feat: add an example of 'before'

Signed-off-by: Brian McGee <brian@bmcgee.ie>

config/config_test.go

@@ -52,13 +52,13 @@ func TestReadConfigFile(t *testing.T) {
 	as.Equal([]string{"*.hs"}, haskell.Includes)
 	as.Equal([]string{"examples/haskell/"}, haskell.Excludes)
 
-	// nix
-	nix, ok := cfg.Formatters["nix"]
-	as.True(ok, "nix formatter not found")
-	as.Equal("alejandra", nix.Command)
-	as.Nil(nix.Options)
-	as.Equal([]string{"*.nix"}, nix.Includes)
-	as.Equal([]string{"examples/nix/sources.nix"}, nix.Excludes)
+	// alejandra
+	alejandra, ok := cfg.Formatters["alejandra"]
+	as.True(ok, "alejandra formatter not found")
+	as.Equal("alejandra", alejandra.Command)
+	as.Nil(alejandra.Options)
+	as.Equal([]string{"*.nix"}, alejandra.Includes)
+	as.Equal([]string{"examples/nix/sources.nix"}, alejandra.Excludes)
 
 	// ruby
 	ruby, ok := cfg.Formatters["ruby"]

nix/formatters.nix

@@ -12,5 +12,7 @@ with pkgs; [
   rustfmt
   shellcheck
   shfmt
+  statix
+  deadnix
   terraform
 ]

test/examples/treefmt.toml

@@ -26,11 +26,17 @@ options = [
 includes = ["*.hs"]
 excludes = ["examples/haskell/"]
 
-[formatter.nix]
+[formatter.alejandra]
 command = "alejandra"
 includes = ["*.nix"]
 # Act as an example on how to exclude specific files
 excludes = ["examples/nix/sources.nix"]
+# Make this run before deadnix
+# Note this formatter determines the file set for any 'downstream' formatters
+before = "deadnix"
+
+[formatter.deadnix]
+command = "deadnix"
 
 [formatter.ruby]
 command = "rufo"