Avoid isValidPath(), use queryPathInfo() instead

src/libfetchers/fetch-to-store.cc

@@ -45,7 +45,7 @@ std::pair<StorePath, Hash> fetchToStore2(
             auto hash = Hash::parseSRI(fetchers::getStrAttr(*res, "hash"));
             auto storePath =
                 store.makeFixedOutputPathFromCA(name, ContentAddressWithReferences::fromParts(method, hash, {}));
-            if (mode == FetchMode::DryRun || store.isValidPath(storePath)) {
+            if (mode == FetchMode::DryRun || store.maybeQueryPathInfo(storePath)) {
                 debug(
                     "source path '%s' cache hit in '%s' (hash '%s')",
                     path,

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

@@ -282,7 +282,9 @@ public:
     StorePath followLinksToStorePath(std::string_view path) const;
 
     /**
-     * Check whether a path is valid.
+     * Check whether a path is valid. NOTE: this function does not
+     * generally cache whether a path is valid. You may want to use
+     * `maybeQueryPathInfo()`, which does cache.
      */
     bool isValidPath(const StorePath & path);
 
@@ -322,10 +324,17 @@ public:
 
     /**
      * Query information about a valid path. It is permitted to omit
-     * the name part of the store path.
+     * the name part of the store path. Throws an exception if the
+     * path is not valid.
      */
     ref<const ValidPathInfo> queryPathInfo(const StorePath & path);
 
+    /**
+     * Like `queryPathInfo()`, but returns `nullptr` if the path is
+     * not valid.
+     */
+    std::shared_ptr<const ValidPathInfo> maybeQueryPathInfo(const StorePath & path);
+
     /**
      * Asynchronous version of queryPathInfo().
      */

src/libstore/local-fs-store.cc

@@ -41,7 +41,7 @@ struct LocalStoreAccessor : PosixSourceAccessor
     void requireStoreObject(const CanonPath & path)
     {
         auto [storePath, rest] = store->toStorePath(store->storeDir + path.abs());
-        if (requireValidPath && !store->isValidPath(storePath))
+        if (requireValidPath && !store->maybeQueryPathInfo(storePath))
             throw InvalidPath("path '%1%' is not a valid store path", store->printStorePath(storePath));
     }
 

src/libstore/store-api.cc

@@ -603,6 +603,23 @@ ref<const ValidPathInfo> Store::queryPathInfo(const StorePath & storePath)
     return promise.get_future().get();
 }
 
+std::shared_ptr<const ValidPathInfo> Store::maybeQueryPathInfo(const StorePath & storePath)
+{
+    std::promise<std::shared_ptr<const ValidPathInfo>> promise;
+
+    queryPathInfo(storePath, {[&](std::future<ref<const ValidPathInfo>> result) {
+                      try {
+                          promise.set_value(result.get());
+                      } catch (InvalidPath &) {
+                          promise.set_value(nullptr);
+                      } catch (...) {
+                          promise.set_exception(std::current_exception());
+                      }
+                  }});
+
+    return promise.get_future().get();
+}
+
 static bool goodStorePath(const StorePath & expected, const StorePath & actual)
 {
     return expected.hashPart() == actual.hashPart()