Add 'nix list-options' command

src/nix/options.cc

@@ -0,0 +1,67 @@
+#include "command.hh"
+#include "common-args.hh"
+#include "shared.hh"
+#include "store-api.hh"
+#include "eval.hh"
+#include "eval-inline.hh"
+#include "json.hh"
+#include "value-to-json.hh"
+
+using namespace nix;
+
+struct CmdListOptions : InstallableCommand
+{
+    CmdListOptions()
+    {
+    }
+
+    std::string description() override
+    {
+        return "show the options provided by a Nix configuration";
+    }
+
+    //Category category() override { return catSecondary; }
+
+    void run(ref<Store> store) override
+    {
+        auto state = getEvalState();
+
+        auto vModule = installable->toValue(*state).first;
+        state->forceAttrs(*vModule);
+
+        auto aAllOptions = vModule->attrs->get(state->symbols.create("_allOptions"));
+        if (!aAllOptions)
+            throw Error("module does not have an '_allOptions' attribute");
+        state->forceAttrs(*aAllOptions->value);
+
+        auto aFinal = vModule->attrs->get(state->symbols.create("final"));
+        if (!aFinal)
+            throw Error("module does not have an 'final' attribute");
+        state->forceAttrs(*aFinal->value);
+
+        for (const auto & [n, option] : enumerate(aAllOptions->value->attrs->lexicographicOrder())) {
+            if (n) logger->stdout("");
+            logger->stdout(ANSI_BOLD "%s" ANSI_NORMAL, option->name);
+
+            state->forceAttrs(*option->value);
+
+            std::string description = ANSI_ITALIC "<no description>" ANSI_NORMAL;
+            auto aDescription = option->value->attrs->get(state->symbols.create("description"));
+            if (aDescription)
+                // FIXME: render markdown.
+                description = state->forceString(*aDescription->value);
+            logger->stdout("  " ANSI_BOLD "Description:" ANSI_NORMAL " %s", description);
+
+            auto aValue = aFinal->value->attrs->get(option->name);
+            assert(aValue);
+
+            std::ostringstream str;
+            JSONPlaceholder jsonOut(str);
+            PathSet context;
+            printValueAsJSON(*state, true, *aValue->value, jsonOut, context);
+            logger->stdout("  " ANSI_BOLD "Value:" ANSI_NORMAL " %s", str.str());
+        }
+    }
+};
+
+static auto r1 = registerCommand<CmdListOptions>("list-options");