From d860d6d2fc3e8f514342d640dd9a70f4a6488e5d Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Fri, 29 Jul 2022 09:01:34 +0100
Subject: [PATCH] api: Hledger.Data.Errors: export
 makeBalanceAssertionErrorExcerpt

---
 hledger-lib/Hledger/Data/Balancing.hs | 26 ++----------------------
 hledger-lib/Hledger/Data/Errors.hs    | 29 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 24 deletions(-)

diff --git a/hledger-lib/Hledger/Data/Balancing.hs b/hledger-lib/Hledger/Data/Balancing.hs
index c3634bab9..300a8db6b 100644
--- a/hledger-lib/Hledger/Data/Balancing.hs
+++ b/hledger-lib/Hledger/Data/Balancing.hs
@@ -42,7 +42,7 @@ import qualified Data.Set as S
 import qualified Data.Text as T
 import Data.Time.Calendar (fromGregorian)
 import qualified Data.Map as M
-import Safe (headDef, headMay)
+import Safe (headDef)
 import Text.Printf (printf)
 
 import Hledger.Utils
@@ -628,29 +628,7 @@ checkBalanceAssertionOneCommodityB p@Posting{paccount=assertedacct} assertedamt
         acct = T.unpack $ paccount p
         ass = fromJust $ pbalanceassertion p  -- PARTIAL: fromJust won't fail, there is a balance assertion
         pos = baposition ass
-        (_,_,_,ex) = makePostingErrorExcerpt p finderrcols
-          where
-            finderrcols p t trendered = Just (col, Just col2)
-              where
-                -- Analyse the rendering to find the columns to highlight.
-                tlines = dbg5 "tlines" $ max 1 $ length $ T.lines $ tcomment t  -- transaction comment can generate extra lines
-                (col, col2) =
-                  let def = (5, maximum (map T.length $ T.lines trendered))  -- fallback: underline whole posting. Shouldn't happen.
-                  in
-                    case transactionFindPostingIndex (==p) t of
-                      Nothing  -> def
-                      Just idx -> fromMaybe def $ do
-                        let
-                          beforeps = take (idx-1) $ tpostings t
-                          beforepslines = dbg5 "beforepslines" $ sum $ map (max 1 . length . T.lines . pcomment) beforeps   -- posting comment can generate extra lines (assume only one commodity shown)
-                        assertionline <- dbg5 "assertionline" $ headMay $ drop (tlines + beforepslines) $ T.lines trendered
-                        let
-                          col2 = T.length assertionline
-                          l = dropWhile (/= '=') $ reverse $ T.unpack assertionline
-                          l' = dropWhile (`elem` ['=','*']) l
-                          col = length l' + 1
-                        return (col, col2)
-
+        (_,_,_,ex) = makeBalanceAssertionErrorExcerpt p
   unless pass $ throwError errmsg
 
 -- | Throw an error if this posting is trying to do an illegal balance assignment.
diff --git a/hledger-lib/Hledger/Data/Errors.hs b/hledger-lib/Hledger/Data/Errors.hs
index c398b2544..419aaed66 100644
--- a/hledger-lib/Hledger/Data/Errors.hs
+++ b/hledger-lib/Hledger/Data/Errors.hs
@@ -7,6 +7,7 @@ Helpers for making error messages.
 module Hledger.Data.Errors (
   makeTransactionErrorExcerpt,
   makePostingErrorExcerpt,
+  makeBalanceAssertionErrorExcerpt,
   transactionFindPostingIndex,
 )
 where
@@ -19,6 +20,8 @@ import qualified Data.Text as T
 import Hledger.Data.Transaction (showTransaction)
 import Hledger.Data.Types
 import Hledger.Utils
+import Data.Maybe
+import Safe (headMay)
 
 -- | Given a problem transaction and a function calculating the best
 -- column(s) for marking the error region:
@@ -100,3 +103,29 @@ transactionFindPostingIndex :: (Posting -> Bool) -> Transaction -> Maybe Int
 transactionFindPostingIndex ppredicate = 
   fmap fst . find (ppredicate.snd) . zip [1..] . tpostings
 
+-- | From the given posting, make an error excerpt showing the transaction with
+-- the balance assertion highlighted.
+makeBalanceAssertionErrorExcerpt :: Posting -> (FilePath, Int, Maybe (Int, Maybe Int), Text)
+makeBalanceAssertionErrorExcerpt p = makePostingErrorExcerpt p finderrcols
+  where
+    finderrcols p t trendered = Just (col, Just col2)
+      where
+        -- Analyse the rendering to find the columns to highlight.
+        tlines = dbg5 "tlines" $ max 1 $ length $ T.lines $ tcomment t  -- transaction comment can generate extra lines
+        (col, col2) =
+          let def = (5, maximum (map T.length $ T.lines trendered))  -- fallback: underline whole posting. Shouldn't happen.
+          in
+            case transactionFindPostingIndex (==p) t of
+              Nothing  -> def
+              Just idx -> fromMaybe def $ do
+                let
+                  beforeps = take (idx-1) $ tpostings t
+                  beforepslines = dbg5 "beforepslines" $ sum $ map (max 1 . length . T.lines . pcomment) beforeps   -- posting comment can generate extra lines (assume only one commodity shown)
+                assertionline <- dbg5 "assertionline" $ headMay $ drop (tlines + beforepslines) $ T.lines trendered
+                let
+                  col2 = T.length assertionline
+                  l = dropWhile (/= '=') $ reverse $ T.unpack assertionline
+                  l' = dropWhile (`elem` ['=','*']) l
+                  col = length l' + 1
+                return (col, col2)
+