feat(fmt): use nixfmt-rfc-style

src/libcmd/installable-flake.hh

@@ -74,7 +74,7 @@ struct InstallableFlake : InstallableValue
  * have their own Nixpkgs input, or other installables.
  *
  * It is a layer violation for Nix to know about Nixpkgs; currently just
- * `nix develop` does. Be wary of using this /
+ * `nix develop` and `nix fmt` does. Be wary of using this /
  * `InstallableFlake::nixpkgsFlakeRef` more places.
  */
 static inline FlakeRef defaultNixpkgsFlakeRef()

src/nix/fmt.cc

@@ -1,5 +1,6 @@
 #include "command.hh"
 #include "installable-value.hh"
+#include "installable-flake.hh"
 #include "eval.hh"
 #include "run.hh"
 
@@ -33,11 +34,89 @@ struct CmdFmt : SourceExprCommand {
         auto evalState = getEvalState();
         auto evalStore = getEvalStore();
 
+        Path nixfmt = "nixfmt";
+        FlakeRef nixpkgs = defaultNixpkgsFlakeRef();
+        nixpkgs = nixpkgs.resolve(evalStore);
+        auto nixpkgsLockFlags = lockFlags;
         auto installable_ = parseInstallable(store, ".");
-        auto & installable = InstallableValue::require(*installable_);
-        auto app = installable.toApp(*evalState).resolve(evalStore, store);
 
-        Strings programArgs{app.program};
+        // Check for "formatters.SYSTEM", too slow on Nixpkgs until lazy-trees
+        /*
+        try {
+            if (auto * i = dynamic_cast<const InstallableFlake *>(&*installable_)) {
+                auto & installable = InstallableFlake::require(*installable_);
+                auto app = installable.toApp(*evalState).resolve(evalStore, store);
+                nixfmt = app.program;
+            }
+        } catch (Error &) {
+            // ignoreException();
+        }
+        */
+
+        // Check for nixpkgs input, too slow on Nixpkgs until lazy-trees
+        /*
+        if (nixfmt == "nixfmt") {
+            try {
+                nixpkgsLockFlags.inputOverrides = {};
+                nixpkgsLockFlags.inputUpdates = {};
+
+                // Hard code the nixpkgs revision from <nixpkgs>/ci/pinned-nixpgs.json
+                if (auto * i = dynamic_cast<const InstallableFlake *>(&*installable_))
+                    nixpkgs = i->nixpkgsFlakeRef();
+            } catch (Error &) {
+                // ignoreException();
+            }
+        }
+        */
+
+        // Check for <nixpkgs>/ci/pinned-nixpkgs.json and resolve it
+        if (nixfmt == "nixfmt") {
+            try {
+                auto res = nixpkgs.fetchTree(store);
+                auto s = store->printStorePath(res.first) + "/ci/pinned-nixpkgs.json";
+                if (pathExists(s)) {
+                    nlohmann::json pinned_json = nlohmann::json::parse(readFile(s));
+                    auto pinned_rev = getString(pinned_json["rev"]);
+                    nixpkgs = FlakeRef::fromAttrs(fetchSettings, {{"type","indirect"}, {"id", "nixpkgs"},{"rev", pinned_rev}});
+                    nixpkgs = nixpkgs.resolve(evalStore);
+                }
+            } catch (Error &) {
+                // ignoreException();
+            }
+        }
+        // Check for nixfmt, otherwise use PATH
+        if (nixfmt == "nixfmt") {
+            try {
+                auto nixfmtInstallable = make_ref<InstallableFlake>(
+                    this,
+                    evalState,
+                    std::move(nixpkgs),
+                    "nixfmt-rfc-style",
+                    ExtendedOutputsSpec::Default(),
+                    Strings{},
+                    Strings{"legacyPackages." + settings.thisSystem.get() + "."},
+                    nixpkgsLockFlags);
+
+                bool found = false;
+
+                for (auto & path : Installable::toStorePathSet(getEvalStore(), store, Realise::Outputs, OperateOn::Output, {nixfmtInstallable})) {
+                    auto s = store->printStorePath(path) + "/bin/nixfmt";
+                    if (pathExists(s)) {
+                        nixfmt = s;
+                        found = true;
+                        break;
+                    }
+                }
+
+                if (!found)
+                    throw Error("package 'nixpkgs#nixfmt-rfc-style' does not provide a 'bin/nixfmt'");
+
+            } catch (Error &) {
+                ignoreException();
+            }
+        }
+
+        Strings programArgs{nixfmt};
 
         // Propagate arguments from the CLI
         if (args.empty()) {
@@ -54,7 +133,7 @@ struct CmdFmt : SourceExprCommand {
         // we are about to exec out of this process without running C++ destructors.
         evalState->evalCaches.clear();
 
-        execProgramInStore(store, UseLookupPath::DontUse, app.program, programArgs);
+        execProgramInStore(store, UseLookupPath::DontUse, nixfmt, programArgs);
     };
 };
 

src/nix/fmt.md

@@ -2,48 +2,24 @@ R""(
 
 # Examples
 
-With [nixpkgs-fmt](https://github.com/nix-community/nixpkgs-fmt):
-
-```nix
-# flake.nix
-{
-  outputs = { nixpkgs, self }: {
-    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixpkgs-fmt;
-  };
-}
-```
+With [nixfmt](https://github.com/NixOS/nixfmt):
 
 - Format the current flake: `$ nix fmt`
 
 - Format a specific folder or file: `$ nix fmt ./folder ./file.nix`
 
-With [nixfmt](https://github.com/serokell/nixfmt):
-
-```nix
-# flake.nix
-{
-  outputs = { nixpkgs, self }: {
-    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt;
-  };
-}
-```
-
 - Format specific files: `$ nix fmt ./file1.nix ./file2.nix`
 
-With [Alejandra](https://github.com/kamadorueda/alejandra):
-
+## **disabled** Overriding the formatter used
 ```nix
 # flake.nix
 {
   outputs = { nixpkgs, self }: {
-    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.alejandra;
+    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt-rfc-style;
   };
 }
 ```
 
-- Format the current flake: `$ nix fmt`
-
-- Format a specific folder or file: `$ nix fmt ./folder ./file.nix`
 
 # Description