Fix a name shadowing warning (#1406) #1407
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parsonsmatt
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Jun 10, 2022
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+1466
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+1473
| fieldUpd con names record name new = do | ||
| pats <- | ||
| fmap mconcat $ forM names $ \k -> do | ||
| varName <- VarP <$> newName (nameBase k) | ||
| pure [(k, varName) | k /= name] | ||
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| pure $ CaseE record | ||
| [ Match (RecP con pats) (NormalB body) []] |
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This is the function that was introducing the problem.
| fieldUpd con names record name new = do | ||
| pats <- | ||
| fmap mconcat $ forM names $ \k -> do | ||
| varName <- VarP <$> newName (nameBase k) |
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And, this line is the real fix. By creating a newName, we're guaranteeing that the variable is fresh and uncapturable and isn't shadowing anything.
@fumieval This is one of those tricky things about TemplateHaskell - it's so easy to use and make names that can cause warnings and bugs! I do it all the time and I really ought to write up a lil' how to on the matter.
| @@ -13,6 +13,8 @@ | |||
| {-# LANGUAGE TypeFamilies #-} | |||
| {-# LANGUAGE UndecidableInstances #-} | |||
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| {-# OPTIONS_GHC -Wname-shadowing -Werror=name-shadowing #-} | |||
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This warning is the 'test' for the feature.
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This PR fixes #1406 which noticed that the code generated name shadowing warnings.
The specific problem si that we'd generate code like:
where
fieldNameshadowedfieldName.Before submitting your PR, check that you've:
@sincedeclarations to the Haddockstylish-haskellon any changed files..editorconfigfile for details)After submitting your PR:
(unreleased)on the Changelog