Make indentation configurable

With a CLI flag for now, though in the future we should use .editorconfig as the default

Co-Authored-By: toastal <toastal@posteo.net>

main/Main.hs

@@ -40,6 +40,7 @@ type Width = Int
 data Nixfmt = Nixfmt
   { files :: [FilePath],
     width :: Width,
+    indent :: Int,
     check :: Bool,
     quiet :: Bool,
     verify :: Bool,
@@ -50,13 +51,15 @@ data Nixfmt = Nixfmt
 options :: Nixfmt
 options =
   let defaultWidth = 100
+      defaultIndent = 2
       addDefaultHint value message =
         message ++ "\n[default: " ++ show value ++ "]"
   in Nixfmt
       { files = [] &= args &= typ "FILES",
         width =
           defaultWidth
             &= help (addDefaultHint defaultWidth "Maximum width in characters"),
+        indent = defaultIndent &= help (addDefaultHint defaultIndent "Number of spaces to use for indentation"),
         check = False &= help "Check whether files are formatted without modifying them",
         quiet = False &= help "Do not report errors",
         verify =
@@ -135,8 +138,8 @@ type Formatter = FilePath -> Text -> Either String Text
 
 toFormatter :: Nixfmt -> Formatter
 toFormatter Nixfmt{ast = True} = Nixfmt.printAst
-toFormatter Nixfmt{width, verify = True} = Nixfmt.formatVerify (layout width)
-toFormatter Nixfmt{width, verify = False} = Nixfmt.format (layout width)
+toFormatter Nixfmt{width, indent, verify = True} = Nixfmt.formatVerify (layout width indent)
+toFormatter Nixfmt{width, indent, verify = False} = Nixfmt.format (layout width indent)
 
 type Operation = Formatter -> Target -> IO Result
 

src/Nixfmt/Predoc.hs

@@ -342,8 +342,8 @@ mergeSpacings Hardspace (Newlines x) = Newlines x
 mergeSpacings _ (Newlines x) = Newlines (x + 1)
 mergeSpacings _ y = y
 
-layout :: (Pretty a) => Int -> a -> Text
-layout w = (<> "\n") . Text.strip . layoutGreedy w . fixup . pretty
+layout :: (Pretty a) => Int -> Int -> a -> Text
+layout w i = (<> "\n") . Text.strip . layoutGreedy w i . fixup . pretty
 
 -- 1. Move and merge Spacings.
 -- 2. Convert Softlines to Grouped Lines and Hardspaces to Texts.
@@ -468,8 +468,8 @@ indent n = Text.replicate n " "
 type St = (Int, NonEmpty (Int, Int))
 
 -- tw   Target Width
-layoutGreedy :: Int -> Doc -> Text
-layoutGreedy tw doc = Text.concat $ evalState (go [Group RegularG doc] []) (0, singleton (0, 0))
+layoutGreedy :: Int -> Int -> Doc -> Text
+layoutGreedy tw iw doc = Text.concat $ evalState (go [Group RegularG doc] []) (0, singleton (0, 0))
   where
     -- Simple helpers around `put` with a tuple state
     putL = modify . first . const
@@ -484,7 +484,7 @@ layoutGreedy tw doc = Text.concat $ evalState (go [Group RegularG doc] []) (0, s
           case textNL `compare` nl of
             -- Push the textNL onto the stack, but only increase the actual indentation (`ci`)
             -- if this is the first one of a line. All subsequent nestings within the line effectively get "swallowed"
-            GT -> putR ((if cc == 0 then ci + 2 else ci, textNL) <| indents) >> go'
+            GT -> putR ((if cc == 0 then ci + iw else ci, textNL) <| indents) >> go'
             -- Need to go down one or more levels
             -- Just pop from the stack and recurse until the indent matches again
             LT -> putR (NonEmpty.fromList indents') >> putText textNL textOffset t
@@ -611,14 +611,14 @@ layoutGreedy tw doc = Text.concat $ evalState (go [Group RegularG doc] []) (0, s
                 _ -> grp
               (nl, off) = nextIndent grp'
 
-              indentWillIncrease = if fst (nextIndent rest) > lineNL then 2 else 0
+              indentWillIncrease = if fst (nextIndent rest) > lineNL then iw else 0
                 where
                   lastLineNL = snd $ NonEmpty.head ci
-                  lineNL = lastLineNL + (if nl > lastLineNL then 2 else 0)
+                  lineNL = lastLineNL + (if nl > lastLineNL then iw else 0)
           in fits indentWillIncrease (tw - firstLineWidth rest) grp'
               <&> \t -> runState (putText nl off t) (cc, ci)
         else
-          let indentWillIncrease = if fst (nextIndent rest) > lineNL then 2 else 0
+          let indentWillIncrease = if fst (nextIndent rest) > lineNL then iw else 0
                 where
                   lineNL = snd $ NonEmpty.head ci
           in fits (indentWillIncrease - cc) (tw - cc - firstLineWidth rest) grp