Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libstore/path-with-outputs.hh

@@ -0,0 +1,48 @@
+#pragma once
+///@file
+
+#include "path.hh"
+#include "derived-path.hh"
+
+namespace nix {
+
+struct StoreDirConfig;
+
+/**
+ * This is a deprecated old type just for use by the old CLI, and older
+ * versions of the RPC protocols. In new code don't use it; you want
+ * `DerivedPath` instead.
+ *
+ * `DerivedPath` is better because it handles more cases, and does so more
+ * explicitly without devious punning tricks.
+ */
+struct StorePathWithOutputs
+{
+    StorePath path;
+    std::set<std::string> outputs;
+
+    std::string to_string(const StoreDirConfig & store) const;
+
+    DerivedPath toDerivedPath() const;
+
+    typedef std::variant<StorePathWithOutputs, StorePath, std::monostate> ParseResult;
+
+    static StorePathWithOutputs::ParseResult tryFromDerivedPath(const DerivedPath &);
+};
+
+std::vector<DerivedPath> toDerivedPaths(const std::vector<StorePathWithOutputs>);
+
+std::pair<std::string_view, StringSet> parsePathWithOutputs(std::string_view s);
+
+/**
+ * Split a string specifying a derivation and a set of outputs
+ * (/nix/store/hash-foo!out1,out2,...) into the derivation path
+ * and the outputs.
+ */
+StorePathWithOutputs parsePathWithOutputs(const StoreDirConfig & store, std::string_view pathWithOutputs);
+
+class Store;
+
+StorePathWithOutputs followLinksToStorePathWithOutputs(const Store & store, std::string_view pathWithOutputs);
+
+}