From c4766d7b8b659ce3f6fb1c339aeeec9ca3c7eeba Mon Sep 17 00:00:00 2001
From: zimbatm <zimbatm@zimbatm.com>
Date: Thu, 5 Sep 2024 10:29:48 +0200
Subject: [PATCH] fix(nix fmt): remove the default "." argument

When `nix fmt` is called without an argument, Nix appends the "." argument before calling the formatter. The comment in the code is:
> Format the current flake out of the box

This also happens when formatting sub-folders.

This means that the formatter is now unable to distinguish, as an interface, whether the "." argument is coming from the flake or the user's intent to format the current folder. This decision should be up to the formatter.

Treefmt, for example, will automatically look up the project's root and format all the files. This is the desired behaviour. But because the "." argument is passed, it cannot function as expected.
---
 doc/manual/rl-next/nix-fmt-default-argument.md | 17 +++++++++++++++++
 src/nix/fmt.cc                                 | 10 ++--------
 tests/functional/fmt.sh                        | 11 +++++++----
 tests/functional/fmt.simple.sh                 |  3 ++-
 4 files changed, 28 insertions(+), 13 deletions(-)
 create mode 100644 doc/manual/rl-next/nix-fmt-default-argument.md

diff --git a/doc/manual/rl-next/nix-fmt-default-argument.md b/doc/manual/rl-next/nix-fmt-default-argument.md
new file mode 100644
index 000000000..54161ab30
--- /dev/null
+++ b/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)
diff --git a/src/nix/fmt.cc b/src/nix/fmt.cc
index d65834495..f444d6add 100644
--- a/src/nix/fmt.cc
+++ b/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
diff --git a/tests/functional/fmt.sh b/tests/functional/fmt.sh
index b29fe64d6..9a79260e6 100755
--- a/tests/functional/fmt.sh
+++ b/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
+[[ "$(nix fmt)" = "Formatting(0):" ]]
+# Argument forwarding check
+nix fmt ./file ./folder | grep 'Formatting(2): ./file ./folder'
 nix flake check
 nix flake show | grep -P "package 'formatter'"
diff --git a/tests/functional/fmt.simple.sh b/tests/functional/fmt.simple.sh
index 4c8c67ebb..e53f6c9be 100755
--- a/tests/functional/fmt.simple.sh
+++ b/tests/functional/fmt.simple.sh
@@ -1 +1,2 @@
-echo Formatting: "${@}"
+#!/usr/bin/env bash
+echo "Formatting(${#}):" "${@}"