDir,
-                        (pure ? "" : "p=$PATH; "),
-                        (pure ? "" : "PATH=$PATH:$p; unset p; "),
-                        (getenv("TZ") ? (string("export TZ='") + getenv("TZ") + "'; ") : ""),
-                        envCommand));
-
-                Strings envStrs;
-                for (auto & i : env)
-                    envStrs.push_back(i.first + "=" + i.second);
-
-                auto args = interactive
-                    ? Strings{"bash", "--rcfile", rcfile}
-                    : Strings{"bash", rcfile};
-
-                auto envPtrs = stringsToCharPtrs(envStrs);
-
-                auto shell = getEnv("NIX_BUILD_SHELL", "");
-
-                if (shell == "") {
-
-                    try {
-
-                        auto expr = state.parseExprFromString("(import <nixpkgs> {}).bashInteractive", absPath("."));
-
-                        Value v;
-                        state.eval(expr, v);
-
-                        auto drv = getDerivation(state, v, false);
-                        if (!drv)
-                            throw Error("the ‘bashInteractive’ attribute in <nixpkgs> did not evaluate to a derivation");
-
-                        auto drvPath = drv->queryDrvPath();
-
-                        unsigned long long downloadSize, narSize;
-                        PathSet willBuild, willSubstitute, unknown;
-                        store->queryMissing({drvPath},
-                            willBuild, willSubstitute, unknown, downloadSize, narSize);
-
-                        if (settings.printMissing)
-                            printMissing(ref<Store>(store), willBuild, willSubstitute, unknown, downloadSize, narSize);
-
-                        store->buildPaths({drvPath});
-
-                        shell = drv->queryOutPath() + "/bin/bash";
-                        if (!pathExists(shell))
-                            throw Error("expected shell ‘%s’ to exist, but it doesn't", shell);
-
-                    } catch (Error & e) {
-                        printError("warning: %s; will use bash from your environment", e.what());
-                        shell = "bash";
-                    }
-                }
+        if (!dryRun)
+            store->buildPaths(paths, buildMode);
+    };
 
-                environ = envPtrs.data();
+    if (runEnv) {
+        if (drvs.size() != 1)
+            throw UsageError("nix-shell requires a single derivation");
 
-                auto argPtrs = stringsToCharPtrs(args);
+        auto & drvInfo = drvs.front();
+        auto drv = store->derivationFromPath(drvInfo.queryDrvPath());
 
-                restoreSignals();
+        PathSet pathsToBuild;
 
-                execvp(shell.c_str(), argPtrs.data());
+        /* Figure out what bash shell to use. If $NIX_BUILD_SHELL
+           is not set, then build bashInteractive from
+           <nixpkgs>. */
+        auto shell = getEnv("NIX_BUILD_SHELL", "");
 
-                throw SysError("executing shell ‘%s’", shell);
-            }
+        if (shell == "") {
 
-            // Ugly hackery to make "nix-build -A foo.all" produce symlinks
-            // ./result, ./result-dev, and so on, rather than ./result,
-            // ./result-2-dev, and so on.  This combines multiple derivation
-            // paths into one "/nix/store/drv-path!out1,out2,..." argument.
-            std::string prevDrvPath;
-            Strings drvPaths2;
-            for (const auto & drvPath : drvPaths) {
-                auto p = drvPath;
-                std::string output = "out";
-                std::smatch match;
-                if (std::regex_match(drvPath, match, std::regex("(.*)!(.*)"))) {
-                    p = match[1].str();
-                    output = match[2].str();
-                }
-                auto target = readLink(p);
-                if (verbose)
-                    std::cerr << "derivation is " << target << '\n';
-                if (target == prevDrvPath) {
-                    auto last = drvPaths2.back();
-                    drvPaths2.pop_back();
-                    drvPaths2.push_back(last + "," + output);
-                } else {
-                    drvPaths2.push_back(target + "!" + output);
-                    prevDrvPath = target;
-                }
-            }
-            // Build.
-            Strings outPaths;
-            Strings nixStoreArgs{"--add-root", outLink, "--indirect", "-r"};
-            for (const auto & arg : buildArgs)
-                nixStoreArgs.push_back(arg);
-            for (const auto & path : drvPaths2)
-                nixStoreArgs.push_back(path);
-
-            std::string nixStoreRes;
             try {
-                nixStoreRes = runProgram(settings.nixBinDir + "/nix-store", false, nixStoreArgs);
-            } catch (ExecError & e) {
-                maybePrintExecError(e);
+                auto expr = state.parseExprFromString("(import <nixpkgs> {}).bashInteractive", absPath("."));
+
+                Value v;
+                state.eval(expr, v);
+
+                auto drv = getDerivation(state, v, false);
+                if (!drv)
+                    throw Error("the ‘bashInteractive’ attribute in <nixpkgs> did not evaluate to a derivation");
+
+                pathsToBuild.insert(drv->queryDrvPath());
+
+                shell = drv->queryOutPath() + "/bin/bash";
+
+            } catch (Error & e) {
+                printError("warning: %s; will use bash from your environment", e.what());
+                shell = "bash";
             }
+        }
+
+        // Build or fetch all dependencies of the derivation.
+        for (const auto & input : drv.inputDrvs)
+            if (std::all_of(envExclude.cbegin(), envExclude.cend(), [&](const string & exclude) { return !std::regex_search(input.first, std::regex(exclude)); }))
+                pathsToBuild.insert(input.first);
+        for (const auto & src : drv.inputSrcs)
+            pathsToBuild.insert(src);
 
-            for (const auto & outpath : tokenizeString<std::vector<string>>(nixStoreRes))
-                outPaths.push_back(chomp(outpath));
+        buildPaths(pathsToBuild);
 
-            if (dryRun)
-                continue;
+        if (dryRun) return;
 
-            for (const auto & outPath : outPaths)
-                std::cout << readLink(outPath) << '\n';
+        // Set the environment.
+        auto env = getEnv();
+
+        auto tmp = getEnv("TMPDIR", getEnv("XDG_RUNTIME_DIR", "/tmp"));
+
+        if (pure) {
+            std::set<string> keepVars{"HOME", "USER", "LOGNAME", "DISPLAY", "PATH", "TERM", "IN_NIX_SHELL", "TZ", "PAGER", "NIX_BUILD_SHELL", "SHLVL"};
+            decltype(env) newEnv;
+            for (auto & i : env)
+                if (keepVars.count(i.first))
+                    newEnv.emplace(i);
+            env = newEnv;
+            // NixOS hack: prevent /etc/bashrc from sourcing /etc/profile.
+            env["__ETC_PROFILE_SOURCED"] = "1";
         }
+
+        env["NIX_BUILD_TOP"] = env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] = tmp;
+        env["NIX_STORE"] = store->storeDir;
+        env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
+
+        auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile", ""));
+
+        bool keepTmp = false;
+        int fileNr = 0;
+
+        for (auto & var : drv.env)
+            if (passAsFile.count(var.first)) {
+                keepTmp = true;
+                string fn = ".attr-" + std::to_string(fileNr++);
+                Path p = (Path) tmpDir + "/" + fn;
+                writeFile(p, var.second);
+                env[var.first + "Path"] = p;
+            } else
+                env[var.first] = var.second;
+
+        restoreAffinity();
+
+        /* Run a shell using the derivation's environment.  For
+           convenience, source $stdenv/setup to setup additional
+           environment variables and shell functions.  Also don't
+           lose the current $PATH directories. */
+        auto rcfile = (Path) tmpDir + "/rc";
+        writeFile(rcfile, fmt(
+                (keepTmp ? "" : "rm -rf '%1%'; "s) +
+                "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc; "
+                "%2%"
+                "dontAddDisableDepTrack=1; "
+                "[ -e $stdenv/setup ] && source $stdenv/setup; "
+                "%3%"
+                "set +e; "
+                R"s([ -n "$PS1" ] && PS1='\n\[\033[1;32m\][nix-shell:\w]\$\[\033[0m\] '; )s"
+                "if [ \"$(type -t runHook)\" = function ]; then runHook shellHook; fi; "
+                "unset NIX_ENFORCE_PURITY; "
+                "unset NIX_INDENT_MAKE; "
+                "shopt -u nullglob; "
+                "unset TZ; %4%"
+                "%5%",
+                (Path) tmpDir,
+                (pure ? "" : "p=$PATH; "),
+                (pure ? "" : "PATH=$PATH:$p; unset p; "),
+                (getenv("TZ") ? (string("export TZ='") + getenv("TZ") + "'; ") : ""),
+                envCommand));
+
+        Strings envStrs;
+        for (auto & i : env)
+            envStrs.push_back(i.first + "=" + i.second);
+
+        auto args = interactive
+            ? Strings{"bash", "--rcfile", rcfile}
+            : Strings{"bash", rcfile};
+
+        auto envPtrs = stringsToCharPtrs(envStrs);
+
+        environ = envPtrs.data();
+
+        auto argPtrs = stringsToCharPtrs(args);
+
+        restoreSignals();
+
+        execvp(shell.c_str(), argPtrs.data());
+
+        throw SysError("executing shell ‘%s’", shell);
+    }
+
+    else {
+
+        PathSet pathsToBuild;
+
+        std::map<Path, Path> drvPrefixes;
+        std::map<Path, Path> resultSymlinks;
+        std::vector<Path> outPaths;
+
+        for (auto & drvInfo : drvs) {
+            auto drvPath = drvInfo.queryDrvPath();
+            pathsToBuild.insert(drvPath);
+
+            auto outputName = drvInfo.queryOutputName();
+            if (outputName == "")
+                throw Error("derivation ‘%s’ lacks an ‘outputName’ attribute", drvPath);
+
+            pathsToBuild.insert(drvPath + (outputName != "out" ? "!" + outputName : ""));
+
+            std::string drvPrefix;
+            auto i = drvPrefixes.find(drvPath);
+            if (i != drvPrefixes.end())
+                drvPrefix = i->second;
+            else {
+                drvPrefix = outLink;
+                if (drvPrefixes.size())
+                    drvPrefix += fmt("-%d", drvPrefixes.size() + 1);
+                drvPrefixes[drvPath] = drvPrefix;
+            }
+
+            std::string symlink = drvPrefix;
+            if (outputName != "out") symlink += "-" + outputName;
+
+            resultSymlinks[symlink] = drvInfo.queryOutPath();
+            outPaths.push_back(drvInfo.queryOutPath());
+        }
+
+        buildPaths(pathsToBuild);
+
+        if (dryRun) return;
+
+        for (auto & symlink : resultSymlinks)
+            if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
+                store2->addPermRoot(symlink.second, absPath(symlink.first), true);
+
+        for (auto & path : outPaths)
+            std::cout << path << '\n';
+    }
+}
+
+int main(int argc, char * * argv)
+{
+    return handleExceptions(argv[0], [&]() {
+        return mainWrapped(argc, argv);
     });
 }