ucsd-progsys/liquidhaskell

"Incomplete patterns" error with GHC <9.0.1

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#1,918 opened on 2021年12月1日

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good first issue

説明

GHC 8.10.7 but not GHC 9.0.1 reports "Pattern match(es) are non-exhaustive" in a few places.

https://github.com/ucsd-progsys/liquidhaskell/pull/1915 added {-# OPTIONS_GHC -Wno-incomplete-patterns #-} to files where this erroneous warning was reported since they are all false positives.

This ticket should be resolved by either investigating the root cause of the erroneous warning under GHC 8.10.7 and fixing it, or by waiting until we're happy to drop support for GHC <9.0.1. Either way, this ticket should not be marked as resolved before all -Wno-incomplete-patterns are removed from the code base: the pattern exhaustiveness check is generally a Good Thing and should not stay disabled longer than absolutely necessary!

コントリビューターガイド

技術スタック
なし
領域
backend
Issue 種別
bug
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
4
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
over 1 week
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
HaskellGHC
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
20
調査方針
Investigate why GHC 8.10.7 reports false positive incomplete pattern warnings while GHC 9.0.1 does not. The issue references PR #1915 which added Wno incomplete patterns flags to certain files. The fix could involve understanding the root cause in GHC 8.10.7 or waiting to drop support for GHC <9.0.1. Ensure all such flags are removed after resolution to restore exhaustiveness checking.