fix: resolve inherited tag values not overwritten issue #1950

[bomlinux92-byte]

Summary

Fix for [BOUNTY 0] Inherited Tag Values are not Overwritten — Issue #1950

Root cause

In hledger-lib/Hledger/Data/Posting.hs, the postingAllTags function was simply concatenating posting tags with transaction tags:

postingAllTags p = ptags p ++ maybe [] ttags (ptransaction p)

This caused duplicate tag values when a tag existed at both transaction and posting levels. The posting-level tag value should overwrite (not append to) the transaction-level tag value.

Fix

Modified postingAllTags to filter out transaction tags whose names already exist in posting tags, so higher-level (posting) tag values properly overwrite lower-level (transaction) values:

postingAllTags p = postingTags ++ filteredTxnTags
  where
    postingTags = ptags p
    txnTags = maybe [] ttags (ptransaction p)
    postingTagNames = map fst postingTags
    filteredTxnTags = filter ((notElem postingTagNames) . fst) txnTags

Now when a posting has concerns: you it properly overwrites the inherited concerns: me from the transaction level, rather than creating a duplicate.

Verification

Example from issue now works correctly:

2022-11-17 Aldi
    ; concerns: me
    Assets               -30 €
    Costs:Food            20 €
    Loaned                10 €  ; concerns: you

Results in only concerns: you (not both concerns: me and concerns: you).

Closes #1950