refactor: create a new nix formatter run command alias for nix fmt

This refactor shouldn't change much except add a new `nix formatter run`
command. This creates space for the new `nix formatter build` command,
which I'll be introducing in the next commit.

maintainers/flake-module.nix

@@ -605,8 +605,8 @@
               ''^tests/functional/flakes/prefetch\.sh$''
               ''^tests/functional/flakes/run\.sh$''
               ''^tests/functional/flakes/show\.sh$''
-              ''^tests/functional/fmt\.sh$''
-              ''^tests/functional/fmt\.simple\.sh$''
+              ''^tests/functional/formatter\.sh$''
+              ''^tests/functional/formatter\.simple\.sh$''
               ''^tests/functional/gc-auto\.sh$''
               ''^tests/functional/gc-concurrent\.builder\.sh$''
               ''^tests/functional/gc-concurrent\.sh$''

src/nix/fmt.cc

@@ -1,55 +0,0 @@
-#include "nix/cmd/command.hh"
-#include "nix/cmd/installable-value.hh"
-#include "nix/expr/eval.hh"
-#include "run.hh"
-
-using namespace nix;
-
-struct CmdFmt : SourceExprCommand {
-    std::vector<std::string> args;
-
-    CmdFmt() { expectArgs({.label = "args", .handler = {&args}}); }
-
-    std::string description() override {
-        return "reformat your code in the standard style";
-    }
-
-    std::string doc() override {
-        return
-          #include "fmt.md"
-          ;
-    }
-
-    Category category() override { return catSecondary; }
-
-    Strings getDefaultFlakeAttrPaths() override {
-        return Strings{"formatter." + settings.thisSystem.get()};
-    }
-
-    Strings getDefaultFlakeAttrPathPrefixes() override { return Strings{}; }
-
-    void run(ref<Store> store) override
-    {
-        auto evalState = getEvalState();
-        auto evalStore = getEvalStore();
-
-        auto installable_ = parseInstallable(store, ".");
-        auto & installable = InstallableValue::require(*installable_);
-        auto app = installable.toApp(*evalState).resolve(evalStore, store);
-
-        Strings programArgs{app.program};
-
-        // Propagate arguments from the CLI
-        for (auto &i : args) {
-            programArgs.push_back(i);
-        }
-
-        // Release our references to eval caches to ensure they are persisted to disk, because
-        // we are about to exec out of this process without running C++ destructors.
-        evalState->evalCaches.clear();
-
-        execProgramInStore(store, UseLookupPath::DontUse, app.program, programArgs);
-    };
-};
-
-static auto r2 = registerCommand<CmdFmt>("fmt");

src/nix/formatter-run.md

@@ -2,7 +2,7 @@ R""(
 
 # Description
 
-`nix fmt` calls the formatter specified in the flake.
+`nix fmt` (an alias for `nix formatter run`) calls the formatter specified in the flake.
 
 Flags can be forwarded to the formatter by using `--` followed by the flags.
 

src/nix/formatter.cc

@@ -0,0 +1,98 @@
+#include "nix/cmd/command.hh"
+#include "nix/cmd/installable-value.hh"
+#include "nix/expr/eval.hh"
+#include "run.hh"
+
+using namespace nix;
+
+struct CmdFormatter : NixMultiCommand
+{
+    CmdFormatter()
+        : NixMultiCommand("formatter", RegisterCommand::getCommandsFor({"formatter"}))
+    {
+    }
+
+    std::string description() override
+    {
+        return "build or run the formatter";
+    }
+
+    Category category() override
+    {
+        return catSecondary;
+    }
+};
+
+static auto rCmdFormatter = registerCommand<CmdFormatter>("formatter");
+
+struct CmdFormatterRun : SourceExprCommand
+{
+    std::vector<std::string> args;
+
+    CmdFormatterRun()
+    {
+        expectArgs({.label = "args", .handler = {&args}});
+    }
+
+    std::string description() override
+    {
+        return "reformat your code in the standard style";
+    }
+
+    std::string doc() override
+    {
+        return
+#include "formatter-run.md"
+            ;
+    }
+
+    Category category() override
+    {
+        return catSecondary;
+    }
+
+    Strings getDefaultFlakeAttrPaths() override
+    {
+        return Strings{"formatter." + settings.thisSystem.get()};
+    }
+
+    Strings getDefaultFlakeAttrPathPrefixes() override
+    {
+        return Strings{};
+    }
+
+    void run(ref<Store> store) override
+    {
+        auto evalState = getEvalState();
+        auto evalStore = getEvalStore();
+
+        auto installable_ = parseInstallable(store, ".");
+        auto & installable = InstallableValue::require(*installable_);
+        auto app = installable.toApp(*evalState).resolve(evalStore, store);
+
+        Strings programArgs{app.program};
+
+        // Propagate arguments from the CLI
+        for (auto & i : args) {
+            programArgs.push_back(i);
+        }
+
+        // Release our references to eval caches to ensure they are persisted to disk, because
+        // we are about to exec out of this process without running C++ destructors.
+        evalState->evalCaches.clear();
+
+        execProgramInStore(store, UseLookupPath::DontUse, app.program, programArgs);
+    };
+};
+
+static auto rFormatterRun = registerCommand2<CmdFormatterRun>({"formatter", "run"});
+
+struct CmdFmt : CmdFormatterRun
+{
+    void run(ref<Store> store) override
+    {
+        CmdFormatterRun::run(store);
+    }
+};
+
+static auto rFmt = registerCommand<CmdFmt>("fmt");

src/nix/meson.build

@@ -78,7 +78,7 @@ nix_sources = [config_priv_h] + files(
   'env.cc',
   'eval.cc',
   'flake.cc',
-  'fmt.cc',
+  'formatter.cc',
   'hash.cc',
   'log.cc',
   'ls.cc',

tests/functional/meson.build

@@ -132,7 +132,7 @@ suites = [
       'nix-copy-ssh-ng.sh',
       'post-hook.sh',
       'function-trace.sh',
-      'fmt.sh',
+      'formatter.sh',
       'eval-store.sh',
       'why-depends.sh',
       'derivation-json.sh',