Merge "Remove static initializers for `RegisterLegacyCommand`" into main

1 files changed, 1553 insertions, 0 deletions

diff --git a/src/legacy/nix-env.cc b/src/legacy/nix-env.cc
new file mode 100644
index 000000000..4674fd783
--- /dev/null
+++ b/src/legacy/nix-env.cc
@@ -0,0 +1,1553 @@
+#include "attr-path.hh"
+#include "common-eval-args.hh"
+#include "derivations.hh"
+#include "terminal.hh"
+#include "eval.hh"
+#include "get-drvs.hh"
+#include "globals.hh"
+#include "names.hh"
+#include "profiles.hh"
+#include "path-with-outputs.hh"
+#include "shared.hh"
+#include "store-api.hh"
+#include "local-fs-store.hh"
+#include "user-env.hh"
+#include "users.hh"
+#include "value-to-json.hh"
+#include "xml-writer.hh"
+#include "legacy.hh"
+#include "eval-settings.hh" // for defexpr
+#include "nix-env.hh"
+
+#include <ctime>
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <nlohmann/json.hpp>
+
+using std::cout;
+
+namespace nix {
+
+
+typedef enum {
+    srcNixExprDrvs,
+    srcNixExprs,
+    srcStorePaths,
+    srcProfile,
+    srcAttrPath,
+    srcUnknown
+} InstallSourceType;
+
+
+struct InstallSourceInfo
+{
+    InstallSourceType type;
+    std::shared_ptr<SourcePath> nixExprPath; /* for srcNixExprDrvs, srcNixExprs */
+    Path profile; /* for srcProfile */
+    std::string systemFilter; /* for srcNixExprDrvs */
+    Bindings * autoArgs;
+};
+
+
+struct Globals
+{
+    InstallSourceInfo instSource;
+    Path profile;
+    std::shared_ptr<EvalState> state;
+    bool dryRun;
+    bool preserveInstalled;
+    bool removeAll;
+    std::string forceName;
+    bool prebuiltOnly;
+};
+
+
+typedef void (* Operation) (Globals & globals,
+    Strings opFlags, Strings opArgs);
+
+
+static std::string needArg(Strings::iterator & i,
+    Strings & args, const std::string & arg)
+{
+    if (i == args.end()) throw UsageError("'%1%' requires an argument", arg);
+    return *i++;
+}
+
+
+static bool parseInstallSourceOptions(Globals & globals,
+    Strings::iterator & i, Strings & args, const std::string & arg)
+{
+    if (arg == "--from-expression" || arg == "-E")
+        globals.instSource.type = srcNixExprs;
+    else if (arg == "--from-profile") {
+        globals.instSource.type = srcProfile;
+        globals.instSource.profile = needArg(i, args, arg);
+    }
+    else if (arg == "--attr" || arg == "-A")
+        globals.instSource.type = srcAttrPath;
+    else return false;
+    return true;
+}
+
+
+static bool isNixExpr(const SourcePath & path, struct InputAccessor::Stat & st)
+{
+    return
+        st.type == InputAccessor::tRegular
+        || (st.type == InputAccessor::tDirectory && (path + "default.nix").pathExists());
+}
+
+
+static constexpr size_t maxAttrs = 1024;
+
+
+static void getAllExprs(EvalState & state,
+    const SourcePath & path, StringSet & seen, BindingsBuilder & attrs)
+{
+    StringSet namesSorted;
+    for (auto & [name, _] : path.readDirectory()) namesSorted.insert(name);
+
+    for (auto & i : namesSorted) {
+        /* Ignore the manifest.nix used by profiles.  This is
+           necessary to prevent it from showing up in channels (which
+           are implemented using profiles). */
+        if (i == "manifest.nix") continue;
+
+        SourcePath path2 = path + i;
+
+        InputAccessor::Stat st;
+        try {
+            st = path2.resolveSymlinks().lstat();
+        } catch (Error &) {
+            continue; // ignore dangling symlinks in ~/.nix-defexpr
+        }
+
+        if (isNixExpr(path2, st) && (st.type != InputAccessor::tRegular || path2.baseName().ends_with(".nix"))) {
+            /* Strip off the `.nix' filename suffix (if applicable),
+               otherwise the attribute cannot be selected with the
+               `-A' option.  Useful if you want to stick a Nix
+               expression directly in ~/.nix-defexpr. */
+            std::string attrName = i;
+            if (attrName.ends_with(".nix"))
+                attrName = std::string(attrName, 0, attrName.size() - 4);
+            if (!seen.insert(attrName).second) {
+                std::string suggestionMessage = "";
+                if (path2.path.abs().find("channels") != std::string::npos && path.path.abs().find("channels") != std::string::npos)
+                    suggestionMessage = fmt("\nsuggestion: remove '%s' from either the root channels or the user channels", attrName);
+                printError("warning: name collision in input Nix expressions, skipping '%1%'"
+                            "%2%", path2, suggestionMessage);
+                continue;
+            }
+            /* Load the expression on demand. */
+            auto vArg = state.allocValue();
+            vArg->mkString(path2.path.abs());
+            if (seen.size() == maxAttrs)
+                throw Error("too many Nix expressions in directory '%1%'", path);
+            attrs.alloc(attrName).mkApp(&state.getBuiltin("import"), vArg);
+        }
+        else if (st.type == InputAccessor::tDirectory)
+            /* `path2' is a directory (with no default.nix in it);
+               recurse into it. */
+            getAllExprs(state, path2, seen, attrs);
+    }
+}
+
+
+
+static void loadSourceExpr(EvalState & state, const SourcePath & path, Value & v)
+{
+    auto st = path.resolveSymlinks().lstat();
+
+    if (isNixExpr(path, st))
+        state.evalFile(path, v);
+
+    /* The path is a directory.  Put the Nix expressions in the
+       directory in a set, with the file name of each expression as
+       the attribute name.  Recurse into subdirectories (but keep the
+       set flat, not nested, to make it easier for a user to have a
+       ~/.nix-defexpr directory that includes some system-wide
+       directory). */
+    else if (st.type == InputAccessor::tDirectory) {
+        auto attrs = state.buildBindings(maxAttrs);
+        attrs.alloc("_combineChannels").mkList(0);
+        StringSet seen;
+        getAllExprs(state, path, seen, attrs);
+        v.mkAttrs(attrs);
+    }
+
+    else throw Error("path '%s' is not a directory or a Nix expression", path);
+}
+
+
+static void loadDerivations(EvalState & state, const SourcePath & nixExprPath,
+    std::string systemFilter, Bindings & autoArgs,
+    const std::string & pathPrefix, DrvInfos & elems)
+{
+    Value vRoot;
+    loadSourceExpr(state, nixExprPath, vRoot);
+
+    Value & v(*findAlongAttrPath(state, pathPrefix, autoArgs, vRoot).first);
+
+    getDerivations(state, v, pathPrefix, autoArgs, elems, true);
+
+    /* Filter out all derivations not applicable to the current
+       system. */
+    for (DrvInfos::iterator i = elems.begin(), j; i != elems.end(); i = j) {
+        j = i; j++;
+        if (systemFilter != "*" && i->querySystem() != systemFilter)
+            elems.erase(i);
+    }
+}
+
+
+static NixInt getPriority(EvalState & state, DrvInfo & drv)
+{
+    return drv.queryMetaInt("priority", NixInt(0));
+}
+
+
+static std::strong_ordering comparePriorities(EvalState & state, DrvInfo & drv1, DrvInfo & drv2)
+{
+    return getPriority(state, drv2) <=> getPriority(state, drv1);
+}
+
+
+// FIXME: this function is rather slow since it checks a single path
+// at a time.
+static bool isPrebuilt(EvalState & state, DrvInfo & elem)
+{
+    auto path = elem.queryOutPath();
+    if (state.store->isValidPath(path)) return true;
+    return state.store->querySubstitutablePaths({path}).count(path);
+}
+
+
+static void checkSelectorUse(DrvNames & selectors)
+{
+    /* Check that all selectors have been used. */
+    for (auto & i : selectors)
+        if (i.hits == 0 && i.fullName != "*")
+            throw Error("selector '%1%' matches no derivations", i.fullName);
+}
+
+
+namespace {
+
+std::set<std::string> searchByPrefix(DrvInfos & allElems, std::string_view prefix) {
+    constexpr std::size_t maxResults = 3;
+    std::set<std::string> result;
+    for (auto & drvInfo : allElems) {
+        const auto drvName = DrvName { drvInfo.queryName() };
+        if (drvName.name.starts_with(prefix)) {
+            result.emplace(drvName.name);
+
+            if (result.size() >= maxResults) {
+                break;
+            }
+        }
+    }
+    return result;
+}
+
+struct Match
+{
+    DrvInfo drvInfo;
+    std::size_t index;
+
+    Match(DrvInfo drvInfo_, std::size_t index_)
+    : drvInfo{std::move(drvInfo_)}
+    , index{index_}
+    {}
+};
+
+/* If a selector matches multiple derivations
+   with the same name, pick the one matching the current
+   system.  If there are still multiple derivations, pick the
+   one with the highest priority.  If there are still multiple
+   derivations, pick the one with the highest version.
+   Finally, if there are still multiple derivations,
+   arbitrarily pick the first one. */
+std::vector<Match> pickNewestOnly(EvalState & state, std::vector<Match> matches) {
+    /* Map from package names to derivations. */
+    std::map<std::string, Match> newest;
+    StringSet multiple;
+
+    for (auto & match : matches) {
+        auto & oneDrv = match.drvInfo;
+
+        const auto drvName = DrvName { oneDrv.queryName() };
+        std::strong_ordering comparison = std::strong_ordering::greater;
+
+        const auto itOther = newest.find(drvName.name);
+
+        if (itOther != newest.end()) {
+            auto & newestDrv = itOther->second.drvInfo;
+
+            comparison =
+                oneDrv.querySystem() == newestDrv.querySystem() ? std::strong_ordering::equal :
+                oneDrv.querySystem() == settings.thisSystem ? std::strong_ordering::greater :
+                newestDrv.querySystem() == settings.thisSystem ? std::strong_ordering::less : std::strong_ordering::equal;
+            if (comparison == 0)
+                comparison = comparePriorities(state, oneDrv, newestDrv);
+            if (comparison == 0)
+                comparison = compareVersions(drvName.version, DrvName { newestDrv.queryName() }.version);
+        }
+
+        if (comparison > 0) {
+            newest.erase(drvName.name);
+            newest.emplace(drvName.name, match);
+            multiple.erase(drvName.fullName);
+        } else if (comparison == 0) {
+            multiple.insert(drvName.fullName);
+        }
+    }
+
+    matches.clear();
+    for (auto & [name, match] : newest) {
+        if (multiple.find(name) != multiple.end())
+            warn(
+                "there are multiple derivations named '%1%'; using the first one",
+                name);
+        matches.push_back(match);
+    }
+
+    return matches;
+}
+
+} // end namespace
+
+static DrvInfos filterBySelector(EvalState & state, DrvInfos & allElems,
+    const Strings & args, bool newestOnly)
+{
+    DrvNames selectors = drvNamesFromArgs(args);
+    if (selectors.empty())
+        selectors.emplace_back("*");
+
+    DrvInfos elems;
+    std::set<std::size_t> done;
+
+    for (auto & selector : selectors) {
+        std::vector<Match> matches;
+        for (auto && [index, drvInfo] : enumerate(allElems)) {
+            const auto drvName = DrvName { drvInfo.queryName() };
+            if (selector.matches(drvName)) {
+                ++selector.hits;
+                matches.emplace_back(drvInfo, index);
+            }
+        }
+
+        if (newestOnly) {
+            matches = pickNewestOnly(state, std::move(matches));
+        }
+
+        /* Insert only those elements in the final list that we
+           haven't inserted before. */
+        for (auto & match : matches)
+            if (done.insert(match.index).second)
+                elems.push_back(match.drvInfo);
+
+        if (selector.hits == 0 && selector.fullName != "*") {
+            const auto prefixHits = searchByPrefix(allElems, selector.name);
+
+            if (prefixHits.empty()) {
+                throw Error("selector '%1%' matches no derivations", selector.fullName);
+            } else {
+                std::string suggestionMessage = ", maybe you meant:";
+                for (const auto & drvName : prefixHits) {
+                    suggestionMessage += fmt("\n%s", drvName);
+                }
+                throw Error("selector '%1%' matches no derivations" + suggestionMessage, selector.fullName);
+            }
+        }
+    }
+
+    return elems;
+}
+
+
+static bool isPath(std::string_view s)
+{
+    return s.find('/') != std::string_view::npos;
+}
+
+
+static void queryInstSources(EvalState & state,
+    InstallSourceInfo & instSource, const Strings & args,
+    DrvInfos & elems, bool newestOnly)
+{
+    InstallSourceType type = instSource.type;
+    if (type == srcUnknown && args.size() > 0 && isPath(args.front()))
+        type = srcStorePaths;
+
+    switch (type) {
+
+        /* Get the available user environment elements from the
+           derivations specified in a Nix expression, including only
+           those with names matching any of the names in `args'. */
+        case srcUnknown:
+        case srcNixExprDrvs: {
+
+            /* Load the derivations from the (default or specified)
+               Nix expression. */
+            DrvInfos allElems;
+            loadDerivations(state, *instSource.nixExprPath,
+                instSource.systemFilter, *instSource.autoArgs, "", allElems);
+
+            elems = filterBySelector(state, allElems, args, newestOnly);
+
+            break;
+        }
+
+        /* Get the available user environment elements from the Nix
+           expressions specified on the command line; these should be
+           functions that take the default Nix expression file as
+           argument, e.g., if the file is `./foo.nix', then the
+           argument `x: x.bar' is equivalent to `(x: x.bar)
+           (import ./foo.nix)' = `(import ./foo.nix).bar'. */
+        case srcNixExprs: {
+
+            Value vArg;
+            loadSourceExpr(state, *instSource.nixExprPath, vArg);
+
+            for (auto & i : args) {
+                Expr & eFun = state.parseExprFromString(i, state.rootPath(CanonPath::fromCwd()));
+                Value vFun, vTmp;
+                state.eval(eFun, vFun);
+                vTmp.mkApp(&vFun, &vArg);
+                getDerivations(state, vTmp, "", *instSource.autoArgs, elems, true);
+            }
+
+            break;
+        }
+
+        /* The available user environment elements are specified as a
+           list of store paths (which may or may not be
+           derivations). */
+        case srcStorePaths: {
+
+            for (auto & i : args) {
+                auto path = state.store->followLinksToStorePath(i);
+
+                std::string name(path.name());
+
+                DrvInfo elem(state, "", nullptr);
+                elem.setName(name);
+
+                if (path.isDerivation()) {
+                    elem.setDrvPath(path);
+                    auto outputs = state.store->queryDerivationOutputMap(path);
+                    elem.setOutPath(outputs.at("out"));
+                    if (name.size() >= drvExtension.size() &&
+                        std::string(name, name.size() - drvExtension.size()) == drvExtension)
+                        name = name.substr(0, name.size() - drvExtension.size());
+                }
+                else
+                    elem.setOutPath(path);
+
+                elems.push_back(elem);
+            }
+
+            break;
+        }
+
+        /* Get the available user environment elements from another
+           user environment.  These are then filtered as in the
+           `srcNixExprDrvs' case. */
+        case srcProfile: {
+            auto installed = queryInstalled(state, instSource.profile);
+            elems = filterBySelector(
+                state,
+                installed,
+                args, newestOnly
+            );
+            break;
+        }
+
+        case srcAttrPath: {
+            Value vRoot;
+            loadSourceExpr(state, *instSource.nixExprPath, vRoot);
+            for (auto & i : args) {
+                Value & v(*findAlongAttrPath(state, i, *instSource.autoArgs, vRoot).first);
+                getDerivations(state, v, "", *instSource.autoArgs, elems, true);
+            }
+            break;
+        }
+    }
+}
+
+
+static void printMissing(EvalState & state, DrvInfos & elems)
+{
+    std::vector<DerivedPath> targets;
+    for (auto & i : elems)
+        if (auto drvPath = i.queryDrvPath())
+            targets.emplace_back(DerivedPath::Built{
+                .drvPath = makeConstantStorePathRef(*drvPath),
+                .outputs = OutputsSpec::All { },
+            });
+        else
+            targets.emplace_back(DerivedPath::Opaque{
+                .path = i.queryOutPath(),
+            });
+
+    printMissing(state.store, targets);
+}
+
+
+static bool keep(DrvInfo & drv)
+{
+    return drv.queryMetaBool("keep", false);
+}
+
+
+static void installDerivations(Globals & globals,
+    const Strings & args, const Path & profile)
+{
+    debug("installing derivations");
+
+    /* Get the set of user environment elements to be installed. */
+    DrvInfos newElems, newElemsTmp;
+    queryInstSources(*globals.state, globals.instSource, args, newElemsTmp, true);
+
+    /* If --prebuilt-only is given, filter out source-only packages. */
+    for (auto & i : newElemsTmp)
+        if (!globals.prebuiltOnly || isPrebuilt(*globals.state, i))
+            newElems.push_back(i);
+
+    StringSet newNames;
+    for (auto & i : newElems) {
+        /* `forceName' is a hack to get package names right in some
+           one-click installs, namely those where the name used in the
+           path is not the one we want (e.g., `java-front' versus
+           `java-front-0.9pre15899'). */
+        if (globals.forceName != "")
+            i.setName(globals.forceName);
+        newNames.insert(DrvName(i.queryName()).name);
+    }
+
+
+    while (true) {
+        auto lockToken = optimisticLockProfile(profile);
+
+        DrvInfos allElems(newElems);
+
+        /* Add in the already installed derivations, unless they have
+           the same name as a to-be-installed element. */
+        if (!globals.removeAll) {
+            DrvInfos installedElems = queryInstalled(*globals.state, profile);
+
+            for (auto & i : installedElems) {
+                DrvName drvName(i.queryName());
+                if (!globals.preserveInstalled &&
+                    newNames.find(drvName.name) != newNames.end() &&
+                    !keep(i))
+                    printInfo("replacing old '%s'", i.queryName());
+                else
+                    allElems.push_back(i);
+            }
+
+            for (auto & i : newElems)
+                printInfo("installing '%s'", i.queryName());
+        }
+
+        printMissing(*globals.state, newElems);
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(*globals.state, allElems,
+                profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opInstall(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        auto arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else if (arg == "--preserve-installed" || arg == "-P")
+            globals.preserveInstalled = true;
+        else if (arg == "--remove-all" || arg == "-r")
+            globals.removeAll = true;
+        else throw UsageError("unknown flag '%1%'", arg);
+    }
+
+    installDerivations(globals, opArgs, globals.profile);
+}
+
+
+typedef enum { utLt, utLeq, utEq, utAlways } UpgradeType;
+
+
+static void upgradeDerivations(Globals & globals,
+    const Strings & args, UpgradeType upgradeType)
+{
+    debug("upgrading derivations");
+
+    /* Upgrade works as follows: we take all currently installed
+       derivations, and for any derivation matching any selector, look
+       for a derivation in the input Nix expression that has the same
+       name and a higher version number. */
+
+    while (true) {
+        auto lockToken = optimisticLockProfile(globals.profile);
+
+        DrvInfos installedElems = queryInstalled(*globals.state, globals.profile);
+
+        /* Fetch all derivations from the input file. */
+        DrvInfos availElems;
+        queryInstSources(*globals.state, globals.instSource, args, availElems, false);
+
+        /* Go through all installed derivations. */
+        DrvInfos newElems;
+        for (auto & i : installedElems) {
+            DrvName drvName(i.queryName());
+
+            try {
+
+                if (keep(i)) {
+                    newElems.push_back(i);
+                    continue;
+                }
+
+                /* Find the derivation in the input Nix expression
+                   with the same name that satisfies the version
+                   constraints specified by upgradeType.  If there are
+                   multiple matches, take the one with the highest
+                   priority.  If there are still multiple matches,
+                   take the one with the highest version.
+                   Do not upgrade if it would decrease the priority. */
+                DrvInfos::iterator bestElem = availElems.end();
+                std::string bestVersion;
+                for (auto j = availElems.begin(); j != availElems.end(); ++j) {
+                    if (comparePriorities(*globals.state, i, *j) > 0)
+                        continue;
+                    DrvName newName(j->queryName());
+                    if (newName.name == drvName.name) {
+                        std::strong_ordering d = compareVersions(drvName.version, newName.version);
+                        if ((upgradeType == utLt && d < 0) ||
+                            (upgradeType == utLeq && d <= 0) ||
+                            (upgradeType == utEq && d == 0) ||
+                            upgradeType == utAlways)
+                        {
+                            std::strong_ordering d2 = std::strong_ordering::less;
+                            if (bestElem != availElems.end()) {
+                                d2 = comparePriorities(*globals.state, *bestElem, *j);
+                                if (d2 == 0) d2 = compareVersions(bestVersion, newName.version);
+                            }
+                            if (d2 < 0 && (!globals.prebuiltOnly || isPrebuilt(*globals.state, *j))) {
+                                bestElem = j;
+                                bestVersion = newName.version;
+                            }
+                        }
+                    }
+                }
+
+                if (bestElem != availElems.end() &&
+                    i.queryOutPath() !=
+                    bestElem->queryOutPath())
+                {
+                    const char * action = compareVersions(drvName.version, bestVersion) <= 0
+                        ? "upgrading" : "downgrading";
+                    printInfo("%1% '%2%' to '%3%'",
+                        action, i.queryName(), bestElem->queryName());
+                    newElems.push_back(*bestElem);
+                } else newElems.push_back(i);
+
+            } catch (Error & e) {
+                e.addTrace(nullptr, "while trying to find an upgrade for '%s'", i.queryName());
+                throw;
+            }
+        }
+
+        printMissing(*globals.state, newElems);
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(*globals.state, newElems,
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opUpgrade(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    UpgradeType upgradeType = utLt;
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        std::string arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else if (arg == "--lt") upgradeType = utLt;
+        else if (arg == "--leq") upgradeType = utLeq;
+        else if (arg == "--eq") upgradeType = utEq;
+        else if (arg == "--always") upgradeType = utAlways;
+        else throw UsageError("unknown flag '%1%'", arg);
+    }
+
+    upgradeDerivations(globals, opArgs, upgradeType);
+}
+
+
+static void setMetaFlag(EvalState & state, DrvInfo & drv,
+    const std::string & name, const std::string & value)
+{
+    auto v = state.allocValue();
+    v->mkString(value);
+    drv.setMeta(name, v);
+}
+
+
+static void opSetFlag(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    if (opArgs.size() < 2)
+        throw UsageError("not enough arguments to '--set-flag'");
+
+    Strings::iterator arg = opArgs.begin();
+    std::string flagName = *arg++;
+    std::string flagValue = *arg++;
+    DrvNames selectors = drvNamesFromArgs(Strings(arg, opArgs.end()));
+
+    while (true) {
+        std::string lockToken = optimisticLockProfile(globals.profile);
+
+        DrvInfos installedElems = queryInstalled(*globals.state, globals.profile);
+
+        /* Update all matching derivations. */
+        for (auto & i : installedElems) {
+            DrvName drvName(i.queryName());
+            for (auto & j : selectors)
+                if (j.matches(drvName)) {
+                    printInfo("setting flag on '%1%'", i.queryName());
+                    j.hits++;
+                    setMetaFlag(*globals.state, i, flagName, flagValue);
+                    break;
+                }
+        }
+
+        checkSelectorUse(selectors);
+
+        /* Write the new user environment. */
+        if (createUserEnv(*globals.state, installedElems,
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opSet(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    auto store2 = globals.state->store.dynamic_pointer_cast<LocalFSStore>();
+    if (!store2) throw Error("--set is not supported for this Nix store");
+
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        std::string arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else throw UsageError("unknown flag '%1%'", arg);
+    }
+
+    DrvInfos elems;
+    queryInstSources(*globals.state, globals.instSource, opArgs, elems, true);
+
+    if (elems.size() != 1)
+        throw Error("--set requires exactly one derivation");
+
+    DrvInfo & drv(elems.front());
+
+    if (globals.forceName != "")
+        drv.setName(globals.forceName);
+
+    auto drvPath = drv.queryDrvPath();
+    std::vector<DerivedPath> paths {
+        drvPath
+        ? (DerivedPath) (DerivedPath::Built {
+            .drvPath = makeConstantStorePathRef(*drvPath),
+            .outputs = OutputsSpec::All { },
+        })
+        : (DerivedPath) (DerivedPath::Opaque {
+            .path = drv.queryOutPath(),
+        }),
+    };
+    printMissing(globals.state->store, paths);
+    if (globals.dryRun) return;
+    globals.state->store->buildPaths(paths, globals.state->repair ? bmRepair : bmNormal);
+
+    debug("switching to new user environment");
+    Path generation = createGeneration(
+        *store2,
+        globals.profile,
+        drv.queryOutPath());
+    switchLink(globals.profile, generation);
+}
+
+
+static void uninstallDerivations(Globals & globals, Strings & selectors,
+    Path & profile)
+{
+    while (true) {
+        auto lockToken = optimisticLockProfile(profile);
+
+        DrvInfos workingElems = queryInstalled(*globals.state, profile);
+
+        for (auto & selector : selectors) {
+            DrvInfos::iterator split = workingElems.begin();
+            if (isPath(selector)) {
+                StorePath selectorStorePath = globals.state->store->followLinksToStorePath(selector);
+                split = std::partition(
+                    workingElems.begin(), workingElems.end(),
+                    [&selectorStorePath, globals](auto &elem) {
+                        return selectorStorePath != elem.queryOutPath();
+                    }
+                );
+            } else {
+                DrvName selectorName(selector);
+                split = std::partition(
+                    workingElems.begin(), workingElems.end(),
+                    [&selectorName](auto &elem){
+                        DrvName elemName(elem.queryName());
+                        return !selectorName.matches(elemName);
+                    }
+                );
+            }
+            if (split == workingElems.end())
+                warn("selector '%s' matched no installed derivations", selector);
+            for (auto removedElem = split; removedElem != workingElems.end(); removedElem++) {
+                printInfo("uninstalling '%s'", removedElem->queryName());
+            }
+            workingElems.erase(split, workingElems.end());
+        }
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(*globals.state, workingElems,
+                profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opUninstall(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    uninstallDerivations(globals, opArgs, globals.profile);
+}
+
+
+static bool cmpChars(char a, char b)
+{
+    return toupper(a) < toupper(b);
+}
+
+
+static bool cmpElemByName(DrvInfo & a, DrvInfo & b)
+{
+    auto a_name = a.queryName();
+    auto b_name = b.queryName();
+    return lexicographical_compare(
+        a_name.begin(), a_name.end(),
+        b_name.begin(), b_name.end(), cmpChars);
+}
+
+
+typedef std::list<Strings> Table;
+
+
+void printTable(Table & table)
+{
+    auto nrColumns = table.size() > 0 ? table.front().size() : 0;
+
+    std::vector<size_t> widths;
+    widths.resize(nrColumns);
+
+    for (auto & i : table) {
+        assert(i.size() == nrColumns);
+        Strings::iterator j;
+        size_t column;
+        for (j = i.begin(), column = 0; j != i.end(); ++j, ++column)
+            if (j->size() > widths[column]) widths[column] = j->size();
+    }
+
+    for (auto & i : table) {
+        Strings::iterator j;
+        size_t column;
+        for (j = i.begin(), column = 0; j != i.end(); ++j, ++column) {
+            std::string s = *j;
+            replace(s.begin(), s.end(), '\n', ' ');
+            cout << s;
+            if (column < nrColumns - 1)
+                cout << std::string(widths[column] - s.size() + 2, ' ');
+        }
+        cout << std::endl;
+    }
+}
+
+
+/* This function compares the version of an element against the
+   versions in the given set of elements.  `cvLess' means that only
+   lower versions are in the set, `cvEqual' means that at most an
+   equal version is in the set, and `cvGreater' means that there is at
+   least one element with a higher version in the set.  `cvUnavail'
+   means that there are no elements with the same name in the set. */
+
+typedef enum { cvLess, cvEqual, cvGreater, cvUnavail } VersionDiff;
+
+static VersionDiff compareVersionAgainstSet(
+    DrvInfo & elem, DrvInfos & elems, std::string & version)
+{
+    DrvName name(elem.queryName());
+
+    VersionDiff diff = cvUnavail;
+    version = "?";
+
+    for (auto & i : elems) {
+        DrvName name2(i.queryName());
+        if (name.name == name2.name) {
+            std::strong_ordering d = compareVersions(name.version, name2.version);
+            if (d < 0) {
+                diff = cvGreater;
+                version = name2.version;
+            }
+            else if (diff != cvGreater && d == 0) {
+                diff = cvEqual;
+                version = name2.version;
+            }
+            else if (diff != cvGreater && diff != cvEqual && d > 0) {
+                diff = cvLess;
+                if (version == "" || compareVersions(version, name2.version) < 0)
+                    version = name2.version;
+            }
+        }
+    }
+
+    return diff;
+}
+
+
+static void queryJSON(Globals & globals, std::vector<DrvInfo> & elems, bool printOutPath, bool printDrvPath, bool printMeta)
+{
+    using nlohmann::json;
+    json topObj = json::object();
+    for (auto & i : elems) {
+        try {
+            if (i.hasFailed()) continue;
+
+
+            auto drvName = DrvName(i.queryName());
+            json &pkgObj = topObj[i.attrPath];
+            pkgObj = {
+                {"name", drvName.fullName},
+                {"pname", drvName.name},
+                {"version", drvName.version},
+                {"system", i.querySystem()},
+                {"outputName", i.queryOutputName()},
+            };
+
+            {
+                DrvInfo::Outputs outputs = i.queryOutputs(printOutPath);
+                json &outputObj = pkgObj["outputs"];
+                outputObj = json::object();
+                for (auto & j : outputs) {
+                    if (j.second)
+                        outputObj[j.first] = globals.state->store->printStorePath(*j.second);
+                    else
+                        outputObj[j.first] = nullptr;
+                }
+            }
+
+            if (printDrvPath) {
+                auto drvPath = i.queryDrvPath();
+                if (drvPath) pkgObj["drvPath"] = globals.state->store->printStorePath(*drvPath);
+            }
+
+            if (printMeta) {
+                json &metaObj = pkgObj["meta"];
+                metaObj = json::object();
+                StringSet metaNames = i.queryMetaNames();
+                for (auto & j : metaNames) {
+                    Value * v = i.queryMeta(j);
+                    if (!v) {
+                        printError("derivation '%s' has invalid meta attribute '%s'", i.queryName(), j);
+                        metaObj[j] = nullptr;
+                    } else {
+                        NixStringContext context;
+                        metaObj[j] = printValueAsJSON(*globals.state, true, *v, noPos, context);
+                    }
+                }
+            }
+        } catch (AssertionError & e) {
+            printMsg(lvlTalkative, "skipping derivation named '%1%' which gives an assertion failure", i.queryName());
+        } catch (Error & e) {
+            e.addTrace(nullptr, "while querying the derivation named '%1%'", i.queryName());
+            throw;
+        }
+    }
+    std::cout << topObj.dump(2);
+}
+
+
+static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    auto & store { *globals.state->store };
+
+    Strings remaining;
+    std::string attrPath;
+
+    bool printStatus = false;
+    bool printName = true;
+    bool printAttrPath = false;
+    bool printSystem = false;
+    bool printDrvPath = false;
+    bool printOutPath = false;
+    bool printDescription = false;
+    bool printMeta = false;
+    bool compareVersions = false;
+    bool xmlOutput = false;
+    bool jsonOutput = false;
+
+    enum { sInstalled, sAvailable } source = sInstalled;
+
+    settings.readOnlyMode = true; /* makes evaluation a bit faster */
+
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        auto arg = *i++;
+        if (arg == "--status" || arg == "-s") printStatus = true;
+        else if (arg == "--no-name") printName = false;
+        else if (arg == "--system") printSystem = true;
+        else if (arg == "--description") printDescription = true;
+        else if (arg == "--compare-versions" || arg == "-c") compareVersions = true;
+        else if (arg == "--drv-path") printDrvPath = true;
+        else if (arg == "--out-path") printOutPath = true;
+        else if (arg == "--meta") printMeta = true;
+        else if (arg == "--installed") source = sInstalled;
+        else if (arg == "--available" || arg == "-a") source = sAvailable;
+        else if (arg == "--xml") xmlOutput = true;
+        else if (arg == "--json") jsonOutput = true;
+        else if (arg == "--attr-path" || arg == "-P") printAttrPath = true;
+        else if (arg == "--attr" || arg == "-A")
+            attrPath = needArg(i, opFlags, arg);
+        else
+            throw UsageError("unknown flag '%1%'", arg);
+    }
+
+    if (printAttrPath && source != sAvailable)
+        throw UsageError("--attr-path(-P) only works with --available");
+
+    /* Obtain derivation information from the specified source. */
+    DrvInfos availElems, installedElems;
+
+    if (source == sInstalled || compareVersions || printStatus)
+        installedElems = queryInstalled(*globals.state, globals.profile);
+
+    if (source == sAvailable || compareVersions)
+        loadDerivations(*globals.state, *globals.instSource.nixExprPath,
+            globals.instSource.systemFilter, *globals.instSource.autoArgs,
+            attrPath, availElems);
+
+    DrvInfos elems_ = filterBySelector(*globals.state,
+        source == sInstalled ? installedElems : availElems,
+        opArgs, false);
+
+    DrvInfos & otherElems(source == sInstalled ? availElems : installedElems);
+
+
+    /* Sort them by name. */
+    /* !!! */
+    std::vector<DrvInfo> elems;
+    for (auto & i : elems_) elems.push_back(i);
+    sort(elems.begin(), elems.end(), cmpElemByName);
+
+
+    /* We only need to know the installed paths when we are querying
+       the status of the derivation. */
+    StorePathSet installed; /* installed paths */
+
+    if (printStatus)
+        for (auto & i : installedElems)
+            installed.insert(i.queryOutPath());
+
+
+    /* Query which paths have substitutes. */
+    StorePathSet validPaths;
+    StorePathSet substitutablePaths;
+    if (printStatus || globals.prebuiltOnly) {
+        StorePathSet paths;
+        for (auto & i : elems)
+            try {
+                paths.insert(i.queryOutPath());
+            } catch (AssertionError & e) {
+                printMsg(lvlTalkative, "skipping derivation named '%s' which gives an assertion failure", i.queryName());
+                i.setFailed();
+            }
+        validPaths = store.queryValidPaths(paths);
+        substitutablePaths = store.querySubstitutablePaths(paths);
+    }
+
+
+    /* Print the desired columns, or XML output. */
+    if (jsonOutput) {
+        queryJSON(globals, elems, printOutPath, printDrvPath, printMeta);
+        cout << '\n';
+        return;
+    }
+
+    RunPager pager;
+
+    Table table;
+    std::ostringstream dummy;
+    XMLWriter xml(true, *(xmlOutput ? &cout : &dummy));
+    XMLOpenElement xmlRoot(xml, "items");
+
+    for (auto & i : elems) {
+        try {
+            if (i.hasFailed()) continue;
+
+            //Activity act(*logger, lvlDebug, "outputting query result '%1%'", i.attrPath);
+
+            if (globals.prebuiltOnly &&
+                !validPaths.count(i.queryOutPath()) &&
+                !substitutablePaths.count(i.queryOutPath()))
+                continue;
+
+            /* For table output. */
+            Strings columns;
+
+            /* For XML output. */
+            XMLAttrs attrs;
+
+            if (printStatus) {
+                auto outPath = i.queryOutPath();
+                bool hasSubs = substitutablePaths.count(outPath);
+                bool isInstalled = installed.count(outPath);
+                bool isValid = validPaths.count(outPath);
+                if (xmlOutput) {
+                    attrs["installed"] = isInstalled ? "1" : "0";
+                    attrs["valid"] = isValid ? "1" : "0";
+                    attrs["substitutable"] = hasSubs ? "1" : "0";
+                } else
+                    columns.push_back(
+                        (std::string) (isInstalled ? "I" : "-")
+                        + (isValid ? "P" : "-")
+                        + (hasSubs ? "S" : "-"));
+            }
+
+            if (xmlOutput)
+                attrs["attrPath"] = i.attrPath;
+            else if (printAttrPath)
+                columns.push_back(i.attrPath);
+
+            if (xmlOutput) {
+                auto drvName = DrvName(i.queryName());
+                attrs["name"] = drvName.fullName;
+                attrs["pname"] = drvName.name;
+                attrs["version"] = drvName.version;
+            } else if (printName) {
+                columns.push_back(i.queryName());
+            }
+
+            if (compareVersions) {
+                /* Compare this element against the versions of the
+                   same named packages in either the set of available
+                   elements, or the set of installed elements.  !!!
+                   This is O(N * M), should be O(N * lg M). */
+                std::string version;
+                VersionDiff diff = compareVersionAgainstSet(i, otherElems, version);
+
+                char ch;
+                switch (diff) {
+                    case cvLess: ch = '>'; break;
+                    case cvEqual: ch = '='; break;
+                    case cvGreater: ch = '<'; break;
+                    case cvUnavail: ch = '-'; break;
+                    default: abort();
+                }
+
+                if (xmlOutput) {
+                    if (diff != cvUnavail) {
+                        attrs["versionDiff"] = ch;
+                        attrs["maxComparedVersion"] = version;
+                    }
+                } else {
+                    auto column = (std::string) "" + ch + " " + version;
+                    if (diff == cvGreater && shouldANSI(StandardOutputStream::Stdout))
+                        column = ANSI_RED + column + ANSI_NORMAL;
+                    columns.push_back(column);
+                }
+            }
+
+            if (xmlOutput) {
+                if (i.querySystem() != "") attrs["system"] = i.querySystem();
+            }
+            else if (printSystem)
+                columns.push_back(i.querySystem());
+
+            if (printDrvPath) {
+                auto drvPath = i.queryDrvPath();
+                if (xmlOutput) {
+                    if (drvPath) attrs["drvPath"] = store.printStorePath(*drvPath);
+                } else
+                    columns.push_back(drvPath ? store.printStorePath(*drvPath) : "-");
+            }
+
+            if (xmlOutput)
+                attrs["outputName"] = i.queryOutputName();
+
+            if (printOutPath && !xmlOutput) {
+                DrvInfo::Outputs outputs = i.queryOutputs();
+                std::string s;
+                for (auto & j : outputs) {
+                    if (!s.empty()) s += ';';
+                    if (j.first != "out") { s += j.first; s += "="; }
+                    s += store.printStorePath(*j.second);
+                }
+                columns.push_back(s);
+            }
+
+            if (printDescription) {
+                auto descr = i.queryMetaString("description");
+                if (xmlOutput) {
+                    if (descr != "") attrs["description"] = descr;
+                } else
+                    columns.push_back(descr);
+            }
+
+            if (xmlOutput) {
+                XMLOpenElement item(xml, "item", attrs);
+                DrvInfo::Outputs outputs = i.queryOutputs(printOutPath);
+                for (auto & j : outputs) {
+                    XMLAttrs attrs2;
+                    attrs2["name"] = j.first;
+                    if (j.second)
+                        attrs2["path"] = store.printStorePath(*j.second);
+                    xml.writeEmptyElement("output", attrs2);
+                }
+                if (printMeta) {
+                    StringSet metaNames = i.queryMetaNames();
+                    for (auto & j : metaNames) {
+                        XMLAttrs attrs2;
+                        attrs2["name"] = j;
+                        Value * v = i.queryMeta(j);
+                        if (!v)
+                            printError(
+                                "derivation '%s' has invalid meta attribute '%s'",
+                                i.queryName(), j);
+                        else {
+                            if (v->type() == nString) {
+                                attrs2["type"] = "string";
+                                attrs2["value"] = v->string.s;
+                                xml.writeEmptyElement("meta", attrs2);
+                            } else if (v->type() == nInt) {
+                                attrs2["type"] = "int";
+                                attrs2["value"] = fmt("%1%", v->integer);
+                                xml.writeEmptyElement("meta", attrs2);
+                            } else if (v->type() == nFloat) {
+                                attrs2["type"] = "float";
+                                attrs2["value"] = fmt("%1%", v->fpoint);
+                                xml.writeEmptyElement("meta", attrs2);
+                            } else if (v->type() == nBool) {
+                                attrs2["type"] = "bool";
+                                attrs2["value"] = v->boolean ? "true" : "false";
+                                xml.writeEmptyElement("meta", attrs2);
+                            } else if (v->type() == nList) {
+                                attrs2["type"] = "strings";
+                                XMLOpenElement m(xml, "meta", attrs2);
+                                for (auto elem : v->listItems()) {
+                                    if (elem->type() != nString) continue;
+                                    XMLAttrs attrs3;
+                                    attrs3["value"] = elem->string.s;
+                                    xml.writeEmptyElement("string", attrs3);
+                                }
+                            } else if (v->type() == nAttrs) {
+                                attrs2["type"] = "strings";
+                                XMLOpenElement m(xml, "meta", attrs2);
+                                Bindings & attrs = *v->attrs;
+                                for (auto &i : attrs) {
+                                    Attr & a(*attrs.find(i.name));
+                                    if(a.value->type() != nString) continue;
+                                    XMLAttrs attrs3;
+                                    attrs3["type"] = globals.state->symbols[i.name];
+                                    attrs3["value"] = a.value->string.s;
+                                    xml.writeEmptyElement("string", attrs3);
+                            }
+                            }
+                        }
+                    }
+                }
+            } else
+                table.push_back(columns);
+
+            cout.flush();
+
+        } catch (AssertionError & e) {
+            printMsg(lvlTalkative, "skipping derivation named '%1%' which gives an assertion failure", i.queryName());
+        } catch (Error & e) {
+            e.addTrace(nullptr, "while querying the derivation named '%1%'", i.queryName());
+            throw;
+        }
+    }
+
+    if (!xmlOutput) printTable(table);
+}
+
+
+static void opSwitchProfile(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    if (opArgs.size() != 1)
+        throw UsageError("exactly one argument expected");
+
+    Path profile = absPath(opArgs.front());
+    Path profileLink = settings.useXDGBaseDirectories ? createNixStateDir() + "/profile" : getHome() + "/.nix-profile";
+
+    switchLink(profileLink, profile);
+}
+
+
+static void opSwitchGeneration(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    if (opArgs.size() != 1)
+        throw UsageError("exactly one argument expected");
+
+    if (auto dstGen = string2Int<GenerationNumber>(opArgs.front()))
+        switchGeneration(globals.profile, *dstGen, globals.dryRun);
+    else
+        throw UsageError("expected a generation number");
+}
+
+
+static void opRollback(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    if (opArgs.size() != 0)
+        throw UsageError("no arguments expected");
+
+    switchGeneration(globals.profile, {}, globals.dryRun);
+}
+
+
+static void opListGenerations(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+    if (opArgs.size() != 0)
+        throw UsageError("no arguments expected");
+
+    PathLocks lock;
+    lockProfile(lock, globals.profile);
+
+    auto [gens, curGen] = findGenerations(globals.profile);
+
+    RunPager pager;
+
+    for (auto & i : gens) {
+        tm t;
+        if (!localtime_r(&i.creationTime, &t)) throw Error("cannot convert time");
+        logger->cout("%|4|   %|4|-%|02|-%|02| %|02|:%|02|:%|02|   %||",
+            i.number,
+            t.tm_year + 1900, t.tm_mon + 1, t.tm_mday,
+            t.tm_hour, t.tm_min, t.tm_sec,
+            i.number == curGen ? "(current)" : "");
+    }
+}
+
+
+static void opDeleteGenerations(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError("unknown flag '%1%'", opFlags.front());
+
+    if (opArgs.size() == 1 && opArgs.front() == "old") {
+        deleteOldGenerations(globals.profile, globals.dryRun);
+    } else if (opArgs.size() == 1 && opArgs.front().find('d') != std::string::npos) {
+        auto t = parseOlderThanTimeSpec(opArgs.front());
+        deleteGenerationsOlderThan(globals.profile, t, globals.dryRun);
+    } else if (opArgs.size() == 1 && opArgs.front().find('+') != std::string::npos) {
+        if (opArgs.front().size() < 2)
+            throw Error("invalid number of generations '%1%'", opArgs.front());
+        auto str_max = opArgs.front().substr(1);
+        auto max = string2Int<GenerationNumber>(str_max);
+        if (!max)
+            throw Error("invalid number of generations to keep '%1%'", opArgs.front());
+        deleteGenerationsGreaterThan(globals.profile, *max, globals.dryRun);
+    } else {
+        std::set<GenerationNumber> gens;
+        for (auto & i : opArgs) {
+            if (auto n = string2Int<GenerationNumber>(i))
+                gens.insert(*n);
+            else
+                throw UsageError("invalid generation number '%1%'", i);
+        }
+        deleteGenerations(globals.profile, gens, globals.dryRun);
+    }
+}
+
+
+static void opVersion(Globals & globals, Strings opFlags, Strings opArgs)
+{
+    printVersion("nix-env");
+}
+
+
+static int main_nix_env(int argc, char * * argv)
+{
+    {
+        Strings opFlags, opArgs;
+        Operation op = 0;
+        std::string opName;
+        bool showHelp = false;
+        std::string file;
+
+        Globals globals;
+
+        globals.instSource.type = srcUnknown;
+        globals.instSource.systemFilter = "*";
+
+        Path nixExprPath = getNixDefExpr();
+
+        if (!pathExists(nixExprPath)) {
+            try {
+                createDirs(nixExprPath);
+                replaceSymlink(
+                    defaultChannelsDir(),
+                    nixExprPath + "/channels");
+                if (getuid() != 0)
+                    replaceSymlink(
+                        rootChannelsDir(),
+                        nixExprPath + "/channels_root");
+            } catch (Error &) { }
+        }
+
+        globals.dryRun = false;
+        globals.preserveInstalled = false;
+        globals.removeAll = false;
+        globals.prebuiltOnly = false;
+
+        struct MyArgs : LegacyArgs, MixEvalArgs
+        {
+            using LegacyArgs::LegacyArgs;
+        };
+
+        MyArgs myArgs(std::string(baseNameOf(argv[0])), [&](Strings::iterator & arg, const Strings::iterator & end) {
+            Operation oldOp = op;
+
+            if (*arg == "--help")
+                showHelp = true;
+            else if (*arg == "--version")
+                op = opVersion;
+            else if (*arg == "--install" || *arg == "-i") {
+                op = opInstall;
+                opName = "-install";
+            }
+            else if (*arg == "--force-name") // undocumented flag for nix-install-package
+                globals.forceName = getArg(*arg, arg, end);
+            else if (*arg == "--uninstall" || *arg == "-e") {
+                op = opUninstall;
+                opName = "-uninstall";
+            }
+            else if (*arg == "--upgrade" || *arg == "-u") {
+                op = opUpgrade;
+                opName = "-upgrade";
+            }
+            else if (*arg == "--set-flag") {
+                op = opSetFlag;
+                opName = arg->substr(1);
+            }
+            else if (*arg == "--set") {
+                op = opSet;
+                opName = arg->substr(1);
+            }
+            else if (*arg == "--query" || *arg == "-q") {
+                op = opQuery;
+                opName = "-query";
+            }
+            else if (*arg == "--profile" || *arg == "-p")
+                globals.profile = absPath(getArg(*arg, arg, end));
+            else if (*arg == "--file" || *arg == "-f")
+                file = getArg(*arg, arg, end);
+            else if (*arg == "--switch-profile" || *arg == "-S") {
+                op = opSwitchProfile;
+                opName = "-switch-profile";
+            }
+            else if (*arg == "--switch-generation" || *arg == "-G") {
+                op = opSwitchGeneration;
+                opName = "-switch-generation";
+            }
+            else if (*arg == "--rollback") {
+                op = opRollback;
+                opName = arg->substr(1);
+            }
+            else if (*arg == "--list-generations") {
+                op = opListGenerations;
+                opName = arg->substr(1);
+            }
+            else if (*arg == "--delete-generations") {
+                op = opDeleteGenerations;
+                opName = arg->substr(1);
+            }
+            else if (*arg == "--dry-run") {
+                printInfo("(dry run; not doing anything)");
+                globals.dryRun = true;
+            }
+            else if (*arg == "--system-filter")
+                globals.instSource.systemFilter = getArg(*arg, arg, end);
+            else if (*arg == "--prebuilt-only" || *arg == "-b")
+                globals.prebuiltOnly = true;
+            else if (*arg != "" && arg->at(0) == '-') {
+                opFlags.push_back(*arg);
+                /* FIXME: hacky */
+                if (*arg == "--from-profile" ||
+                    (op == opQuery && (*arg == "--attr" || *arg == "-A")))
+                    opFlags.push_back(getArg(*arg, arg, end));
+            }
+            else
+                opArgs.push_back(*arg);
+
+            if (oldOp && oldOp != op)
+                throw UsageError("only one operation may be specified");
+
+            return true;
+        });
+
+        myArgs.parseCmdline(argvToStrings(argc, argv));
+
+        if (showHelp) showManPage("nix-env" + opName);
+        if (!op) throw UsageError("no operation specified");
+
+        auto store = openStore();
+
+        globals.state = std::shared_ptr<EvalState>(new EvalState(myArgs.searchPath, store));
+        globals.state->repair = myArgs.repair;
+
+        globals.instSource.nixExprPath = std::make_shared<SourcePath>(
+            file != ""
+            ? lookupFileArg(*globals.state, file)
+            : globals.state->rootPath(CanonPath(nixExprPath)));
+
+        globals.instSource.autoArgs = myArgs.getAutoArgs(*globals.state);
+
+        if (globals.profile == "")
+            globals.profile = getEnv("NIX_PROFILE").value_or("");
+
+        if (globals.profile == "")
+            globals.profile = getDefaultProfile();
+
+        op(globals, std::move(opFlags), std::move(opArgs));
+
+        globals.state->maybePrintStats();
+
+        return 0;
+    }
+}
+
+void registerNixEnv() {
+    LegacyCommands::add("nix-env", main_nix_env);
+}
+
+}