Merge branch 'document-store-options' of https://github.com/tweag/nix

src/libexpr/flake/lockfile.hh

@@ -6,7 +6,7 @@
 
 namespace nix {
 class Store;
-struct StorePath;
+class StorePath;
 }
 
 namespace nix::flake {

src/libfetchers/fetchers.hh

@@ -23,7 +23,7 @@ struct InputScheme;
 
 struct Input
 {
-    friend class InputScheme;
+    friend struct InputScheme;
 
     std::shared_ptr<InputScheme> scheme; // note: can be null
     Attrs attrs;

src/libstore/binary-cache-store.cc

@@ -22,7 +22,8 @@
 namespace nix {
 
 BinaryCacheStore::BinaryCacheStore(const Params & params)
-    : Store(params)
+    : BinaryCacheStoreConfig(params)
+    , Store(params)
 {
     if (secretKeyFile != "")
         secretKey = std::unique_ptr<SecretKey>(new SecretKey(readFile(secretKeyFile)));

src/libstore/binary-cache-store.hh

@@ -11,17 +11,21 @@ namespace nix {
 
 struct NarInfo;
 
-class BinaryCacheStore : public Store
+struct BinaryCacheStoreConfig : virtual StoreConfig
 {
-public:
+    using StoreConfig::StoreConfig;
 
-    const Setting<std::string> compression{this, "xz", "compression", "NAR compression method ('xz', 'bzip2', or 'none')"};
+    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression", "NAR compression method ('xz', 'bzip2', or 'none')"};
-    const Setting<bool> writeNARListing{this, false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
+    const Setting<bool> writeNARListing{(StoreConfig*) this, false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
-    const Setting<bool> writeDebugInfo{this, false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
+    const Setting<bool> writeDebugInfo{(StoreConfig*) this, false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
-    const Setting<Path> secretKeyFile{this, "", "secret-key", "path to secret key used to sign the binary cache"};
+    const Setting<Path> secretKeyFile{(StoreConfig*) this, "", "secret-key", "path to secret key used to sign the binary cache"};
-    const Setting<Path> localNarCache{this, "", "local-nar-cache", "path to a local cache of NARs"};
+    const Setting<Path> localNarCache{(StoreConfig*) this, "", "local-nar-cache", "path to a local cache of NARs"};
-    const Setting<bool> parallelCompression{this, false, "parallel-compression",
+    const Setting<bool> parallelCompression{(StoreConfig*) this, false, "parallel-compression",
         "enable multi-threading compression, available for xz only currently"};
+};
+
+class BinaryCacheStore : public Store, public virtual BinaryCacheStoreConfig
+{
 
 private:
 
@@ -58,7 +62,7 @@ public:
 
 public:
 
-    virtual void init();
+    virtual void init() override;
 
 private:
 

src/libstore/build.cc

@@ -2872,18 +2872,23 @@ void DerivationGoal::writeStructuredAttrs()
     chownToBuilder(tmpDir + "/.attrs.sh");
 }
 
+struct RestrictedStoreConfig : LocalFSStoreConfig
+{
+    using LocalFSStoreConfig::LocalFSStoreConfig;
+    const std::string name() { return "Restricted Store"; }
+};
 
 /* A wrapper around LocalStore that only allows building/querying of
    paths that are in the input closures of the build or were added via
    recursive Nix calls. */
-struct RestrictedStore : public LocalFSStore
+struct RestrictedStore : public LocalFSStore, public virtual RestrictedStoreConfig
 {
     ref<LocalStore> next;
 
     DerivationGoal & goal;
 
     RestrictedStore(const Params & params, ref<LocalStore> next, DerivationGoal & goal)
-        : Store(params), LocalFSStore(params), next(next), goal(goal)
+        : StoreConfig(params), Store(params), LocalFSStore(params), next(next), goal(goal)
     { }
 
     Path getRealStoreDir() override

src/libstore/dummy-store.cc

@@ -2,17 +2,27 @@
 
 namespace nix {
 
-static std::string uriScheme = "dummy://";
+struct DummyStoreConfig : virtual StoreConfig {
+    using StoreConfig::StoreConfig;
 
-struct DummyStore : public Store
+    const std::string name() override { return "Dummy Store"; }
+};
+
+struct DummyStore : public Store, public virtual DummyStoreConfig
 {
-    DummyStore(const Params & params)
+    DummyStore(const std::string scheme, const std::string uri, const Params & params)
-        : Store(params)
+        : DummyStore(params)
     { }
 
+    DummyStore(const Params & params)
+        : StoreConfig(params)
+        , Store(params)
+    {
+    }
+
     string getUri() override
     {
-        return uriScheme;
+        return *uriSchemes().begin();
     }
 
     void queryPathInfoUncached(const StorePath & path,
@@ -21,6 +31,10 @@ struct DummyStore : public Store
         callback(nullptr);
     }
 
+    static std::set<std::string> uriSchemes() {
+        return {"dummy"};
+    }
+
     std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { unsupported("queryPathFromHashPart"); }
 
@@ -48,12 +62,6 @@ struct DummyStore : public Store
     { unsupported("buildDerivation"); }
 };
 
-static RegisterStoreImplementation regStore([](
+static RegisterStoreImplementation<DummyStore, DummyStoreConfig> regStore;
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    if (uri != uriScheme) return nullptr;
-    return std::make_shared<DummyStore>(params);
-});
 
 }

src/libstore/globals.cc

@@ -162,11 +162,6 @@ template<> std::string BaseSetting<SandboxMode>::to_string() const
     else abort();
 }
 
-template<> nlohmann::json BaseSetting<SandboxMode>::toJSON()
-{
-    return AbstractSetting::toJSON();
-}
-
 template<> void BaseSetting<SandboxMode>::convertToArg(Args & args, const std::string & category)
 {
     args.addFlag({

src/libstore/globals.hh

@@ -2,6 +2,7 @@
 
 #include "types.hh"
 #include "config.hh"
+#include "abstractsettingtojson.hh"
 #include "util.hh"
 
 #include <map>

src/libstore/http-binary-cache-store.cc

@@ -7,7 +7,14 @@ namespace nix {
 
 MakeError(UploadToHTTP, Error);
 
-class HttpBinaryCacheStore : public BinaryCacheStore
+struct HttpBinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
+{
+    using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
+
+    const std::string name() override { return "Http Binary Cache Store"; }
+};
+
+class HttpBinaryCacheStore : public BinaryCacheStore, public HttpBinaryCacheStoreConfig
 {
 private:
 
@@ -24,9 +31,12 @@ private:
 public:
 
     HttpBinaryCacheStore(
-        const Params & params, const Path & _cacheUri)
+        const std::string & scheme,
-        : BinaryCacheStore(params)
+        const Path & _cacheUri,
-        , cacheUri(_cacheUri)
+        const Params & params)
+        : StoreConfig(params)
+        , BinaryCacheStore(params)
+        , cacheUri(scheme + "://" + _cacheUri)
     {
         if (cacheUri.back() == '/')
             cacheUri.pop_back();
@@ -55,6 +65,13 @@ public:
         }
     }
 
+    static std::set<std::string> uriSchemes()
+    {
+        static bool forceHttp = getEnv("_NIX_FORCE_HTTP") == "1";
+        auto ret = std::set<std::string>({"http", "https"});
+        if (forceHttp) ret.insert("file");
+        return ret;
+    }
 protected:
 
     void maybeDisable()
@@ -162,18 +179,6 @@ protected:
 
 };
 
-static RegisterStoreImplementation regStore([](
+static RegisterStoreImplementation<HttpBinaryCacheStore, HttpBinaryCacheStoreConfig> regStore;
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    static bool forceHttp = getEnv("_NIX_FORCE_HTTP") == "1";
-    if (std::string(uri, 0, 7) != "http://" &&
-        std::string(uri, 0, 8) != "https://" &&
-        (!forceHttp || std::string(uri, 0, 7) != "file://"))
-        return 0;
-    auto store = std::make_shared<HttpBinaryCacheStore>(params, uri);
-    store->init();
-    return store;
-});
 
 }

src/libstore/legacy-ssh-store.cc

@@ -9,18 +9,24 @@
 
 namespace nix {
 
-static std::string uriScheme = "ssh://";
+struct LegacySSHStoreConfig : virtual StoreConfig
-
-struct LegacySSHStore : public Store
 {
-    const Setting<int> maxConnections{this, 1, "max-connections", "maximum number of concurrent SSH connections"};
+    using StoreConfig::StoreConfig;
-    const Setting<Path> sshKey{this, "", "ssh-key", "path to an SSH private key"};
+    const Setting<int> maxConnections{(StoreConfig*) this, 1, "max-connections", "maximum number of concurrent SSH connections"};
-    const Setting<bool> compress{this, false, "compress", "whether to compress the connection"};
+    const Setting<Path> sshKey{(StoreConfig*) this, "", "ssh-key", "path to an SSH private key"};
-    const Setting<Path> remoteProgram{this, "nix-store", "remote-program", "path to the nix-store executable on the remote system"};
+    const Setting<bool> compress{(StoreConfig*) this, false, "compress", "whether to compress the connection"};
-    const Setting<std::string> remoteStore{this, "", "remote-store", "URI of the store on the remote system"};
+    const Setting<Path> remoteProgram{(StoreConfig*) this, "nix-store", "remote-program", "path to the nix-store executable on the remote system"};
+    const Setting<std::string> remoteStore{(StoreConfig*) this, "", "remote-store", "URI of the store on the remote system"};
 
+    const std::string name() override { return "Legacy SSH Store"; }
+};
+
+struct LegacySSHStore : public Store, public virtual LegacySSHStoreConfig
+{
     // Hack for getting remote build log output.
-    const Setting<int> logFD{this, -1, "log-fd", "file descriptor to which SSH's stderr is connected"};
+    // Intentionally not in `LegacySSHStoreConfig` so that it doesn't appear in
+    // the documentation
+    const Setting<int> logFD{(StoreConfig*) this, -1, "log-fd", "file descriptor to which SSH's stderr is connected"};
 
     struct Connection
     {
@@ -37,8 +43,11 @@ struct LegacySSHStore : public Store
 
     SSHMaster master;
 
-    LegacySSHStore(const string & host, const Params & params)
+    static std::set<std::string> uriSchemes() { return {"ssh"}; }
-        : Store(params)
+
+    LegacySSHStore(const string & scheme, const string & host, const Params & params)
+        : StoreConfig(params)
+        , Store(params)
         , host(host)
         , connections(make_ref<Pool<Connection>>(
             std::max(1, (int) maxConnections),
@@ -84,7 +93,7 @@ struct LegacySSHStore : public Store
 
     string getUri() override
     {
-        return uriScheme + host;
+        return *uriSchemes().begin() + "://" + host;
     }
 
     void queryPathInfoUncached(const StorePath & path,
@@ -325,12 +334,6 @@ public:
     }
 };
 
-static RegisterStoreImplementation regStore([](
+static RegisterStoreImplementation<LegacySSHStore, LegacySSHStoreConfig> regStore;
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    if (std::string(uri, 0, uriScheme.size()) != uriScheme) return 0;
-    return std::make_shared<LegacySSHStore>(std::string(uri, uriScheme.size()), params);
-});
 
 }

src/libstore/local-binary-cache-store.cc

@@ -4,7 +4,14 @@
 
 namespace nix {
 
-class LocalBinaryCacheStore : public BinaryCacheStore
+struct LocalBinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
+{
+    using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
+
+    const std::string name() override { return "Local Binary Cache Store"; }
+};
+
+class LocalBinaryCacheStore : public BinaryCacheStore, public virtual LocalBinaryCacheStoreConfig
 {
 private:
 
@@ -13,8 +20,11 @@ private:
 public:
 
     LocalBinaryCacheStore(
-        const Params & params, const Path & binaryCacheDir)
+        const std::string scheme,
-        : BinaryCacheStore(params)
+        const Path & binaryCacheDir,
+        const Params & params)
+        : StoreConfig(params)
+        , BinaryCacheStore(params)
         , binaryCacheDir(binaryCacheDir)
     {
     }
@@ -26,6 +36,8 @@ public:
         return "file://" + binaryCacheDir;
     }
 
+    static std::set<std::string> uriSchemes();
+
 protected:
 
     bool fileExists(const std::string & path) override;
@@ -85,16 +97,14 @@ bool LocalBinaryCacheStore::fileExists(const std::string & path)
     return pathExists(binaryCacheDir + "/" + path);
 }
 
-static RegisterStoreImplementation regStore([](
+std::set<std::string> LocalBinaryCacheStore::uriSchemes()
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
 {
-    if (getEnv("_NIX_FORCE_HTTP_BINARY_CACHE_STORE") == "1" ||
+    if (getEnv("_NIX_FORCE_HTTP_BINARY_CACHE_STORE") == "1")
-        std::string(uri, 0, 7) != "file://")
+        return {};
-        return 0;
+    else
-    auto store = std::make_shared<LocalBinaryCacheStore>(params, std::string(uri, 7));
+        return {"file"};
-    store->init();
+}
-    return store;
+
-});
+static RegisterStoreImplementation<LocalBinaryCacheStore, LocalBinaryCacheStoreConfig> regStore;
 
 }

src/libstore/local-store.cc

@@ -42,7 +42,8 @@ namespace nix {
 
 
 LocalStore::LocalStore(const Params & params)
-    : Store(params)
+    : StoreConfig(params)
+    , Store(params)
     , LocalFSStore(params)
     , realStoreDir_{this, false, rootDir != "" ? rootDir + "/nix/store" : storeDir, "real",
         "physical path to the Nix store"}

src/libstore/local-store.hh

@@ -30,8 +30,19 @@ struct OptimiseStats
     uint64_t blocksFreed = 0;
 };
 
+struct LocalStoreConfig : virtual LocalFSStoreConfig
+{
+    using LocalFSStoreConfig::LocalFSStoreConfig;
 
-class LocalStore : public LocalFSStore
+    Setting<bool> requireSigs{(StoreConfig*) this,
+        settings.requireSigs,
+        "require-sigs", "whether store paths should have a trusted signature on import"};
+
+    const std::string name() override { return "Local Store"; }
+};
+
+
+class LocalStore : public LocalFSStore, public virtual LocalStoreConfig
 {
 private:
 
@@ -95,10 +106,6 @@ public:
 
 private:
 
-    Setting<bool> requireSigs{(Store*) this,
-        settings.requireSigs,
-        "require-sigs", "whether store paths should have a trusted signature on import"};
-
     const PublicKeys & getPublicKeys();
 
 public:

src/libstore/remote-store.cc

@@ -94,6 +94,7 @@ void write(const Store & store, Sink & out, const std::optional<StorePath> & sto
 /* TODO: Separate these store impls into different files, give them better names */
 RemoteStore::RemoteStore(const Params & params)
     : Store(params)
+    , RemoteStoreConfig(params)
     , connections(make_ref<Pool<Connection>>(
             std::max(1, (int) maxConnections),
             [this]() { return openConnectionWrapper(); },
@@ -123,19 +124,21 @@ ref<RemoteStore::Connection> RemoteStore::openConnectionWrapper()
 
 
 UDSRemoteStore::UDSRemoteStore(const Params & params)
-    : Store(params)
+    : StoreConfig(params)
+    , Store(params)
     , LocalFSStore(params)
     , RemoteStore(params)
 {
 }
 
 
-UDSRemoteStore::UDSRemoteStore(std::string socket_path, const Params & params)
+UDSRemoteStore::UDSRemoteStore(
-    : Store(params)
+        const std::string scheme,
-    , LocalFSStore(params)
+        std::string socket_path,
-    , RemoteStore(params)
+        const Params & params)
-    , path(socket_path)
+    : UDSRemoteStore(params)
 {
+    path.emplace(socket_path);
 }
 
 
@@ -982,14 +985,6 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
     return nullptr;
 }
 
-static std::string uriScheme = "unix://";
+static RegisterStoreImplementation<UDSRemoteStore, UDSRemoteStoreConfig> regStore;
-
-static RegisterStoreImplementation regStore([](
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    if (std::string(uri, 0, uriScheme.size()) != uriScheme) return 0;
-    return std::make_shared<UDSRemoteStore>(std::string(uri, uriScheme.size()), params);
-});
 
 }

src/libstore/remote-store.hh

@@ -16,19 +16,23 @@ struct FdSource;
 template<typename T> class Pool;
 struct ConnectionHandle;
 
+struct RemoteStoreConfig : virtual StoreConfig
+{
+    using StoreConfig::StoreConfig;
+
+    const Setting<int> maxConnections{(StoreConfig*) this, 1,
+            "max-connections", "maximum number of concurrent connections to the Nix daemon"};
+
+    const Setting<unsigned int> maxConnectionAge{(StoreConfig*) this, std::numeric_limits<unsigned int>::max(),
+            "max-connection-age", "number of seconds to reuse a connection"};
+};
 
 /* FIXME: RemoteStore is a misnomer - should be something like
    DaemonStore. */
-class RemoteStore : public virtual Store
+class RemoteStore : public virtual Store, public virtual RemoteStoreConfig
 {
 public:
 
-    const Setting<int> maxConnections{(Store*) this, 1,
-            "max-connections", "maximum number of concurrent connections to the Nix daemon"};
-
-    const Setting<unsigned int> maxConnectionAge{(Store*) this, std::numeric_limits<unsigned int>::max(),
-            "max-connection-age", "number of seconds to reuse a connection"};
-
     virtual bool sameMachine() = 0;
 
     RemoteStore(const Params & params);
@@ -141,15 +145,35 @@ private:
 
 };
 
-class UDSRemoteStore : public LocalFSStore, public RemoteStore
+struct UDSRemoteStoreConfig : virtual LocalFSStoreConfig, virtual RemoteStoreConfig
+{
+    UDSRemoteStoreConfig(const Store::Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , RemoteStoreConfig(params)
+    {
+    }
+
+    UDSRemoteStoreConfig()
+        : UDSRemoteStoreConfig(Store::Params({}))
+    {
+    }
+
+    const std::string name() override { return "Local Daemon Store"; }
+};
+
+class UDSRemoteStore : public LocalFSStore, public RemoteStore, public virtual UDSRemoteStoreConfig
 {
 public:
 
     UDSRemoteStore(const Params & params);
-    UDSRemoteStore(std::string path, const Params & params);
+    UDSRemoteStore(const std::string scheme, std::string path, const Params & params);
 
     std::string getUri() override;
 
+    static std::set<std::string> uriSchemes()
+    { return {"unix"}; }
+
     bool sameMachine() override
     { return true; }
 

src/libstore/s3-binary-cache-store.cc

@@ -172,20 +172,26 @@ S3Helper::FileTransferResult S3Helper::getObject(
     return res;
 }
 
-struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
+struct S3BinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
 {
-    const Setting<std::string> profile{this, "", "profile", "The name of the AWS configuration profile to use."};
+    using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
-    const Setting<std::string> region{this, Aws::Region::US_EAST_1, "region", {"aws-region"}};
+    const Setting<std::string> profile{(StoreConfig*) this, "", "profile", "The name of the AWS configuration profile to use."};
-    const Setting<std::string> scheme{this, "", "scheme", "The scheme to use for S3 requests, https by default."};
+    const Setting<std::string> region{(StoreConfig*) this, Aws::Region::US_EAST_1, "region", {"aws-region"}};
-    const Setting<std::string> endpoint{this, "", "endpoint", "An optional override of the endpoint to use when talking to S3."};
+    const Setting<std::string> scheme{(StoreConfig*) this, "", "scheme", "The scheme to use for S3 requests, https by default."};
-    const Setting<std::string> narinfoCompression{this, "", "narinfo-compression", "compression method for .narinfo files"};
+    const Setting<std::string> endpoint{(StoreConfig*) this, "", "endpoint", "An optional override of the endpoint to use when talking to S3."};
-    const Setting<std::string> lsCompression{this, "", "ls-compression", "compression method for .ls files"};
+    const Setting<std::string> narinfoCompression{(StoreConfig*) this, "", "narinfo-compression", "compression method for .narinfo files"};
-    const Setting<std::string> logCompression{this, "", "log-compression", "compression method for log/* files"};
+    const Setting<std::string> lsCompression{(StoreConfig*) this, "", "ls-compression", "compression method for .ls files"};
+    const Setting<std::string> logCompression{(StoreConfig*) this, "", "log-compression", "compression method for log/* files"};
     const Setting<bool> multipartUpload{
-        this, false, "multipart-upload", "whether to use multi-part uploads"};
+        (StoreConfig*) this, false, "multipart-upload", "whether to use multi-part uploads"};
     const Setting<uint64_t> bufferSize{
-        this, 5 * 1024 * 1024, "buffer-size", "size (in bytes) of each part in multi-part uploads"};
+        (StoreConfig*) this, 5 * 1024 * 1024, "buffer-size", "size (in bytes) of each part in multi-part uploads"};
 
+    const std::string name() override { return "S3 Binary Cache Store"; }
+};
+
+struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore, virtual S3BinaryCacheStoreConfig
+{
     std::string bucketName;
 
     Stats stats;
@@ -193,8 +199,11 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
     S3Helper s3Helper;
 
     S3BinaryCacheStoreImpl(
-        const Params & params, const std::string & bucketName)
+        const std::string & scheme,
-        : S3BinaryCacheStore(params)
+        const std::string & bucketName,
+        const Params & params)
+        : StoreConfig(params)
+        , S3BinaryCacheStore(params)
         , bucketName(bucketName)
         , s3Helper(profile, region, scheme, endpoint)
     {
@@ -426,17 +435,11 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
         return paths;
     }
 
+    static std::set<std::string> uriSchemes() { return {"s3"}; }
+
 };
 
-static RegisterStoreImplementation regStore([](
+static RegisterStoreImplementation<S3BinaryCacheStoreImpl, S3BinaryCacheStoreConfig> regStore;
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    if (std::string(uri, 0, 5) != "s3://") return 0;
-    auto store = std::make_shared<S3BinaryCacheStoreImpl>(params, std::string(uri, 5));
-    store->init();
-    return store;
-});
 
 }
 

src/libstore/ssh-store.cc

@@ -8,19 +8,25 @@
 
 namespace nix {
 
-static std::string uriScheme = "ssh-ng://";
+struct SSHStoreConfig : virtual RemoteStoreConfig
+{
+    using RemoteStoreConfig::RemoteStoreConfig;
 
-class SSHStore : public RemoteStore
+    const Setting<Path> sshKey{(StoreConfig*) this, "", "ssh-key", "path to an SSH private key"};
+    const Setting<bool> compress{(StoreConfig*) this, false, "compress", "whether to compress the connection"};
+    const Setting<Path> remoteProgram{(StoreConfig*) this, "nix-daemon", "remote-program", "path to the nix-daemon executable on the remote system"};
+    const Setting<std::string> remoteStore{(StoreConfig*) this, "", "remote-store", "URI of the store on the remote system"};
+
+    const std::string name() override { return "SSH Store"; }
+};
+
+class SSHStore : public virtual RemoteStore, public virtual SSHStoreConfig
 {
 public:
 
-    const Setting<Path> sshKey{(Store*) this, "", "ssh-key", "path to an SSH private key"};
+    SSHStore(const std::string & scheme, const std::string & host, const Params & params)
-    const Setting<bool> compress{(Store*) this, false, "compress", "whether to compress the connection"};
+        : StoreConfig(params)
-    const Setting<Path> remoteProgram{(Store*) this, "nix-daemon", "remote-program", "path to the nix-daemon executable on the remote system"};
+        , Store(params)
-    const Setting<std::string> remoteStore{(Store*) this, "", "remote-store", "URI of the store on the remote system"};
-
-    SSHStore(const std::string & host, const Params & params)
-        : Store(params)
         , RemoteStore(params)
         , host(host)
         , master(
@@ -32,9 +38,11 @@ public:
     {
     }
 
+    static std::set<std::string> uriSchemes() { return {"ssh-ng"}; }
+
     std::string getUri() override
     {
-        return uriScheme + host;
+        return *uriSchemes().begin() + "://" + host;
     }
 
     bool sameMachine() override
@@ -76,12 +84,6 @@ ref<RemoteStore::Connection> SSHStore::openConnection()
     return conn;
 }
 
-static RegisterStoreImplementation regStore([](
+static RegisterStoreImplementation<SSHStore, SSHStoreConfig> regStore;
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
-{
-    if (std::string(uri, 0, uriScheme.size()) != uriScheme) return 0;
-    return std::make_shared<SSHStore>(std::string(uri, uriScheme.size()), params);
-});
 
 }

src/libstore/store-api.cc

@@ -346,7 +346,7 @@ ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
 
 
 Store::Store(const Params & params)
-    : Config(params)
+    : StoreConfig(params)
     , state({(size_t) pathInfoCacheSize})
 {
 }
@@ -1009,7 +1009,6 @@ Derivation Store::readDerivation(const StorePath & drvPath)
     }
 }
 
-
 }
 
 
@@ -1019,9 +1018,6 @@ Derivation Store::readDerivation(const StorePath & drvPath)
 
 namespace nix {
 
-
-RegisterStoreImplementation::Implementations * RegisterStoreImplementation::implementations = 0;
-
 /* Split URI into protocol+hierarchy part and its parameter set. */
 std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri_)
 {
@@ -1035,24 +1031,6 @@ std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri_
     return {uri, params};
 }
 
-ref<Store> openStore(const std::string & uri_,
-    const Store::Params & extraParams)
-{
-    auto [uri, uriParams] = splitUriAndParams(uri_);
-    auto params = extraParams;
-    params.insert(uriParams.begin(), uriParams.end());
-
-    for (auto fun : *RegisterStoreImplementation::implementations) {
-        auto store = fun(uri, params);
-        if (store) {
-            store->warnUnknownSettings();
-            return ref<Store>(store);
-        }
-    }
-
-    throw Error("don't know how to open Nix store '%s'", uri);
-}
-
 static bool isNonUriPath(const std::string & spec) {
     return
         // is not a URL
@@ -1080,10 +1058,7 @@ StoreType getStoreType(const std::string & uri, const std::string & stateDir)
     }
 }
 
-
+std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Params & params)
-static RegisterStoreImplementation regStore([](
-    const std::string & uri, const Store::Params & params)
-    -> std::shared_ptr<Store>
 {
     switch (getStoreType(uri, get(params, "state").value_or(settings.nixStateDir))) {
         case tDaemon:
@@ -1098,8 +1073,41 @@ static RegisterStoreImplementation regStore([](
         default:
             return nullptr;
     }
-});
+}
 
+ref<Store> openStore(const std::string & uri_,
+    const Store::Params & extraParams)
+{
+    auto params = extraParams;
+    try {
+        auto parsedUri = parseURL(uri_);
+        params.insert(parsedUri.query.begin(), parsedUri.query.end());
+
+        auto baseURI = parsedUri.authority.value_or("") + parsedUri.path;
+
+        for (auto implem : *Implementations::registered) {
+            if (implem.uriSchemes.count(parsedUri.scheme)) {
+                auto store = implem.create(parsedUri.scheme, baseURI, params);
+                if (store) {
+                    store->init();
+                    store->warnUnknownSettings();
+                    return ref<Store>(store);
+                }
+            }
+        }
+    }
+    catch (BadURL &) {
+        auto [uri, uriParams] = splitUriAndParams(uri_);
+        params.insert(uriParams.begin(), uriParams.end());
+
+        if (auto store = openFromNonUri(uri, params)) {
+            store->warnUnknownSettings();
+            return ref<Store>(store);
+        }
+    }
+
+    throw Error("don't know how to open Nix store '%s'", uri_);
+}
 
 std::list<ref<Store>> getDefaultSubstituters()
 {
@@ -1133,5 +1141,6 @@ std::list<ref<Store>> getDefaultSubstituters()
     return stores;
 }
 
+std::vector<StoreFactory> * Implementations::registered = 0;
 
 }

src/libstore/store-api.hh

@@ -24,6 +24,31 @@
 
 namespace nix {
 
+/**
+ * About the class hierarchy of the store implementations:
+ *
+ * Each store type `Foo` consists of two classes:
+ *
+ * 1. A class `FooConfig : virtual StoreConfig` that contains the configuration
+ *   for the store
+ *
+ *   It should only contain members of type `const Setting<T>` (or subclasses
+ *   of it) and inherit the constructors of `StoreConfig`
+ *   (`using StoreConfig::StoreConfig`).
+ *
+ * 2. A class `Foo : virtual Store, virtual FooConfig` that contains the
+ *   implementation of the store.
+ *
+ *   This class is expected to have a constructor `Foo(const Params & params)`
+ *   that calls `StoreConfig(params)` (otherwise you're gonna encounter an
+ *   `assertion failure` when trying to instantiate it).
+ *
+ * You can then register the new store using:
+ *
+ * ```
+ * cpp static RegisterStoreImplementation<Foo, FooConfig> regStore;
+ * ```
+ */
 
 MakeError(SubstError, Error);
 MakeError(BuildError, Error); // denotes a permanent build failure
@@ -33,6 +58,7 @@ MakeError(SubstituteGone, Error);
 MakeError(SubstituterDisabled, Error);
 MakeError(BadStorePath, Error);
 
+MakeError(InvalidStoreURI, Error);
 
 class FSAccessor;
 class NarInfoDiskCache;
@@ -144,12 +170,31 @@ struct BuildResult
     }
 };
 
-
+struct StoreConfig : public Config
-class Store : public std::enable_shared_from_this<Store>, public Config
 {
-public:
+    using Config::Config;
 
-    typedef std::map<std::string, std::string> Params;
+    /**
+     * When constructing a store implementation, we pass in a map `params` of
+     * parameters that's supposed to initialize the associated config.
+     * To do that, we must use the `StoreConfig(StringMap & params)`
+     * constructor, so we'd like to `delete` its default constructor to enforce
+     * it.
+     *
+     * However, actually deleting it means that all the subclasses of
+     * `StoreConfig` will have their default constructor deleted (because it's
+     * supposed to call the deleted default constructor of `StoreConfig`). But
+     * because we're always using virtual inheritance, the constructors of
+     * child classes will never implicitely call this one, so deleting it will
+     * be more painful than anything else.
+     *
+     * So we `assert(false)` here to ensure at runtime that the right
+     * constructor is always called without having to redefine a custom
+     * constructor for each `*Config` class.
+     */
+    StoreConfig() { assert(false); }
+
+    virtual const std::string name() = 0;
 
     const PathSetting storeDir_{this, false, settings.nixStore,
         "store", "path to the Nix store"};
@@ -167,6 +212,14 @@ public:
         "system-features",
         "Optional features that the system this store builds on implements (like \"kvm\")."};
 
+};
+
+class Store : public std::enable_shared_from_this<Store>, public virtual StoreConfig
+{
+public:
+
+    typedef std::map<std::string, std::string> Params;
+
 protected:
 
     struct PathInfoCacheValue {
@@ -200,6 +253,11 @@ protected:
     Store(const Params & params);
 
 public:
+    /**
+     * Perform any necessary effectful operation to make the store up and
+     * running
+     */
+    virtual void init() {};
 
     virtual ~Store() { }
 
@@ -626,22 +684,25 @@ protected:
 
 };
 
-
+struct LocalFSStoreConfig : virtual StoreConfig
-class LocalFSStore : public virtual Store
 {
-public:
+    using StoreConfig::StoreConfig;
-
+    // FIXME: the (StoreConfig*) cast works around a bug in gcc that causes
-    // FIXME: the (Store*) cast works around a bug in gcc that causes
     // it to omit the call to the Setting constructor. Clang works fine
     // either way.
-    const PathSetting rootDir{(Store*) this, true, "",
+    const PathSetting rootDir{(StoreConfig*) this, true, "",
         "root", "directory prefixed to all other paths"};
-    const PathSetting stateDir{(Store*) this, false,
+    const PathSetting stateDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/var/nix" : settings.nixStateDir,
         "state", "directory where Nix will store state"};
-    const PathSetting logDir{(Store*) this, false,
+    const PathSetting logDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/var/log/nix" : settings.nixLogDir,
         "log", "directory where Nix will store state"};
+};
+
+class LocalFSStore : public virtual Store, public virtual LocalFSStoreConfig
+{
+public:
 
     const static string drvsLogDir;
 
@@ -744,23 +805,43 @@ StoreType getStoreType(const std::string & uri = settings.storeUri.get(),
    ‘substituters’ option and various legacy options. */
 std::list<ref<Store>> getDefaultSubstituters();
 
-
+struct StoreFactory
-/* Store implementation registration. */
-typedef std::function<std::shared_ptr<Store>(
-    const std::string & uri, const Store::Params & params)> OpenStore;
-
-struct RegisterStoreImplementation
 {
-    typedef std::vector<OpenStore> Implementations;
+    std::set<std::string> uriSchemes;
-    static Implementations * implementations;
+    std::function<std::shared_ptr<Store> (const std::string & scheme, const std::string & uri, const Store::Params & params)> create;
+    std::function<std::shared_ptr<StoreConfig> ()> getConfig;
+};
+struct Implementations
+{
+    static std::vector<StoreFactory> * registered;
 
-    RegisterStoreImplementation(OpenStore fun)
+    template<typename T, typename TConfig>
+    static void add()
     {
-        if (!implementations) implementations = new Implementations;
+        if (!registered) registered = new std::vector<StoreFactory>();
-        implementations->push_back(fun);
+        StoreFactory factory{
+            .uriSchemes = T::uriSchemes(),
+            .create =
+                ([](const std::string & scheme, const std::string & uri, const Store::Params & params)
+                 -> std::shared_ptr<Store>
+                 { return std::make_shared<T>(scheme, uri, params); }),
+            .getConfig =
+                ([]()
+                 -> std::shared_ptr<StoreConfig>
+                 { return std::make_shared<TConfig>(StringMap({})); })
+        };
+        registered->push_back(factory);
     }
 };
 
+template<typename T, typename TConfig>
+struct RegisterStoreImplementation
+{
+    RegisterStoreImplementation()
+    {
+        Implementations::add<T, TConfig>();
+    }
+};
 
 
 /* Display a set of paths in human-readable form (i.e., between quotes

src/libutil/abstractsettingtojson.hh

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <nlohmann/json.hpp>
+#include "config.hh"
+
+namespace nix {
+template<typename T>
+std::map<std::string, nlohmann::json> BaseSetting<T>::toJSONObject()
+{
+    auto obj = AbstractSetting::toJSONObject();
+    obj.emplace("value", value);
+    obj.emplace("defaultValue", defaultValue);
+    return obj;
+}
+}

src/libutil/config.cc

@@ -1,5 +1,6 @@
 #include "config.hh"
 #include "args.hh"
+#include "abstractsettingtojson.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -137,11 +138,7 @@ nlohmann::json Config::toJSON()
     auto res = nlohmann::json::object();
     for (auto & s : _settings)
         if (!s.second.isAlias) {
-            auto obj = nlohmann::json::object();
+            res.emplace(s.first, s.second.setting->toJSON());
-            obj.emplace("description", s.second.setting->description);
-            obj.emplace("aliases", s.second.setting->aliases);
-            obj.emplace("value", s.second.setting->toJSON());
-            res.emplace(s.first, obj);
         }
     return res;
 }
@@ -168,19 +165,21 @@ void AbstractSetting::setDefault(const std::string & str)
 
 nlohmann::json AbstractSetting::toJSON()
 {
-    return to_string();
+    return nlohmann::json(toJSONObject());
+}
+
+std::map<std::string, nlohmann::json> AbstractSetting::toJSONObject()
+{
+    std::map<std::string, nlohmann::json> obj;
+    obj.emplace("description", description);
+    obj.emplace("aliases", aliases);
+    return obj;
 }
 
 void AbstractSetting::convertToArg(Args & args, const std::string & category)
 {
 }
 
-template<typename T>
-nlohmann::json BaseSetting<T>::toJSON()
-{
-    return value;
-}
-
 template<typename T>
 void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
 {
@@ -259,11 +258,6 @@ template<> std::string BaseSetting<Strings>::to_string() const
     return concatStringsSep(" ", value);
 }
 
-template<> nlohmann::json BaseSetting<Strings>::toJSON()
-{
-    return value;
-}
-
 template<> void BaseSetting<StringSet>::set(const std::string & str)
 {
     value = tokenizeString<StringSet>(str);
@@ -274,11 +268,6 @@ template<> std::string BaseSetting<StringSet>::to_string() const
     return concatStringsSep(" ", value);
 }
 
-template<> nlohmann::json BaseSetting<StringSet>::toJSON()
-{
-    return value;
-}
-
 template class BaseSetting<int>;
 template class BaseSetting<unsigned int>;
 template class BaseSetting<long>;

src/libutil/config.hh

@@ -206,7 +206,9 @@ protected:
 
     virtual std::string to_string() const = 0;
 
-    virtual nlohmann::json toJSON();
+    nlohmann::json toJSON();
+
+    virtual std::map<std::string, nlohmann::json> toJSONObject();
 
     virtual void convertToArg(Args & args, const std::string & category);
 
@@ -220,6 +222,7 @@ class BaseSetting : public AbstractSetting
 protected:
 
     T value;
+    const T defaultValue;
 
 public:
 
@@ -229,6 +232,7 @@ public:
         const std::set<std::string> & aliases = {})
         : AbstractSetting(name, description, aliases)
         , value(def)
+        , defaultValue(def)
     { }
 
     operator const T &() const { return value; }
@@ -251,7 +255,7 @@ public:
 
     void convertToArg(Args & args, const std::string & category) override;
 
-    nlohmann::json toJSON() override;
+    std::map<std::string, nlohmann::json> toJSONObject() override;
 };
 
 template<typename T>

src/libutil/tests/config.cc

@@ -161,7 +161,7 @@ namespace nix {
         Setting<std::string> setting{&config, "", "name-of-the-setting", "description"};
         setting.assign("value");
 
-        ASSERT_EQ(config.toJSON().dump(), R"#({"name-of-the-setting":{"aliases":[],"description":"description\n","value":"value"}})#");
+        ASSERT_EQ(config.toJSON().dump(), R"#({"name-of-the-setting":{"aliases":[],"defaultValue":"","description":"description\n","value":"value"}})#");
     }
 
     TEST(Config, setSettingAlias) {

src/libutil/url.hh

@@ -31,7 +31,7 @@ ParsedURL parseURL(const std::string & url);
 
 // URI stuff.
 const static std::string pctEncoded = "(?:%[0-9a-fA-F][0-9a-fA-F])";
-const static std::string schemeRegex = "(?:[a-z+]+)";
+const static std::string schemeRegex = "(?:[a-z+.-]+)";
 const static std::string ipv6AddressRegex = "(?:\\[[0-9a-fA-F:]+\\])";
 const static std::string unreservedRegex = "(?:[a-zA-Z0-9-._~])";
 const static std::string subdelimsRegex = "(?:[!$&'\"()*+,;=])";

src/nix/describe-stores.cc

@@ -0,0 +1,44 @@
+#include "command.hh"
+#include "common-args.hh"
+#include "shared.hh"
+#include "store-api.hh"
+
+#include <nlohmann/json.hpp>
+
+using namespace nix;
+
+struct CmdDescribeStores : Command, MixJSON
+{
+    std::string description() override
+    {
+        return "show registered store types and their available options";
+    }
+
+    Category category() override { return catUtility; }
+
+    void run() override
+    {
+        auto res = nlohmann::json::object();
+        for (auto & implem : *Implementations::registered) {
+            auto storeConfig = implem.getConfig();
+            auto storeName = storeConfig->name();
+            res[storeName] = storeConfig->toJSON();
+        }
+        if (json) {
+            std::cout << res;
+        } else {
+            for (auto & [storeName, storeConfig] : res.items()) {
+                std::cout << "## " << storeName << std::endl << std::endl;
+                for (auto & [optionName, optionDesc] : storeConfig.items()) {
+                    std::cout << "### " << optionName << std::endl << std::endl;
+                    std::cout << optionDesc["description"].get<std::string>() << std::endl;
+                    std::cout << "default: " << optionDesc["defaultValue"] << std::endl <<std::endl;
+                    if (!optionDesc["aliases"].empty())
+                        std::cout << "aliases: " << optionDesc["aliases"] << std::endl << std::endl;
+                }
+            }
+        }
+    }
+};
+
+static auto r1 = registerCommand<CmdDescribeStores>("describe-stores");

src/nix/develop.cc

@@ -392,7 +392,7 @@ struct CmdDevelop : Common, MixEnvironment
 
             auto bashInstallable = std::make_shared<InstallableFlake>(
                 state,
-                std::move(installable->nixpkgsFlakeRef()),
+                installable->nixpkgsFlakeRef(),
                 Strings{"bashInteractive"},
                 Strings{"legacyPackages." + settings.thisSystem.get() + "."},
                 lockFlags);

src/nix/diff-closures.cc

@@ -81,7 +81,7 @@ void printClosureDiff(
         auto beforeSize = totalSize(beforeVersions);
         auto afterSize = totalSize(afterVersions);
         auto sizeDelta = (int64_t) afterSize - (int64_t) beforeSize;
-        auto showDelta = abs(sizeDelta) >= 8 * 1024;
+        auto showDelta = std::abs(sizeDelta) >= 8 * 1024;
 
         std::set<std::string> removed, unchanged;
         for (auto & [version, _] : beforeVersions)

src/nix/installables.hh

@@ -69,7 +69,7 @@ struct Installable
 
     virtual FlakeRef nixpkgsFlakeRef() const
     {
-        return std::move(FlakeRef::fromAttrs({{"type","indirect"}, {"id", "nixpkgs"}}));
+        return FlakeRef::fromAttrs({{"type","indirect"}, {"id", "nixpkgs"}});
     }
 };
 

tests/describe-stores.sh

@@ -0,0 +1,8 @@
+source common.sh
+
+# Query an arbitrary value in `nix describe-stores --json`'s output just to
+# check that it has the right structure
+[[ $(nix --experimental-features 'nix-command flakes' describe-stores --json | jq '.["SSH Store"]["compress"]["defaultValue"]') == false ]]
+
+# Ensure that the output of `nix describe-stores` isn't empty
+[[ -n $(nix --experimental-features 'nix-command flakes' describe-stores) ]]

tests/local.mk

@@ -32,6 +32,7 @@ nix_tests = \
   post-hook.sh \
   function-trace.sh \
   recursive.sh \
+  describe-stores.sh \
   flakes.sh \
   content-addressed.sh
   # parallel.sh