diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index fb851ac23..33ae0aa60 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -2027,13 +2027,10 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
     }
 
     if (v.type() == nPath) {
-        auto path = v.path().to_string();
-        if (canonicalizePath)
-            // FIXME: unnecessary?
-            path = canonPath(path);
-        if (copyToStore)
-            path = copyPathToStore(context, path);
-        return path;
+        auto path = v.path();
+        return copyToStore
+            ? store->printStorePath(copyPathToStore(context, path))
+            : path.path;
     }
 
     if (v.type() == nAttrs) {
@@ -2075,39 +2072,34 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
 }
 
 
-std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
+StorePath EvalState::copyPathToStore(PathSet & context, const SourcePath & path)
 {
-    #if 0
-    if (nix::isDerivation(path))
-        throwEvalError("file names are not allowed to end in '%1%'", drvExtension);
+    if (nix::isDerivation(path.path))
+        throw EvalError("file names are not allowed to end in '%s'", drvExtension);
 
-    Path dstPath;
     auto i = srcToStore.find(path);
-    if (i != srcToStore.end())
-        dstPath = store->printStorePath(i->second);
-    else {
-        // FIXME: use SourcePath
-        auto path2 = unpackPath(path);
-        #if 0
-        auto p = settings.readOnlyMode
-            ? store->computeStorePathForPath(path2.baseName(), canonPath(path)).first
-            : store->addToStore(path2.baseName(), canonPath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
-        #endif
-        auto source = sinkToSource([&](Sink & sink) {
-            path2.dumpPath(sink);
-        });
-        // FIXME: readOnlyMode
-        auto p = store->addToStoreFromDump(*source, path2.baseName(), FileIngestionMethod::Recursive, htSHA256, repair);
-        dstPath = store->printStorePath(p);
-        allowPath(p);
-        srcToStore.insert_or_assign(path, std::move(p));
-        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
-    }
 
-    context.insert(dstPath);
+    auto dstPath = i != srcToStore.end()
+        ? i->second
+        : [&]() {
+            #if 0
+            auto p = settings.readOnlyMode
+                ? store->computeStorePathForPath(path2.baseName(), canonPath(path)).first
+                : store->addToStore(path2.baseName(), canonPath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
+            #endif
+            auto source = sinkToSource([&](Sink & sink) {
+                path.dumpPath(sink);
+            });
+            // FIXME: readOnlyMode
+            auto dstPath = store->addToStoreFromDump(*source, path.baseName(), FileIngestionMethod::Recursive, htSHA256, repair);
+            allowPath(dstPath);
+            srcToStore.insert_or_assign(path, dstPath);
+            printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, store->printStorePath(dstPath));
+            return dstPath;
+        }();
+
+    context.insert(store->printStorePath(dstPath));
     return dstPath;
-    #endif
-    abort();
 }
 
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index ecd72dab0..c007a235b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -50,11 +50,6 @@ struct Env
 void copyContext(const Value & v, PathSet & context);
 
 
-/* Cache for calls to addToStore(); maps source paths to the store
-   paths. */
-typedef std::map<Path, StorePath> SrcToStore;
-
-
 std::ostream & printValue(const EvalState & state, std::ostream & str, const Value & v);
 std::string printValue(const EvalState & state, const Value & v);
 
@@ -112,7 +107,10 @@ public:
     RootValue vImportedDrvToDerivation = nullptr;
 
 private:
-    SrcToStore srcToStore;
+
+    /* Cache for calls to addToStore(); maps source paths to the store
+       paths. */
+    std::map<SourcePath, StorePath> srcToStore;
 
     /* A cache from path names to parse trees. */
 #if HAVE_BOEHMGC
@@ -308,7 +306,7 @@ public:
         bool coerceMore = false, bool copyToStore = true,
         bool canonicalizePath = true);
 
-    std::string copyPathToStore(PathSet & context, const Path & path);
+    StorePath copyPathToStore(PathSet & context, const SourcePath & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7858733aa..2f47c54d3 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1549,7 +1549,8 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value * * args, V
     // FIXME: checkSourcePath?
     v.mkPath(state.findFile(searchPath, path, pos));
     #endif
-    abort();
+
+    throw ThrownError("findFile('%s'): not implemented", path);
 }
 
 static RegisterPrimOp primop_findFile(RegisterPrimOp::Info {
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 7b26e8125..547540de7 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -2,6 +2,7 @@
 #include "json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
+#include "store-api.hh"
 
 #include <cstdlib>
 #include <iomanip>
@@ -33,7 +34,9 @@ void printValueAsJSON(EvalState & state, bool strict,
 
         case nPath:
             // FIXME: handle accessors
-            out.write(state.copyPathToStore(context, v.path().path));
+            out.write(
+                state.store->printStorePath(
+                    state.copyPathToStore(context, v.path())));
             break;
 
         case nNull:
diff --git a/src/libfetchers/input-accessor.hh b/src/libfetchers/input-accessor.hh
index 93e891ac2..90e8abbf7 100644
--- a/src/libfetchers/input-accessor.hh
+++ b/src/libfetchers/input-accessor.hh
@@ -42,6 +42,16 @@ struct InputAccessor
         const Path & path,
         Sink & sink,
         PathFilter & filter = defaultPathFilter);
+
+    bool operator == (const InputAccessor & x) const
+    {
+        return number == x.number;
+    }
+
+    bool operator < (const InputAccessor & x) const
+    {
+        return number < x.number;
+    }
 };
 
 struct FSInputAccessor : InputAccessor
@@ -94,6 +104,16 @@ struct SourcePath
     std::string to_string() const;
 
     SourcePath append(std::string_view s) const;
+
+    bool operator == (const SourcePath & x) const
+    {
+        return std::tie(accessor, path) == std::tie(x.accessor, x.path);
+    }
+
+    bool operator < (const SourcePath & x) const
+    {
+        return std::tie(accessor, path) < std::tie(x.accessor, x.path);
+    }
 };
 
 std::ostream & operator << (std::ostream & str, const SourcePath & path);