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Fix Signature Help inside do Notation in GHC >= 9.10 #4904

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Fix Signature Help inside do Notation in GHC >= 9.10 #4904

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85b02d3
Traverse Generated Nodes
vidit-od Apr 19, 2026
e108151
Add regression tests
vidit-od Apr 21, 2026
9344a71
Add one more regression test
vidit-od May 1, 2026
20e9d05
Handle identifier info
vidit-od May 1, 2026
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18 changes: 16 additions & 2 deletions plugins/hls-signature-help-plugin/src/Ide/Plugin/SignatureHelp.hs
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Expand Up @@ -4,6 +4,7 @@

module Ide.Plugin.SignatureHelp (descriptor) where

import Control.Applicative

@jian-lin jian-lin Jun 4, 2026

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nitpicking:

The existing import style of this file is explicit. I think it's a good idea to follow that.

Suggested change
import Control.Applicative
import Control.Applicative ((<|>))

import Control.Arrow ((>>>))
import Control.Monad.Trans.Except (ExceptT (ExceptT))
import Data.Bifunctor (bimap)
Expand All @@ -29,6 +30,7 @@ import Development.IDE.Core.PluginUtils (runIdeActionE,
import Development.IDE.Core.PositionMapping (fromCurrentPosition)
import Development.IDE.GHC.Compat (FastStringCompat, Name,
RealSrcSpan,
generatedNodeInfo,
getSourceNodeIds,
isAnnotationInNodeInfo,
mkRealSrcLoc,
Expand All @@ -48,6 +50,7 @@ import GHC.Iface.Ext.Types (ContextInfo (Use),
HieAST (nodeChildren, nodeSpan),
HieASTs (getAsts),
IdentifierDetails (identInfo, identType),
NodeInfo (nodeIdentifiers),
nodeType)
import GHC.Iface.Ext.Utils (smallestContainingSatisfying)
import GHC.Types.Name.Env (lookupNameEnv)
Expand Down Expand Up @@ -294,12 +297,23 @@ getNodeNameAndTypes hieKind hieAst =
case extractName identifier of
Nothing -> Nothing
Just name ->
let mTypeOfName = identType identifierDetails
let mTypeOfName = identType identifierDetails <|> do
nodeInfo <- generatedNodeInfo hieAst
details <- M.lookup identifier (nodeIdentifiers nodeInfo)

@jian-lin jian-lin Jun 4, 2026

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For some identifier, are Identifiers of SourceInfo and GeneratedInfo the same? In other words, does this M.lookup always return Nothing?

Needs to verify.

identType details
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Comment on lines +300 to +303

@fendor fendor Jun 3, 2026

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@vidit-od Can we extract this do block into a function with some documentation?

-- types from the source NodeInfo
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typesOfNode = case sourceNodeInfo hieAst of

@jian-lin jian-lin Jun 4, 2026

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The fallback logic is:

  • get mTypeOfName from SourceInfo or GeneratedInfo
  • get typesOfNode from SourceInfo or GeneratedInfo

The current implementation uses two separated checks for mTypeOfName and typesOfNode. Alternatively, we can use only one check for both mTypeOfName and typesOfNode. Which way is better needs further investigation.

Nothing -> []
Just nodeInfo -> nodeType nodeInfo
-- fall back to generated NodeInfo when source has no types
Comment on lines +304 to +308

@jian-lin jian-lin Jun 4, 2026

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The comment is kind of confusing: it comes too late because mTypeOfName also has the fallback logic.

I think we should move the comment to the top of the let block.

typesOfGeneratedNode = case generatedNodeInfo hieAst of
Nothing -> []
Just nodeInfo -> nodeType nodeInfo
allTypes = case mTypeOfName of
Nothing -> typesOfNode
Nothing ->
case typesOfNode of
[] -> typesOfGeneratedNode
ts -> ts
Comment on lines -302 to +316

@jian-lin jian-lin Jun 4, 2026

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blocking:

This handles the fallback of typesOfNode. The fallback should be done in all cases. However, currently, it is only done in the Nothing case, but not the Just case.

I would handle the fallback in one place before allTypes and keep the allTypes code unchanged.

-- (the last?) one type of 'typesOfNode' may (always?) be the same as 'typeOfName'
-- To avoid generating two identical signature helps, we do a filtering here
-- This is similar to 'dropEnd1' in Development.IDE.Spans.AtPoint.atPoint
Expand Down
17 changes: 17 additions & 0 deletions plugins/hls-signature-help-plugin/test/Main.hs
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Expand Up @@ -381,6 +381,23 @@ main =
Nothing,
Nothing,
Just $ SimilarSignatureHelp $ SignatureHelp [SignatureInformation "f :: forall a b c. a -> b -> c" Nothing (Just [ParameterInformation (InR (19, 20)) Nothing, ParameterInformation (InR (24, 25)) Nothing]) (Just (InL 0))] (Just 0) (Just (InL 0))
],
-- Prevents https://github.com/haskell/haskell-language-server/issues/4769
mkTest
"inside do block"
[__i|
f :: Int -> Int -> Int
f = _
test :: IO ()
test = do
x <- pure 1
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^
print (f x 2)
^ ^
|]
[ Just $ SimilarSignatureHelp $ SignatureHelp [SignatureInformation "pure :: forall (f :: Type -> Type) a. Applicative f => a -> f a" (Just $ InR $ MarkupContent MarkupKind_Markdown "Lift a value") (Just [ParameterInformation (InR (55,56)) Nothing]) (Just (InL 0)), SignatureInformation "pure :: Int -> IO Int" (Just $ InR $ MarkupContent MarkupKind_Markdown "Lift a value") (Just [ParameterInformation (InR (8,11)) Nothing]) (Just (InL 0)), SignatureInformation "pure :: forall a. a -> IO a" (Just $ InR $ MarkupContent MarkupKind_Markdown "Lift a value") (Just [ParameterInformation (InR (18,19)) Nothing]) (Just (InL 0))] (Just 0) (Just (InL 0)),
Just $ SimilarSignatureHelp $ SignatureHelp [SignatureInformation "f :: Int -> Int -> Int" Nothing (Just [ParameterInformation (InR (5, 8)) Nothing, ParameterInformation (InR (12, 15)) Nothing]) (Just (InL 0))] (Just 0) (Just (InL 0)),
Just $ SimilarSignatureHelp $ SignatureHelp [SignatureInformation "f :: Int -> Int -> Int" Nothing (Just [ParameterInformation (InR (5, 8)) Nothing, ParameterInformation (InR (12, 15)) Nothing]) (Just (InL 1))] (Just 0) (Just (InL 1))
]
]

Expand Down
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