fix(nix fmt): remove the default "." argument

doc/manual/rl-next/nix-fmt-default-argument.md

@@ -0,0 +1,17 @@
+---
+synopsis: Removing the default argument passed to the `nix fmt` formatter
+issues: []
+prs: [11438]
+---
+
+The underlying formatter no longer receives the ". " default argument when `nix fmt` is called with no arguments.
+
+This change was necessary as the formatter wasn't able to distinguish between
+a user wanting to format the current folder with `nix fmt .` or the generic
+`nix fmt`.
+
+The default behaviour is now the responsibility of the formatter itself, and
+allows tools such as treefmt to format the whole tree instead of only the
+current directory and below.
+
+Author: [**@zimbatm**](https://github.com/zimbatm)

src/nix/fmt.cc

@@ -40,14 +40,8 @@ struct CmdFmt : SourceExprCommand {
         Strings programArgs{app.program};
 
         // Propagate arguments from the CLI
-        if (args.empty()) {
-            // Format the current flake out of the box
-            programArgs.push_back(".");
-        } else {
-            // User wants more power, let them decide which paths to include/exclude
-            for (auto &i : args) {
-                programArgs.push_back(i);
-            }
+        for (auto &i : args) {
+            programArgs.push_back(i);
         }
 
         // Release our references to eval caches to ensure they are persisted to disk, because

tests/functional/fmt.sh

@@ -5,11 +5,11 @@ source common.sh
 TODO_NixOS # Provide a `shell` variable. Try not to `export` it, perhaps.
 
 clearStoreIfPossible
-rm -rf $TEST_HOME/.cache $TEST_HOME/.config $TEST_HOME/.local
+rm -rf "$TEST_HOME"/.cache "$TEST_HOME"/.config "$TEST_HOME"/.local
 
-cp ./simple.nix ./simple.builder.sh ./fmt.simple.sh ./config.nix $TEST_HOME
+cp ./simple.nix ./simple.builder.sh ./fmt.simple.sh ./config.nix "$TEST_HOME"
 
-cd $TEST_HOME
+cd "$TEST_HOME"
 
 nix fmt --help | grep "Format"
 
@@ -30,6 +30,9 @@ cat << EOF > flake.nix
   };
 }
 EOF
-nix fmt ./file ./folder | grep 'Formatting: ./file ./folder'
+# No arguments check
+[[ "$(nix fmt)" = "Formatting(0):" ]]
+# Argument forwarding check
+nix fmt ./file ./folder | grep 'Formatting(2): ./file ./folder'
 nix flake check
 nix flake show | grep -P "package 'formatter'"

tests/functional/fmt.simple.sh

@@ -1 +1,2 @@
-echo Formatting: "${@}"
+#!/usr/bin/env bash
+echo "Formatting(${#}):" "${@}"