Merge pull request #13139 from NixOS/singleton-pattern

Simplify plugin registrations

Author: Mic92

src/libcmd/command.cc

@@ -14,12 +14,10 @@
 
 namespace nix {
 
-RegisterCommand::Commands * RegisterCommand::commands = nullptr;
-
 nix::Commands RegisterCommand::getCommandsFor(const std::vector<std::string> & prefix)
 {
     nix::Commands res;
-    for (auto & [name, command] : *RegisterCommand::commands)
+    for (auto & [name, command] : RegisterCommand::commands())
         if (name.size() == prefix.size() + 1) {
             bool equal = true;
             for (size_t i = 0; i < prefix.size(); ++i)

src/libcmd/include/nix/cmd/command.hh

@@ -285,13 +285,16 @@ struct StorePathCommand : public StorePathsCommand
 struct RegisterCommand
 {
     typedef std::map<std::vector<std::string>, std::function<ref<Command>()>> Commands;
-    static Commands * commands;
+
+    static Commands & commands()
+    {
+        static Commands commands;
+        return commands;
+    }
 
     RegisterCommand(std::vector<std::string> && name, std::function<ref<Command>()> command)
     {
-        if (!commands)
-            commands = new Commands;
-        commands->emplace(name, command);
+        commands().emplace(name, command);
     }
 
     static nix::Commands getCommandsFor(const std::vector<std::string> & prefix);

src/libcmd/include/nix/cmd/legacy.hh

@@ -12,12 +12,15 @@ typedef std::function<void(int, char * *)> MainFunction;
 struct RegisterLegacyCommand
 {
     typedef std::map<std::string, MainFunction> Commands;
-    static Commands * commands;
+
+    static Commands & commands() {
+        static Commands commands;
+        return commands;
+    }
 
     RegisterLegacyCommand(const std::string & name, MainFunction fun)
     {
-        if (!commands) commands = new Commands;
-        (*commands)[name] = fun;
+        commands()[name] = fun;
     }
 };
 

src/libcmd/legacy.cc

@@ -71,7 +71,6 @@ sources = files(
   'installable-flake.cc',
   'installable-value.cc',
   'installables.cc',
-  'legacy.cc',
   'markdown.cc',
   'misc-store-flags.cc',
   'network-proxy.cc',

src/libcmd/meson.build

@@ -27,7 +27,12 @@ constexpr size_t conservativeStackReservation = 16;
 struct RegisterPrimOp
 {
     typedef std::vector<PrimOp> PrimOps;
-    static PrimOps * primOps;
+
+    static PrimOps & primOps()
+    {
+        static PrimOps primOps;
+        return primOps;
+    }
 
     /**
      * You can register a constant by passing an arity of 0. fun

src/libexpr/include/nix/expr/primops.hh

@@ -4713,13 +4713,9 @@ static RegisterPrimOp primop_splitVersion({
  *************************************************************/
 
 
-RegisterPrimOp::PrimOps * RegisterPrimOp::primOps;
-
-
 RegisterPrimOp::RegisterPrimOp(PrimOp && primOp)
 {
-    if (!primOps) primOps = new PrimOps;
-    primOps->push_back(std::move(primOp));
+    primOps().push_back(std::move(primOp));
 }
 
 
@@ -4973,14 +4969,12 @@ void EvalState::createBaseEnv(const EvalSettings & evalSettings)
         )",
     });
 
-    if (RegisterPrimOp::primOps)
-        for (auto & primOp : *RegisterPrimOp::primOps)
-            if (experimentalFeatureSettings.isEnabled(primOp.experimentalFeature))
-            {
-                auto primOpAdjusted = primOp;
-                primOpAdjusted.arity = std::max(primOp.args.size(), primOp.arity);
-                addPrimOp(std::move(primOpAdjusted));
-            }
+    for (auto & primOp : RegisterPrimOp::primOps())
+        if (experimentalFeatureSettings.isEnabled(primOp.experimentalFeature)) {
+            auto primOpAdjusted = primOp;
+            primOpAdjusted.arity = std::max(primOp.args.size(), primOp.arity);
+            addPrimOp(std::move(primOpAdjusted));
+        }
 
     for (auto & primOp : evalSettings.extraPrimOps) {
         auto primOpAdjusted = primOp;

src/libexpr/primops.cc

@@ -12,24 +12,26 @@ namespace nix::fetchers {
 
 using InputSchemeMap = std::map<std::string_view, std::shared_ptr<InputScheme>>;
 
-std::unique_ptr<InputSchemeMap> inputSchemes = nullptr;
+static InputSchemeMap & inputSchemes()
+{
+    static InputSchemeMap inputSchemeMap;
+    return inputSchemeMap;
+}
 
 void registerInputScheme(std::shared_ptr<InputScheme> && inputScheme)
 {
-    if (!inputSchemes)
-        inputSchemes = std::make_unique<InputSchemeMap>();
     auto schemeName = inputScheme->schemeName();
-    if (inputSchemes->count(schemeName) > 0)
+    if (!inputSchemes().emplace(schemeName, std::move(inputScheme)).second)
         throw Error("Input scheme with name %s already registered", schemeName);
-    inputSchemes->insert_or_assign(schemeName, std::move(inputScheme));
 }
 
-nlohmann::json dumpRegisterInputSchemeInfo() {
+nlohmann::json dumpRegisterInputSchemeInfo()
+{
     using nlohmann::json;
 
     auto res = json::object();
 
-    for (auto & [name, scheme] : *inputSchemes) {
+    for (auto & [name, scheme] : inputSchemes()) {
         auto & r = res[name] = json::object();
         r["allowedAttrs"] = scheme->allowedAttrs();
     }
@@ -57,7 +59,7 @@ Input Input::fromURL(
     const Settings & settings,
     const ParsedURL & url, bool requireTree)
 {
-    for (auto & [_, inputScheme] : *inputSchemes) {
+    for (auto & [_, inputScheme] : inputSchemes()) {
         auto res = inputScheme->inputFromURL(settings, url, requireTree);
         if (res) {
             experimentalFeatureSettings.require(inputScheme->experimentalFeature());
@@ -91,8 +93,8 @@ Input Input::fromAttrs(const Settings & settings, Attrs && attrs)
     };
 
     std::shared_ptr<InputScheme> inputScheme = ({
-        auto i = inputSchemes->find(schemeName);
-        i == inputSchemes->end() ? nullptr : i->second;
+        auto i = get(inputSchemes(), schemeName);
+        i ? *i : nullptr;
     });
 
     if (!inputScheme) return raw();

src/libfetchers/fetchers.cc

@@ -902,12 +902,11 @@ struct StoreFactory
 
 struct Implementations
 {
-    static std::vector<StoreFactory> * registered;
+    static std::vector<StoreFactory> & registered();
 
     template<typename T, typename TConfig>
     static void add()
     {
-        if (!registered) registered = new std::vector<StoreFactory>();
         StoreFactory factory{
             .uriSchemes = TConfig::uriSchemes(),
             .create =
@@ -919,7 +918,7 @@ struct Implementations
                  -> std::shared_ptr<StoreConfig>
                  { return std::make_shared<TConfig>(StringMap({})); })
         };
-        registered->push_back(factory);
+        registered().push_back(factory);
     }
 };
 

src/libstore/include/nix/store/store-api.hh

@@ -1355,7 +1355,7 @@ ref<Store> openStore(StoreReference && storeURI)
                 return std::make_shared<LocalStore>(params);
         },
         [&](const StoreReference::Specified & g) {
-            for (const auto & implem : *Implementations::registered)
+            for (const auto & implem : Implementations::registered())
                 if (implem.uriSchemes.count(g.scheme))
                     return implem.create(g.scheme, g.authority, params);
 
@@ -1399,6 +1399,10 @@ std::list<ref<Store>> getDefaultSubstituters()
     return stores;
 }
 
-std::vector<StoreFactory> * Implementations::registered = 0;
+std::vector<StoreFactory> & Implementations::registered()
+{
+    static std::vector<StoreFactory> registered;
+    return registered;
+}
 
 }