Add 'nix dump-args' to dump all commands/flags for manpage generation

src/libutil/args.cc

@@ -3,6 +3,8 @@
 
 #include <glob.h>
 
+#include <nlohmann/json.hpp>
+
 namespace nix {
 
 void Args::addFlag(Flag && flag_)
@@ -205,6 +207,42 @@ bool Args::processArgs(const Strings & args, bool finish)
     return res;
 }
 
+nlohmann::json Args::toJSON()
+{
+    auto flags = nlohmann::json::object();
+
+    for (auto & [name, flag] : longFlags) {
+        auto j = nlohmann::json::object();
+        if (flag->shortName)
+            j["shortName"] = std::string(1, flag->shortName);
+        if (flag->description != "")
+            j["description"] = flag->description;
+        if (flag->category != "")
+            j["category"] = flag->category;
+        if (flag->handler.arity != ArityAny)
+            j["arity"] = flag->handler.arity;
+        if (!flag->labels.empty())
+            j["labels"] = flag->labels;
+        flags[name] = std::move(j);
+    }
+
+    auto args = nlohmann::json::array();
+
+    for (auto & arg : expectedArgs) {
+        auto j = nlohmann::json::object();
+        j["label"] = arg.label;
+        j["optional"] = arg.optional;
+        if (arg.handler.arity != ArityAny)
+            j["arity"] = arg.handler.arity;
+        args.push_back(std::move(j));
+    }
+
+    auto res = nlohmann::json::object();
+    res["flags"] = std::move(flags);
+    res["args"] = std::move(args);
+    return res;
+}
+
 static void hashTypeCompleter(size_t index, std::string_view prefix) 
 {
     for (auto & type : hashTypes)
@@ -313,6 +351,22 @@ void Command::printHelp(const string & programName, std::ostream & out)
     }
 }
 
+nlohmann::json Command::toJSON()
+{
+    auto exs = nlohmann::json::array();
+
+    for (auto & example : examples()) {
+        auto ex = nlohmann::json::object();
+        ex["description"] = example.description;
+        ex["command"] = example.command;
+        exs.push_back(std::move(ex));
+    }
+
+    auto res = Args::toJSON();
+    res["examples"] = std::move(exs);
+    return res;
+}
+
 MultiCommand::MultiCommand(const Commands & commands)
     : commands(commands)
 {
@@ -387,4 +441,20 @@ bool MultiCommand::processArgs(const Strings & args, bool finish)
         return Args::processArgs(args, finish);
 }
 
+nlohmann::json MultiCommand::toJSON()
+{
+    auto cmds = nlohmann::json::object();
+
+    for (auto & [name, commandFun] : commands) {
+        auto command = commandFun();
+        auto j = command->toJSON();
+        j["category"] = categories[command->category()];
+        cmds[name] = std::move(j);
+    }
+
+    auto res = Args::toJSON();
+    res["commands"] = std::move(cmds);
+    return res;
+}
+
 }

src/libutil/args.hh

@@ -4,6 +4,8 @@
 #include <map>
 #include <memory>
 
+#include <nlohmann/json_fwd.hpp>
+
 #include "util.hh"
 
 namespace nix {
@@ -203,6 +205,8 @@ public:
         });
     }
 
+    virtual nlohmann::json toJSON();
+
     friend class MultiCommand;
 };
 
@@ -234,6 +238,8 @@ struct Command : virtual Args
     virtual Category category() { return catDefault; }
 
     void printHelp(const string & programName, std::ostream & out) override;
+
+    nlohmann::json toJSON() override;
 };
 
 typedef std::map<std::string, std::function<ref<Command>()>> Commands;
@@ -259,6 +265,8 @@ public:
     bool processFlag(Strings::iterator & pos, Strings::iterator end) override;
 
     bool processArgs(const Strings & args, bool finish) override;
+
+    nlohmann::json toJSON() override;
 };
 
 Strings argvToStrings(int argc, char * * argv);

src/nix/command.cc

@@ -4,12 +4,25 @@
 #include "nixexpr.hh"
 #include "profiles.hh"
 
+#include <nlohmann/json.hpp>
+
 extern char * * environ __attribute__((weak));
 
 namespace nix {
 
 Commands * RegisterCommand::commands = nullptr;
 
+void NixMultiCommand::printHelp(const string & programName, std::ostream & out)
+{
+    MultiCommand::printHelp(programName, out);
+}
+
+nlohmann::json NixMultiCommand::toJSON()
+{
+    // FIXME: use Command::toJSON() as well.
+    return MultiCommand::toJSON();
+}
+
 StoreCommand::StoreCommand()
 {
 }

src/nix/command.hh

@@ -21,6 +21,13 @@ static constexpr Command::Category catSecondary = 100;
 static constexpr Command::Category catUtility = 101;
 static constexpr Command::Category catNixInstallation = 102;
 
+struct NixMultiCommand : virtual MultiCommand, virtual Command
+{
+    void printHelp(const string & programName, std::ostream & out) override;
+
+    nlohmann::json toJSON() override;
+};
+
 /* A command that requires a Nix store. */
 struct StoreCommand : virtual Command
 {

src/nix/flake.cc

@@ -933,7 +933,7 @@ struct CmdFlakeShow : FlakeCommand
     }
 };
 
-struct CmdFlake : virtual MultiCommand, virtual Command
+struct CmdFlake : NixMultiCommand
 {
     CmdFlake()
         : MultiCommand({
@@ -963,11 +963,6 @@ struct CmdFlake : virtual MultiCommand, virtual Command
         command->second->prepare();
         command->second->run();
     }
-
-    void printHelp(const string & programName, std::ostream & out) override
-    {
-        MultiCommand::printHelp(programName, out);
-    }
 };
 
 static auto r1 = registerCommand<CmdFlake>("flake");

src/nix/main.cc

@@ -17,6 +17,8 @@
 #include <netdb.h>
 #include <netinet/in.h>
 
+#include <nlohmann/json.hpp>
+
 extern std::string chrootHelperName;
 
 void chrootHelper(int argc, char * * argv);
@@ -172,6 +174,11 @@ void mainWrapped(int argc, char * * argv)
 
     NixArgs args;
 
+    if (argc == 2 && std::string(argv[1]) == "dump-args") {
+        std::cout << args.toJSON().dump() << "\n";
+        return;
+    }
+
     Finally printCompletions([&]()
     {
         if (completions) {

src/nix/profile.cc

@@ -437,7 +437,7 @@ struct CmdProfileDiffClosures : virtual StoreCommand, MixDefaultProfile
     }
 };
 
-struct CmdProfile : virtual MultiCommand, virtual Command
+struct CmdProfile : NixMultiCommand
 {
     CmdProfile()
         : MultiCommand({
@@ -461,11 +461,6 @@ struct CmdProfile : virtual MultiCommand, virtual Command
         command->second->prepare();
         command->second->run();
     }
-
-    void printHelp(const string & programName, std::ostream & out) override
-    {
-        MultiCommand::printHelp(programName, out);
-    }
 };
 
 static auto r1 = registerCommand<CmdProfile>("profile");

src/nix/registry.cc

@@ -115,7 +115,7 @@ struct CmdRegistryPin : virtual Args, EvalCommand
     }
 };
 
-struct CmdRegistry : virtual MultiCommand, virtual Command
+struct CmdRegistry : virtual NixMultiCommand
 {
     CmdRegistry()
         : MultiCommand({
@@ -141,11 +141,6 @@ struct CmdRegistry : virtual MultiCommand, virtual Command
         command->second->prepare();
         command->second->run();
     }
-
-    void printHelp(const string & programName, std::ostream & out) override
-    {
-        MultiCommand::printHelp(programName, out);
-    }
 };
 
 static auto r1 = registerCommand<CmdRegistry>("registry");