Move warnings to the top of the term

unison-cli/src/Unison/LSP/Conversions.hs

@@ -49,3 +49,10 @@ annToRange = \case
   Ann.External -> Nothing
   Ann.GeneratedFrom a -> annToRange a
   Ann.Ann start end -> Just $ Range (uToLspPos start) (uToLspPos end)
+
+annToURange :: Ann.Ann -> Maybe Range.Range
+annToURange = \case
+  Ann.Intrinsic -> Nothing
+  Ann.External -> Nothing
+  Ann.GeneratedFrom a -> annToURange a
+  Ann.Ann start end -> Just $ Range.Range start end

unison-cli/src/Unison/LSP/FileAnalysis.hs

@@ -112,8 +112,7 @@ checkFile doc = runMaybeT do
           & toRangeMap
   let typeSignatureHints = fromMaybe mempty (mkTypeSignatureHints <$> parsedFile <*> typecheckedFile)
   let fileSummary = FileSummary.mkFileSummary parsedFile typecheckedFile
-  let unusedBindingDiagnostics = fileSummary ^.. _Just . to termsBySymbol . folded . _3 . folding (UnusedBindings.analyseTerm fileUri)
-  Debug.debugM Debug.Temp "Unused binding diagnostics" unusedBindingDiagnostics
+  let unusedBindingDiagnostics = fileSummary ^.. _Just . to termsBySymbol . folded . folding (\(topLevelAnn, _refId, trm, _type) -> UnusedBindings.analyseTerm fileUri topLevelAnn trm)
   let tokenMap = getTokenMap tokens
   conflictWarningDiagnostics <-
     fold <$> for fileSummary \fs ->

unison-cli/src/Unison/LSP/FileAnalysis/UnusedBindings.hs

@@ -3,6 +3,7 @@ module Unison.LSP.FileAnalysis.UnusedBindings where
 import Data.Foldable qualified as Foldable
 import Data.Map qualified as Map
 import Data.Set qualified as Set
+import Data.Text qualified as Text
 import Language.LSP.Protocol.Types (Diagnostic)
 import Language.LSP.Protocol.Types qualified as Lsp
 import U.Core.ABT (ABT (..))
@@ -11,22 +12,36 @@ import Unison.LSP.Conversions qualified as Cv
 import Unison.LSP.Diagnostics qualified as Diagnostic
 import Unison.Parser.Ann (Ann)
 import Unison.Prelude
-import Unison.Symbol (Symbol)
+import Unison.Symbol (Symbol (..))
 import Unison.Term (Term)
+import Unison.Util.Range qualified as Range
+import Unison.Var qualified as Var
+import Unison.Lexer.Pos qualified as Pos
 
-analyseTerm :: Lsp.Uri -> Term Symbol Ann -> [Diagnostic]
-analyseTerm fileUri tm =
+analyseTerm :: Lsp.Uri -> Ann -> Term Symbol Ann -> [Diagnostic]
+analyseTerm fileUri topLevelTermAnn tm =
   let (unusedVars, _) = ABT.cata alg tm
-   in Map.toList unusedVars & mapMaybe \(v, ann) -> do
-        range <- Cv.annToRange ann
-        pure $ Diagnostic.mkDiagnostic fileUri range Diagnostic.DiagnosticSeverity_Warning ("Unused binding " <> tShow v) []
+   in Map.toList unusedVars & mapMaybe \(v, _ann) -> do
+        name <- getRelevantVarName v
+        -- Unfortunately we don't capture the annotation of the actual binding when parsing :'(, for now the least
+        -- annoying thing to do is just highlight the top of the binding.
+        urange <- Cv.annToURange topLevelTermAnn <&> (\(Range.Range start@(Pos.Pos line _col) _end) -> Range.Range start (Pos.Pos line 9999))
+        let lspRange = Cv.uToLspRange urange
+        pure $ Diagnostic.mkDiagnostic fileUri lspRange Diagnostic.DiagnosticSeverity_Warning ("Unused binding " <> tShow name <> " inside this term.\nUse the binding, or prefix it with an _ to dismiss this warning.") []
   where
+    getRelevantVarName :: Symbol -> Maybe Text
+    getRelevantVarName = \case
+      -- We only care about user bindings which don't start with an underscore
+      Symbol _ (Var.User n) -> do
+        guard (not (Text.isPrefixOf "_" n))
+        pure n
+      _ -> Nothing
     alg :: (Foldable f, Ord v) => Ann -> ABT f v (Map v Ann, Set v) -> (Map v Ann, Set v)
     alg ann abt = case abt of
       Var v -> (mempty, Set.singleton v)
       Cycle x -> x
       Abs v (unusedBindings, usedVars) ->
         if v `Set.member` usedVars
-          then (mempty, Set.delete v usedVars)
+          then (unusedBindings, Set.delete v usedVars)
           else (Map.insert v ann unusedBindings, usedVars)
       Tm fx -> Foldable.fold fx