Merge pull request #8084 from edolstra/store-docs

Auto-generate store documentation

src/libstore/binary-cache-store.hh

@@ -16,17 +16,33 @@ struct BinaryCacheStoreConfig : virtual StoreConfig
 {
     using StoreConfig::StoreConfig;
 
-    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression", "NAR compression method ('xz', 'bzip2', 'gzip', 'zstd', or 'none')"};
-    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{(StoreConfig*) this, false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
-    const Setting<Path> secretKeyFile{(StoreConfig*) this, "", "secret-key", "path to secret key used to sign the binary cache"};
-    const Setting<Path> localNarCache{(StoreConfig*) this, "", "local-nar-cache", "path to a local cache of NARs"};
+    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression",
+        "NAR compression method (`xz`, `bzip2`, `gzip`, `zstd`, or `none`)."};
+
+    const Setting<bool> writeNARListing{(StoreConfig*) this, false, "write-nar-listing",
+        "Whether to write a JSON file that lists the files in each NAR."};
+
+    const Setting<bool> writeDebugInfo{(StoreConfig*) this, false, "index-debug-info",
+        R"(
+          Whether to index DWARF debug info files by build ID. This allows [`dwarffs`](https://github.com/edolstra/dwarffs) to
+          fetch debug info on demand
+        )"};
+
+    const Setting<Path> secretKeyFile{(StoreConfig*) this, "", "secret-key",
+        "Path to the secret key used to sign the binary cache."};
+
+    const Setting<Path> localNarCache{(StoreConfig*) this, "", "local-nar-cache",
+        "Path to a local cache of NARs fetched from this binary cache, used by commands such as `nix store cat`."};
+
     const Setting<bool> parallelCompression{(StoreConfig*) this, false, "parallel-compression",
-        "enable multi-threading compression for NARs, available for xz and zstd only currently"};
+        "Enable multi-threaded compression of NARs. This is currently only available for `xz` and `zstd`."};
+
     const Setting<int> compressionLevel{(StoreConfig*) this, -1, "compression-level",
-        "specify 'preset level' of compression to be used with NARs: "
-        "meaning and accepted range of values depends on compression method selected, "
-        "other than -1 which we reserve to indicate Nix defaults should be used"};
+        R"(
+          The *preset level* to be used when compressing NARs.
+          The meaning and accepted values depend on the compression method selected.
+          `-1` specifies that the default compression level should be used.
+        )"};
 };
 
 class BinaryCacheStore : public virtual BinaryCacheStoreConfig,

src/libstore/dummy-store.cc

@@ -7,6 +7,13 @@ struct DummyStoreConfig : virtual StoreConfig {
     using StoreConfig::StoreConfig;
 
     const std::string name() override { return "Dummy Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "dummy-store.md"
+          ;
+    }
 };
 
 struct DummyStore : public virtual DummyStoreConfig, public virtual Store

src/libstore/dummy-store.md

@@ -0,0 +1,13 @@
+R"(
+
+**Store URL format**: `dummy://`
+
+This store type represents a store that contains no store paths and
+cannot be written to. It's useful when you want to use the Nix
+evaluator when no actual Nix store exists, e.g.
+
+```console
+# nix eval --store dummy:// --expr '1 + 2'
+```
+
+)"

src/libstore/globals.hh

@@ -98,7 +98,12 @@ public:
     Path nixDaemonSocketFile;
 
     Setting<std::string> storeUri{this, getEnv("NIX_REMOTE").value_or("auto"), "store",
-        "The default Nix store to use."};
+        R"(
+          The [URL of the Nix store](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format)
+          to use for most operations.
+          See [`nix help-stores`](@docroot@/command-ref/new-cli/nix3-help-stores.md)
+          for supported store types and settings.
+        )"};
 
     Setting<bool> keepFailed{this, false, "keep-failed",
         "Whether to keep temporary directories of failed builds."};
@@ -679,8 +684,9 @@ public:
         Strings{"https://cache.nixos.org/"},
         "substituters",
         R"(
-          A list of URLs of substituters, separated by whitespace. Substituters
-          are tried based on their Priority value, which each substituter can set
+          A list of [URLs of Nix stores](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format)
+          to be used as substituters, separated by whitespace.
+          Substituters are tried based on their Priority value, which each substituter can set
           independently. Lower value means higher priority.
           The default is `https://cache.nixos.org`, with a Priority of 40.
 
@@ -698,7 +704,8 @@ public:
     Setting<StringSet> trustedSubstituters{
         this, {}, "trusted-substituters",
         R"(
-          A list of URLs of substituters, separated by whitespace. These are
+          A list of [URLs of Nix stores](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format),
+          separated by whitespace. These are
           not used by default, but can be enabled by users of the Nix daemon
           by specifying `--option substituters urls` on the command
           line. Unprivileged users are only allowed to pass a subset of the

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

@@ -12,7 +12,14 @@ struct HttpBinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
 {
     using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
 
-    const std::string name() override { return "Http Binary Cache Store"; }
+    const std::string name() override { return "HTTP Binary Cache Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "http-binary-cache-store.md"
+          ;
+    }
 };
 
 class HttpBinaryCacheStore : public virtual HttpBinaryCacheStoreConfig, public virtual BinaryCacheStore

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

@@ -0,0 +1,8 @@
+R"(
+
+**Store URL format**: `http://...`, `https://...`
+
+This store allows a binary cache to be accessed via the HTTP
+protocol.
+
+)"

src/libstore/legacy-ssh-store.cc

@@ -1,3 +1,4 @@
+#include "ssh-store-config.hh"
 #include "archive.hh"
 #include "pool.hh"
 #include "remote-store.hh"
@@ -12,17 +13,24 @@
 
 namespace nix {
 
-struct LegacySSHStoreConfig : virtual StoreConfig
+struct LegacySSHStoreConfig : virtual CommonSSHStoreConfig
 {
-    using StoreConfig::StoreConfig;
-    const Setting<int> maxConnections{(StoreConfig*) this, 1, "max-connections", "maximum number of concurrent SSH connections"};
-    const Setting<Path> sshKey{(StoreConfig*) this, "", "ssh-key", "path to an SSH private key"};
-    const Setting<std::string> sshPublicHostKey{(StoreConfig*) this, "", "base64-ssh-public-host-key", "The public half of the host's SSH key"};
-    const Setting<bool> compress{(StoreConfig*) this, false, "compress", "whether to compress the connection"};
-    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"};
+    using CommonSSHStoreConfig::CommonSSHStoreConfig;
 
-    const std::string name() override { return "Legacy SSH Store"; }
+    const Setting<Path> remoteProgram{(StoreConfig*) this, "nix-store", "remote-program",
+        "Path to the `nix-store` executable on the remote machine."};
+
+    const Setting<int> maxConnections{(StoreConfig*) this, 1, "max-connections",
+        "Maximum number of concurrent SSH connections."};
+
+    const std::string name() override { return "SSH Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "legacy-ssh-store.md"
+          ;
+    }
 };
 
 struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Store
@@ -51,6 +59,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
     LegacySSHStore(const std::string & scheme, const std::string & host, const Params & params)
         : StoreConfig(params)
+        , CommonSSHStoreConfig(params)
         , LegacySSHStoreConfig(params)
         , Store(params)
         , host(host)

src/libstore/legacy-ssh-store.md

@@ -0,0 +1,8 @@
+R"(
+
+**Store URL format**: `ssh://[username@]hostname`
+
+This store type allows limited access to a remote store on another
+machine via SSH.
+
+)"

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

@@ -11,6 +11,13 @@ struct LocalBinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
     using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
 
     const std::string name() override { return "Local Binary Cache Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "local-binary-cache-store.md"
+          ;
+    }
 };
 
 class LocalBinaryCacheStore : public virtual LocalBinaryCacheStoreConfig, public virtual BinaryCacheStore

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

@@ -0,0 +1,16 @@
+R"(
+
+**Store URL format**: `file://`*path*
+
+This store allows reading and writing a binary cache stored in *path*
+in the local filesystem. If *path* does not exist, it will be created.
+
+For example, the following builds or downloads `nixpkgs#hello` into
+the local store and then copies it to the binary cache in
+`/tmp/binary-cache`:
+
+```
+# nix copy --to file:///tmp/binary-cache nixpkgs#hello
+```
+
+)"

src/libstore/local-fs-store.hh

@@ -9,20 +9,28 @@ namespace nix {
 struct LocalFSStoreConfig : virtual StoreConfig
 {
     using StoreConfig::StoreConfig;
+
     // FIXME: the (StoreConfig*) 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{(StoreConfig*) this, true, "",
-        "root", "directory prefixed to all other paths"};
+        "root",
+        "Directory prefixed to all other paths."};
+
     const PathSetting stateDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/var/nix" : settings.nixStateDir,
-        "state", "directory where Nix will store state"};
+        "state",
+        "Directory where Nix will store state."};
+
     const PathSetting logDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/var/log/nix" : settings.nixLogDir,
-        "log", "directory where Nix will store state"};
+        "log",
+        "directory where Nix will store log files."};
+
     const PathSetting realStoreDir{(StoreConfig*) this, false,
         rootDir != "" ? rootDir + "/nix/store" : storeDir, "real",
-        "physical path to the Nix store"};
+        "Physical path of the Nix store."};
 };
 
 class LocalFSStore : public virtual LocalFSStoreConfig,

src/libstore/local-store.cc

@@ -44,6 +44,13 @@
 
 namespace nix {
 
+std::string LocalStoreConfig::doc()
+{
+    return
+        #include "local-store.md"
+        ;
+}
+
 struct LocalStore::State::Stmts {
     /* Some precompiled SQLite statements. */
     SQLiteStmt RegisterValidPath;
@@ -413,6 +420,13 @@ LocalStore::LocalStore(const Params & params)
 }
 
 
+LocalStore::LocalStore(std::string scheme, std::string path, const Params & params)
+    : LocalStore(params)
+{
+    throw UnimplementedError("LocalStore");
+}
+
+
 AutoCloseFD LocalStore::openGCLock()
 {
     Path fnGCLock = stateDir + "/gc.lock";
@@ -1950,5 +1964,6 @@ std::optional<std::string> LocalStore::getVersion()
     return nixVersion;
 }
 
+static RegisterStoreImplementation<LocalStore, LocalStoreConfig> regLocalStore;
 
 }  // namespace nix

src/libstore/local-store.hh

@@ -38,11 +38,13 @@ struct LocalStoreConfig : virtual LocalFSStoreConfig
 
     Setting<bool> requireSigs{(StoreConfig*) this,
         settings.requireSigs,
-        "require-sigs", "whether store paths should have a trusted signature on import"};
+        "require-sigs",
+        "Whether store paths copied into this store should have a trusted signature."};
 
     const std::string name() override { return "Local Store"; }
-};
 
+    std::string doc() override;
+};
 
 class LocalStore : public virtual LocalStoreConfig, public virtual LocalFSStore, public virtual GcStore
 {
@@ -100,9 +102,13 @@ public:
     /* Initialise the local store, upgrading the schema if
        necessary. */
     LocalStore(const Params & params);
+    LocalStore(std::string scheme, std::string path, const Params & params);
 
     ~LocalStore();
 
+    static std::set<std::string> uriSchemes()
+    { return {}; }
+
     /* Implementations of abstract store API methods. */
 
     std::string getUri() override;

src/libstore/local-store.md

@@ -0,0 +1,39 @@
+R"(
+
+**Store URL format**: `local`, *root*
+
+This store type accesses a Nix store in the local filesystem directly
+(i.e. not via the Nix daemon). *root* is an absolute path that is
+prefixed to other directories such as the Nix store directory. The
+store pseudo-URL `local` denotes a store that uses `/` as its root
+directory.
+
+A store that uses a *root* other than `/` is called a *chroot
+store*. With such stores, the store directory is "logically" still
+`/nix/store`, so programs stored in them can only be built and
+executed by `chroot`-ing into *root*. Chroot stores only support
+building and running on Linux when [`mount namespaces`](https://man7.org/linux/man-pages/man7/mount_namespaces.7.html) and [`user namespaces`](https://man7.org/linux/man-pages/man7/user_namespaces.7.html) are
+enabled.
+
+For example, the following uses `/tmp/root` as the chroot environment
+to build or download `nixpkgs#hello` and then execute it:
+
+```console
+# nix run --store /tmp/root nixpkgs#hello
+Hello, world!
+```
+
+Here, the "physical" store location is `/tmp/root/nix/store`, and
+Nix's store metadata is in `/tmp/root/nix/var/nix/db`.
+
+It is also possible, but not recommended, to change the "logical"
+location of the Nix store from its default of `/nix/store`. This makes
+it impossible to use default substituters such as
+`https://cache.nixos.org/`, and thus you may have to build everything
+locally. Here is an example:
+
+```console
+# nix build --store 'local?store=/tmp/my-nix/store&state=/tmp/my-nix/state&log=/tmp/my-nix/log' nixpkgs#hello
+```
+
+)"

src/libstore/remote-store.hh

@@ -22,11 +22,13 @@ 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<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"};
+    const Setting<unsigned int> maxConnectionAge{(StoreConfig*) this,
+        std::numeric_limits<unsigned int>::max(),
+        "max-connection-age",
+        "Maximum age of a connection before it is closed."};
 };
 
 /* FIXME: RemoteStore is a misnomer - should be something like

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

@@ -192,19 +192,72 @@ S3BinaryCacheStore::S3BinaryCacheStore(const Params & params)
 struct S3BinaryCacheStoreConfig : virtual BinaryCacheStoreConfig
 {
     using BinaryCacheStoreConfig::BinaryCacheStoreConfig;
-    const Setting<std::string> profile{(StoreConfig*) this, "", "profile", "The name of the AWS configuration profile to use."};
-    const Setting<std::string> region{(StoreConfig*) this, Aws::Region::US_EAST_1, "region", {"aws-region"}};
-    const Setting<std::string> scheme{(StoreConfig*) this, "", "scheme", "The scheme to use for S3 requests, https by default."};
-    const Setting<std::string> endpoint{(StoreConfig*) this, "", "endpoint", "An optional override of the endpoint to use when talking to S3."};
-    const Setting<std::string> narinfoCompression{(StoreConfig*) this, "", "narinfo-compression", "compression method for .narinfo 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<std::string> profile{(StoreConfig*) this, "", "profile",
+        R"(
+          The name of the AWS configuration profile to use. By default
+          Nix will use the `default` profile.
+        )"};
+
+    const Setting<std::string> region{(StoreConfig*) this, Aws::Region::US_EAST_1, "region",
+        R"(
+          The region of the S3 bucket. If your bucket is not in
+          `us–east-1`, you should always explicitly specify the region
+          parameter.
+        )"};
+
+    const Setting<std::string> scheme{(StoreConfig*) this, "", "scheme",
+        R"(
+          The scheme used for S3 requests, `https` (default) or `http`. This
+          option allows you to disable HTTPS for binary caches which don't
+          support it.
+
+          > **Note**
+          > 
+          > HTTPS should be used if the cache might contain sensitive
+          > information.
+        )"};
+
+    const Setting<std::string> endpoint{(StoreConfig*) this, "", "endpoint",
+        R"(
+          The URL of the endpoint of an S3-compatible service such as MinIO.
+          Do not specify this setting if you're using Amazon S3.
+
+          > **Note**
+          > 
+          > This endpoint must support HTTPS and will use path-based
+          > addressing instead of virtual host based addressing.
+        )"};
+
+    const Setting<std::string> narinfoCompression{(StoreConfig*) this, "", "narinfo-compression",
+        "Compression method for `.narinfo` files."};
+
+    const Setting<std::string> lsCompression{(StoreConfig*) this, "", "ls-compression",
+        "Compression method for `.ls` files."};
+
+    const Setting<std::string> logCompression{(StoreConfig*) this, "", "log-compression",
+        R"(
+          Compression method for `log/*` files. It is recommended to
+          use a compression method supported by most web browsers
+          (e.g. `brotli`).
+        )"};
+
     const Setting<bool> multipartUpload{
-        (StoreConfig*) 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{
-        (StoreConfig*) 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"; }
+
+    std::string doc() override
+    {
+        return
+          #include "s3-binary-cache-store.md"
+          ;
+    }
 };
 
 struct S3BinaryCacheStoreImpl : virtual S3BinaryCacheStoreConfig, public virtual S3BinaryCacheStore

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

@@ -0,0 +1,8 @@
+R"(
+
+**Store URL format**: `s3://`*bucket-name*
+
+This store allows reading and writing a binary cache stored in an AWS
+S3 bucket.
+
+)"

src/libstore/ssh-store-config.hh

@@ -0,0 +1,26 @@
+#include "store-api.hh"
+
+namespace nix {
+
+struct CommonSSHStoreConfig : virtual StoreConfig
+{
+    using StoreConfig::StoreConfig;
+
+    const Setting<Path> sshKey{(StoreConfig*) this, "", "ssh-key",
+        "Path to the SSH private key used to authenticate to the remote machine."};
+
+    const Setting<std::string> sshPublicHostKey{(StoreConfig*) this, "", "base64-ssh-public-host-key",
+        "The public host key of the remote machine."};
+
+    const Setting<bool> compress{(StoreConfig*) this, false, "compress",
+        "Whether to enable SSH compression."};
+
+    const Setting<std::string> remoteStore{(StoreConfig*) this, "", "remote-store",
+        R"(
+          [Store URL](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format)
+          to be used on the remote machine. The default is `auto`
+          (i.e. use the Nix daemon or `/nix/store` directly).
+        )"};
+};
+
+}

src/libstore/ssh-store.cc

@@ -1,3 +1,4 @@
+#include "ssh-store-config.hh"
 #include "store-api.hh"
 #include "remote-store.hh"
 #include "remote-fs-accessor.hh"
@@ -8,17 +9,22 @@
 
 namespace nix {
 
-struct SSHStoreConfig : virtual RemoteStoreConfig
+struct SSHStoreConfig : virtual RemoteStoreConfig, virtual CommonSSHStoreConfig
 {
     using RemoteStoreConfig::RemoteStoreConfig;
+    using CommonSSHStoreConfig::CommonSSHStoreConfig;
 
-    const Setting<Path> sshKey{(StoreConfig*) this, "", "ssh-key", "path to an SSH private key"};
-    const Setting<std::string> sshPublicHostKey{(StoreConfig*) this, "", "base64-ssh-public-host-key", "The public half of the host's SSH 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 Setting<Path> remoteProgram{(StoreConfig*) this, "nix-daemon", "remote-program",
+        "Path to the `nix-daemon` executable on the remote machine."};
 
-    const std::string name() override { return "SSH Store"; }
+    const std::string name() override { return "Experimental SSH Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "ssh-store.md"
+          ;
+    }
 };
 
 class SSHStore : public virtual SSHStoreConfig, public virtual RemoteStore
@@ -28,6 +34,7 @@ public:
     SSHStore(const std::string & scheme, const std::string & host, const Params & params)
         : StoreConfig(params)
         , RemoteStoreConfig(params)
+        , CommonSSHStoreConfig(params)
         , SSHStoreConfig(params)
         , Store(params)
         , RemoteStore(params)

src/libstore/ssh-store.md

@@ -0,0 +1,8 @@
+R"(
+
+**Store URL format**: `ssh-ng://[username@]hostname`
+
+Experimental store type that allows full access to a Nix store on a
+remote machine.
+
+)"

src/libstore/store-api.hh

@@ -101,17 +101,41 @@ struct StoreConfig : public Config
 
     virtual const std::string name() = 0;
 
+    virtual std::string doc()
+    {
+        return "";
+    }
+
     const PathSetting storeDir_{this, false, settings.nixStore,
-        "store", "path to the Nix store"};
+        "store",
+        R"(
+          Logical location of the Nix store, usually
+          `/nix/store`. Note that you can only copy store paths
+          between stores if they have the same `store` setting.
+        )"};
     const Path storeDir = storeDir_;
 
-    const Setting<int> pathInfoCacheSize{this, 65536, "path-info-cache-size", "size of the in-memory store path information cache"};
+    const Setting<int> pathInfoCacheSize{this, 65536, "path-info-cache-size",
+        "Size of the in-memory store path metadata cache."};
 
-    const Setting<bool> isTrusted{this, false, "trusted", "whether paths from this store can be used as substitutes even when they lack trusted signatures"};
+    const Setting<bool> isTrusted{this, false, "trusted",
+        R"(
+          Whether paths from this store can be used as substitutes
+          even if they are not signed by a key listed in the
+          [`trusted-public-keys`](@docroot@/command-ref/conf-file.md#conf-trusted-public-keys)
+          setting.
+        )"};
 
-    Setting<int> priority{this, 0, "priority", "priority of this substituter (lower value means higher priority)"};
+    Setting<int> priority{this, 0, "priority",
+        R"(
+          Priority of this store when used as a substituter. A lower value means a higher priority.
+        )"};
 
-    Setting<bool> wantMassQuery{this, false, "want-mass-query", "whether this substituter can be queried efficiently for path validity"};
+    Setting<bool> wantMassQuery{this, false, "want-mass-query",
+        R"(
+          Whether this store (when used as a substituter) can be
+          queried efficiently for path validity.
+        )"};
 
     Setting<StringSet> systemFeatures{this, getDefaultSystemFeatures(),
         "system-features",
@@ -125,8 +149,6 @@ public:
 
     typedef std::map<std::string, std::string> Params;
 
-
-
 protected:
 
     struct PathInfoCacheValue {

src/libstore/uds-remote-store.cc

@@ -26,9 +26,9 @@ UDSRemoteStore::UDSRemoteStore(const Params & params)
 
 
 UDSRemoteStore::UDSRemoteStore(
-        const std::string scheme,
-        std::string socket_path,
-        const Params & params)
+    const std::string scheme,
+    std::string socket_path,
+    const Params & params)
     : UDSRemoteStore(params)
 {
     path.emplace(socket_path);

src/libstore/uds-remote-store.hh

@@ -15,6 +15,13 @@ struct UDSRemoteStoreConfig : virtual LocalFSStoreConfig, virtual RemoteStoreCon
     }
 
     const std::string name() override { return "Local Daemon Store"; }
+
+    std::string doc() override
+    {
+        return
+          #include "uds-remote-store.md"
+          ;
+    }
 };
 
 class UDSRemoteStore : public virtual UDSRemoteStoreConfig, public virtual LocalFSStore, public virtual RemoteStore

src/libstore/uds-remote-store.md

@@ -0,0 +1,9 @@
+R"(
+
+**Store URL format**: `daemon`, `unix://`*path*
+
+This store type accesses a Nix store by talking to a Nix daemon
+listening on the Unix domain socket *path*. The store pseudo-URL
+`daemon` is equivalent to `unix:///nix/var/nix/daemon-socket/socket`.
+
+)"