Legacy vs non-legacy `to_string`/`parse` for `DerivedPath`

As requested by @roberth, it is good to call out the specific instances
we care about, which is `!` for the RPC protocols, and `^` for humans.

This doesn't take advantage of parametricity as much, but since the
human and computer interfaces are good to decouple anyways (we don't
care if they drift further apart over time in the slightest) some
separation and slight duplication is fine.

Also, unit test both round trips.

1 files changed, 31 insertions, 6 deletions

diff --git a/src/libstore/derived-path.cc b/src/libstore/derived-path.cc
index 6baca70a3..9a2ffda39 100644
--- a/src/libstore/derived-path.cc
+++ b/src/libstore/derived-path.cc
@@ -59,17 +59,32 @@ std::string DerivedPath::Opaque::to_string(const Store & store) const
     return store.printStorePath(path);
 }
 
-std::string DerivedPath::Built::to_string(const Store & store, char separator) const
+std::string DerivedPath::Built::to_string(const Store & store) const
 {
     return store.printStorePath(drvPath)
-        + separator
+        + '^'
         + outputs.to_string();
 }
 
-std::string DerivedPath::to_string(const Store & store, char separator) const
+std::string DerivedPath::Built::to_string_legacy(const Store & store) const
+{
+    return store.printStorePath(drvPath)
+        + '!'
+        + outputs.to_string();
+}
+
+std::string DerivedPath::to_string(const Store & store) const
 {
     return std::visit(overloaded {
-        [&](const DerivedPath::Built & req) { return req.to_string(store, separator); },
+        [&](const DerivedPath::Built & req) { return req.to_string(store); },
+        [&](const DerivedPath::Opaque & req) { return req.to_string(store); },
+    }, this->raw());
+}
+
+std::string DerivedPath::to_string_legacy(const Store & store) const
+{
+    return std::visit(overloaded {
+        [&](const DerivedPath::Built & req) { return req.to_string_legacy(store); },
         [&](const DerivedPath::Opaque & req) { return req.to_string(store); },
     }, this->raw());
 }
@@ -88,14 +103,24 @@ DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_vi
     };
 }
 
-DerivedPath DerivedPath::parse(const Store & store, std::string_view s)
+static inline DerivedPath parseWith(const Store & store, std::string_view s, std::string_view separator)
 {
-    size_t n = s.find("!");
+    size_t n = s.find(separator);
     return n == s.npos
         ? (DerivedPath) DerivedPath::Opaque::parse(store, s)
         : (DerivedPath) DerivedPath::Built::parse(store, s.substr(0, n), s.substr(n + 1));
 }
 
+DerivedPath DerivedPath::parse(const Store & store, std::string_view s)
+{
+	return parseWith(store, s, "^");
+}
+
+DerivedPath DerivedPath::parseLegacy(const Store & store, std::string_view s)
+{
+	return parseWith(store, s, "!");
+}
+
 RealisedPath::Set BuiltPath::toRealisedPaths(Store & store) const
 {
     RealisedPath::Set res;