Make the Store API more type-safe

Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.

Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.

Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).

1 files changed, 7 insertions, 7 deletions

diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 87be8a24e..d0f289a0f 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -2,8 +2,8 @@
 
 namespace nix {
 
-ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
-    : drvPath(drvPath), drv(drv)
+ParsedDerivation::ParsedDerivation(StorePath && drvPath, BasicDerivation & drv)
+    : drvPath(std::move(drvPath)), drv(drv)
 {
     /* Parse the __json attribute, if any. */
     auto jsonAttr = drv.env.find("__json");
@@ -11,7 +11,7 @@ ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
         try {
             structuredAttrs = nlohmann::json::parse(jsonAttr->second);
         } catch (std::exception & e) {
-            throw Error("cannot process __json attribute of '%s': %s", drvPath, e.what());
+            throw Error("cannot process __json attribute of '%s': %s", drvPath.to_string(), e.what());
         }
     }
 }
@@ -24,7 +24,7 @@ std::optional<std::string> ParsedDerivation::getStringAttr(const std::string & n
             return {};
         else {
             if (!i->is_string())
-                throw Error("attribute '%s' of derivation '%s' must be a string", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a string", name, drvPath.to_string());
             return i->get<std::string>();
         }
     } else {
@@ -44,7 +44,7 @@ bool ParsedDerivation::getBoolAttr(const std::string & name, bool def) const
             return def;
         else {
             if (!i->is_boolean())
-                throw Error("attribute '%s' of derivation '%s' must be a Boolean", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a Boolean", name, drvPath.to_string());
             return i->get<bool>();
         }
     } else {
@@ -64,11 +64,11 @@ std::optional<Strings> ParsedDerivation::getStringsAttr(const std::string & name
             return {};
         else {
             if (!i->is_array())
-                throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath.to_string());
             Strings res;
             for (auto j = i->begin(); j != i->end(); ++j) {
                 if (!j->is_string())
-                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath);
+                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath.to_string());
                 res.push_back(j->get<std::string>());
             }
             return res;