Move querySubstitutablePathInfos from LocalStore to Store

The code is not local-store-specific, so we should share it with all
stores. More uniform behavior is better, and a less store-specific
functionality is more maintainable.

This fixes a FIXME added in f73d911628 by @edolstra himself.

src/libstore/local-store.cc

@@ -1134,54 +1134,6 @@ StorePathSet LocalStore::querySubstitutablePaths(const StorePathSet & paths)
 }
 
 
-// FIXME: move this, it's not specific to LocalStore.
-void LocalStore::querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos)
-{
-    if (!settings.useSubstitutes) return;
-    for (auto & sub : getDefaultSubstituters()) {
-        for (auto & path : paths) {
-            if (infos.count(path.first))
-                // Choose first succeeding substituter.
-                continue;
-
-            auto subPath(path.first);
-
-            // Recompute store path so that we can use a different store root.
-            if (path.second) {
-                subPath = makeFixedOutputPathFromCA(path.first.name(), *path.second);
-                if (sub->storeDir == storeDir)
-                    assert(subPath == path.first);
-                if (subPath != path.first)
-                    debug("replaced path '%s' with '%s' for substituter '%s'", printStorePath(path.first), sub->printStorePath(subPath), sub->getUri());
-            } else if (sub->storeDir != storeDir) continue;
-
-            debug("checking substituter '%s' for path '%s'", sub->getUri(), sub->printStorePath(subPath));
-            try {
-                auto info = sub->queryPathInfo(subPath);
-
-                if (sub->storeDir != storeDir && !(info->isContentAddressed(*sub) && info->references.empty()))
-                    continue;
-
-                auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
-                    std::shared_ptr<const ValidPathInfo>(info));
-                infos.insert_or_assign(path.first, SubstitutablePathInfo{
-                    info->deriver,
-                    info->references,
-                    narInfo ? narInfo->fileSize : 0,
-                    info->narSize});
-            } catch (InvalidPath &) {
-            } catch (SubstituterDisabled &) {
-            } catch (Error & e) {
-                if (settings.tryFallback)
-                    logError(e.info());
-                else
-                    throw;
-            }
-        }
-    }
-}
-
-
 void LocalStore::registerValidPath(const ValidPathInfo & info)
 {
     registerValidPaths({{info.path, info}});

src/libstore/local-store.hh

@@ -134,9 +134,6 @@ public:
 
     StorePathSet querySubstitutablePaths(const StorePathSet & paths) override;
 
-    void querySubstitutablePathInfos(const StorePathCAMap & paths,
-        SubstitutablePathInfos & infos) override;
-
     bool pathInfoIsUntrusted(const ValidPathInfo &) override;
     bool realisationIsUntrusted(const Realisation & ) override;
 

src/libstore/store-api.cc

@@ -507,6 +507,54 @@ StorePathSet Store::queryDerivationOutputs(const StorePath & path)
     return outputPaths;
 }
 
+
+void Store::querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos)
+{
+    if (!settings.useSubstitutes) return;
+    for (auto & sub : getDefaultSubstituters()) {
+        for (auto & path : paths) {
+            if (infos.count(path.first))
+                // Choose first succeeding substituter.
+                continue;
+
+            auto subPath(path.first);
+
+            // Recompute store path so that we can use a different store root.
+            if (path.second) {
+                subPath = makeFixedOutputPathFromCA(path.first.name(), *path.second);
+                if (sub->storeDir == storeDir)
+                    assert(subPath == path.first);
+                if (subPath != path.first)
+                    debug("replaced path '%s' with '%s' for substituter '%s'", printStorePath(path.first), sub->printStorePath(subPath), sub->getUri());
+            } else if (sub->storeDir != storeDir) continue;
+
+            debug("checking substituter '%s' for path '%s'", sub->getUri(), sub->printStorePath(subPath));
+            try {
+                auto info = sub->queryPathInfo(subPath);
+
+                if (sub->storeDir != storeDir && !(info->isContentAddressed(*sub) && info->references.empty()))
+                    continue;
+
+                auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
+                    std::shared_ptr<const ValidPathInfo>(info));
+                infos.insert_or_assign(path.first, SubstitutablePathInfo{
+                    info->deriver,
+                    info->references,
+                    narInfo ? narInfo->fileSize : 0,
+                    info->narSize});
+            } catch (InvalidPath &) {
+            } catch (SubstituterDisabled &) {
+            } catch (Error & e) {
+                if (settings.tryFallback)
+                    logError(e.info());
+                else
+                    throw;
+            }
+        }
+    }
+}
+
+
 bool Store::isValidPath(const StorePath & storePath)
 {
     {

src/libstore/store-api.hh

@@ -456,7 +456,7 @@ public:
      * resulting ‘infos’ map.
      */
     virtual void querySubstitutablePathInfos(const StorePathCAMap & paths,
-        SubstitutablePathInfos & infos) { return; };
+        SubstitutablePathInfos & infos);
 
     /**
      * Import a path into the store.