treewide: Add Store::requireStoreObjectAccessor, simplify uses of getFSAccessor

This is a simple wrapper around getFSAccessor that throws an InvalidPath
error. This simplifies usage in callsites that only care about getting
a non-null accessor.

src/libfetchers/fetchers.cc

@@ -332,8 +332,7 @@ std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(ref<Store> sto
 
             debug("using substituted/cached input '%s' in '%s'", to_string(), store->printStorePath(storePath));
 
-            // We just ensured the store object was there
+            auto accessor = store->requireStoreObjectAccessor(storePath);
-            auto accessor = ref{store->getFSAccessor(storePath)};
 
             accessor->fingerprint = getFingerprint(store);
 

src/libfetchers/github.cc

@@ -399,7 +399,8 @@ struct GitHubInputScheme : GitArchiveInputScheme
         Headers headers = makeHeadersWithAuthTokens(*input.settings, host, input);
 
         auto downloadResult = downloadFile(store, *input.settings, url, "source", headers);
-        auto json = nlohmann::json::parse(store->getFSAccessor(downloadResult.storePath)->readFile(CanonPath::root));
+        auto json = nlohmann::json::parse(
+            store->requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
 
         return RefInfo{
             .rev = Hash::parseAny(std::string{json["sha"]}, HashAlgorithm::SHA1),
@@ -473,7 +474,8 @@ struct GitLabInputScheme : GitArchiveInputScheme
         Headers headers = makeHeadersWithAuthTokens(*input.settings, host, input);
 
         auto downloadResult = downloadFile(store, *input.settings, url, "source", headers);
-        auto json = nlohmann::json::parse(store->getFSAccessor(downloadResult.storePath)->readFile(CanonPath::root));
+        auto json = nlohmann::json::parse(
+            store->requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
 
         if (json.is_array() && json.size() >= 1 && json[0]["id"] != nullptr) {
             return RefInfo{.rev = Hash::parseAny(std::string(json[0]["id"]), HashAlgorithm::SHA1)};
@@ -549,7 +551,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         std::string refUri;
         if (ref == "HEAD") {
             auto downloadFileResult = downloadFile(store, *input.settings, fmt("%s/HEAD", base_url), "source", headers);
-            auto contents = nix::ref(store->getFSAccessor(downloadFileResult.storePath))->readFile(CanonPath::root);
+            auto contents = store->requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
 
             auto remoteLine = git::parseLsRemoteLine(getLine(contents).first);
             if (!remoteLine) {
@@ -563,7 +565,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
 
         auto downloadFileResult =
             downloadFile(store, *input.settings, fmt("%s/info/refs", base_url), "source", headers);
-        auto contents = nix::ref(store->getFSAccessor(downloadFileResult.storePath))->readFile(CanonPath::root);
+        auto contents = store->requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
         std::istringstream is(contents);
 
         std::string line;

src/libfetchers/mercurial.cc

@@ -329,9 +329,7 @@ struct MercurialInputScheme : InputScheme
         Input input(_input);
 
         auto storePath = fetchToStore(store, input);
-
+        auto accessor = store->requireStoreObjectAccessor(storePath);
-        // We just added it, it should be there.
-        auto accessor = ref{store->getFSAccessor(storePath)};
 
         accessor->setPathDisplay("«" + input.to_string() + "»");
 

src/libfetchers/path.cc

@@ -138,7 +138,7 @@ struct PathInputScheme : InputScheme
             storePath = store->addToStoreFromDump(*src, "source");
         }
 
-        auto accessor = ref{store->getFSAccessor(*storePath)};
+        auto accessor = store->requireStoreObjectAccessor(*storePath);
 
         // To prevent `fetchToStore()` copying the path again to Nix
         // store, pre-create an entry in the fetcher cache.

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

@@ -724,10 +724,28 @@ public:
      * the Nix store.
      *
      * @return nullptr if the store doesn't contain an object at the
-     * givine path.
+     * given path.
      */
     virtual std::shared_ptr<SourceAccessor> getFSAccessor(const StorePath & path, bool requireValidPath = true) = 0;
 
+    /**
+     * Get an accessor for the store object or throw an Error if it's invalid or
+     * doesn't exist.
+     *
+     * @throws InvalidPath if the store object doesn't exist or (if requireValidPath = true) is
+     * invalid.
+     */
+    [[nodiscard]] ref<SourceAccessor> requireStoreObjectAccessor(const StorePath & path, bool requireValidPath = true)
+    {
+        auto accessor = getFSAccessor(path, requireValidPath);
+        if (!accessor) {
+            throw InvalidPath(
+                requireValidPath ? "path '%1%' is not a valid store path" : "store path '%1%' does not exist",
+                printStorePath(path));
+        }
+        return ref<SourceAccessor>{accessor};
+    }
+
     /**
      * Repair the contents of the given path by redownloading it using
      * a substituter (if available).

src/libstore/store-api.cc

@@ -1130,7 +1130,7 @@ Derivation Store::derivationFromPath(const StorePath & drvPath)
 
 static Derivation readDerivationCommon(Store & store, const StorePath & drvPath, bool requireValidPath)
 {
-    auto accessor = store.getFSAccessor(drvPath, requireValidPath);
+    auto accessor = store.requireStoreObjectAccessor(drvPath, requireValidPath);
     try {
         return parseDerivation(store, accessor->readFile(CanonPath::root), Derivation::nameFromPath(drvPath));
     } catch (FormatError & e) {

src/nix/cat.cc

@@ -41,10 +41,7 @@ struct CmdCatStore : StoreCommand, MixCat
     void run(ref<Store> store) override
     {
         auto [storePath, rest] = store->toStorePath(path);
-        auto accessor = store->getFSAccessor(storePath);
+        cat(store->requireStoreObjectAccessor(storePath), CanonPath{rest});
-        if (!accessor)
-            throw InvalidPath("path '%1%' is not a valid store path", store->printStorePath(storePath));
-        cat(ref{std::move(accessor)}, CanonPath{rest});
     }
 };
 

src/nix/ls.cc

@@ -115,10 +115,7 @@ struct CmdLsStore : StoreCommand, MixLs
     void run(ref<Store> store) override
     {
         auto [storePath, rest] = store->toStorePath(path);
-        auto accessor = store->getFSAccessor(storePath);
+        list(store->requireStoreObjectAccessor(storePath), CanonPath{rest});
-        if (!accessor)
-            throw InvalidPath("path '%1%' is not a valid store path", store->printStorePath(storePath));
-        list(ref{std::move(accessor)}, CanonPath{rest});
     }
 };
 

src/nix/nix-store/nix-store.cc

@@ -603,7 +603,7 @@ static void registerValidity(bool reregister, bool hashGiven, bool canonicalise)
 #endif
             if (!hashGiven) {
                 HashResult hash = hashPath(
-                    {ref{store->getFSAccessor(info->path, false)}},
+                    {store->requireStoreObjectAccessor(info->path, /*requireValidPath=*/false)},
                     FileSerialisationMethod::NixArchive,
                     HashAlgorithm::SHA256);
                 info->narHash = hash.hash;

src/nix/why-depends.cc

@@ -207,7 +207,7 @@ struct CmdWhyDepends : SourceExprCommand, MixOperateOnOptions
                contain the reference. */
             std::map<std::string, Strings> hits;
 
-            auto accessor = store->getFSAccessor(node.path);
+            auto accessor = store->requireStoreObjectAccessor(node.path);
 
             auto visitPath = [&](this auto && recur, const CanonPath & p) -> void {
                 auto st = accessor->maybeLstat(p);