From 4200d2ed8a8d77d166060b9ddafa00fbe2cabcdc Mon Sep 17 00:00:00 2001
From: piegames <git@piegames.de>
Date: Mon, 2 Dec 2024 22:12:26 +0100
Subject: [PATCH] Fix string parsing of tab indentation

As much as everyone would wish for, tabs are not whitespace according to
Nix whitespace stripping.
Fixes #116, but my overall confidence level in Nixfmt's correctness in
parsing the mess which is the Nix syntax remains rather low.
---
 src/Nixfmt/Parser.hs | 1 +
 src/Nixfmt/Util.hs   | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/Nixfmt/Parser.hs b/src/Nixfmt/Parser.hs
index ddfb558d..a4c0c6f8 100644
--- a/src/Nixfmt/Parser.hs
+++ b/src/Nixfmt/Parser.hs
@@ -292,6 +292,7 @@ stripIndentation parts = case commonIndentation $ mapMaybe lineHead parts of
   Nothing -> map (const []) parts
   Just indentation -> map (stripParts indentation) parts
 
+-- Merge adjacent string parts which resulted as parsing artifacts
 normalizeLine :: [StringPart] -> [StringPart]
 normalizeLine [] = []
 normalizeLine (TextPart "" : xs) = normalizeLine xs
diff --git a/src/Nixfmt/Util.hs b/src/Nixfmt/Util.hs
index 8bc59866..c2ae1828 100644
--- a/src/Nixfmt/Util.hs
+++ b/src/Nixfmt/Util.hs
@@ -12,7 +12,7 @@ module Nixfmt.Util (
 )
 where
 
-import Data.Char (isAlpha, isDigit, isSpace)
+import Data.Char (isAlpha, isDigit)
 import Data.Text as Text (
   Text,
   all,
@@ -73,7 +73,7 @@ commonPrefix a b =
 -- prefix of zero texts is infinite, represented as Nothing.
 commonIndentation :: [Text] -> Maybe Text
 commonIndentation [] = Nothing
-commonIndentation [x] = Just $ Text.takeWhile isSpace x
+commonIndentation [x] = Just $ Text.takeWhile (== ' ') x
 commonIndentation (x : y : xs) = commonIndentation (commonPrefix x y : xs)
 
 isSpaces :: Text -> Bool