Merge branch 'master' into structured-attrs-shell

 Conflicts:
        src/nix/develop.cc
        src/nix/get-env.sh
        tests/shell.nix

10 files changed, 408 insertions, 134 deletions

diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index ee782c4ec..26f53db09 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -8,7 +8,7 @@
 #include "affinity.hh"
 #include "progress-bar.hh"
 
-#include <regex>
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
@@ -25,94 +25,142 @@ static DevelopSettings developSettings;
 
 static GlobalConfig::Register rDevelopSettings(&developSettings);
 
-struct Var
-{
-    bool exported = true;
-    bool associative = false;
-    std::string quoted; // quoted string or array
-};
-
 struct BuildEnvironment
 {
-    std::map<std::string, Var> env;
-    std::string bashFunctions;
-};
+    struct String
+    {
+        bool exported;
+        std::string value;
 
-BuildEnvironment readEnvironment(const Path & path)
-{
-    BuildEnvironment res;
+        bool operator == (const String & other) const
+        {
+            return exported == other.exported && value == other.value;
+        }
+    };
 
-    std::set<std::string> exported;
+    using Array = std::vector<std::string>;
 
-    debug("reading environment file '%s'", path);
+    using Associative = std::map<std::string, std::string>;
 
-    auto file = readFile(path);
+    using Value = std::variant<String, Array, Associative>;
 
-    auto pos = file.cbegin();
+    std::map<std::string, Value> vars;
+    std::map<std::string, std::string> bashFunctions;
 
-    static std::string varNameRegex =
-        R"re((?:[a-zA-Z_][a-zA-Z0-9_]*))re";
+    static BuildEnvironment fromJSON(std::string_view in)
+    {
+        BuildEnvironment res;
 
-    static std::string simpleStringRegex =
-        R"re((?:[a-zA-Z0-9_/:\.\-\+=]*))re";
+        std::set<std::string> exported;
 
-    static std::string dquotedStringRegex =
-        R"re((?:\$?"(?:[^"\\]|\\[$`"\\\n])*"))re";
+        auto json = nlohmann::json::parse(in);
 
-    static std::string squotedStringRegex =
-        R"re((?:\$?(?:'(?:[^'\\]|\\[abeEfnrtv\\'"?])*'|\\')+))re";
+        for (auto & [name, info] : json["variables"].items()) {
+            std::string type = info["type"];
+            if (type == "var" || type == "exported")
+                res.vars.insert({name, BuildEnvironment::String { .exported = type == "exported", .value = info["value"] }});
+            else if (type == "array")
+                res.vars.insert({name, (Array) info["value"]});
+            else if (type == "associative")
+                res.vars.insert({name, (Associative) info["value"]});
+        }
 
-    static std::string indexedArrayRegex =
-        R"re((?:\(( *\[[0-9]+\]="(?:[^"\\]|\\.)*")*\)))re";
+        for (auto & [name, def] : json["bashFunctions"].items()) {
+            res.bashFunctions.insert({name, def});
+        }
 
-    static std::regex declareRegex(
-        "^declare -a?x (" + varNameRegex + ")(=(" +
-        dquotedStringRegex + "|" + indexedArrayRegex + "))?\n");
+        return res;
+    }
 
-    static std::regex varRegex(
-        "^(" + varNameRegex + ")=(" + simpleStringRegex + "|" + squotedStringRegex + "|" + indexedArrayRegex + ")\n");
+    std::string toJSON() const
+    {
+        auto res = nlohmann::json::object();
+
+        auto vars2 = nlohmann::json::object();
+        for (auto & [name, value] : vars) {
+            auto info = nlohmann::json::object();
+            if (auto str = std::get_if<String>(&value)) {
+                info["type"] = str->exported ? "exported" : "var";
+                info["value"] = str->value;
+            }
+            else if (auto arr = std::get_if<Array>(&value)) {
+                info["type"] = "array";
+                info["value"] = *arr;
+            }
+            else if (auto arr = std::get_if<Associative>(&value)) {
+                info["type"] = "associative";
+                info["value"] = *arr;
+            }
+            vars2[name] = std::move(info);
+        }
+        res["variables"] = std::move(vars2);
 
-    /* Note: we distinguish between an indexed and associative array
-       using the space before the closing parenthesis. Will
-       undoubtedly regret this some day. */
-    static std::regex assocArrayRegex(
-        "^(" + varNameRegex + ")=" + R"re((?:\(( *\[[^\]]+\]="(?:[^"\\]|\\.)*")* *\)))re" + "\n");
+        res["bashFunctions"] = bashFunctions;
 
-    static std::regex functionRegex(
-        "^" + varNameRegex + " \\(\\) *\n");
+        auto json = res.dump();
 
-    while (pos != file.end()) {
+        assert(BuildEnvironment::fromJSON(json) == *this);
 
-        std::smatch match;
+        return json;
+    }
 
-        if (std::regex_search(pos, file.cend(), match, declareRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            exported.insert(match[1]);
+    void toBash(std::ostream & out, const std::set<std::string> & ignoreVars) const
+    {
+        for (auto & [name, value] : vars) {
+            if (!ignoreVars.count(name)) {
+                if (auto str = std::get_if<String>(&value)) {
+                    out << fmt("%s=%s\n", name, shellEscape(str->value));
+                    if (str->exported)
+                        out << fmt("export %s\n", name);
+                }
+                else if (auto arr = std::get_if<Array>(&value)) {
+                    out << "declare -a " << name << "=(";
+                    for (auto & s : *arr)
+                        out << shellEscape(s) << " ";
+                    out << ")\n";
+                }
+                else if (auto arr = std::get_if<Associative>(&value)) {
+                    out << "declare -A " << name << "=(";
+                    for (auto & [n, v] : *arr)
+                        out << "[" << shellEscape(n) << "]=" << shellEscape(v) << " ";
+                    out << ")\n";
+                }
+            }
         }
 
-        else if (std::regex_search(pos, file.cend(), match, varRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            res.env.insert({match[1], Var { .exported = exported.count(match[1]) > 0, .quoted = match[2] }});
+        for (auto & [name, def] : bashFunctions) {
+            out << name << " ()\n{\n" << def << "}\n";
         }
+    }
 
-        else if (std::regex_search(pos, file.cend(), match, assocArrayRegex, std::regex_constants::match_continuous)) {
-            pos = match[0].second;
-            res.env.insert({match[1], Var { .associative = true, .quoted = match[2] }});
-        }
+    static std::string getString(const Value & value)
+    {
+        if (auto str = std::get_if<String>(&value))
+            return str->value;
+        else
+            throw Error("bash variable is not a string");
+    }
 
-        else if (std::regex_search(pos, file.cend(), match, functionRegex, std::regex_constants::match_continuous)) {
-            res.bashFunctions = std::string(pos, file.cend());
-            break;
+    static Array getStrings(const Value & value)
+    {
+        if (auto str = std::get_if<String>(&value))
+            return tokenizeString<Array>(str->value);
+        else if (auto arr = std::get_if<Array>(&value)) {
+            return *arr;
+        } else if (auto assoc = std::get_if<Associative>(&value)) {
+            Array assocKeys;
+            std::for_each(assoc->begin(), assoc->end(), [&](auto & n) { assocKeys.push_back(n.first); });
+            return assocKeys;
         }
-
-        else throw Error("shell environment '%s' has unexpected line '%s'",
-            path, file.substr(pos - file.cbegin(), 60));
+        else
+            throw Error("bash variable is not a string or array");
     }
 
-    res.env.erase("__output");
-
-    return res;
-}
+    bool operator == (const BuildEnvironment & other) const
+    {
+        return vars == other.vars && bashFunctions == other.bashFunctions;
+    }
+};
 
 const static std::string getEnvSh =
     #include "get-env.sh.gen.hh"
@@ -144,17 +192,26 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
     /* Rehash and write the derivation. FIXME: would be nice to use
        'buildDerivation', but that's privileged. */
     drv.name += "-env";
-    for (auto & output : drv.outputs) {
-        output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
-        drv.env[output.first] = "";
-    }
     drv.inputSrcs.insert(std::move(getEnvShPath));
-    Hash h = std::get<0>(hashDerivationModulo(*store, drv, true));
+    if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+        for (auto & output : drv.outputs) {
+            output.second = {
+                .output = DerivationOutputDeferred{},
+            };
+            drv.env[output.first] = hashPlaceholder(output.first);
+        }
+    } else {
+        for (auto & output : drv.outputs) {
+            output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
+            drv.env[output.first] = "";
+        }
+        Hash h = std::get<0>(hashDerivationModulo(*store, drv, true));
 
-    for (auto & output : drv.outputs) {
-        auto outPath = store->makeOutputPath(output.first, h, drv.name);
-        output.second = { .output = DerivationOutputInputAddressed { .path = outPath } };
-        drv.env[output.first] = store->printStorePath(outPath);
+        for (auto & output : drv.outputs) {
+            auto outPath = store->makeOutputPath(output.first, h, drv.name);
+            output.second = { .output = DerivationOutputInputAddressed { .path = outPath } };
+            drv.env[output.first] = store->printStorePath(outPath);
+        }
     }
 
     auto shellDrvPath = writeDerivation(*store, drv);
@@ -162,8 +219,7 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
     /* Build the derivation. */
     store->buildPaths({DerivedPath::Built{shellDrvPath}});
 
-    for (auto & [_0, outputAndOptPath] : drv.outputsAndOptPaths(*store)) {
-        auto & [_1, optPath] = outputAndOptPath;
+    for (auto & [_0, optPath] : store->queryPartialDerivationOutputMap(shellDrvPath)) {
         assert(optPath);
         auto & outPath = *optPath;
         assert(store->isValidPath(outPath));
@@ -177,19 +233,15 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
 
 struct Common : InstallableCommand, MixProfile
 {
-    std::set<string> ignoreVars{
+    std::set<std::string> ignoreVars{
         "BASHOPTS",
-        "EUID",
         "HOME", // FIXME: don't ignore in pure mode?
-        "HOSTNAME",
         "NIX_BUILD_TOP",
         "NIX_ENFORCE_PURITY",
         "NIX_LOG_FD",
         "NIX_REMOTE",
         "PPID",
-        "PWD",
         "SHELLOPTS",
-        "SHLVL",
         "SSL_CERT_FILE", // FIXME: only want to ignore /no-cert-file.crt
         "TEMP",
         "TEMPDIR",
@@ -225,22 +277,10 @@ struct Common : InstallableCommand, MixProfile
 
         out << "nix_saved_PATH=\"$PATH\"\n";
 
-        for (auto & i : buildEnvironment.env) {
-            if (!ignoreVars.count(i.first) && !hasPrefix(i.first, "BASH_")) {
-                if (i.second.associative)
-                    out << fmt("declare -A %s=(%s)\n", i.first, i.second.quoted);
-                else {
-                    out << fmt("%s=%s\n", i.first, i.second.quoted);
-                    if (i.second.exported)
-                        out << fmt("export %s\n", i.first);
-                }
-            }
-        }
+        buildEnvironment.toBash(out, ignoreVars);
 
         out << "PATH=\"$PATH:$nix_saved_PATH\"\n";
 
-        out << buildEnvironment.bashFunctions << "\n";
-
         out << "export NIX_BUILD_TOP=\"$(mktemp -d -t nix-shell.XXXXXX)\"\n";
         for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
             out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
@@ -250,24 +290,16 @@ struct Common : InstallableCommand, MixProfile
         auto script = out.str();
 
         /* Substitute occurrences of output paths. */
-        auto outputs = buildEnvironment.env.find("outputs");
-        assert(outputs != buildEnvironment.env.end());
+        auto outputs = buildEnvironment.vars.find("outputs");
+        assert(outputs != buildEnvironment.vars.end());
 
         // FIXME: properly unquote 'outputs'.
         StringMap rewrites;
-        for (auto & outputName : tokenizeString<std::vector<std::string>>(replaceStrings(outputs->second.quoted, "'", ""))) {
-            // Hacky way to obtain the key of an associate array. This is needed for strctured attrs where
-            // `outputs` is an associative array. If the regex isn't matched, the non-structured-attrs behavior will
-            // be used.
-            std::regex ptrn(R"re(\[([A-z0-9]+)\]=.*)re");
-            std::smatch match;
-            if (std::regex_match(outputName, match, ptrn)) {
-                outputName = match[1];
-            }
-            auto from = buildEnvironment.env.find(outputName);
-            assert(from != buildEnvironment.env.end());
+        for (auto & outputName : BuildEnvironment::getStrings(outputs->second)) {
+            auto from = buildEnvironment.vars.find(outputName);
+            assert(from != buildEnvironment.vars.end());
             // FIXME: unquote
-            rewrites.insert({from->second.quoted, outputsDir + "/" + outputName});
+            rewrites.insert({BuildEnvironment::getString(from->second), outputsDir + "/" + outputName});
         }
 
         /* Substitute redirects. */
@@ -321,7 +353,9 @@ struct Common : InstallableCommand, MixProfile
 
         updateProfile(shellOutPath);
 
-        return {readEnvironment(strPath), strPath};
+        debug("reading environment file '%s'", strPath);
+
+        return {BuildEnvironment::fromJSON(readFile(strPath)), strPath};
     }
 };
 
@@ -443,13 +477,17 @@ struct CmdDevelop : Common, MixEnvironment
         try {
             auto state = getEvalState();
 
+            auto nixpkgsLockFlags = lockFlags;
+            nixpkgsLockFlags.inputOverrides = {};
+            nixpkgsLockFlags.inputUpdates = {};
+
             auto bashInstallable = std::make_shared<InstallableFlake>(
                 this,
                 state,
                 installable->nixpkgsFlakeRef(),
                 Strings{"bashInteractive"},
                 Strings{"legacyPackages." + settings.thisSystem.get() + "."},
-                lockFlags);
+                nixpkgsLockFlags);
 
             shell = state->store->printStorePath(
                 toStorePath(state->store, Realise::Outputs, OperateOn::Output, bashInstallable)) + "/bin/bash";
@@ -470,7 +508,7 @@ struct CmdDevelop : Common, MixEnvironment
     }
 };
 
-struct CmdPrintDevEnv : Common
+struct CmdPrintDevEnv : Common, MixJSON
 {
     std::string description() override
     {
@@ -492,7 +530,10 @@ struct CmdPrintDevEnv : Common
 
         stopProgressBar();
 
-        std::cout << makeRcScript(store, buildEnvironment);
+        logger->writeToStdout(
+            json
+            ? buildEnvironment.toJSON()
+            : makeRcScript(store, buildEnvironment));
     }
 };
 
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 64fcfc000..9055b07eb 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -84,6 +84,7 @@ struct CmdFlakeUpdate : FlakeCommand
 
         lockFlags.recreateLockFile = true;
         lockFlags.writeLockFile = true;
+        lockFlags.applyNixConfig = true;
 
         lockFlake();
     }
@@ -114,6 +115,7 @@ struct CmdFlakeLock : FlakeCommand
         settings.tarballTtl = 0;
 
         lockFlags.writeLockFile = true;
+        lockFlags.applyNixConfig = true;
 
         lockFlake();
     }
@@ -270,6 +272,8 @@ struct CmdFlakeCheck : FlakeCommand
         settings.readOnlyMode = !build;
 
         auto state = getEvalState();
+
+        lockFlags.applyNixConfig = true;
         auto flake = lockFlake();
 
         bool hasErrors = false;
diff --git a/src/nix/get-env.sh b/src/nix/get-env.sh
index 431440516..42c806450 100644
--- a/src/nix/get-env.sh
+++ b/src/nix/get-env.sh
@@ -8,6 +8,109 @@ if [[ -n $stdenv ]]; then
     source $stdenv/setup
 fi
 
+# Better to use compgen, but stdenv bash doesn't have it.
+__vars="$(declare -p)"
+__functions="$(declare -F)"
+
+__dumpEnv() {
+    printf '{\n'
+
+    printf '  "bashFunctions": {\n'
+    local __first=1
+    while read __line; do
+        if ! [[ $__line =~ ^declare\ -f\ (.*) ]]; then continue; fi
+        __fun_name="${BASH_REMATCH[1]}"
+        __fun_body="$(type $__fun_name)"
+        if [[ $__fun_body =~ \{(.*)\} ]]; then
+            if [[ -z $__first ]]; then printf ',\n'; else __first=; fi
+            __fun_body="${BASH_REMATCH[1]}"
+            printf "    "
+            __escapeString "$__fun_name"
+            printf ':'
+            __escapeString "$__fun_body"
+        else
+            printf "Cannot parse definition of function '%s'.\n" "$__fun_name" >&2
+            return 1
+        fi
+    done < <(printf "%s\n" "$__functions")
+    printf '\n  },\n'
+
+    printf '  "variables": {\n'
+    local __first=1
+    while read __line; do
+        if ! [[ $__line =~ ^declare\ (-[^ ])\ ([^=]*) ]]; then continue; fi
+        local type="${BASH_REMATCH[1]}"
+        local __var_name="${BASH_REMATCH[2]}"
+
+        if [[ $__var_name =~ ^BASH_ || \
+              $__var_name = _ || \
+              $__var_name = DIRSTACK || \
+              $__var_name = EUID || \
+              $__var_name = FUNCNAME || \
+              $__var_name = HISTCMD || \
+              $__var_name = HOSTNAME || \
+              $__var_name = GROUPS || \
+              $__var_name = PIPESTATUS || \
+              $__var_name = PWD || \
+              $__var_name = RANDOM || \
+              $__var_name = SHLVL || \
+              $__var_name = SECONDS \
+            ]]; then continue; fi
+
+        if [[ -z $__first ]]; then printf ',\n'; else __first=; fi
+
+        printf "    "
+        __escapeString "$__var_name"
+        printf ': {'
+
+        # FIXME: handle -i, -r, -n.
+        if [[ $type == -x ]]; then
+            printf '"type": "exported", "value": '
+            __escapeString "${!__var_name}"
+        elif [[ $type == -- ]]; then
+            printf '"type": "var", "value": '
+            __escapeString "${!__var_name}"
+        elif [[ $type == -a ]]; then
+            printf '"type": "array", "value": ['
+            local __first2=1
+            __var_name="$__var_name[@]"
+            for __i in "${!__var_name}"; do
+                if [[ -z $__first2 ]]; then printf ', '; else __first2=; fi
+                __escapeString "$__i"
+                printf ' '
+            done
+            printf ']'
+        elif [[ $type == -A ]]; then
+            printf '"type": "associative", "value": {\n'
+            local __first2=1
+            declare -n __var_name2="$__var_name"
+            for __i in "${!__var_name2[@]}"; do
+                if [[ -z $__first2 ]]; then printf ',\n'; else __first2=; fi
+                printf "      "
+                __escapeString "$__i"
+                printf ": "
+                __escapeString "${__var_name2[$__i]}"
+            done
+            printf '\n    }'
+        else
+            printf '"type": "unknown"'
+        fi
+
+        printf "}"
+    done < <(printf "%s\n" "$__vars")
+    printf '\n  }\n}'
+}
+
+__escapeString() {
+    local __s="$1"
+    __s="${__s//\\/\\\\}"
+    __s="${__s//\"/\\\"}"
+    __s="${__s//$'\n'/\\n}"
+    __s="${__s//$'\r'/\\r}"
+    __s="${__s//$'\t'/\\t}"
+    printf '"%s"' "$__s"
+}
+
 # In case of `__structuredAttrs = true;` the list of outputs is an associative
 # array with a format like `outname => /nix/store/hash-drvname-outname`, so `__olist`
 # must contain the array's keys (hence `${!...[@]}`) in this case.
@@ -19,8 +122,7 @@ fi
 
 for __output in $__olist; do
     if [[ -z $__done ]]; then
-        export > "${!__output}"
-        set >> "${!__output}"
+        __dumpEnv > ${!__output}
         __done=1
     else
         echo -n >> "${!__output}"
diff --git a/src/nix/print-dev-env.md b/src/nix/print-dev-env.md
index b80252acf..2aad491de 100644
--- a/src/nix/print-dev-env.md
+++ b/src/nix/print-dev-env.md
@@ -8,12 +8,43 @@ R""(
   # . <(nix print-dev-env nixpkgs#hello)
   ```
 
+* Get the build environment in JSON format:
+
+  ```console
+  # nix print-dev-env nixpkgs#hello --json
+  ```
+
+  The output will look like this:
+
+  ```json
+  {
+    "bashFunctions": {
+      "buildPhase": " \n    runHook preBuild;\n...",
+      ...
+    },
+    "variables": {
+      "src": {
+        "type": "exported",
+        "value": "/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz"
+      },
+      "postUnpackHooks": {
+        "type": "array",
+        "value": ["_updateSourceDateEpochFromSourceRoot"]
+      },
+      ...
+    }
+  }
+  ```
+
 # Description
 
-This command prints a shell script that can be sourced by `b`ash and
-that sets the environment variables and shell functions defined by the
-build process of *installable*. This allows you to get a similar build
+This command prints a shell script that can be sourced by `bash` and
+that sets the variables and shell functions defined by the build
+process of *installable*. This allows you to get a similar build
 environment in your current shell rather than in a subshell (as with
 `nix develop`).
 
+With `--json`, the output is a JSON serialisation of the variables and
+functions defined by the build process.
+
 )""
diff --git a/src/nix/profile-remove.md b/src/nix/profile-remove.md
index dcf825da9..ba85441d8 100644
--- a/src/nix/profile-remove.md
+++ b/src/nix/profile-remove.md
@@ -15,6 +15,7 @@ R""(
   ```
 
 * Remove all packages:
+
   ```console
   # nix profile remove '.*'
   ```
diff --git a/src/nix/registry-add.md b/src/nix/registry-add.md
index 80a31996a..a947fa0b3 100644
--- a/src/nix/registry-add.md
+++ b/src/nix/registry-add.md
@@ -21,6 +21,13 @@ R""(
   # nix registry add nixpkgs/nixos-20.03 ~/Dev/nixpkgs
   ```
 
+* Add `nixpkgs` pointing to `github:nixos/nixpkgs` to your custom flake
+  registry:
+
+  ```console
+  nix registry add --registry ./custom-flake-registry.json nixpkgs github:nixos/nixpkgs
+  ```
+
 # Description
 
 This command adds an entry to the user registry that maps flake
diff --git a/src/nix/registry-pin.md b/src/nix/registry-pin.md
index 6e97e003e..ebc0e3eff 100644
--- a/src/nix/registry-pin.md
+++ b/src/nix/registry-pin.md
@@ -24,6 +24,13 @@ R""(
   …
   ```
 
+* Pin `nixpkgs` in a custom registry to its most recent Git revision:
+
+  ```console
+  # nix registry pin --registry ./custom-flake-registry.json nixpkgs
+  ```
+
+
 # Description
 
 This command adds an entry to the user registry that maps flake
diff --git a/src/nix/registry-remove.md b/src/nix/registry-remove.md
index 4c0eb4947..eecd4c6e7 100644
--- a/src/nix/registry-remove.md
+++ b/src/nix/registry-remove.md
@@ -8,6 +8,12 @@ R""(
   # nix registry remove nixpkgs
   ```
 
+* Remove the entry `nixpkgs` from a custom registry:
+
+  ```console
+  # nix registry remove --registry ./custom-flake-registry.json nixpkgs
+  ```
+
 # Description
 
 This command removes from the user registry any entry for flake
diff --git a/src/nix/registry.cc b/src/nix/registry.cc
index f9719600f..6a92576c7 100644
--- a/src/nix/registry.cc
+++ b/src/nix/registry.cc
@@ -10,6 +10,46 @@
 using namespace nix;
 using namespace nix::flake;
 
+
+class RegistryCommand : virtual Args
+{
+    std::string registry_path;
+
+    std::shared_ptr<fetchers::Registry> registry;
+
+public:
+
+    RegistryCommand()
+    {
+        addFlag({
+            .longName = "registry",
+            .description = "The registry to operate on.",
+            .labels = {"registry"},
+            .handler = {&registry_path},
+        });
+    }
+
+    std::shared_ptr<fetchers::Registry> getRegistry()
+    {
+        if (registry) return registry;
+        if (registry_path.empty()) {
+            registry = fetchers::getUserRegistry();
+        } else {
+            registry = fetchers::getCustomRegistry(registry_path);
+        }
+        return registry;
+    }
+
+    Path getRegistryPath()
+    {
+        if (registry_path.empty()) {
+            return fetchers::getUserRegistryPath();
+        } else {
+            return registry_path;
+        }
+    }
+};
+
 struct CmdRegistryList : StoreCommand
 {
     std::string description() override
@@ -45,7 +85,7 @@ struct CmdRegistryList : StoreCommand
     }
 };
 
-struct CmdRegistryAdd : MixEvalArgs, Command
+struct CmdRegistryAdd : MixEvalArgs, Command, RegistryCommand
 {
     std::string fromUrl, toUrl;
 
@@ -71,16 +111,16 @@ struct CmdRegistryAdd : MixEvalArgs, Command
     {
         auto fromRef = parseFlakeRef(fromUrl);
         auto toRef = parseFlakeRef(toUrl);
+        auto registry = getRegistry();
         fetchers::Attrs extraAttrs;
         if (toRef.subdir != "") extraAttrs["dir"] = toRef.subdir;
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(fromRef.input);
-        userRegistry->add(fromRef.input, toRef.input, extraAttrs);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        registry->remove(fromRef.input);
+        registry->add(fromRef.input, toRef.input, extraAttrs);
+        registry->write(getRegistryPath());
     }
 };
 
-struct CmdRegistryRemove : virtual Args, MixEvalArgs, Command
+struct CmdRegistryRemove : RegistryCommand, Command
 {
     std::string url;
 
@@ -103,19 +143,21 @@ struct CmdRegistryRemove : virtual Args, MixEvalArgs, Command
 
     void run() override
     {
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(parseFlakeRef(url).input);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        auto registry = getRegistry();
+        registry->remove(parseFlakeRef(url).input);
+        registry->write(getRegistryPath());
     }
 };
 
-struct CmdRegistryPin : virtual Args, EvalCommand
+struct CmdRegistryPin : RegistryCommand, EvalCommand
 {
     std::string url;
 
+    std::string locked;
+
     std::string description() override
     {
-        return "pin a flake to its current version in user flake registry";
+        return "pin a flake to its current version or to the current version of a flake URL";
     }
 
     std::string doc() override
@@ -128,18 +170,31 @@ struct CmdRegistryPin : virtual Args, EvalCommand
     CmdRegistryPin()
     {
         expectArg("url", &url);
+
+        expectArgs({
+            .label = "locked",
+            .optional = true,
+            .handler = {&locked},
+            .completer = {[&](size_t, std::string_view prefix) {
+                completeFlakeRef(getStore(), prefix);
+            }}
+        });
     }
 
     void run(nix::ref<nix::Store> store) override
     {
+        if (locked.empty()) {
+            locked = url;
+        }
+        auto registry = getRegistry();
         auto ref = parseFlakeRef(url);
-        auto userRegistry = fetchers::getUserRegistry();
-        userRegistry->remove(ref.input);
-        auto [tree, resolved] = ref.resolve(store).input.fetch(store);
+        auto locked_ref = parseFlakeRef(locked);
+        registry->remove(ref.input);
+        auto [tree, resolved] = locked_ref.resolve(store).input.fetch(store);
         fetchers::Attrs extraAttrs;
         if (ref.subdir != "") extraAttrs["dir"] = ref.subdir;
-        userRegistry->add(ref.input, resolved, extraAttrs);
-        userRegistry->write(fetchers::getUserRegistryPath());
+        registry->add(ref.input, resolved, extraAttrs);
+        registry->write(getRegistryPath());
     }
 };
 
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index eed79c332..0275feae7 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -104,6 +104,26 @@ NixRepl::~NixRepl()
     write_history(historyFile.c_str());
 }
 
+string runNix(Path program, const Strings & args,
+    const std::optional<std::string> & input = {})
+{
+    auto experimentalFeatures = concatStringsSep(" ", settings.experimentalFeatures.get());
+    auto nixConf = getEnv("NIX_CONFIG").value_or("");
+    nixConf.append("\nexperimental-features = " + experimentalFeatures);
+    auto subprocessEnv = getEnv();
+    subprocessEnv["NIX_CONFIG"] = nixConf;
+    RunOptions opts(settings.nixBinDir+ "/" + program, args);
+    opts.input = input;
+    opts.environment = subprocessEnv;
+
+    auto res = runProgram(opts);
+
+    if (!statusOk(res.first))
+        throw ExecError(res.first, fmt("program '%1%' %2%", program, statusToString(res.first)));
+
+    return res.second;
+}
+
 static NixRepl * curRepl; // ugly
 
 static char * completionCallback(char * s, int *match) {
@@ -463,7 +483,7 @@ bool NixRepl::processLine(string line)
         state->callFunction(f, v, result, Pos());
 
         StorePath drvPath = getDerivationPath(result);
-        runProgram(settings.nixBinDir + "/nix-shell", true, {state->store->printStorePath(drvPath)});
+        runNix("nix-shell", {state->store->printStorePath(drvPath)});
     }
 
     else if (command == ":b" || command == ":i" || command == ":s") {
@@ -477,7 +497,7 @@ bool NixRepl::processLine(string line)
                but doing it in a child makes it easier to recover from
                problems / SIGINT. */
             try {
-                runProgram(settings.nixBinDir + "/nix", true, {"build", "--no-link", drvPathRaw});
+                runNix("nix", {"build", "--no-link", drvPathRaw});
                 auto drv = state->store->readDerivation(drvPath);
                 std::cout << std::endl << "this derivation produced the following outputs:" << std::endl;
                 for (auto & i : drv.outputsAndOptPaths(*state->store))
@@ -485,9 +505,9 @@ bool NixRepl::processLine(string line)
             } catch (ExecError &) {
             }
         } else if (command == ":i") {
-            runProgram(settings.nixBinDir + "/nix-env", true, {"-i", drvPathRaw});
+            runNix("nix-env", {"-i", drvPathRaw});
         } else {
-            runProgram(settings.nixBinDir + "/nix-shell", true, {drvPathRaw});
+            runNix("nix-shell", {drvPathRaw});
         }
     }