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).

src/nix-build/nix-build.cc

@@ -317,11 +317,11 @@ static void _main(int argc, char * * argv)
 
     state->printStats();
 
-    auto buildPaths = [&](const PathSet & paths) {
+    auto buildPaths = [&](const std::vector<StorePathWithOutputs> & paths) {
         /* Note: we do this even when !printMissing to efficiently
            fetch binary cache data. */
         unsigned long long downloadSize, narSize;
-        PathSet willBuild, willSubstitute, unknown;
+        StorePathSet willBuild, willSubstitute, unknown;
         store->queryMissing(paths,
             willBuild, willSubstitute, unknown, downloadSize, narSize);
 
@@ -337,9 +337,9 @@ static void _main(int argc, char * * argv)
             throw UsageError("nix-shell requires a single derivation");
 
         auto & drvInfo = drvs.front();
-        auto drv = store->derivationFromPath(drvInfo.queryDrvPath());
+        auto drv = store->derivationFromPath(store->parseStorePath(drvInfo.queryDrvPath()));
 
-        PathSet pathsToBuild;
+        std::vector<StorePathWithOutputs> pathsToBuild;
 
         /* Figure out what bash shell to use. If $NIX_BUILD_SHELL
            is not set, then build bashInteractive from
@@ -358,7 +358,7 @@ static void _main(int argc, char * * argv)
                 if (!drv)
                     throw Error("the 'bashInteractive' attribute in <nixpkgs> did not evaluate to a derivation");
 
-                pathsToBuild.insert(drv->queryDrvPath());
+                pathsToBuild.emplace_back(store->parseStorePath(drv->queryDrvPath()));
 
                 shell = drv->queryOutPath() + "/bin/bash";
 
@@ -370,10 +370,11 @@ static void _main(int argc, char * * argv)
 
         // Build or fetch all dependencies of the derivation.
         for (const auto & input : drv.inputDrvs)
-            if (std::all_of(envExclude.cbegin(), envExclude.cend(), [&](const string & exclude) { return !std::regex_search(input.first, std::regex(exclude)); }))
-                pathsToBuild.insert(makeDrvPathWithOutputs(input.first, input.second));
+            if (std::all_of(envExclude.cbegin(), envExclude.cend(),
+                    [&](const string & exclude) { return !std::regex_search(store->printStorePath(input.first), std::regex(exclude)); }))
+                pathsToBuild.emplace_back(input.first, input.second);
         for (const auto & src : drv.inputSrcs)
-            pathsToBuild.insert(src);
+            pathsToBuild.emplace_back(src);
 
         buildPaths(pathsToBuild);
 
@@ -399,7 +400,7 @@ static void _main(int argc, char * * argv)
         env["NIX_STORE"] = store->storeDir;
         env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
 
-        auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile", ""));
+        auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile").value_or(""));
 
         bool keepTmp = false;
         int fileNr = 0;
@@ -468,7 +469,7 @@ static void _main(int argc, char * * argv)
 
     else {
 
-        PathSet pathsToBuild;
+        std::vector<StorePathWithOutputs> pathsToBuild;
 
         std::map<Path, Path> drvPrefixes;
         std::map<Path, Path> resultSymlinks;
@@ -482,7 +483,7 @@ static void _main(int argc, char * * argv)
             if (outputName == "")
                 throw Error("derivation '%s' lacks an 'outputName' attribute", drvPath);
 
-            pathsToBuild.insert(drvPath + "!" + outputName);
+            pathsToBuild.emplace_back(store->parseStorePath(drvPath), StringSet{outputName});
 
             std::string drvPrefix;
             auto i = drvPrefixes.find(drvPath);
@@ -508,7 +509,7 @@ static void _main(int argc, char * * argv)
 
         for (auto & symlink : resultSymlinks)
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
-                store2->addPermRoot(symlink.second, absPath(symlink.first), true);
+                store2->addPermRoot(store->parseStorePath(symlink.second), absPath(symlink.first), true);
 
         for (auto & path : outPaths)
             std::cout << path << '\n';