Use Nix's Machine type in a mimimal way

This is *just* using the fields from that type, and only where the types
coincide. (There are two fields with different types, `speedFactor` most
interestingly.) No code is reused, so we can be sure that no behavior is
changed.

Once the types are reconciled on the Nix side, then we can start
carefully actually reusing code.

Progress on #1164

src/hydra-queue-runner/dispatcher.cc

@@ -231,11 +231,11 @@ system_time State::doDispatch()
         sort(machinesSorted.begin(), machinesSorted.end(),
             [](const MachineInfo & a, const MachineInfo & b) -> bool
             {
-                float ta = std::round(a.currentJobs / a.machine->speedFactor);
-                float tb = std::round(b.currentJobs / b.machine->speedFactor);
+                float ta = std::round(a.currentJobs / a.machine->speedFactorFloat);
+                float tb = std::round(b.currentJobs / b.machine->speedFactorFloat);
                 return
                     ta != tb ? ta < tb :
-                    a.machine->speedFactor != b.machine->speedFactor ? a.machine->speedFactor > b.machine->speedFactor :
+                    a.machine->speedFactorFloat != b.machine->speedFactorFloat ? a.machine->speedFactorFloat > b.machine->speedFactorFloat :
                     a.currentJobs > b.currentJobs;
             });
 

src/hydra-queue-runner/hydra-queue-runner.cc

@@ -1,6 +1,7 @@
 #include <iostream>
 #include <thread>
 #include <optional>
+#include <type_traits>
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -140,23 +141,43 @@ void State::parseMachines(const std::string & contents)
         if (tokens.size() < 3) continue;
         tokens.resize(8);
 
-        auto machine = std::make_shared<::Machine>();
-        machine->sshName = tokens[0];
-        machine->systemTypes = tokenizeString<StringSet>(tokens[1], ",");
-        machine->sshKey = tokens[2] == "-" ? std::string("") : tokens[2];
-        if (tokens[3] != "")
-            machine->maxJobs = string2Int<decltype(machine->maxJobs)>(tokens[3]).value();
-        else
-            machine->maxJobs = 1;
-        machine->speedFactor = atof(tokens[4].c_str());
         if (tokens[5] == "-") tokens[5] = "";
-        machine->supportedFeatures = tokenizeString<StringSet>(tokens[5], ",");
+        auto supportedFeatures = tokenizeString<StringSet>(tokens[5], ",");
+
         if (tokens[6] == "-") tokens[6] = "";
-        machine->mandatoryFeatures = tokenizeString<StringSet>(tokens[6], ",");
-        for (auto & f : machine->mandatoryFeatures)
-            machine->supportedFeatures.insert(f);
-        if (tokens[7] != "" && tokens[7] != "-")
-            machine->sshPublicHostKey = base64Decode(tokens[7]);
+        auto mandatoryFeatures = tokenizeString<StringSet>(tokens[6], ",");
+
+        for (auto & f : mandatoryFeatures)
+            supportedFeatures.insert(f);
+
+        using MaxJobs = std::remove_const<decltype(nix::Machine::maxJobs)>::type;
+
+        auto machine = std::make_shared<::Machine>(nix::Machine {
+            // `storeUri`, not yet used
+            "",
+            // `systemTypes`, not yet used
+            {},
+            // `sshKey`
+            tokens[2] == "-" ? "" : tokens[2],
+            // `maxJobs`
+            tokens[3] != ""
+                ? string2Int<MaxJobs>(tokens[3]).value()
+                : 1,
+            // `speedFactor`, not yet used
+            1,
+            // `supportedFeatures`
+            std::move(supportedFeatures),
+            // `mandatoryFeatures`
+            std::move(mandatoryFeatures),
+            // `sshPublicHostKey`
+            tokens[7] != "" && tokens[7] != "-"
+                ? base64Decode(tokens[7])
+                : "",
+        });
+
+        machine->sshName = tokens[0];
+        machine->systemTypesSet = tokenizeString<StringSet>(tokens[1], ",");
+        machine->speedFactorFloat = atof(tokens[4].c_str());
 
         /* Re-use the State object of the previous machine with the
            same name. */
@@ -596,7 +617,7 @@ void State::dumpStatus(Connection & conn)
 
                 json machine = {
                     {"enabled",  m->enabled},
-                    {"systemTypes", m->systemTypes},
+                    {"systemTypes", m->systemTypesSet},
                     {"supportedFeatures", m->supportedFeatures},
                     {"mandatoryFeatures", m->mandatoryFeatures},
                     {"nrStepsDone", s->nrStepsDone.load()},

src/hydra-queue-runner/state.hh

@@ -22,6 +22,7 @@
 #include "sync.hh"
 #include "nar-extractor.hh"
 #include "serve-protocol.hh"
+#include "machines.hh"
 
 
 typedef unsigned int BuildID;
@@ -234,17 +235,21 @@ void getDependents(Step::ptr step, std::set<Build::ptr> & builds, std::set<Step:
 void visitDependencies(std::function<void(Step::ptr)> visitor, Step::ptr step);
 
 
-struct Machine
+struct Machine : nix::Machine
 {
     typedef std::shared_ptr<Machine> ptr;
 
-    bool enabled{true};
+    /* TODO Get rid of: `nix::Machine::storeUri` is normalized in a way
+       we are not yet used to, but once we are, we don't need this. */
+    std::string sshName;
 
-    std::string sshName, sshKey;
-    std::set<std::string> systemTypes, supportedFeatures, mandatoryFeatures;
-    unsigned int maxJobs = 1;
-    float speedFactor = 1.0;
-    std::string sshPublicHostKey;
+    /* TODO Get rid once `nix::Machine::systemTypes` is a set not
+       vector. */
+    std::set<std::string> systemTypesSet;
+
+    /* TODO Get rid once `nix::Machine::systemTypes` is a `float` not
+       an `int`. */
+    float speedFactorFloat = 1.0;
 
     struct State {
         typedef std::shared_ptr<State> ptr;
@@ -272,7 +277,7 @@ struct Machine
     {
         /* Check that this machine is of the type required by the
            step. */
-        if (!systemTypes.count(step->drv->platform == "builtin" ? nix::settings.thisSystem : step->drv->platform))
+        if (!systemTypesSet.count(step->drv->platform == "builtin" ? nix::settings.thisSystem : step->drv->platform))
             return false;
 
         /* Check that the step requires all mandatory features of this