Fix toMethodName bug of the Class plugin

plugins/hls-class-plugin/src/Ide/Plugin/Class.hs

@@ -119,7 +119,7 @@ addMethodPlaceholders lf state AddMinimalMethodsParams{..} = fmap (fromMaybe err
 
     toMethodName n
       | Just (h, _) <- T.uncons n
-      , not (isAlpha h)
+      , not (isAlpha h || h == '_')
       = "(" <> n <> ")"
       | otherwise
       = n

test/functional/Class.hs

@@ -48,6 +48,9 @@ tests = testGroup
   , glodenTest "Creates a placeholder for multiple methods 2" "T3" "2"
     $ \(_:mmAction:_) -> do
       executeCodeAction mmAction
+  , glodenTest "Creates a placeholder for a method starting with '_'" "T4" ""
+    $ \(_fAction:_) -> do
+      executeCodeAction _fAction
   ]
 
 _CACodeAction :: Prism' CAResult CodeAction
@@ -60,14 +63,18 @@ classPath = "test" </> "testdata" </> "class"
 
 glodenTest :: String -> FilePath -> FilePath -> ([CodeAction] -> Session ()) -> TestTree
 glodenTest name fp deco execute
-  = goldenVsStringDiff name goldenGitDiff (classPath </> fp <.> deco <.> "expected" <.> "hs")
+  = goldenVsStringDiff name goldenGitDiff (classPath </> fpWithDeco <.> "expected" <.> "hs")
     $ runSession hlsCommand fullCaps classPath
     $ do
       doc <- openDoc (fp <.> "hs") "haskell"
       _ <- waitForDiagnosticsFromSource doc "typecheck"
       actions <- concatMap (^.. _CACodeAction) <$> getAllCodeActions doc
       execute actions
       BS.fromStrict . T.encodeUtf8 <$> getDocumentEdit doc
+  where
+    fpWithDeco
+      | deco == "" = fp
+      | otherwise  = fp <.> deco
 
 goldenGitDiff :: FilePath -> FilePath -> [String]
 goldenGitDiff fRef fNew = ["git", "diff", "--no-index", "--text", "--exit-code", fRef, fNew]

test/testdata/class/T4.expected.hs

@@ -0,0 +1,8 @@
+module T4 where
+
+class Test a where
+  _f :: a
+  {-# MINIMAL _f #-}
+
+instance Test Int where
+  _f = _

test/testdata/class/T4.hs

@@ -0,0 +1,7 @@
+module T4 where
+
+class Test a where
+  _f :: a
+  {-# MINIMAL _f #-}
+
+instance Test Int where