Get rid of virtual Goal::init()

Now, each class provides the initial coroutine by value. This avoids
some sketchy virtual function stuff, and will also be further put to
good use in the next commit.

src/libstore/build/derivation-goal.cc

@@ -25,7 +25,7 @@ namespace nix {
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath,
     const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker)
+    : Goal(worker, init())
     , useDerivation(true)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)
@@ -43,7 +43,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath,
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
     const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker)
+    : Goal(worker, init())
     , useDerivation(false)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)

src/libstore/build/drv-output-substitution-goal.cc

@@ -12,7 +12,7 @@ DrvOutputSubstitutionGoal::DrvOutputSubstitutionGoal(
     Worker & worker,
     RepairFlag repair,
     std::optional<ContentAddress> ca)
-    : Goal(worker)
+    : Goal(worker, init())
     , id(id)
 {
     name = fmt("substitution of '%s'", id.to_string());

src/libstore/build/substitution-goal.cc

@@ -9,7 +9,7 @@
 namespace nix {
 
 PathSubstitutionGoal::PathSubstitutionGoal(const StorePath & storePath, Worker & worker, RepairFlag repair, std::optional<ContentAddress> ca)
-    : Goal(worker)
+    : Goal(worker, init())
     , storePath(storePath)
     , repair(repair)
     , ca(ca)

src/libstore/include/nix/store/build/derivation-goal.hh

@@ -166,7 +166,7 @@ struct DerivationGoal : public Goal
     /**
      * The states.
      */
-    Co init() override;
+    Co init();
     Co haveDerivation();
     Co gaveUpOnSubstitution();
     Co tryToBuild();

src/libstore/include/nix/store/build/drv-output-substitution-goal.hh

@@ -33,7 +33,7 @@ public:
     typedef void (DrvOutputSubstitutionGoal::*GoalState)();
     GoalState state;
 
-    Co init() override;
+    Co init();
     Co realisationFetched(Goals waitees, std::shared_ptr<const Realisation> outputInfo, nix::ref<nix::Store> sub);
 
     void timedOut(Error && ex) override { unreachable(); };

src/libstore/include/nix/store/build/goal.hh

@@ -338,17 +338,6 @@ protected:
      */
     std::optional<Co> top_co;
 
-    /**
-     * The entry point for the goal
-     */
-    virtual Co init() = 0;
-
-    /**
-     * Wrapper around @ref init since virtual functions
-     * can't be used in constructors.
-     */
-    inline Co init_wrapper();
-
     /**
      * Signals that the goal is done.
      * `co_return` the result. If you're not inside a coroutine, you can ignore
@@ -376,8 +365,8 @@ public:
      */
     std::optional<Error> ex;
 
-    Goal(Worker & worker)
+    Goal(Worker & worker, Co init)
-        : worker(worker), top_co(init_wrapper())
+        : worker(worker), top_co(std::move(init))
     {
         // top_co shouldn't have a goal already, should be nullptr.
         assert(!top_co->handle.promise().goal);
@@ -440,7 +429,3 @@ template<typename... ArgTypes>
 struct std::coroutine_traits<nix::Goal::Co, ArgTypes...> {
     using promise_type = nix::Goal::promise_type;
 };
-
-nix::Goal::Co nix::Goal::init_wrapper() {
-    co_return init();
-}

src/libstore/include/nix/store/build/substitution-goal.hh

@@ -64,7 +64,7 @@ public:
     /**
      * The states.
      */
-    Co init() override;
+    Co init();
     Co gotInfo();
     Co tryToRun(StorePath subPath, nix::ref<Store> sub, std::shared_ptr<const ValidPathInfo> info, bool & substituterFailed);
     Co finished();