Merge pull request #4304 from NixOS/separate-manpages

Separate manpages for 'nix' subcommands

src/nix/eval.cc

@@ -3,6 +3,7 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "eval.hh"
+#include "eval-inline.hh"
 #include "json.hh"
 #include "value-to-json.hh"
 #include "progress-bar.hh"
@@ -13,6 +14,7 @@ struct CmdEval : MixJSON, InstallableCommand
 {
     bool raw = false;
     std::optional<std::string> apply;
+    std::optional<Path> writeTo;
 
     CmdEval()
     {
@@ -24,6 +26,13 @@ struct CmdEval : MixJSON, InstallableCommand
             .labels = {"expr"},
             .handler = {&apply},
         });
+
+        addFlag({
+            .longName = "write-to",
+            .description = "write a string or attrset of strings to 'path'",
+            .labels = {"path"},
+            .handler = {&writeTo},
+        });
     }
 
     std::string description() override
@@ -66,7 +75,7 @@ struct CmdEval : MixJSON, InstallableCommand
 
         auto state = getEvalState();
 
-        auto v = installable->toValue(*state).first;
+        auto [v, pos] = installable->toValue(*state);
         PathSet context;
 
         if (apply) {
@@ -77,13 +86,51 @@ struct CmdEval : MixJSON, InstallableCommand
             v = vRes;
         }
 
-        if (raw) {
+        if (writeTo) {
+            stopProgressBar();
+
+            if (pathExists(*writeTo))
+                throw Error("path '%s' already exists", *writeTo);
+
+            std::function<void(Value & v, const Pos & pos, const Path & path)> recurse;
+
+            recurse = [&](Value & v, const Pos & pos, const Path & path)
+            {
+                state->forceValue(v);
+                if (v.type == tString)
+                    // FIXME: disallow strings with contexts?
+                    writeFile(path, v.string.s);
+                else if (v.type == tAttrs) {
+                    if (mkdir(path.c_str(), 0777) == -1)
+                        throw SysError("creating directory '%s'", path);
+                    for (auto & attr : *v.attrs)
+                        try {
+                            if (attr.name == "." || attr.name == "..")
+                                throw Error("invalid file name '%s'", attr.name);
+                            recurse(*attr.value, *attr.pos, path + "/" + std::string(attr.name));
+                        } catch (Error & e) {
+                            e.addTrace(*attr.pos, hintfmt("while evaluating the attribute '%s'", attr.name));
+                            throw;
+                        }
+                }
+                else
+                    throw TypeError("value at '%s' is not a string or an attribute set", pos);
+            };
+
+            recurse(*v, pos, *writeTo);
+        }
+
+        else if (raw) {
             stopProgressBar();
             std::cout << state->coerceToString(noPos, *v, context);
-        } else if (json) {
+        }
+
+        else if (json) {
             JSONPlaceholder jsonOut(std::cout);
             printValueAsJSON(*state, true, *v, jsonOut, context);
-        } else {
+        }
+
+        else {
             state->forceValueDeep(*v);
             logger->cout("%s", *v);
         }

src/nix/main.cc

@@ -149,6 +149,50 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
     }
 };
 
+static void showHelp(std::vector<std::string> subcommand)
+{
+    showManPage(subcommand.empty() ? "nix" : fmt("nix3-%s", concatStringsSep("-", subcommand)));
+}
+
+struct CmdHelp : Command
+{
+    std::vector<std::string> subcommand;
+
+    CmdHelp()
+    {
+        expectArgs({
+            .label = "subcommand",
+            .handler = {&subcommand},
+        });
+    }
+
+    std::string description() override
+    {
+        return "show help about 'nix' or a particular subcommand";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To show help about 'nix' in general:",
+                "nix help"
+            },
+            Example{
+                "To show help about a particular subcommand:",
+                "nix help run"
+            },
+        };
+    }
+
+    void run() override
+    {
+        showHelp(subcommand);
+    }
+};
+
+static auto rCmdHelp = registerCommand<CmdHelp>("help");
+
 void mainWrapped(int argc, char * * argv)
 {
     /* The chroot helper needs to be run before any threads have been