libstore: Do not normalize daemon -> unix://, local -> local://

This is relied upon (specifically the `local` store) by existing
tooling [1] and we broke this in 3e7879e6df (which
was first released in 2.31).

To lessen the scope of the breakage we should not normalize "auto" references
and explicitly specified references like "local" or "daemon". It also makes
sense to canonicalize local://,daemon:// to be more compatible with prior
behavior.

[1]: 05e1b3cba2/lib/NOM/Builds.hs (L60-L64)

src/libstore-tests/data/store-reference/daemon_shorthand.txt

@@ -0,0 +1 @@
+daemon

src/libstore-tests/data/store-reference/local_shorthand_3.txt

@@ -0,0 +1 @@
+local

src/libstore-tests/local-store.cc

@@ -33,4 +33,10 @@ TEST(LocalStore, constructConfig_rootPath)
     EXPECT_EQ(config.rootDir.get(), std::optional{"/foo/bar"});
 }
 
+TEST(LocalStore, constructConfig_to_string)
+{
+    LocalStoreConfig config{"local", "", {}};
+    EXPECT_EQ(config.getReference().to_string(), "local");
+}
+
 } // namespace nix

src/libstore-tests/store-reference.cc

@@ -107,6 +107,13 @@ URI_TEST_READ(local_shorthand_1, localExample_1)
 
 URI_TEST_READ(local_shorthand_2, localExample_2)
 
+URI_TEST(
+    local_shorthand_3,
+    (StoreReference{
+        .variant = StoreReference::Local{},
+        .params = {},
+    }))
+
 static StoreReference unixExample{
     .variant =
         StoreReference::Specified{
@@ -134,4 +141,11 @@ URI_TEST(
         .params = {},
     }))
 
+URI_TEST(
+    daemon_shorthand,
+    (StoreReference{
+        .variant = StoreReference::Daemon{},
+        .params = {},
+    }))
+
 } // namespace nix

src/libstore-tests/uds-remote-store.cc

@@ -16,4 +16,10 @@ TEST(UDSRemoteStore, constructConfigWrongScheme)
     EXPECT_THROW(UDSRemoteStoreConfig("http", "/tmp/socket", {}), UsageError);
 }
 
+TEST(UDSRemoteStore, constructConfig_to_string)
+{
+    UDSRemoteStoreConfig config{"unix", "", {}};
+    EXPECT_EQ(config.getReference().to_string(), "daemon");
+}
+
 } // namespace nix

src/libstore/include/nix/store/store-reference.hh

@@ -64,7 +64,29 @@ struct StoreReference
         auto operator<=>(const Specified & rhs) const = default;
     };
 
-    typedef std::variant<Auto, Specified> Variant;
+    /**
+     * Special case for `daemon` to avoid normalization.
+     */
+    struct Daemon : Specified
+    {
+        Daemon()
+            : Specified({.scheme = "unix"})
+        {
+        }
+    };
+
+    /**
+     * Special case for `local` to avoid normalization.
+     */
+    struct Local : Specified
+    {
+        Local()
+            : Specified({.scheme = "local"})
+        {
+        }
+    };
+
+    typedef std::variant<Auto, Specified, Daemon, Local> Variant;
 
     Variant variant;
 

src/libstore/local-store.cc

@@ -456,12 +456,17 @@ LocalStore::~LocalStore()
 
 StoreReference LocalStoreConfig::getReference() const
 {
+    auto params = getQueryParams();
+    /* Back-compatibility kludge. Tools like nix-output-monitor expect 'local'
+       and can't parse 'local://'. */
+    if (params.empty())
+        return {.variant = StoreReference::Local{}};
     return {
         .variant =
             StoreReference::Specified{
                 .scheme = *uriSchemes().begin(),
             },
-        .params = getQueryParams(),
+        .params = std::move(params),
     };
 }
 

src/libstore/store-api.cc

@@ -818,7 +818,13 @@ makeCopyPathMessage(const StoreConfig & srcCfg, const StoreConfig & dstCfg, std:
 
     auto isShorthand = [](const StoreReference & ref) {
         /* At this point StoreReference **must** be resolved. */
-        const auto & specified = std::get<StoreReference::Specified>(ref.variant);
+        const auto & specified = std::visit(
+            overloaded{
+                [](const StoreReference::Auto &) -> const StoreReference::Specified & { unreachable(); },
+                [](const StoreReference::Specified & specified) -> const StoreReference::Specified & {
+                    return specified;
+                }},
+            ref.variant);
         const auto & scheme = specified.scheme;
         return (scheme == "local" || scheme == "unix") && specified.authority.empty();
     };

src/libstore/store-reference.cc

@@ -25,6 +25,8 @@ std::string StoreReference::render(bool withParams) const
     std::visit(
         overloaded{
             [&](const StoreReference::Auto &) { res = "auto"; },
+            [&](const StoreReference::Daemon &) { res = "daemon"; },
+            [&](const StoreReference::Local &) { res = "local"; },
             [&](const StoreReference::Specified & g) {
                 res = g.scheme;
                 res += "://";
@@ -66,21 +68,17 @@ StoreReference StoreReference::parse(const std::string & uri, const StoreReferen
                 .params = std::move(params),
             };
         } else if (baseURI == "daemon") {
+            if (params.empty())
+                return {.variant = Daemon{}};
             return {
-                .variant =
-                    Specified{
-                        .scheme = "unix",
-                        .authority = "",
-                    },
+                .variant = Specified{.scheme = "unix", .authority = ""},
                 .params = std::move(params),
             };
         } else if (baseURI == "local") {
+            if (params.empty())
+                return {.variant = Local{}};
             return {
-                .variant =
-                    Specified{
-                        .scheme = "local",
-                        .authority = "",
-                    },
+                .variant = Specified{.scheme = "local", .authority = ""},
                 .params = std::move(params),
             };
         } else if (isNonUriPath(baseURI)) {

src/libstore/uds-remote-store.cc

@@ -57,15 +57,16 @@ UDSRemoteStore::UDSRemoteStore(ref<const Config> config)
 
 StoreReference UDSRemoteStoreConfig::getReference() const
 {
+    /* We specifically return "daemon" here instead of "unix://" or "unix://${path}"
+     * to be more compatible with older versions of nix. Some tooling out there
+     * tries hard to parse store references and it might not be able to handle "unix://". */
+    if (path == settings.nixDaemonSocketFile)
+        return {.variant = StoreReference::Daemon{}};
     return {
         .variant =
             StoreReference::Specified{
                 .scheme = *uriSchemes().begin(),
-                // We return the empty string when the path looks like the
-                // default path, but we could also just return the path
-                // verbatim always, to be robust to overall config changes
-                // at the cost of some verbosity.
-                .authority = path == settings.nixDaemonSocketFile ? "" : path,
+                .authority = path,
             },
     };
 }

tests/functional/store-info.sh

@@ -13,14 +13,20 @@ normalize_nix_store_url () {
             # Need to actually ask Nix in this case
             echo "$defaultStore"
             ;;
+        local | 'local://' )
+            echo 'local'
+            ;;
+        daemon | 'unix://' )
+            echo 'daemon'
+            ;;
         'local://'* )
             # To not be captured by next pattern
             echo "$url"
             ;;
-        local | 'local?'* )
+        'local?'* )
             echo "local://${url#local}"
             ;;
-        daemon | 'daemon?'* )
+        'daemon?'* )
             echo "unix://${url#daemon}"
             ;;
         * )
@@ -38,13 +44,13 @@ defaultStore="$(normalize_nix_store_url "$(echo "$STORE_INFO_JSON" | jq -r ".url
 # Test cases for `normalize_nix_store_url` itself
 
 # Normalize local store
-[[ "$(normalize_nix_store_url "local://")" = "local://" ]]
-[[ "$(normalize_nix_store_url "local")" = "local://" ]]
+[[ "$(normalize_nix_store_url "local://")" = "local" ]]
+[[ "$(normalize_nix_store_url "local")" = "local" ]]
 [[ "$(normalize_nix_store_url "local?foo=bar")" = "local://?foo=bar" ]]
 
 # Normalize unix domain socket remote store
-[[ "$(normalize_nix_store_url "unix://")" = "unix://" ]]
-[[ "$(normalize_nix_store_url "daemon")" = "unix://" ]]
+[[ "$(normalize_nix_store_url "unix://")" = "daemon" ]]
+[[ "$(normalize_nix_store_url "daemon")" = "daemon" ]]
 [[ "$(normalize_nix_store_url "daemon?x=y")" = "unix://?x=y" ]]
 
 # otherwise unchanged